14 CFR Part 171 — Non-Federal Navigation Facilities

Federal Aviation Administration, DOT § 171.1 171.211 Maintenance and operations require- Subpart B—Nondirectional Radio Beacon ments.

Facilities 171.213 Reports.

171.21 Scope.

171.23 Requests for IFR procedure.

Subpart I—Interim Standard Microwave 171.25 Minimum requirements for approval.

Landing System (ISMLS) 171.27 Performance requirements.

171.29 Installation requirements.

171.251 Scope.

171.31 Maintenance and operations require- 171.253 Definitions.

ments.

171.255 Requests for IFR procedures.

171.33 Reports.

171.257 Minimum requirements for approval.

171.259 Performance requirements: General.

Subpart C—Instrument Landing System 171.261 Localizer performance requirements.

(ILS) Facilities 171.263 Localizer automatic monitor sys- tem.

171.41 Scope.

171.265 Glide path performance require- 171.43 Requests for IFR procedure.

ments.

171.45 Minimum requirements for approval.

171.267 Glide path automatic monitor sys- 171.47 Performance requirements.

tem.

171.49 Installation requirements.

171.51 Maintenance and operations require- 171.269 Marker beacon performance require- ments. ments.

171.53 Reports. 171.271 Installation requirements.

171.273 Maintenance and operations require- Subpart D—True Lights ments.

171.275 Reports.

171.61 Air navigation certificate: Revoca- tion and termination.

Subpart J—Microwave Landing System (MLS) Subpart E—General 171.301 Scope.

171.71 Materials incorporated by reference.

171.303 Definitions.

171.73 Alternative forms of reports.

171.305 Requests for IFR procedure.

171.75 Submission of requests.

171.307 Minimum requirements for approval.

Subpart F—Simplified Directional Facility 171.309 General requirements.

(SDF) 171.311 Signal format requirements.

171.313 Azimuth performance requirements.

171.101 Scope.

171.315 Azimuth monitor system require- 171.103 Requests for IFR procedure.

ments.

171.105 Minimum requirements for approval.

171.317 Approach elevation performance re- 171.107 Definition.

quirements.

171.109 Performance requirements.

171.319 Approach elevation monitor system 171.111 Ground standards and tolerances.

requirements.

171.113 Installation requirements.

171.321 DME and marker beacon perform- 171.115 Maintenance and operations require- ance requirements.

ments.

171.323 Fabrication and installation require- 171.117 Reports.

ments.

171.325 Maintenance and operations require- Subpart G—Distance Measuring Equipment ments.

(DME) 171.327 Operational records.

171.151 Scope.

A UTHORITY : 49 U.S.C. 106(g), 40103–40107, 171.153 Requests for IFR procedure.

40109, 40113, 44502, 44701–44702, 44708–44709, 171.155 Minimum requirements for approval.

44711, 44719–44721, 45303, 46308.

171.157 Performance requirements.

171.159 Installation requirements.

OURCE : Docket 5034, 29 FR 11337, Aug. 6, S 171.161 Maintenance and operations require- 1964, unless otherwise noted.

ments.

171.163 Reports.

Subpart A—VOR Facilities Subpart H—VHF Marker Beacons § 171.1 Scope.

171.201 Scope.

This subpart sets forth minimum re- 171.203 Requests for IFR procedure.

quirements for the approval and oper- 171.205 Minimum requirements for approval.

ation on non-Federal VOR facilities 171.207 Performance requirements.

171.209 Installation requirements. that are to be involved in the approval VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00829 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.3 of instrument flight rules and air traf- (4) The owner must agree to furnish fic control procedures related to those periodic reports, as set forth in § 171.13, facilities.

and must agree to allow the FAA to in- spect the facility and its operation [Docket 5034, 29 FR 11337, Aug. 6, 1964, as whenever necessary.

amended by Amdt. 171–2, 31 FR 5408, Apr. 6, 1966; Amdt. 171–7, 35 FR 12711, Aug. 11, 1970] (5) The owner must assure the FAA that he will not withdraw the facility § 171.3 Requests for IFR procedure.

from service without the permission of (a) Each person who requests an IFR the FAA.

procedure based on a VOR facility that (6) The owner must bear all costs of he owns must submit the following in- meeting the requirements of this sec- formation with that request: tion and of any flight or ground inspec- (1) A description of the facility and tions made before the facility is com- evidence that the equipment meets the missioned, except that the Federal performance requirements of § 171.7 and Aviation Administration may bear cer- is installed in accordance with § 171.9.

tain of these costs subject to budgetary (2) A proposed procedure for oper- limitations and policy established by ating the facility.

the Administrator.

(3) A proposed maintenance organiza- (b) If the applicant for approval tion and maintenance manual that meets the requirements of paragraph meets the requirements of § 171.11.

(a) of this section, the FAA commis- (4) A statement of intention to meet sions the facility as a prerequisite to the requirements of this subpart.

its approval for use in an IFR proce- (5) A showing that the facility has an dure. The approval is withdrawn at any acceptable level of operational reli- time the facility does not continue to ability and an acceptable standard of meet those requirements.

performance. Previous equivalent oper- ational experience with a facility with [Docket 5034, 29 FR 11337, Aug. 6, 1964, as identical design and operational char- amended by Amdt. 171–6, 35 FR 10288, June acteristics will be considered in show- 24, 1970] ing compliance with this paragraph.

§ 171.7 Performance requirements.

(b) After the FAA inspects and evalu- ates the facility, it advises the owner (a) The VOR must perform in accord- of the results and of any required ance with the ‘‘International Stand- changes in the facility or the mainte- ards and Recommended Practices, nance manual or maintenance organi- Aeronautical Telecommunications,’’ zation. The owner must then correct Part I, paragraph 3.3 (Annex 10 to the the deficiencies, if any, and operate the Convention on International Civil facility for an in-service evaluation by Aviation), except that part of para- the FAA.

graph 3.3.2.1 specifying a radio fre- [Docket 5034, 29 FR 11337, Aug. 6, 1964, as quency tolerance of 0.005 percent, and amended by Amdt. 171–7, 35 FR 12711, Aug. 11, that part of paragraph 3.3.7 requiring 1970] removal of only the bearing informa- tion. In place thereof, the frequency § 171.5 Minimum requirements for ap- tolerance of the radio frequency carrier proval.

must not exceed plus or minus 0.002 (a) The following are the minimum percent, and all radiation must be re- requirements that must be met before moved during the specified deviations the FAA will approve an IFR procedure from established conditions and during for a non-Federal VOR: periods of monitor failure.

(1) The facility’s performance, as de- (b) Ground inspection consists of an termined by air and ground inspection, examination of the design features of must meet the requirements of § 171.7.

the equipment to determine that there (2) The installation of the equipment will not be conditions that will allow must meet the requirements of § 171.9.

(3) The owner must agree to operate unsafe operations because of compo- and maintain the facility in accord- nent failure or deterioration.

ance with § 171.11.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00830 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.11 (c) The monitor is checked periodi- pending on circumstances) the fol- cally, during the in-service test evalua- lowing ground-air or landline commu- tion period, for calibration and sta- nications services: bility The tests are made with a stand- (1) At facilities outside of and not im- ard ‘‘Reference and variable phase sig- mediately adjacent to controlled air- nal generator’’ and associated test space, there must be ground-air com- equipment, including an oscilloscope munications from the airport served by and portable field detector. In general, the facility. Separate communications the ground check is conducted in channels are acceptable.

accord- ance with section 8.4 of FAA (2) At facilities within or imme- Handbook AF P 6790.9 ‘‘Maintenance diately adjacent to controlled airspace, Instruction for VHF Omniranges’’, there must be the ground-air commu- adapted for the facility concerned.

nications required by paragraph (e)(1) (d) Flight tests to determine the fa- of this section and reliable communica- cility’s adequacy for operational re- tions (at least a landline telephone) quirements and compliance with appli- from the airport to the nearest FAA cable ‘‘Standards and Recommended air traffic control or communication Practices’’ are conducted in accordance with the ‘‘U.S. Standard Flight Inspec- facility.

tion Manual’’, particularly section 201.

Paragraphs (e) (1) and (2) of this sec- (e) After January 1, 1975, the owner of tion are not mandatory at airports the VOR shall modify the facility to where an adjacent FAA facility can perform in accordance with paragraph communicate with aircraft on the 3.3.5.7 of Annex 10 to the Convention on ground at the airport and during the International Civil Aviation within 180 entire proposed instrument approach days after receipt of notice from the procedure. In addition, at low traffic Administrator that 50 kHz channel density airports within or immediately spacing is to be implemented in the area and that a requirement exists for adjacent to controlled airspace and suppression of 9960 Hz subcarrier where extensive delays are not a fac- harmonics. tor, the requirements of paragraphs (e) (1) and (2) of this section may be re- [Docket 5034, 29 FR 11337, Aug. 6, 1964, as duced to reliable communications (at amended by Amdt. 171–7, 35 FR 12711, Aug. 11, 1970; Amdt. 171–9, 38 FR 28557, Oct. 15, 1973] least a landline telephone) from the airport to the nearest FAA air traffic § 171.9 Installation requirements.

control or communication facility, if an adjacent FAA facility can commu- (a) The facility must be installed ac- cording to accepted good engineering nicate with aircraft during the pro- practices, applicable electric and safe- posed instrument approach procedure, ty codes, and the installation must at least down to the minimum en route meet at least the Federal Communica- altitude for the controlled airspace tion Commission’s licensing require- area.

ments.

[Docket 5034, 29 FR 11337, Aug. 6, 1964, as (b) The facility must have a reliable amended by Amdt. 171–7, 35 FR 12711, Aug. 11, source of suitable primary power, ei- 1970; Amdt. 171–16, 56 FR 65664, Dec. 17, 1991] ther from a power distribution system or locally generated, with a supple- § 171.11 Maintenance and operations mental standby system, if needed.

requirements.

(c) Dual transmitting equipment (a) The owner of the facility must es- with automatic changeover is preferred tablish an adequate maintenance sys- and may be required to support certain tem and provide qualified maintenance IFR procedures.

personnel to maintain the facility at (d) There must be a means for deter- the level attained at the time it was mining, from the ground, the perform- commissioned. Each person who main- ance of the equipment, including the tains a facility must meet at least the antenna, initially and periodically.

Federal Communications Commission’s (e) A facility intended for use as an instrument approach aid for an airport licensing requirements and show that must have or be supplemented by (de- he has the special knowledge and skills VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00831 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.11 needed to maintain the facility includ- (17) An acceptable procedure for ing proficiency in maintenance proce- amending or revising the manual.

dures and the use of specialized test (18) The following information con- equipment. cerning the facility: (b) The owner must prepare, and ob- (i) Location by latitude and lon- tain FAA approval of, an operations gitude to the nearest second, and its and maintenance manual that sets position with respect to airport lay- forth mandatory procedures for oper- outs.

ations, preventive maintenance, and (ii) The type, make, and model of the emergency maintenance, including in- basic radio equipment that will provide structions on each of the following: the service.

(1) Physical security of the facility.

(iii) The station power emission and (2) Maintenance and operations by frequency.

authorized persons only.

(iv) The hours of operation.

(3) FCC licensing requirements for (v) Station identification call letters operating and maintenance personnel.

and method of station identification, (4) Posting of licenses and signs.

whether by Morse code or recorded (5) Relations between the facility and voice announcement, and the time FAA air traffic control facilities, with spacing of the identification.

a description of the boundaries of con- (vi) A description of the critical parts trolled airspace over or near the facil- that may not be changed, adjusted, or ity, instructions for relaying air traffic repaired without an FAA flight check control instructions and information to confirm published operations.

(if applicable), and instructions for the (c) The owner shall make a ground operation of an air traffic advisory check of course accuracy each month service if the VOR is located outside of in accordance with procedures ap- controlled airspace.

proved by the FAA at the time of com- (6) Notice to the Administrator of missioning, and shall report the results any suspension of service.

of the checks as provided in § 171.13.

(7) Detailed and specific maintenance (d) If the owner desires to modify the procedures and servicing guides stating facility, he must submit the proposal the frequency of servicing.

to the FAA and may not allow any (8) Air-ground communications, if modifications to be made without spe- provided, expressly written or incor- cific approval.

porating appropriate sections of FAA (e) The owner’s maintenance per- manuals by reference.

sonnel must participate in initial in- (9) Keeping of station logs and other spections made by the FAA. In the case technical reports, and the submission of subsequent inspections, the owner or of reports required by § 171.13.

his representative shall participate.

(10) Monitoring of the facility.

(f) Whenever it is required by the (11) Inspections by United States per- FAA, the owner shall incorporate im- sonnel.

provements in VOR maintenance (12) Names, addresses, and telephone brought about by progress in the state numbers of persons to be notified in an of the art. In addition, he shall provide emergency.

a stock of spare parts, including vacu- (13) Shutdowns for routine mainte- um tubes, of such a quantity to make nance and issue of ‘‘Notices to Airmen’’ possible the prompt replacement of for routine or emergency shutdowns components that fail or deteriorate in (private use facilities may omit the service.

‘‘Notices to Airmen’’).

(g) The owner shall provide all ap- (14) An explanation of the kinds of proved test instruments needed for activity (such as construction or grad- maintenance of the facility.

ing) in the vicinity of the facility that (h) The owner shall close the facility may require shutdown or recertifi- upon receiving two successive pilot re- cation of the facility by FAA flight ports of its malfunctioning.

check.

(15) Procedures for conducting a [Docket 5034, 29 FR 11337, Aug. 6, 1964, as ground check of course accuracy.

amended by Amdt. 171–2, 31 FR 5408, Apr. 6, (16) Commissioning of the facility. 1966] VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00832 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR

Federal Aviation Administration, DOT § 171.23 § 171.13 Reports.

Subpart B—Nondirectional Radio Beacon Facilities The owner of each facility to which this subpart applies shall make the fol- § 171.21 Scope.

lowing reports on forms furnished by the FAA, at the times indicated, to the (a) This subpart sets forth minimum FAA Regional office for the area in requirements for the approval and op- which the facility is located: eration of non-Federal, nondirectional (a) Record of meter readings and adjust- radio beacon facilities that are to be ments ( Form FAA–198 ). To be filled out involved in the approval of instrument by the owner with the equipment ad- flight rules and air traffic control pro- justments and meter readings as of the cedures related to those facilities.

time of commissioning, with one copy (b) A nondirectional radio beacon to be kept in the permanent records of (‘‘H’’ facilities domestically—NDB fa- the facility and two copies to the ap- cilities internationally) radiates a con- propriate Regional office of the FAA.

tinuous carrier of approximately equal The owner shall revise the form after intensity at all azimuths. The carrier any major repair, modernization, or re- is modulated at 1020 cycles per second turning, to reflect an accurate record for station identification purposes.

of facility operation and adjustment.

[Docket 5034, 29 FR 11337, Aug. 6, 1964, as (b) Facility maintenance log ( FAA Form amended by Amdt. 171–2, 31 FR 5408, Apr. 6, 6003–1 ). This form is a permanent 1966; Amdt. 171–7, 35 FR 12711, Aug. 11, 1970] record of all equipment malfunctioning met in maintaining the facility, in- § 171.23 Requests for IFR procedure.

cluding information on the kind of (a) Each person who requests an IFR work and adjustments made, equip- procedure based on a nondirectional ment failures, causes (if determined), radio beacon facility that he owns and corrective action taken. The owner must submit the following information shall keep the original of each report with that request: at the facility and send a copy to the (1) A description of the facility and appropriate Regional office of the FAA evidence that the equipment meets the at the end of the month in which it is performance requirements of § 171.27 prepared.

and is installed in accordance with (c) Radio equipment operation record § 171.29.

( Form FAA–418 ). To contain a complete (2) A proposed procedure for oper- record of meter readings, recorded on ating the facility.

each scheduled visit to the facility.

(3) A proposed maintenance arrange- The owner shall keep the original of ment and a maintenance manual that each month’s record at the facility and meets the requirements of § 171.31.

send a copy of it to the appropriate Re- (4) A statement of intention to meet gional office of the FAA.

the requirements of this subpart.

(d) [Reserved] (5) A showing that the facility has an (e) VOR ground check error data acceptable level of operational reli- ( Forms FAA–2396 and 2397 ). To contain ability and an acceptable standard of results of the monthly course accuracy performance. Previous equivalent oper- ground check in accordance with FAA ational experience with a facility with Handbook AF P 6790.9 ‘‘Maintenance Instructions for VHF Omniranges’’. identical design and operational char- The owner shall keep the originals in acteristics will be considered in show- the facility and send a copy of each ing compliance with this subparagraph.

form to the appropriate Regional office (b) After the FAA inspects and evalu- of the FAA on a monthly basis.

ates the facility, it advises the owner of the results and of any required (49 U.S.C. 1348) changes in the facility or the mainte- [Docket 5034, 29 FR 11337, Aug. 6, 1964, as nance manual or maintenance organi- amended by Amdt. 171–5, 34 FR 15245, Sept.

zation. The owner must then correct 30, 1969; Amdt. 171–10, 40 FR 36110, Aug. 19, the deficiencies, if any, and operate the 1975] VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00833 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.25 facility for an in-service evaluation by ommended Practices, Aeronautical the FAA. Telecommunications, Part I, paragraph 3.4’’ (Annex 10 to the Convention on [Docket 5034, 29 FR 11337, Aug. 6, 1964, as International Civil Aviation), except amended by Amdt. 171–7, 35 FR 12711, Aug. 11, that identification by on-off keying of 1970] a second carrier frequency, separated § 171.25 Minimum requirements for ap- from the main carrier by 1020 Hz plus proval.

or minus 50 Hz, is also acceptable.

(a) The following are the minimum (b) The facility must perform in ac- requirements that must be met before cordance with recognized and accepted the FAA will approve an IFR procedure good electronic engineering practices for a non-Federal, nondirectional radio for the desired service.

beacon facility under this subpart: (c) Ground inspection consists of an (1) The facility’s performances, as de- examination of the design features of termined by air and ground inspection, the equipment to determine (based on must meet the requirements of § 171.27.

recognized and accepted good engineer- (2) The installation of the equipment ing practices) that there will not be must meet the requirements of § 171.29.

conditions that will allow unsafe oper- (3) The owner must agree to operate ations because of component failure or and maintain the facility in accord- deterioration.

ance with § 171.31.

(d) Flight tests to determine the fa- (4) The owner must agree to furnish cility’s adequacy for operational re- periodic reports, as set forth in § 171.33, quirements and compliance with appli- and agree to allow the FAA to inspect cable ‘‘Standards and Recommended the facility and its operation whenever Practices’’ are conducted in accord- necessary.

ance with the ‘‘U.S. Standard Flight (5) The owner must assure the FAA Inspection Manual’’, particularly sec- that he will not withdraw the facility tion 207. The original test is made by from service without the permission of the FAA and later tests shall be made the FAA.

under arrangements, satisfactory to (6) The owner must bear all costs of the FAA, that are made by the owner.

meeting the requirements of this sec- [Docket 5034, 29 FR 11337, Aug. 6, 1964, as tion and of any flight or ground inspec- amended by Amdt. 171–7, 35 FR 12711, Aug. 11, tions made before the facility is com- 1970] missioned, except that the Federal Aviation Administration may bear cer- § 171.29 Installation requirements.

tain of these costs subject to budgetary limitations and policy established by (a) The facility must be installed ac- the Administrator. cording to accepted good engineering (b) If the applicant for approval practices, applicable electric and safe- meets the requirements of paragraph ty codes, and FCC licensing require- (a) of this section, the FAA commis- ments.

sions the facility as a prerequisite to (b) The facility must have a reliable its approval for use in an IFR proce- source of suitable primary power.

dure. The approval is withdrawn at any (c) Dual transmitting equipment may time the facility does not continue to be required to support some IFR proce- meet those requirements. In addition, dures.

the facility may be de-commissioned (d) A facility intended for use as an whenever the frequency channel is instrument approach aid for an airport needed for higher priority common sys- must have or be supplemented by (de- tem service.

pending on the circumstances) the fol- lowing ground-air or landline commu- [Docket 5034, 29 FR 11337, Aug. 6, 1964, as nications services: amended by Amdt. 171–6, 35 FR 10288, June 24, 1970] (1) At facilities outside of and not im- mediately adjacent to controlled air- § 171.27 Performance requirements.

space, there must be ground-air com- (a) The facility must meet the per- munications from the airport served by formance requirements set forth in the the facility. Voice on the aid con- ‘‘International Standards and Rec- trolled from the airport is acceptable.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00834 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.31 (2) At facilities within or imme- (2) Maintenance and operations by diately adjacent to controlled airspace, authorized persons only.

there must be the ground-air commu- (3) FCC licensing requirements for nications required by paragraph (d)(1) operating and maintenance personnel.

of this section and reliable communica- (4) Posting of licenses and signs.

tions (at least a landline telephone) (5) Relations between the facility and from the airport to the nearest FAA FAA air traffic control facilities, with air traffic control or communication a description of the boundaries of con- facility.

trolled airspace over or near the facil- ity, instructions for relaying air traffic Paragraphs (d) (1) and (2) of this sec- control instructions and information tion are not mandatory at airports (if applicable), and instructions for the where an adjacent FAA facility can operation of an air traffic advisory communicate with aircraft on the service if the facility is located outside ground at the airport and during the of controlled airspace.

entire proposed instrument approach procedure. In addition, at low traffic (6) Notice to the Administrator of density airports within or immediately any suspension of service.

adjacent to controlled airspace, and (7) Detailed arrangements for main- where extensive delays are not a fac- tenance flight inspection and servicing tor, the requirements of paragraphs (d) stating the frequency of servicing.

(1) and (2) of this section may be re- (8) Air-ground communications, if duced to reliable communications (at provided, expressly written or incor- least a landline telephone) from the porating appropriate sections of FAA airport to the nearest FAA air traffic manuals by reference.

control or communications facility, if (9) Keeping of station logs and other an adjacent FAA facility can commu- technical reports, and the submission nicate with aircraft during the pro- of reports required by § 171.33.

posed instrument approach procedure, (10) Monitoring of the facility, at at least down to the minimum en route least once each half hour, to assure altitude for the controlled airspace continuous operation.

area.

(11) Inspections by United States per- [Docket 5034, 29 FR 11337, Aug. 6, 1964, as sonnel.

amended by Amdt. 171–16, 56 FR 65664, Dec.

(12) Names, addresses, and telephone 17, 1991] numbers of persons to be notified in an emergency.

§ 171.31 Maintenance and operations (13) Shutdowns for routine mainte- requirements.

nance and issue of ‘‘Notices to Airmen’’ (a) The owner of the facility must es- for routine or emergency shutdowns tablish an adequate maintenance sys- (private use facilities may omit the tem and provide qualified maintenance ‘‘Notices to Airmen’’).

personnel to maintain the facility at (14) Commissioning of the facility.

the level attained at the time it was (15) An acceptable procedure for commissioned. Each person who main- amending or revising the manual.

tains a facility must meet at least the (16) The following information con- Federal Communications Commission’s cerning the facility: licensing requirements and show that (i) Location by latitude and lon- he has the special knowledge and skills gitude to the nearest second, and its needed to maintain the facility includ- position with respect to airport lay- ing proficiency in maintenance proce- outs.

dures and the use of specialized test (ii) The type, make, and model of the equipment.

basic radio equipment that will provide (b) The owner must prepare, and ob- the service.

tain approval of, an operations and (iii) The station power emission and maintenance manual that sets forth frequency.

mandatory procedures for operations, preventive maintenance, and emer- (iv) The hours of operation.

gency maintenance, including instruc- (v) Station identification call letters tions on each of the following: and method of station identification, (1) Physical security of the facility. whether by Morse code or recorded VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00835 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.33 voice announcement, and the time The owner shall keep the original of spacing of the identification. each month’s record at the facility and (c) If the owner desires to modify the send a copy of it to the appropriate Re- facility, he must submit the proposal gional Office of the FAA.

to the FAA and meet applicable re- [Docket 5034, 29 FR 11337, Aug. 6, 1964, as quirements of the FCC.

amended by Amdt. 171–10, 40 FR 36110, Aug.

(d) The owner’s maintenance per- 19, 1975] sonnel must participate in initial in- spections made by the FAA. In the case of subsequent inspections, the owner or Subpart C—Instrument Landing his representative shall participate.

System (ILS) Facilities (e) The owner shall provide a stock of spare parts, including vacuum tubes, of § 171.41 Scope.

such a quantity to make possible the This subpart sets forth minimum re- prompt replacement of components quirements for the approval and oper- that fail or deteriorate in service.

ation of non-Federal Instrument Land- (f) The owner shall close the facility ing System (ILS) Facilities that are to upon receiving two successive pilot re- be involved in the approval of instru- ports of its malfunctioning.

ment flight rules and air traffic control [Docket 5034, 29 FR 11337, Aug. 6, 1964, as procedures related to those facilities.

amended by Amdt. 171–2, 31 FR 5408, Apr. 6, 1966] [Docket 5034, 29 FR 11337, Aug. 6, 1964, as amended by Amdt. 171–2, 31 FR 5408, Apr. 6, § 171.33 Reports.

1966; Amdt. 171–7, 35 FR 12711, Aug. 11, 1970] The owner of each facility to which § 171.43 Requests for IFR procedure.

this subpart applies shall make the fol- lowing reports, at the times indicated, (a) Each person who requests an IFR to the FAA Regional office for the area procedure based on an ILS facility that in which the facility is located: he owns must submit the following in- (a) Record of meter readings and adjust- formation with that request: ments ( Form FAA–198 ). To be filled out (1) A description of the facility and by the owner or his maintenance rep- evidence that the equipment meets the resentative with the equipment adjust- performance requirements of § 171.47 ments and meter readings as of the and is installed in accordance with time of commissioning, with one copy § 171.49.

to be kept in the permanent records of (2) A proposed procedure for oper- the facility and two copies to the ap- ating the facility.

propriate Regional Office of the FAA.

(3) A proposed maintenance organiza- The owner shall revise the form after tion and a maintenance manual that any major repair, modernization, or re- turning, to reflect an accurate record meets the requirements of § 171.51.

of facility operation and adjustment. (4) A statement of intent to meet the (b) Facility maintenance log ( FAA Form requirements of this subpart.

6030–1 ). This form is a permanent (5) A showing that the facility has an record of all equipment malfunctioning acceptable level of operational reli- met in maintaining the facility, in- ability and an acceptable standard of cluding information on the kind of performance. Previous equivalent oper- work and adjustments made, equip- ational experience with a facility with ment failures, causes (if determined), identical design and operational char- and corrective action taken. The owner acteristics will be considered in show- shall keep the original of each report ing compliance with this subparagraph.

at the facility and send a copy to the (b) After the FAA inspects and evalu- appropriate Regional Office of the FAA ates the facility, it advises the owner at the end of the month in which it is of the results and of any required prepared.

changes in the facility or the mainte- (c) Radio equipment operation record nance manual or maintenance organi- ( Form FAA–418 ). To contain a complete zation. The owner must then correct record of meter readings, recorded on the deficiencies, if any, and operate the each scheduled visit to the facility.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00836 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.47 facility for an in-service evaluation by ommended Practices, Aeronautical the FAA. Telecommunications, Part I, Para- graph 3.1’’ (Annex 10 to the Convention [Docket 5034, 29 FR 11337, Aug. 6, 1964, as on International Civil Aviation) except amended by Amdt. 171–7, 35 FR 12711, Aug. 11, 1970] as follows: (1) The first part of paragraph 3.1.3, § 171.45 Minimum requirements for ap- relating to suppression of radiation proval.

wholly or in part in any or all direc- (a) The following are the minimum tions outside the 20-degree sector cen- requirements that must be met before tered on the course line to reduce lo- the FAA will approve an IFR procedure calizer does not apply.

for a non-Federal Instrument Landing (2) Radiation patterns must conform System: to limits specified in 3.1.3.3 and 3.1.3.4, (1) The facility’s performance, as de- but this does not mean that suppres- termined by air and ground inspection, sion of radiation to the rear of the an- must meet the requirements of § 171.47.

tenna array to satisfy difficult siting (2) The installation of the equipment positions (as per 3.1.3.1.4) is not al- must meet the requirements of § 171.49.

lowed. For example, if a reflector (3) The owner must agree to operate screen for the antenna array is re- and maintain the facility in accord- ance with § 171.51. quired to overcome a siting problem, (4) The owner must agree to furnish the area to the rear of the localizer periodic reports, as set forth in § 171.53 may be made unusable and should be so and agree to allow the FAA to inspect advertised.

the facility and its operation whenever (3) A third marker beacon (inner necessary.

marker) is not required.

(5) The owner must assure the FAA (4) The frequency tolerance of the that he will not withdraw the facility radio frequency carrier must not ex- from service without the permission of ceed plus or minus 0.002 percent.

the FAA.

(b) Ground inspection consists of an (6) The owner must bear all costs of examination of the design features of meeting the requirements of this sec- the equipment to determine that there tion and of any flight or ground inspec- will not be conditions that will allow tions made before the facility is com- unsafe operations because of compo- missioned, except that the Federal nent failure or deterioration.

Aviation Administration may bear cer- tain of these costs subject to budgetary (c) The monitor is checked periodi- limitations and policy established by cally, during the in-service test evalua- the Administrator.

tion period, for calibration and sta- (b) If the applicant for approval bility. These tests, and ground checks meets the requirements of paragraph of glide slope and localizer radiation (a) of this section, the FAA commis- characteristics, are conducted in ac- sions the facility as a prerequisite to cordance with FAA Handbooks AF P its approval for use in an IFR proce- 6750.1 and AF P 6750.2 ‘‘Maintenance In- dure. The approval is withdrawn at any structions for ILS Localizer Equip- time the facility does not continue to ment’’ and ‘‘Maintenance Instructions meet those requirements. In addition, for ILS Glide Slope Equipment’’.

the facility may be de-commissioned (d) Flight tests to determine the fa- whenever the frequency channel is cility’s adequacy for operational re- needed for higher priority common sys- quirements and compliance with appli- tem service.

cable ‘‘Standards and Recommended [Docket 5034, 29 FR 11337, Aug. 6, 1964, as Practices’’ are conducted in accord- amended by Amdt. 171–6, 35 FR 10288, June ance with the ‘‘U.S. Standard Flight 24, 1970] Inspection Manual’’, particularly sec- § 171.47 Performance requirements. tion 217.

(a) The Instrument Landing System [Docket 5034, 29 FR 11337, Aug. 6, 1974, as must perform in accordance with the amended by Amdt. 171–9, 38 FR 28557, Oct. 15, ‘‘International Standards and Rec- 1973] VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00837 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.49 procedure. In addition, at low traffic § 171.49 Installation requirements.

density airports within or immediately (a) The facility must be of a perma- adjacent to controlled airspace, and nent nature, located, constructed, and where extensive delays are not a fac- installed according to ICAO Standards tor, the requirements of paragraphs (Annex 10), accepted good engineering (e)(1) and (e)(2) of this section may be practices, applicable electric and safe- reduced to reliable communications (at ty codes, and FCC licensing require- least a landline telephone) from the ments.

airport to the nearest FAA air traffic (b) The facility must have a reliable control or communications facility, if source of suitable primary power, ei- an adjacent FAA facility can commu- ther from a power distribution system nicate with aircraft during the pro- or locally generated. A determination posed instrument approach procedure by the Administrator as to whether a down to the airport surface or at least facility will be required to have stand- to the minimum approach altitude.

by power for the localizer, glide slope [Docket 5034, 29 FR 11337, Aug. 6, 1964, as and monitor accessories to supplement amended by Amdt. 171–6, 35 FR 10288, June the primary power, will be made for 24, 1970; Amdt. 171–16, 56 FR 65664, Dec. 17, each airport based upon operational 1991] minimums and density of air traffic.

(c) A determination by the Adminis- § 171.51 Maintenance and operations trator as to whether a facility will be requirements.

required to have dual transmitting (a) The owner of the facility must es- equipment with automatic changeover tablish an adequate maintenance sys- for localizer and glide slope compo- tem and provide qualified maintenance nents, will be made for each airport personnel to maintain the facility at based upon operational minimums and the level attained at the time it was density of air traffic.

commissioned. Each person who main- (d) There must be a means for deter- tains a facility must meet at least the mining, from the ground, the perform- Federal Communications Commission’s ance of the equipment (including an- licensing requirements and show that tennae), initially and periodically.

he has the special knowledge and skills (e) The facility must have, or be sup- needed to maintain the facility includ- plemented by (depending on the cir- ing proficiency in maintenance proce- cumstances) the following ground-air dures and the use of specialized test or landline communications services: equipment.

(1) At facilities outside of and not im- (b) The owner must prepare, and ob- mediately adjacent to controlled air- tain approval of, an operations and space, there must be ground-air com- maintenance manual that sets forth munications from the airport served by mandatory procedures for operations, the facility. The utilization of voice on preventive maintenance, and emer- the ILS frequency should be deter- gency maintenance, including instruc- mined by the facility operator on an tions on each of the following: individual basis.

(1) Physical security of the facility.

(2) At facilities within or imme- (2) Maintenance and operations by diately adjacent to controlled airspace, authorized persons only.

there must be the ground-air commu- (3) FCC licensing requirements for nications required by paragraph (e)(1) operating and maintenance personnel.

of this section and reliable communica- (4) Posting of licenses and signs.

tions (at least a landline telephone) (5) Relation between the facility and from the airport to the nearest FAA FAA air traffic control facilities, with air traffic control or communications a description of the boundaries of con- facility.

trolled airspace over or near the facil- Paragraphs (e)(1) and (e)(2) of this sec- ity, instructions for relaying air traffic tion are not mandatory at airports control instructions and information where an adjacent FAA facility can (if applicable), and instructions for the communicate with aircraft on the operations of an air traffic advisory ground at the airport and during the service if the facility is located outside entire proposed instrument approach of controlled airspace.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00838 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.53 (6) Notice to the Administrator of cordance with procedures approved by any suspension of service. the FAA at the time of commissioning, (7) Detailed and specific maintenance and shall report the results of the procedures and servicing guides stating checks as provided in § 171.53.

the frequency of servicing.

(d) If the owner desires to modify the (8) Air-ground communications, if facility, he must submit the proposal provided, expressly written or incor- to the FAA and may not allow any porating appropriate sections of FAA modifications to be made without spe- manuals by reference.

cific approval.

(9) Keeping of station logs and other (e) ‘‘The owner’s maintenance per- technical reports, and the submission sonnel must participate in initial in- of reports required by § 171.53.

spections made by the FAA. In the case (10) Monitoring of the facility.

of subsequent inspections, the owner or (11) Inspections by United States per- his representative shall participate.’’ sonnel.

(f) Whenever it is required by the (12) Names, addresses, and telephone FAA, the owner shall incorporate im- numbers of persons to be notified in an provements in ILS maintenance emergency.

brought about by progress in the state (13) Shutdowns for routine mainte- of the art. In addition, he shall provide nance and issue of ‘‘Notices to Airmen’’ a stock of spare parts, including vacu- for routine or emergency shutdowns um tubes, of such a quantity to make (private use facilities may omit the possible the prompt replacement of ‘‘Notices to Airmen’’).

components that fail or deteriorate in (14) Commissioning of the facility.

service.

(15) An acceptable procedure for (g) The owner shall provide FAA ap- amending or revising the manual.

proved test instruments needed for (16) An explanation of the kinds of maintenance of the facility.

activities (such as construction or (h) The owner shall close the facility grading) in the vicinity of the facility upon receiving two successive pilot re- that may require shutdown or recertifi- ports of its malfunctioning.

cation of the facility by FAA flight [Docket 5034, 29 FR 11337, Aug. 6, 1964, as check.

amended by Amdt. 171–2, 31 FR 5408, Apr. 6, (17) Procedures for conducting a 1966] ground check or localizer course align- ment width, and clearance, and glide § 171.53 Reports.

slope elevation angle and width.

The owner of each facility to which (18) The following information con- this subpart applies shall make the fol- cerning the facility: lowing reports, at the times indicated, (i) Facility component locations with to the FAA Regional Office for the area respect to airport layout, instrument in which the facility is located: runway, and similar areas.

(a) Record of meter readings and adjust- (ii) The type, make, and model of the ments ( Form FAA–198 ). To be filled out basic radio equipment that will provide by the owner or his maintenance rep- the service.

resentative with the equipment adjust- (iii) The station power emission and ments and meter readings as of the frequencies of the localizer, glide slope, time of commissioning, with one copy markers, and associated compass loca- to be kept in the permanent records of tors, if any.

the facility and two copies to the ap- (iv) The hours of operation.

propriate Regional Office of the FAA.

(v) Station identification call letters The owner shall revise the form after and method of station identification any major repair, modernization, or re- and the time spacing of the identifica- tuning, to reflect an accurate record of tion.

facility operation and adjustment.

(vi) A description of the critical parts that may not be changed, adjusted, or (b) Facility maintenance log ( FormFAA repaired without an FAA flight check 6030–1 ). This form is a permanent to confirm published operations. record of all equipment malfunctioning (c) The owner shall make a ground met in maintaining the facility, in- check of the facility each month in ac- cluding information on the kind of VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00839 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.61 work and adjustments made, equip- quarters. An historical file of these ma- ment failures, causes (if determined), terials is maintained at Headquarters, and corrective action taken. The owner Federal Aviation Administration, 800 shall keep the original of each report Independence Avenue SW., Washington, at the facility and send a copy to the DC 20590.

appropriate Regional Office of the FAA [Amdt. 171–8, 36 FR 5584, Mar. 25, 1971] at the end of each month in which it is prepared.

§ 171.73 Alternative forms of reports.

(c) Radio equipment operation record ( Form FAA–418 ). To contain a complete On a case-by-case basis, a Regional record of meter readings, recorded on Administrator may accept any report each scheduled visit to the facility. in a format other than the FAA form The owner shall keep the original of required by this part if he is satisfied each month’s record at the facility and that the report contains all the infor- send a copy of it to the appropriate Re- mation required on the FAA form and gional Office of the FAA.

can be processed by FAA as conven- iently as the FAA form.

[Docket 5034, 29 FR 11337, Aug. 6, 1964, as amended by Amdt. 171–5, 34 FR 15245, Sept.

(49 U.S.C. 1348) 30, 1969; Amdt. 171–10, 40 FR 36110, Aug. 19, 1975] [Amdt. 171–5, 34 FR 15245, Sept. 30, 1969, as amended by Amdt. 171–15, 54 FR 39296, Sept.

25, 1989] Subpart D—True Lights § 171.75 Submission of requests.

§ 171.61 Air navigation certificate: Revocation and termination.

(a) Requests for approval of facilities (a) Except as provided in paragraph not having design and operational (b) of this section, each air navigation characteristics identical to those of fa- certificate of ‘‘Lawful Authority to Op- cilities currently approved under this erate a True Light’’ is hereby revoked, part, including requests for deviations and each application therefor is hereby from this part for such facilities, must terminated.

be submitted to the Director, Advanced (b) Paragraph (a) of this section does Systems Design Service.

not apply to— (b) The following requests must be (1) A certificate issued to a Federal- submitted to the Regional Adminis- Aid Airport Program sponsor who was trator of the region in which the facil- required to apply for that certificate ity is located: under regulations then in effect, and (1) Requests for approval of facilities who has not surrendered that certifi- that have design and operational char- cate under § 151.86(e) of this chapter; or acteristics identical to those of facili- (2) An application made by a Federal- ties currently approved under this Aid Airport Program sponsor who was part, including requests for deviations required to make that application from this part for such facilities.

under regulations then in effect, and (2) Requests for deviations from this who has not terminated that applica- part for facilities currently approved tion under § 151.86(e) of this chapter.

under this part.

(49 U.S.C. 1101–1120; sec. 307, 72 Stat. 749, 49 (3) Requests for modification of fa- U.S.C. 1348) cilities currently approved under this [Amdt. 171–4, 33 FR 12545, Sept. 5, 1968] part.

[Amdt. 171–7, 35 FR 12711, Aug. 11, 1970, as Subpart E—General amended by Amdt. 171–15, 54 FR 39296, Sept.

25, 1989] § 171.71 Materials incorporated by ref- erence.

Subpart F—Simplified Directional Copies of standards, recommended Facility (SDF) practices and documents incorporated by reference in this part are available for the use of interested persons at any S OURCE : Docket 10116, 35 FR 12711, Aug. 11, FAA Regional Office and FAA Head- 1970, unless otherwise noted.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00840 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.107 must meet the requirements of § 171.101 Scope.

§§ 171.109 and 171.111.

This subpart sets forth minimum re- (3) The installation of the equipment quirements for the approval and oper- must meet the requirements of ation of non-Federal Simplified Direc- § 171.113.

tional Facilities (SDF) that are to be (4) The owner must agree to operate involved in the approval of instrument and maintain the facility in accord- flight rules and air traffic control pro- ance with § 171.115.

cedures related to those facilities.

(5) The owner must agree to furnish § 171.103 Requests for IFR procedure.

periodic reports as set forth in § 171.117, and agree to allow the FAA to inspect (a) Each person who requests an IFR the facility and its operation whenever procedure based on an SDF that he necessary.

owns must submit the following infor- mation with that request: (6) The owner must assure the FAA (1) A description of the facility and that he will not withdraw the facility evidence that the equipment meets the from service without the permission of performance requirements of § 171.109 the FAA.

and the standards and tolerances of (7) The owner must bear all costs of § 171.111, and is installed in accordance meeting the requirements of this sec- with § 171.113.

tion and of any flight or ground inspec- (2) A proposed procedure for oper- tions made before the facility is com- ating the facility.

missioned, except that the FAA may (3) A proposed maintenance organiza- bear certain of these costs subject to tion and a maintenance manual that budgetary limitations and policy estab- meets the requirements of § 171.115.

lished by the Administrator.

(4) A statement of intent to meet the (b) If the applicant for approval requirements of this subpart.

meets the requirements of paragraph (5) A showing that the facility has an (a) of this section, the FAA commis- acceptable level of operational reli- sions the facility as a prerequisite to ability as prescribed in § 171.111(k), and its approval for use in an IFR proce- an acceptable standard of performance.

dure. The approval is withdrawn at any Previous equivalent operational experi- time the facility does not continue to ence with a facility with identical de- meet those requirements. In addition, sign and operational characteristics the facility is licensed by the Federal will be considered in showing compli- Communications Commission. The ance with this paragraph.

Federal Aviation Administration rec- (b) After the Federal Aviation Ad- ommends cancellation or nonrenewal ministration inspects and evaluates of the Federal Communications Com- the facility, it advises the owner of the mission license whenever the frequency results and of any required changes in channel is needed for higher priority the facility or the maintenance manual common system service.

or maintenance organization. The owner must then correct the defi- § 171.107 Definition.

ciencies, if any, and operate the facil- As used in this subpart: ity for an in-service evaluation by the SDF (simplified directional facility) Federal Aviation Administration.

means a directional aid facility pro- § 171.105 Minimum requirements for viding only lateral guidance (front or approval.

back course) for approach from a final approach fix.

(a) The following are the minimum DDM (difference in depth of modula- requirements that must be met before tion) means the percentage modulation the Federal Aviation Administration depth of the larger signal minus the will approve an IFR procedure for a percentage modulation depth of the non-Federal Simplified Directional Fa- smaller signal, divided by 100.

cility: (1) A suitable frequency channel Angular displacement sensitivity means must be available. the ratio of measured DDM to the cor- (2) The facility’s performance, as de- responding angular displacement from termined by air and ground inspection, the appropriate reference line.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00841 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.109 Back course sector means the course tone predominating on one side of the sector on the opposite end of the run- course and with the 150 Hz tone pre- way from the front course sector. dominating on the opposite side.

Course line means the locus of points (2) When an observer faces the SDF along the final approach course at from the approach end of runway, the which the DDM is zero. depth of modulation of the radio fre- Course sector means a sector in a hori- quency carrier due to the 150 Hz tone zontal plane containing the course line must predominate on his right hand and limited by the loci of points near- and that due to the 90 Hz tone must est to the course line at which the predominate on his left hand.

DDM is 0.155. (3) All horizontal angles employed in Displacement sensitivity means the specifying the SDF field patterns must ratio of measured DDM to the cor- originate from the center of the an- responding lateral displacement from tenna system which provides the sig- the appropriate reference line. nals used in the front course sector.

Front course sector means the course (4) The SDF must operate on odd sector centered on the course line in tenths or odd tenths plus a twentieth the direction from the runway in which MHz within the frequency band 108.1 a normal final approach is made. MHz to 111.95 MHz. The frequency tol- Half course sector means the sector in erance of the radio frequency carrier a horizontal plane containing the must not exceed plus or minus 0.002 course line and limited by the loci of percent.

points nearest to the course line, at (5) The radiated emission from the which the DDM is 0.0775.

SDF must be horizontally polarized.

Point A means a point on the front The vertically polarized component of course in the approach direction a dis- the radiation on the course line must tance of 4 nautical miles from the not exceed that which corresponds to threshold.

an error one-twentieth of the course Point A1 means a point on the front sector width when an aircraft is posi- course in the approach direction a dis- tioned on the course line and is in a tance of 1 statute mile from the thresh- roll attitude of 20 ° from the horizontal.

old.

(6) The SDF must provide signals suf- Point A2 means a point on the front ficient to allow satisfactory operation course at the threshold.

of a typical aircraft installation within Reference datum means a point at a the sector which extends from the cen- specified height located vertically ter of the SDF antenna system to dis- above the intersection of the course tances of 18 nautical miles within a and the threshold.

plus or minus 10 ° sector and 10 nautical Missed approach point means the miles within the remainder of the cov- point on the final approach course, not erage when alternative navigational fa- farther from the final approach fix cilities provide satisfactory coverage than Point ‘‘A2’’, at which the ap- within the intermediate approach area.

proach must be abandoned, if the ap- SDF signals must be receivable at the proach and subsequent landing cannot distances specified at and above a be safely completed by visual ref- height of 1,000 feet above the elevation erence, whether or not the aircraft has of the threshold, or the lowest altitude descended to the minimum descent al- authorized for transition, whichever is titude.

higher. Such signals must be receiv- able, to the distances specified, up to a § 171.109 Performance requirements.

surface extending outward from the (a) The Simplified Directional Facil- SDF antenna and inclined at 7 ° above ity must perform in accordance with the horizontal.

the following standards and practices: (7) The modulation tones must be (1) The radiation from the SDF an- phase-locked so that within the half tenna system must produce a com- course sector, the demodulated 90 Hz posite field pattern which is amplitude and 150 Hz wave forms pass through modulated by a 90 Hz and a 150 Hz tone. zero in the same direction within 20 ° of The radiation field pattern must phase relative to the 150 Hz component, produce a course sector with the 90 Hz every half cycle of the combined 90 Hz VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00842 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.109 and 150 Hz wave form. However, the the SDF antenna within the sector ± 10 ° phase need not be measured within the to ± 35 ° each side of course line.

half course sector.

(11) The SDF may provide a ground- (8) The angle of convergence of the to-air radiotelephone communication final approach course and the extended channel to be operated simultaneously with the navigation and identification runway centerline must not exceed 30 ° .

signals, if that operation does not The final approach course must be interfere with the basic function. If a aligned to intersect the extended run- way centerline between points A1 and channel is provided, it must conform the runway threshold. When an oper- with the following standards: (i) The channel must be on the same ational advantage can be achieved, a final approach course that does not radio frequency carrier or carriers as intersect the runway or that intersects used for the SDF function, and the ra- it at a distance greater than point A1 diation must be horizontally polarized.

from the threshold, may be established, Where two carriers are modulated with if that course lies within 500 feet lat- speech, the relative phases of the mod- ulations on the two carriers must avoid erally of the extended runway center- the occurrence of nulls within the cov- line at a point 3,000 feet outward from erage of the SDF.

the runway threshold. The mean course line must be maintained within ± 10 per- (ii) On centerline, the peak modula- cent of the course sector width. tion depth of the carrier or carriers due to the radiotelephone communications (9) The nominal displacement sensi- must not exceed 50 percent but must be tivity within the half course sector adjusted so that the ratio of peak mod- must be 50 microamperes/degree. The nominal course sector width must be ulation depth due to the radio- 6 ° . When an operational advantage can telephone communications to that due be achieved, a nominal displacement to the identification signal is approxi- sensitivity of 25 microamperes/degree mately 9:1.

may be established, with a nominal (iii) The audio frequency characteris- course sector width of 12 ° with propor- tics of the radiotelephone channel tional displacement sensitivity. The must be flat to within 3 db relative to lateral displacement sensitivity must the level at 1,000 Hz over the range be adjusted and maintained within the from 300 Hz to 3,000 Hz.

limits of plus or minus 17 percent of (12)(i) The SDF must provide for the the nominal value.

simultaneous transmission of an iden- (10) The off-course (clearance) signal tification signal, specific to the runway must increase at a substantially linear and approach direction, on the same rate with respect to the angular dis- radio frequency carrier or carriers as placement from the course line up to used for the SDF function. The trans- an angle on either side of the course mission of the identification signal line where 175 microamperes of deflec- must not interfere in any way with the tion is obtained. From that angle to basic SDF function.

± 10 ° , the off-course deflection must not (ii) The identification signal must be be less than 175 microamperes. From produced by Class A2 modulation of the ± 10 ° to ± 35 ° the off-course deflection radio frequency carrier or carriers must not be less than 150 micro- using a modulation tone of 1020 Hz amperes. With the course adjusted to within ± 50 Hz. The depth of modulation cause any of several monitor alarm must be between the limits of 5 and 15 conditions, the aforementioned values percent except that, where a radio- of 175 microamperes in the sector 10 ° telephone communication channel is each side of course and 150 micro- provided, the depth of modulation must amperes in the sector ± 10 ° to ± 35 ° may be adjusted so that the ratio of peak be reduced to 160 microamperes and 135 modulation depth due to radio- microamperes, respectively. These con- telephone communications to that due ditions must be met at a distance of 18 to the identification signal modulation nautical miles from the SDF antenna is approximately 9:1. The emissions within the sector 10 ° each side of carrying the identification signal must course line and 10 nautical miles from be horizontally polarized.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00843 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.111 (iii) The identification signal must (2) Course alignment. The mean course employ the International Morse Code line must be adjusted and maintained and consist of three letters. within the limits of ± 10 percent of the (iv) The identification signal must be nominal course sector width.

transmitted at a speed corresponding (3) Course structure. Course deviations to approximately seven words per due to roughness, scalloping, or bends minute, and must be repeated at ap- must be within the following limita- proximately equal intervals, not less tions: than six times per minute. When SDF (i) Front course. ( a ) Course structure transmission is not available for oper- from 18 miles from runway threshold to ational use, including periods of re- Point A must not exceed ± 40 micro- moval of navigational components or amperes; during maintenance or test trans- ( b ) Point A to Point A–1—linear de- missions, the identification signal crease from not more than ± 40 micro- must be suppressed.

amperes at Point A to not more than (b) It must be shown during ground ± 20 microamperes at Point A–1; inspection of the design features of the ( c ) Point A–1 to Missed Approach equipment that there will not be condi- Point—not more than ± 20 micro- tions that will allow unsafe operations amperes; because of component failure or dete- ( d ) Monitor tolerances: width ± 17 per- rioration.

cent of nominal; alignment— ± 10 per- (c) The monitor must be checked pe- cent of nominal course sector width.

riodically during the in-service test (ii) Back course. ( a ) Course structure evaluation period for calibration and 18 miles from runway threshold to 4 stability. These tests, and ground miles from runway threshold must not checks of SDF radiation characteris- exceed ± 40 microamperes. Four miles tics must be conducted in accordance to 1 mile from R/W must not exceed ± 40 with the maintenance manual required microamperes decreasing to not more by § 171.115(c) and must meet the stand- than ± 20 microamperes, at a linear ards and tolerances contained in rate.

§ 171.111(j).

( b ) Monitor tolerances: width— ± 17 (d) The monitor system must provide percent of nominal; alignment— ± 10 a warning to the designated control percent of nominal course sector width.

point(s) when any of the conditions of [Docket 10116, 35 FR 12711, Aug. 11, 1970, as § 171.111(j) occur, within the time peri- amended by Amdt. 171–9, 38 FR 28557, Oct. 15, ods specified in that paragraph.

1973] (e) Flight inspection to determine the adequacy of the facility’s oper- § 171.111 Ground standards and toler- ational performance and compliance ances.

with applicable performance require- Compliance with this section must be ments must be conducted in accord- shown as a condition to approval and ance with the ‘‘U.S. Standard Flight must be maintained during operation Inspection Manual.’’ Tolerances con- of the SDF.

tained in the U.S. Standard Flight In- (a) Frequency. (1) The SDF must oper- spection Manual, section 217, must be ate on odd tenths or odd tenths plus a complied with except as stated in para- twentieth MHz within the frequency graph (f) of this section.

band 108.1 MHz to 111.95 MHz. The fre- (f) Flight inspection tolerances speci- quency tolerance of the radio fre- fied in section 217 of the ‘‘U.S. Stand- quency carrier must not exceed plus or ard Flight Inspection Manual’’ must be minus 0.002 percent.

complied with except as follows: (2) The modulating tones must be 90 (1) Course sector width. The nominal Hz and 150 Hz within ± 2.5 percent.

course sector width must be 6 ° . When (3) The identification signal must be an operational advantage can be 1020 Hz within ± 50 Hz.

achieved, a nominal course sector width of 12 ° may be established. Course (4) The total harmonic content of the sector width must be adjusted and 90 Hz tone must not exceed 10 percent.

maintained within the limits of ± 17 (5) The total harmonic content of the percent of the nominal value. 150 Hz tone must not exceed 10 percent.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00844 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.113 (b) Power output. The normal carrier (3) RF power reduction alarm: The power output must be of a value which monitor must alarm and cause radi- will provide coverage requirements of ation to cease, or identification and § 171.109(a)(6) when reduced by 3 dB to navigation signals must be removed, if the monitor RF power reduction alarm the output power is reduced by 3 db or more from normal.

point specified in § 171.111(j)(3).

(4) Modulation level alarm: The mon- (c) VSWR. (1) The VSWR of carrier itor must alarm and cause radiation to and sideband feedlines must be a nomi- cease, or identification and navigation nal value of 1/1 and must not exceed 1.2/ signals must be removed, if the 90 Hz 1.

and 150 Hz modulation levels decrease (2) The sponsor will also provide addi- by 17 percent or more.

tional manufacturer’s ground stand- (5) Course sector width alarm: The ards and tolerances for all VSWR pa- monitor must alarm and cause radi- rameters peculiar to the equipment ation to cease, or identification and which can effect performance of the fa- navigation signals must be removed, cility in meeting the requirements for a change in course sector width to specified in §§ 171.109 and 171.111.

a value differing by ± 17 percent or more (d) Insulation resistance. The insula- from the standard.

tion resistance of all coaxial feedlines (6) Monitor delay before shutdown: must be greater than 20 megohms.

Radiation must cease, or identification (e) Depth of modulation. (1) The depth and navigation signals must be re- of modulation of the radio frequency moved, within 10 seconds after a fault carrier due to each of the 90 Hz and 150 is detected by the monitor, and no at- Hz tones must be 20 percent ± 2 percent tempt must be made to resume radi- along the course line.

ation for a period of at least 20 seconds.

(2) The depth of modulation of the If an automatic recycle device is used, radio frequency carrier due to the 1020 not more than three successive recy- Hz identification signal must be within cles may be permitted before a com- 5 percent to 15 percent.

plete SDF shutdown occurs.

(f) Course sector width. The standard (k) Mean time between failures. The course sector width must be 6 ° or 12 ° .

mean time between failures must not The course sector must be maintained be less than 800 hours. This measure is with ± 17 percent of the standard.

applied only to equipment failures (g) Course alignment. Course align- (monitor or transmitting equipment, ment must be as specified in including out of tolerance conditions) § 171.109(a)(8).

which result in facility shutdown. It (h) Back course alignment and width. If does not relate to the responsiveness of a back course is provided, standards the maintenance organization.

and tolerances for back course sector (l) Course alignment stability. Drift of width and alignment must be the same the course alignment must not exceed as course sector width and course one-half the monitor limit in a 1-week alignment specified in paragraphs (f) period.

and (g) of this section.

(i) Clearance. Clearance must be as [Docket 10116, 35 FR 12711, Aug. 11, 1970, as specified in § 171.109(a)(10).

amended by Amdt. 171–9, 38 FR 28558, Oct. 15, (j) Monitor standards and tolerances. 1973] (1) The monitor system must provide a § 171.113 Installation requirements.

warning to the designated control point(s) when any of the conditions de- (a) The facility must be installed ac- scribed in this paragraph occur, within cording to accepted good engineering the time periods specified in paragraph practices, applicable electric and safe- (j)(6) of this section.

ty codes, and FCC requirements.

(2) Course shift alarm: The monitor (b) The SDF facility must have the must alarm and cause radiation to following basic components: cease, or identification and navigation (1) VHF SDF equipment and associ- signals must be removed, if the course ated monitor system; alignment deviates from standard (2) Remote control, and indicator alignment by 10 percent or more of the equipment (remote monitor) when re- standard course sector width. quired by the FAA; VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00845 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.115 (3) A final approach fix; and adjacent to controlled airspace, and (4) Compass locator (COMLO) or where extensive delays are not a fac- marker if suitable fixes and initial ap- tor, the requirements of paragraphs (f) proach routes are not available from (1) and (2) of this section may be re- existing facilities.

duced to reliable communications (at (c) The facility must have a reliable least a landline telephone) from the source of suitable primary power, ei- airport to the nearest Federal Aviation ther from a power distribution system Administration air traffic control or or locally generated. Also, adequate communications facility, if an adjacent power capacity must be provided for Federal Aviation Administration facil- operation of test and working equip- ity can communicate with aircraft dur- ment at the SDF. A determination by ing the proposed instrument approach the Federal Aviation Administration procedure down to the airport surface as to whether a facility will be required or at least down to the minimum ap- to have standby power for the SDF and proach altitude.

monitor accessories to supplement the (g) At those locations where two sep- primary power will be made for each arate SDF facilities serve opposite airport based upon operational mini- ends of a single runway, an interlock mums and density of air traffic.

must insure that only the facility serv- (d) A determination by the Federal ing the approach direction in use can Aviation Administration as to whether radiate, except where no operationally a facility will be required to have dual harmful interference results.

transmitting equipment with auto- (h) At those locations where, in order matic changeover for the SDF will be to alleviate frequency congestion, the made for each airport based upon oper- SDF facilities serving opposite ends of ational minimums and density of air one runway employ identical fre- traffic.

quencies, an interlock must insure that (e) There must be a means for deter- the facility not in operational use can- mining, from the ground, the perform- not radiate.

ance of the equipment (including an- (i) Provisions for maintenance and tennae), initially and periodically.

operations by authorized persons only.

(f) The facility must have the fol- (j) Where an operational advantage lowing ground-air or landline commu- exists, the installation may omit a nication services: back course.

(1) At facilities outside of and not im- [Docket 10116, 35 FR 12711, Aug. 11, 1970, as mediately adjacent to controlled air- amended by Amdt. 171–16, 56 FR 65664, Dec.

space, there must be ground-air com- 17, 1991] munications from the airport served by the facility. The utilization of voice on § 171.115 Maintenance and operations the SDF should be determined by the requirements.

facility operator on an individual basis.

(a) The owner of the facility shall es- (2) At facilities within or imme- tablish an adequate maintenance sys- diately adjacent to controlled airspace, tem and provide qualified maintenance there must be ground/air communica- personnel to maintain the facility at tions required by paragraph (b)(1) of the level attained at the time it was this section and reliable communica- commissioned. Each person who main- tions (at least a landline telephone) tains a facility shall meet at a min- from the airport to the nearest Federal imum the Federal Communications Aviation Administration air traffic Commission’s licensing requirements control or communications facility.

and show that he has the special Compliance with paragraphs (f) (1) and knowledge and skills needed to main- (2) of this section need not be shown at tain the facility, including proficiency airports where an adjacent Federal in maintenance procedures and the use Aviation Administration facility can of specialized test equipment.

communicate with aircraft on the (b) The SDF must be designed and ground at the airport and during the maintained so that the probability of entire proposed instrument approach operation within the performance re- procedure. In addition, at low traffic quirements specified is high enough to density airports within or immediately insure an adequate level of safety. In VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00846 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.115 the event out-of-tolerance conditions (14) Commissioning of the facility.

develop, the facility shall be removed (15) An acceptable procedure for from operation, and the designated amending or revising the manual.

control point notified.

(16) An explanation of the kinds of (c) The owner must prepare, and ob- activities (such as construction or tain approval of, and each person oper- grading) in the vicinity of the facility ating or maintaining the facility shall that may require shutdown or certifi- comply with, an operations and main- cation of the facility by Federal Avia- tenance manual that sets forth proce- tion Administration flight check.

dures for operations, preventive main- (17) Procedure for conducting a tenance, and emergency maintenance, ground check of SDF course alignment, including instructions on each of the width and clearance.

following: (18) The following information con- (1) Physical security of the facility.

cerning the facility: This includes provisions for desig- (i) Facility component locations with nating critical areas relative to the fa- respect to airport layout, instrument cility and preventing or controlling runway, and similar areas; movements within the facility that (ii) The type, make, and model of the may adversely affect SDF operations.

basic radio equipment that will provide (2) Maintenance and operations by the service; authorized persons only.

(iii) The station power emission and (3) Federal Communications Commis- frequencies of the SDF, markers and sion requirements for operating per- associated COMLOs, if any; sonnel and maintenance personnel.

(iv) The hours of operation; (4) Posting of licenses and signs.

(v) Station identification call letters (5) Relation between the facility and and method of station identification Federal Aviation Administration air and the time spacing of the identifica- traffic control facilities, with a de- tion; scription of the boundaries of con- (vi) A description of the critical parts trolled airspace over or near the facil- that may not be changed, adjusted, or ity, instructions for relaying air traffic repaired without a Federal Aviation control instructions and information Administration flight check to confirm (if applicable), and instructions for the published operations.

operation of an air traffic advisory (d) The owner shall make a ground service if the facility is located outside check of the facility each month in ac- of controlled airspace.

cordance with procedures approved by (6) Notice to the Administrator of the Federal Aviation Administration any suspension of service.

at the time of commissioning, and (7) Detailed and specific maintenance shall report the results of the checks as procedures and servicing guides stating provided in § 171.117.

the frequency of servicing.

(e) If the owner desires to modify the (8) Air-ground communications, if facility, he shall submit the proposal provided, expressly written or incor- to the Federal Aviation Administra- porating appropriate sections of Fed- tion and may not allow any modifica- eral Aviation Administration manuals tions to be made without specific ap- by reference.

proval.

(9) Keeping of station logs and other (f) The owner’s maintenance per- technical reports, and the submission sonnel shall participate in initial in- of reports required by § 171.117.

spections made by the Federal Avia- (10) Monitoring of the facility.

tion Administration. In the case of sub- (11) Names, addresses, and telephone sequent inspections, the owner or his numbers of persons to be notified in an representatives shall participate.

emergency.

(12) Inspection by U.S. personnel. (g) Whenever it is required by the (13) Shutdowns for routine mainte- Federal Aviation Administration, the nance and issue of ‘‘Notices to Airmen’’ owner shall incorporate improvements for routine or emergency shutdowns, in SDF maintenance. In addition, he except that private use facilities may shall provide a stock of spare parts, of omit ‘‘Notices to Airmen.’’ such a quantity, to make possible the VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00847 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.117 prompt replacement of components gional Office of the Federal Aviation that fail or deteriorate in service. Administration.

(h) The owner shall provide Federal [Docket 10116, 35 FR 12711, Aug. 11, 1970, as Aviation Administration approved test amended by Amdt. 171–10, 40 FR 36110, Aug.

instruments needed for maintenance of 19, 1975] the facility.

(i) The owner shall close the facility Subpart G—Distance Measuring by ceasing radiation and shall issue a Equipment (DME) ‘‘Notice to Airmen’’ that the facility is out of service (except that private use S OURCE : Docket 10116, 35 FR 12715, Aug. 11, facilities may omit ‘‘Notices to Air- 1970, unless otherwise noted.

men’’), upon receiving two successive pilot reports of its malfunctioning.

§ 171.151 Scope.

This subpart sets forth minimum re- § 171.117 Reports.

quirements for the approval and oper- The owner of each facility to which ation of non-Federal DME facilities this subpart applies shall make the fol- that are to be involved in the approval lowing reports, at the time indicated, of instrument flight rules and air traf- to the Federal Aviation Administra- fic control procedures related to those tion Regional Office for the area in facilities.

which the facility is located: (a) Record of meter readings and ad- § 171.153 Requests for IFR procedure.

justments (Form FAA–198). To be filled (a) Each person who requests an IFR out by the owner or his maintenance procedure based on a DME facility that representative with the equipment ad- he owns must submit the following in- justments and meter readings as of the formation with that request: time of commissioning, with one copy (1) A description of the facility and to be kept in the permanent records of evidence that the equipment meets the the facility and two copies to the ap- performance requirements of § 171.157 propriate Regional Office of the Fed- and is installed in accordance with eral Aviation Administration. The § 171.159.

owner shall revise the form after any (2) A proposed procedure for oper- major repair, modification, or re- ating the facility.

tuning, to reflect an accurate record of (3) A proposed maintenance organiza- facility operation and adjustment.

tion and maintenance manual that (b) Facility maintenance log (FAA meets the requirement of § 171.161.

Form 6030–1) This form is a permanent (4) A statement of intention to meet record of all equipment malfunctioning the requirements of this subpart.

met in maintaining the facility, in- (5) A showing that the facility has an cluding information on the kind of acceptable level of operational reli- work and adjustments made, equip- ability and an acceptable standard of ment failures, causes (if determined), performance. Previous equivalent oper- and corrective action taken. The owner ational experience with a facility with shall keep the original of each report identical design and operational char- at the facility and send a copy to the acteristics will be considered in show- appropriate Regional Office of the Fed- ing compliance with this paragraph.

eral Aviation Administration at the (b) After the Federal Aviation Ad- end of each month in which it is pre- ministration inspects and evaluates pared.

the facility, it advises the owner of the (c) Radio equipment operation record results and of any required changes in (Form FAA–418), containing a complete the facility or the maintenance manual record of meter readings, recorded on or maintenance organization. The each scheduled visit to the facility.

owner must then correct the defi- The owner shall keep the original of ciencies, if any, and operate the facil- each month’s record at the facility and ity for an in-service evaluation by the send a copy of it to the appropriate Re- Federal Aviation Administration.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00848 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.159 equipment that there will not be condi- § 171.155 Minimum requirements for approval. tions that will allow unsafe operations because of component failure or dete- (a) The following are the minimum rioration.

requirements that must be met before (c) The monitor must be checked pe- the Federal Aviation Administration riodically, during the in-service test will approve an IFR procedure for a evaluation period, for calibration and non-Federal DME: stability. These tests and ground tests (1) A suitable frequency channel of the functional and performance must be available.

characteristics of the DME transponder (2) The facility’s performance, as de- must be conducted in accordance with termined by air and ground inspection, the maintenance manual required by must meet the requirements of § 171.157. § 171.161(b).

(3) The installation of the equipment (d) Flight inspection to determine must meet the requirements of the adequacy of the facility’s oper- § 171.159. ational performance and compliance (4) The owner must agree to operate with applicable ‘‘Standards and Rec- and maintain the facility in accord- ommended Practices’’ must be accom- ance with § 171.161. plished in accordance with the ‘‘U.S.

(5) The owner must agree to furnish Standard Flight Inspection Manual.’’ periodic reports, as set forth in [Docket 10116, 35 FR 12715, Aug. 11, 1970, as § 171.163, and must agree to allow the amended by Amdt. 171–13, 50 FR 4875, Nov. 27, Federal Aviation Administration to in- 1985] spect the facility and its operation whenever necessary.

§ 171.159 Installation requirements.

(6) The owner must assure the Fed- (a) The facility must be installed ac- eral Aviation Administration that he cording to accepted good engineering will not withdraw the facility from practices, applicable electric and safe- service without the permission of the ty codes, and Federal Communications Federal Aviation Administration.

Commission requirements.

(7) The owner must bear all costs of (b) The facility must have a reliable meeting the requirements of this sec- source of suitable primary power, ei- tion and of any flight or ground inspec- ther from a power distribution system tions made before the facility is com- or locally generated, with a supple- missioned, except that the Federal mental standby system, if needed.

Aviation Administration may bear cer- (c) Dual transmitting equipment tain of these costs subject to budgetary with automatic changeover is preferred limitations and policy established by and may be required to support certain the Administrator.

IFR procedures.

(b) If the applicant for approval (d) There must be a means for deter- meets the requirements of paragraph mining from the ground, the perform- (a) of this section, the Federal Aviation ance of the equipment, initially and pe- Administration commissions the facil- riodically.

ity as a prerequisite to its approval for (e) A facility intended for use as an use in an IFR procedure. The approval instrument approach aid for an airport is withdrawn at any time the facility must have or be supplemented by the does not continue to meet those re- following ground air or landline com- quirements.

munications services: § 171.157 Performance requirements.

(1) At facilities outside of and not im- mediately adjacent to controlled air- (a) The DME must meet the perform- space, there must be ground-air com- ance requirements set forth in the munications from the airport served by ‘‘International Standards and Rec- the facility. Separate communications ommended Practices. Aeronautical channels are acceptable.

Telecommunications, Part I, Para- graph 3.5’’ (Annex 10 to the Convention (2) At facilities within or imme- of International Civil Aviation). diately adjacent to controlled airspace, (b) It must be shown during ground there must be the ground-air commu- inspection of the design features of the nications required by paragraph (e)(1) VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00849 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.161 of this section and reliable communica- including instructions on each of the tions (at least a landline telephone) following: from the airport to the nearest Federal (1) Physical security of the facility.

Aviation Administration air traffic (2) Maintenance and operations by control or communications facility.

authorized persons only.

Separate communications channels are (3) Federal Communications Commis- acceptable.

sion’s requirements and maintenance personnel.

Compliance with paragraphs (e) (1) and (4) Posting of licenses and signs.

(2) of this section need not be shown at (5) Relations between the facility and airports where an adjacent Federal Federal Aviation Administration air Aviation Administration facility can traffic control facilities, with a de- communicate with aircraft on the scription of the boundaries of con- ground at the airport and during the trolled airspace over or near the facil- entire proposed instrument approach procedure. In addition, at low traffic ity, instructions for relaying air traffic density airports within or immediately control instructions and information adjacent to controlled airspace, and (if applicable), and instructions for the where extensive delays are not a fac- operation of an air traffic advisory tor, the requirements of paragraphs (e) service if the DME is located outside of (1) and (2) of this section may be re- controlled airspace.

duced to reliable communications (at (6) Notice to the Administrator of least a landline telephone) from the any suspension of service.

airport to the nearest Federal Aviation (7) Detailed and specific maintenance Administration air traffic control or procedures and servicing guides stating communications facility, if an adjacent the frequency of servicing.

Federal Aviation Administration facil- (8) Air-ground communications, if ity can communicate with aircraft dur- provided, expressly written or incor- ing the proposed instrument approach porating appropriate sections of Fed- procedure, at least down to the min- eral Aviation Administration manuals imum en route altitude for the con- by reference.

trolled airspace area.

(9) Keeping of station logs and other [Docket 10116, 35 FR 12715, Aug. 11, 1970, as technical reports, and the submission amended by Amdt. 171–16, 56 FR 65665, Dec.

of reports required by § 171.163.

17, 1991] (10) Monitoring of the facility.

(11) Inspections by U.S. personnel.

§ 171.161 Maintenance and operations (12) Names, addresses, and telephone requirements.

numbers of persons to be notified in an (a) The owner of the facility shall es- emergency.

tablish an adequate maintenance sys- (13) Shutdowns for routine mainte- tem and provide qualified maintenance nance and issue of ‘‘Notices to Airmen’’ personnel to maintain the facility at for routine or emergency shutdowns, the level attained at the time it was except that private use facilities may commissioned. Each person who main- omit the ‘‘Notices to Airmen.’’ tains a facility shall meet at a min- (14) An explanation of the kinds of imum the Federal Communications activity (such as construction or grad- Commission’s licensing requirements ing) in the vicinity of the facility that and show that he has the special may require shutdown or reapproval of knowledge and skills needed to main- the facility by Federal Aviation Ad- tain the facility, including proficiency ministration flight check.

in maintenance procedures and the use (15) Commissioning of the facility.

of specialized test equipment.

(16) An acceptable procedure for (b) The owner must prepare and ob- amending or revising the manual.

tain Federal Aviation Administration (17) The following information con- approval of, and each person operating cerning the facility: or maintaining the facility shall com- ply with, an operations and mainte- (i) Location by latitude and lon- nance manual that sets forth proce- gitude to the nearest second, and its dures for operations, preventive main- position with respect to airport lay- tenance, and emergency maintenance, outs.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00850 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.203 (ii) The type, make, and model of the the time of commissioning, with one basic radio equipment that will provide copy to be kept in the permanent the service. records of the facility and two copies (iii) The station power emission and to the appropriate Regional office of frequency. the FAA. The owner shall revise the (iv) The hours of operation. form after any major repair, modifica- (v) Station identification call letters tion, or returning, to reflect an accu- and methods of station identification, rate record of facility operation and whether by Morse code or recorded adjustment.

voice announcement, and the time (b) Facility maintenance log (FAA spacing of the identification.

Form 6030–1). This form is a permanent (vi) A description of the critical parts record of all equipment malfunctioning that may not be changed, adjusted, or met in maintaining the facility, in- repaired without an FAA flight check cluding information on the kind of to confirm published operations.

work and adjustments made, equip- (c) The owner shall make a monthly ment failures, causes (if determined), ground operational check in accord- and corrective action taken. The owner ance with procedures approved by the shall keep the original of each report FAA at the time of commissioning, and at the facility and send a copy to the shall report the results of the checks as appropriate Regional Office of the Fed- provided in § 171.163.

eral Aviation Administration at the (d) If the owner desires to modify the end of the month in which it is pre- facility, he shall submit the proposal pared.

to the FAA and may not allow any (c) Radio equipment operation record modifications to be made without spe- (Form FAA–418), containing a complete cific approval.

record of meter readings, recorded on (e) The owner’s maintenance per- each scheduled visit to the facility.

sonnel shall participate in initial in- The owner shall keep the original of spections made by the FAA. In the case each month’s record at the facility and of subsequent inspections, the owner or send a copy of it to the appropriate Re- his representative shall participate.

gional Office of the Federal Aviation (f) Whenever it is required by the Administration.

FAA, the owner shall incorporate im- provements in DME maintenance.

[Docket 10116, 35 FR 12715, Aug. 11, 1970, as (g) The owner shall provide a stock of amended by Amdt. 171–10, 40 FR 36110, Aug.

19, 1975] spare parts of such a quantity to make possible the prompt replacement of components that fail or deteriorate in Subpart H—VHF Marker Beacons service.

(h) The owner shall provide FAA-ap- S OURCE : Docket 10116, 35 FR 12716, Aug. 11, proved test instruments needed for 1970, unless otherwise noted.

maintenance of the facility.

(i) The owner shall shut down the fa- § 171.201 Scope.

cility ( i.e. , cease radiation and issue a (a) This subpart sets forth minimum NOTAM that the facility is out-of-serv- requirements for the approval and op- ice) upon receiving two successive pilot eration of non-Federal VHF marker reports of its malfunctioning.

beacon facilities that are to be in- § 171.163 Reports. volved in the approval of instrument flight rules and air traffic control pro- The owner of each facility to which cedures related to those facilities.

this subpart applies shall make the fol- (b) [Reserved] lowing reports on forms furnished by the FAA, at the time indicated, to the § 171.203 Requests for IFR procedure.

FAA Regional office for the area in which the facility is located: (a) Each person who requests an IFR (a) Record of meter readings and ad- procedure which will incorporate the justments (Form FAA–198). To be filled use of a VHF marker beacon facility out by the owner with the equipment that he owns must submit the fol- adjustments and meter readings as of lowing information with that request: VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00851 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.205 (1) A description of the facility and (6) The owner must bear all costs of evidence that the equipment meets the meeting the requirements of this sec- performance requirements of § 171.207 tion and of any flight or ground inspec- and is installed in accordance with tions made before the facility is com- § 171.209. missioned, except that the Federal (2) A proposed procedure for oper- Aviation Administration may bear cer- ating the facility.

tain of these costs subject to budgetary (3) A proposed maintenance organiza- limitations and policy established by tion and a maintenance manual that the Administrator.

meets the requirements of § 171.211.

(b) If the applicant for approval (4) A statement of intent to meet the meets the requirements of paragraph requirement of this subpart.

(a) of this section, the Federal Aviation (5) A showing that the facility has an Administration commissions the facil- acceptable level of operational reli- ity as a prerequisite to its approval for ability, and an acceptable standard of use in an IFR procedure. The approval performance. Previous equivalent oper- is withdrawn at any time the facility ational experience may be shown to does not continue to meet those re- comply with this subparagraph.

quirements.

(b) After the Federal Aviation Ad- ministration inspects and evaluates § 171.207 Performance requirements.

the facility, it advises the owner of the (a) VHF Marker Beacons must meet results and of any required changes in the performance requirements set forth the facility or the maintenance manual in the ‘‘International Standards and or maintenance organization. The Recommended Practices, Aeronautical owner shall then correct the defi- Telecommunications, Part I, para- ciencies, if any, and operate the facil- graphs 3.1.6 and 3.6.’’ (Annex 10 to the ity for an in-service evaluation by the Convention on International Civil Federal Aviation Administration.

Aviation) except those portions that pertain to identification. Identification § 171.205 Minimum requirements for approval. of a marker beacon (75 MHz) must be in accordance with ‘‘U.S. Standard Flight (a) The following are the minimum Inspection Manual,’’ § 219.

requirements that must be met before (b) The facility must perform in ac- the Federal Aviation Administration cordance with recognized and accepted will approve an IFR procedure which good electronic engineering practices incorporates the use of a non-Federal for the desired service. The facility VHF marker beacon facility under this must be checked periodically during subpart: the in-service test evaluation period (1) The facility’s performances, as de- for calibration and stability. These termined by air and ground inspection, tests and ground tests of the marker must meet the requirements of radiation characteristics must be con- § 171.207.

ducted in accordance with the mainte- (2) The installation of the equipment nance manual required by § 171.211(b).

must meet the requirements of (c) It must be shown during ground § 171.209.

inspection of the design features of the (3) The owner must agree to operate equipment that there will not be condi- and maintain the facility in accord- tions that will allow unsafe operations ance with § 171.211.

because of component failure or dete- (4) The owner must agree to furnish rioration.

periodic reports, as set forth in § 171.213, and agree to allow the Federal (d) Flight inspection to determine Aviation Administration to inspect the the adequacy of the facility’s oper- facility and its operation whenever ational performance and compliance necessary. with applicable ‘‘Standards and Rec- (5) The owner must assure the Fed- ommended Practices’’ are conducted in eral Aviation Administration that he accordance with the ‘‘U.S. Standard will not withdraw the facility from Flight Inspection Manual.’’ The origi- service without the permission of the nal test is made by the Federal Avia- Federal Aviation Administration. tion Administration and later tests VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00852 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.211 must be made under arrangements, sat- commissioned. Each person who main- isfactory to the Federal Aviation Ad- tains a facility shall meet at a min- ministration, that are made by the imum the Federal Communications owner. Commission’s licensing requirements and show that he has the special § 171.209 Installation requirements.

knowledge and skills needed to main- (a) The facility must be installed ac- tain the facility, including proficiency cording to accepted good engineering in maintenance procedures and the use practices, applicable electric and safe- of specialized test equipment.

ty codes, and Federal Communications (b) The owner must prepare, and ob- Commission requirements. tain approval of, and each person who (b) The facility must have a reliable operates or maintains the facility shall source of suitable primary power. comply with, an operations and main- (c) Dual transmitting equipment may tenance manual that sets forth proce- be required, if applicable, to support dures for operations, preventive main- certain IFR procedures.

tenance, and emergency maintenance, (d) At facilities within or imme- including instructions on each of the diately adjacent to controlled airspace following: and that are intended for use as instru- (1) Physical security of the facility.

ment approach aids for an airport, (2) Maintenance and operations by there must be ground-air communica- authorized persons only.

tions or reliable communications (at (3) Federal Communications Commis- least a landline telephone) from the sion’s requirements for operating and airport to the nearest Federal Aviation maintenance personnel.

Administration air traffic control or (4) Posting of licenses and signs.

communication facility. Compliance (5) Relations between the facility and with this paragraph need not be shown Federal Aviation Administration air at airports where an adjacent Federal traffic control facilities, with a de- Aviation Administration facility can scription of the boundaries of con- communicate with aircraft on the trolled airspace over or near the facil- ground at the airport and during the ity, instructions for relaying air traffic entire proposed instrument approach control instructions and information procedure. In addition, at low traffic (if applicable).

density airports within or immediately (6) Notice to the Administrator of adjacent to controlled airspace, and any suspension of service.

where extensive delays are not a fac- (7) Detailed arrangements for main- tor, the requirements of this paragraph tenance, flight inspection, and serv- may be reduced to reliable communica- icing, stating the frequency of serv- tions (at least a landline telephone) icing.

from the airport to the nearest Federal (8) Keeping of station logs and other Aviation Administration air traffic technical reports, and the submission control or communications facility, if of reports required by § 171.213.

an adjacent Federal Aviation Adminis- (9) Monitoring of the facility, at least tration facility can communicate with once each half hour, to assure contin- aircraft during the proposed instru- uous operation.

ment approach procedure, at least (10) Inspections by U.S. personnel.

down to the minimum en route alti- (11) Names, addresses, and telephone tude for the controlled airspace area.

numbers of persons to be notified in an emergency.

[Docket 10116, 35 FR 12716, Aug. 11, 1970, as (12) Shutdowns for routine mainte- amended by Amdt. 171–16, 56 FR 65665, Dec.

17, 1991] nance and issue of ‘‘Notices to Airmen’’ for routine or emergency shutdowns § 171.211 Maintenance and operations (private use facilities may omit the requirements.

‘‘Notice to Airmen’’).

(a) The owner of the facility shall es- (13) Commissioning of the facility.

tablish an adequate maintenance sys- (14) An acceptable procedure for tem and provide qualified maintenance amending or revising the manual.

personnel to maintain the facility at (15) The following information con- the level attained at the time it was cerning the facility: VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00853 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.213 (i) Location by latitude and lon- eral Aviation Administration. The gitude to the nearest second, and its owner must revise the form after any position with respect to airport lay- major repair, modification, or re- outs. tuning, to reflect an accurate record of (ii) The type, make, and model of the facility operation and adjustment.

basic radio equipment that will provide (b) Facility maintenance log (FAA the service. Form 6030–1). This form is a permanent (iii) The station power emission and record of all equipment malfunctioning frequency. met in maintaining the facility, in- (iv) The hours of operation. cluding information on the kind of (v) Station identification call letters work and adjustments made, equip- and methods of station identification, ment failures, causes (if determined), whether by Morse Code or recorded and corrective action taken. The owner voice announcement, and the time shall keep the original of each report spacing of the identification. at the facility and send a copy to the (c) If the owner desires to modify the appropriate Regional Office of the Fed- facility, he shall submit the proposal eral Aviation Administration at the to the Federal Aviation Administra- end of the month in which it is pre- tion and meet applicable requirements pared.

of the Federal Communications Com- (c) Radio equipment operation record mission, and must not allow any modi- (Form FAA–418), containing a complete fication to be made without specific record of meter readings, recorded on approval by the Federal Aviation Ad- each scheduled visit to the facility.

ministration.

The owner shall keep the original of (d) The owner’s maintenance per- each month’s record at the facility and sonnel shall participate in initial in- send a copy of it to the appropriate Re- spections made by the Federal Avia- gional Office of the Federal Aviation tion Administration. In the case of sub- Administration.

sequent inspections, the owner or his [Docket 10116, 35 FR 12716, Aug. 11, 1970, as representative shall participate.

amended by Amdt. 171–10, 40 FR 36110, Aug.

(e) The owner shall provide a stock of 19, 1975] spare parts, of such a quantity to make possible the prompt replacement of Subpart I—Interim Standard components that fail or deteriorate in Microwave Landing System service.

(ISMLS) (f) The owner shall shut down the fa- cility by ceasing radiation, and shall issue a ‘‘Notice to Airmen’’ that the fa- S OURCE : Docket 14120, 40 FR 36110, Aug. 19, 1975, unless otherwise noted.

cility is out of service (except that pri- vate use facilities may omit ‘‘Notices § 171.251 Scope.

to Airmen’’) upon receiving two succes- sive pilot reports of its malfunctioning. This subpart sets forth minimum re- quirements for the approval and oper- § 171.213 Reports.

ation of non-Federal Interim Standard Microwave Landing System (ISMLS) The owner of each facility to which facilities that are to be involved in the this subpart applies shall make the fol- approval of instrument flight rules and lowing reports, at the times indicated, air traffic control procedures related to to the Federal Aviation Administra- those facilities.

tion Regional Office for the area in which the facility is located: § 171.253 Definitions.

(a) Record of meter readings and ad- justments (Form FAA–198). To be filled As used in this subpart: out by the owner or his maintenance Angular displacement sensitivity (Glide representative with the equipment ad- Slope) means the ratio of measured justments and meter readings as of the DDM to the corresponding angular dis- time of commissioning, with one copy placement from the appropriate ref- to be kept in the permanent records of erence line.

the facility and two copies to the ap- Collocated ground station means the propriate Regional Office of the Fed- type of ground station which transmits VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00854 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.253 two or more guidance signals simulta- ISMLS Point ‘A’ means an imaginary neously from a common location. point on the glide path/localizer course Course line means the locus of points measured along the runway centerline nearest to the runway centerline in extended, in the approach direction, any horizontal plane at which the DDM four nautical miles from the runway is zero.

threshold.

Course sector (full) means a sector in a ISMLS Point ‘B’ means an imaginary horizontal plane containing the course point on the glide path/localizer course line and limited by the loci of points measured along the runway centerline nearest to the course line at which the extended, in the approach direction, DDM is 0.155.

3500 feet from the runway threshold.

Course sector (half) means the sector ISMLS Point ‘C’ means a point in a horizontal plane containing the through which the downward extended course line and limited by the loci of straight portion of the glide path (at points nearest to the course line at the commissioned angle) passes at a which DDM is 0.0775.

height of 100 feet above the horizontal DDM means difference in depth of plane containing the runway threshold.

modulation. The percentage modula- Interim standard microwave landing tion depth of the larger signal minus system (ISMLS) means a ground station the percentage modulation depth of the smaller signal, divided by 100. which transmits azimuth and elevation Displacement sensitivity (Localizer) angle information which, when decoded means the ratio of measured DDM to and processed by the airborne unit, the corresponding lateral displacement provides signal performance capable of from the appropriate reference line.

supporting approach minima for V/ Facility Performance Category I— STOL and CTOL operations and oper- ISMLS means an ISMLS which provides ates with the signal format and toler- guidance information from the cov- ances specified in §§ 171.259, 171.261, erage limit of the ISMLS to the point 171.263, 171.265, and 171.267.

at which the localizer course line inter- Integrity means that quality which sects the ISMLS glide path at a height relates to the trust which can be placed of 200 feet or less above the horizontal in the correctness of the information plane containing the threshold.

supplied by the facility.

Glide path means that locus of points Mean corrective time means the aver- in the vertical plane containing the age time required to correct an equip- runway center line at which the DDM ment failure over a given period, after is zero, which, of all such loci, is the a service man reaches the facility.

closest to the horizontal plane.

Mean time between failures means the Glide path angle ( q ) means the angle average time between equipment fail- between a straight line which rep- resents the mean of the ISMLS glide ure over a given period.

path and the horizontal. Reference datum means a point at a Glide path sector (full) means the sec- specified height located vertically tor in the vertical plane containing the above the intersection of the runway ISMLS glide path and limited by the centerline and the threshold and loci of points nearest to the glide path through which the downward extended at which the DDM is 0.175. The ISMLS straight portion of the ISMLS glide glide path sector is located in the path passes.

vertical plane containing the runway Split type ground station means the centerline, and is divided by the radi- type of ground station in which the ated glide path in two parts called electronic components for the azimuth upper sector and lower sector, referring and elevation guidance are contained respectively to the sectors above and in separate housings or shelters at dif- below the glide path.

ferent locations, with the azimuth por- Glide path sector (half) means the sec- tion of the ground station located at tor in the vertical plane containing the the stop end of the runway, and the ISMLS glide path and limited by the elevation guidance near the approach loci of points nearest to the glide path end of the runway.

at which the DDM is 0.0875.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00855 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.255 the facility and its operation whenever § 171.255 Requests for IFR procedures.

necessary.

(a) Each person who requests an IFR (5) The owner must assure the FAA procedure based on an ISMLS facility that he will not withdraw the ISMLS that he owns must submit the fol- facility from service without the per- lowing information with that request: mission of the FAA.

(1) A description of the facility and (6) The owner must bear all costs of evidence that the equipment meets the meeting the requirements of this sec- performance requirements of §§ 171.259, tion and of any flight or ground inspec- 171.261, 171.263, 171.265, 171.267, and tion made before the ISMLS facility is 171.269, and is installed in accordance commissioned, except that the FAA with § 171.271.

may bear certain costs subject to budg- (2) A proposed procedure for oper- etary limitations and policy estab- ating the facility.

lished by the Administrator.

(3) A proposed maintenance organiza- (b) If the applicant for approval tion and a maintenance manual that meets the requirements of paragraph meets the requirements of § 171.273.

(a) of this section, the FAA approves (4) A statement of intent to meet the the ISMLS facility for use in an IFR requirements of this subpart.

procedure. The approval is withdrawn (5) A showing that the ISMLS facil- at any time that the ISMLS facility ity has an acceptable level of oper- does not continue to meet those re- ational reliability, maintainability and quirements. In addition, the ISMLS fa- acceptable standard of performance.

cility may be de-commissioned when- Previous equivalent operational experi- ever the frequency channel is needed ence with a facility with identical de- for higher priority common system sign and operational characteristics service.

will be considered in showing compli- § 171.259 Performance requirements: ance with this paragraph.

General.

(b) After the FAA inspects and evalu- ates the ISMLS facility, it advises the (a) The ISMLS consists of the fol- owner of the results and of any re- lowing basic components: (1) C-Band (5000 MHz–5030 MHz) local- quired changes in the ISMLS facility izer equipment, associated monitor or in the maintenance manual or main- system, and remote indicator equip- tenance organization. The owner must ment; then correct the deficiencies, if any, (2) C-Band (5220 MHz–5250 MHz) glide and operate the ISMLS facility for an path equipment, associated monitor inservice evaluation by the FAA.

system, and remote indicator equip- § 171.257 Minimum requirements for ment; approval.

(3) VHF marker beacons (75 MHz), as- sociated monitor systems, and remote (a) The following are the minimum indicator equipment.

requirements that must be met before (4) An ISMLS airborne receiver or a the FAA approves an IFR procedure for VHF/UHF ILS receiver modified to be a non-Federal ISMLS facility: capable of receiving the ISMLS signals.

(1) The performance of the ISMLS fa- This modification requires the addition cility, as determined by flight and of a C-Band antenna, a converter unit, ground inspection conducted by the a microwave/ILS mode control, and a FAA, must meet the requirements of VHF/UHF receiver modification kit.

§§ 171.259, 171.261, 171.263, 171.265, 171.267, (b) The electronic ground equipments and 171.269.

in paragraph (a)(1), (2), and (3) of this (2) The installation of the equipment section, must be designed to operate on must meet the requirements of a nominal 120/240 volt, 60 Hz, 3-wire sin- § 171.271.

gle phase AC power source.

(3) The owner must agree to operate (c) ISMLS ground equipment must and maintain the ISMLS facility in ac- meet the following service conditions: cordance with § 171.273.

(1) AC line parameters, DC voltage, (4) The owner must agree to furnish elevation, and duty: periodic reports as set forth in § 171.275 and agree to allow the FAA to inspect 120 V nominal value, 102 V to 138 V ( ± 1 V).* VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00856 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.259 208 V nominal value, 177 V to 239 V ( ± 2 V).* standard performance requirements 240 V nominal value, 204 V to 276 V ( ± 0.2 specified in subpart H of this part.

V).* (3) The ISMLS must be so designed AC line frequency (60 Hz), 57 Hz to 63 Hz and maintained that the probability of ( ± 0.2 Hz).* operation is within the performance re- DC voltage (48 V), 44 V to 52 V ( ± 0.5 V).* quirements specified in § 171.273(k).

* N OTE : Where discrete values of the above (e) The signal format and pairing of frequency or voltages are specified for test- the runway localizer and glide path ing purposes, the tolerances given in paren- theses indicated by an asterisk apply to the transmitter frequencies of an ISMLS test instruments used to measure these pa- must be in accordance with the fre- rameters.

quency plan approved by the FAA, and Elevation, 0 to 10,000 ft. above sea level.

must meet the following signal format Duty, continuous, unattended.

requirements: (2) Ambient conditions for localizer (1) The localizer and glide slope sta- and glide path equipment: tions must transmit angular guidance information on a C-band microwave Temperature, ¥ 10 ° C to + 50 ° C.

carrier on narrow, scanned antenna Relative humidity, 5% to 90%.

beams that are encoded to produce a (3) Ambient conditions for marker modulation in space which, after aver- beacon facilities and all other equip- aging over several beam scans, is ment installed outdoors (for example, equivalent to the modulation used for antennae, field detectors, and shelters): conventional ILS as specified in sub- part C of this part, except that the fre- Temperature, ¥ 50 ° C. to + 70 ° C.

Relative humidity, 5% to 100%. quency tolerance may not exceed ± 0.0001 percent.

(4) All equipment installed outdoors (2) Guidance modulation must be im- must operate satisfactorily under the pressed on the microwave carrier of the following conditions: radiated signal in the form of a sum- Wind velocity, 0–100 MPH (not including mation of 90 Hz and 150 Hz sinusoidal gusts).

modulation corresponding to the point- Hail stones, ⁄2 ″ diameter.

ing direction of the particular beam Rain, provide coverage through a distance which radiates the signal.

of 5 nautical miles with rain falling at a rate (3) Each of the effective beam posi- of 50 millimeters per hour, and with rain fall- tions must be illuminated in a par- ing at the rate of 25 millimeters per hour for the additional design performance range of ticular sequence for a short time inter- the system.

val. The modulation impressed on each Ice loading, encased in ⁄2 ″ radial thickness beam must be a sample of the com- of clear ice.

bined 90 Hz and 150 Hz waveform appro- (d) The ISMLS must perform in ac- priate for that particular beam direc- cordance with the following standards tion and time slot, and must be accom- and practices for Facility Performance plished by appropriately varying the Category I operation: length of time the carrier is radiated (1) The ISMLS must be constructed during each beam illumination inter- and adjusted so that, at a specified dis- val.

tance from the threshold, similar in- (4) For those cases where the scan- strumental indications in the aircraft ning beam fills the coverage space in represent similar displacements from steps, the incremental step must not the course line or ISMLS glide path, as exceed 0.6 times the beam width where appropriate, regardless of the par- the beam is in the proportional guid- ticular ground installation in use. ance sector. In the clearance region, (2) The localizer and glide path com- the step may not exceed 0.8 times the ponents listed in paragraphs (a)(1) and beam width.

(a)(2) of this section which form part of (5) At least one pulse duration modu- an ISMLS, must comply at least with lation (pdm) sample pulse per beam the standard performance requirements width of scan must be provided.

specified herein. The marker beacon (6) The minimum pulse duration components listed in paragraph (a)(3) must be 40 microseconds.

of this section which form part of an (7) The minimum beam scan cycle ISMLS, must comply at least with the must be 600 Hz.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00857 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.261 (8) The minimum duty ratio detect- (c) At locations where two separate able by a receiver located anywhere in ISMLS facilities serve opposite ends of the coverage areas defined by this spec- of a single runway, an interlock must ification may not be less than 0.1. De- ensure that only the facility serving tected duty ratio means the ratio of the approach direction being used will the average energy per scan detected at radiate.

a point in space to the average energy (d) The radiation from the localizer per scan transmitted in all directions antenna system must produce a com- through the transmitting antenna. posite field pattern which is pulse du- (9) The localizer must produce a C- ration modulated, the time average band unmodulated reference frequency equivalent to amplitude modulation by signal of sufficient strength to allow a 90 Hz and 150 Hz tone. The localizer satisfactory operation of an aircraft re- station must transmit angular guid- ceiver within the specified localizer ance information over a C-band micro- and glide path coverage sectors. Pair- wave carrier on narrow, scanned an- ing of this reference frequency with the tenna beams that are encoded to localizer and glide slope frequencies produce a modulation in space which, must be in accordance with a frequency after averaging over several beam plan approved by the FAA. scans, is equivalent to the modulation used for conventional ILS as specified § 171.261 Localizer performance re- in subpart C of this part. The radiation quirements.

field pattern must produce a course This section prescribes the perform- sector with one tone predominating on ance requirements for localizer equip- one side of the course and with the ment components of the ISMLS. other tone predominating on the oppo- (a) The localizer antenna system site side. When an observer faces the must: localizer from the approach end of the (1) Be located on the extension of the runway, the depth of modulation of the centerline of the runway at the stop radio frequency carrier due to the 150 end; Hz tone must predominate on his right (2) Be adjusted so that the course line hand and that due to the 90 Hz tone be on a vertical plane containing the must predominate on his left hand.

centerline of the runway served; (e) All horizontal angles employed in (3) Have the minimum height nec- specifying the localizer field patterns essary to comply with the coverage re- must originate from the center of the quirements prescribed in paragraph (j) localizer antenna system which pro- of this section; vides the signals used in the front (4) Be located at a distance from the course sector.

stop end of the runway that is con- (f) The ISMLS course sector angle sistent with safe obstruction clearance must be adjustable between 3 degrees practices; and 9 degrees. The applicable course (5) Not obscure any light of the ap- sector angle will be established and ap- proach landing system; and proved on an individual basis.

(6) Be installed on frangible mounts (g) The ISMLS localizer must operate or beyond the 1000 ′ light bar. in the band 5000 MHz to 5030 MHz. The (b) On runways where limited terrain frequency tolerance may not exceed prevents the localizer antennae from ± 0.0001 percent.

being positioned on the runway center- (h) The emission from the localizer line extended, and the cost of the land must be vertically polarized. The hori- fill or a tall tower antenna support is zontally polarized component of the ra- prohibitive, the localizer antenna array diation of the course line may not ex- may be offset, including a collocated ceed that which corresponds to a DDM ground station, so that the course error of 0.016 when an aircraft is posi- intercepts the centerline at a point de- tioned on the course line and is in a termined by the amount of the angular roll attitude of 20 degrees from the hor- offset and the glide path angle. If other izontal.

than a runway centerline localizer is (i) The localizer must provide signals used, the criteria in subpart C of part sufficient to allow satisfactory oper- 97 of this chapter is applicable. ation of a typical aircraft installation VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00858 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.261 within the localizer and glide path cov- the 90 Hz and 150 Hz tones must be be- erage sectors. The localizer coverage tween 18 and 22 percent.

sector must extend from the center of (3) The frequency tolerance of the 90 the localizer antenna system to dis- Hz and 150 Hz modulated tones must be tances of 18 nautical miles minimum within ± 25 percent.

within ± 10 degrees from the front (4) Total harmonic content of the 90 course line, and 10 nautical miles min- Hz tone may not exceed 10 percent.

imum between ± 10 degrees and ± 35 de- (5) Total harmonic content of the 150 grees from the front course line. The Hz tone may not exceed 10 percent.

ISMLS localizer signals must be re- However, a 300 Hz tone may be trans- ceivable at the distances specified up mitted for identification purposes.

from a surface extending outward from (6) At every half cycle of the com- the localizer antenna and within a sec- bined 90 Hz and 150 Hz wave form, the tor in the elevation plane from 0.300 to modulation tones must be phase-locked 1.750 of the established glide path angle so that within the half course sector, ( q ).

the demodulated 90 Hz and 150 Hz wave (j) Except as provided in paragraph forms pass through zero in the same di- (k) of this section, in all parts of the rection within 20 degrees with phase coverage volume specified in paragraph relative to the 150 Hz component. How- (i) of this section, the peak field ever, the phase need not be measured strength may not be less than ¥ 87 within the half course sector.

dBW/m , and must permit satisfactory operational usage of ISMLS localizer (p) The mean course line must be ad- facilities. justed and maintained within (k) The minimum peak field strength ± .015DDM from the runway centerline on the ISMLS glide path and within at the ISMLS reference datum.

the localizer course sector from a dis- (q) The nominal displacement sensi- tance of 10 nautical miles to a height of tivity within the half course sector at 100 feet (30 meters) above the hori- the ISMLS reference datum, must be zontal plane containing the threshold, 0.00145 DDM/meter (0.00044DDM/foot).

may not be less than + 87 dBW/m .

However, where the specified nominal (l) Above 16 degrees, the ISMLS lo- displacement sensitivity cannot be calizer signals must be reduced to as met, the displacement sensitivity must low a value as practicable.

be adjusted as near as possible to that (m) Bends in the course line may not value.

have amplitudes which exceed the fol- (r) The lateral displacement sensi- lowing: tivity must be adjusted and maintained within 17 percent of the nominal value.

Amplitude (DDM) Zone (95 pct. probability) Nominal sector width at the ISMLS reference datum is 210 meters (700 feet).

Outer limit of coverage to: ISMLS point ‘‘A’’ ............. 0.031.

(s) The increase of DDM must be sub- ISMLS point ‘‘A’’ to 0.031 at ISMLS point ‘‘A’’ de- stantially linear with respect to angu- ISMLS point ‘‘B’’. creasing at linear rate to 0.015 at ISMLS point ‘‘B’’. lar displacement from the front course ISMLS point ‘‘B’’ to 0.015.

line where DDM is zero, up to angle on ISMLS point ‘‘C’’.

either side of the front course line where the DDM is 0.180. From that (n) The amplitudes referred to in angle to ± 10 degrees, the DDM may not paragraph (m) of this section are the be less than 0.180. From ± 10 degrees to DDMs due to bends as realized on the ± 35 degrees, the DDM may not be less mean course line, when correctly ad- than 0.155.

justed.

(t) The localizer must provide for the (o) The radio frequency carrier must simultaneous transmission of an iden- meet the following requirements: tification signal which meets the fol- (1) The nominal depth of modulation lowing: of the radio frequency carrier due to (1) It must be specific to the runway each of the 90 Hz and 150 Hz tones must be 20 percent along the course line. and approach direction, on the same (2) The depth of modulation of the radio frequency carrier, as used for the radio frequency carrier due to each of localizer function.

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pulse duration modulation of the radio frequency carrier resulting in a de- (b) Within 10 seconds of the occur- tected audio tone in the airborne VHF rence of any of the conditions pre- receiver of 1020 Hz ± 50Hz. scribed in paragraph (a) of this section, (4) The depth of modulation must be including periods of zero radiation, lo- between the limits of 10 and 12 percent. calizer signal radiation must cease or the navigation and identification com- (5) The emissions carrying the identi- ponents must be removed.

fication signal must be vertically po- larized.

§ 171.265 Glide path performance re- (6) The identification signal must quirements.

employ the International Morse Code and consist of three letters. It must be This section prescribes the perform- preceded by the International Morse ance requirements for glide path equip- Code signal of the letter ‘‘M’’ followed ment components of the ISMLS. These by a short pause where it is necessary requirements are based on the assump- to distinguish the ISMLS facility from tion that the aircraft is heading di- other navigational facilities in the im- rectly toward the facility.

mediate area. At airports where both (a) The glide slope antenna system an ISMLS and an ILS are in operation, must be located near the approach end each facility must have a different of the runway, and the equipment must identification call sign.

be adjusted so that the vertical path (7) The signal must be transmitted at line will be in a sloping horizontal a speed corresponding to approxi- plane containing the centerline of the mately seven words per minute, and runway being served, and satisfy the must be repeated at approximately coverage requirements prescribed in equal intervals, not less than six times paragraph (g) of this section. For the per minute, during which time the lo- purpose of obstacle clearance, location calizer is available for operational use.

of the glide slope antenna system must When the localizer is not available for be in accordance with the criteria spec- transmission, the identification signal ified in subpart C of part 97 of this must be suppressed.

chapter.

(b) The radiation from the glide path § 171.263 Localizer automatic monitor antenna system must produce a com- system.

posite field pattern which is pulse du- (a) The ISMLS localizer equipment ration modulated by a 90 Hz and a 150 must provide an automatic monitor Hz tone, which is the time average system that transmits a warning to equivalent to amplitude modulation.

designated local and remote control The pattern must be arranged to pro- points when any of the following oc- vide a straight line descent path in the curs: vertical plane containing the center- (1) A shift of the mean course line of line of the runway, with the 150 Hz tone the localizer from the runway center- predominating below the path and the line equivalent to more than 0.015 DDM 90 Hz tone predominating above the at the ISMLS reference datum.

path to at least an angle equal to (2) For localizers in which the basic 1.752 q . As used in this section theta ( q ), functions are provided by the use of a denotes the nominal glide path angle.

single-frequency system, a reduction of The glide path angle must be adjusted power output to less than 50 percent of and maintained within 0.075 q .

normal or a loss of ground station iden- (c) The glide path equipment must be tification transmissions.

capable of producing a radiated glide (3) Changes of displacement sensi- path from 3 to 9 degrees with respect to tivity to a value differing by more than the horizontal. However, ISMLS glide 17 percent from nominal value for the path angles in excess of 3 degrees may localizer. be used to satisfy instrument approach VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00860 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR

Federal Aviation Administration, DOT § 171.265 procedures or to overcome an obstruc- of a unique summation of 90 Hz and 150 tion clearance problem, only in accord- Hz sinusoidal modulation cor- ance with the criteria specified in sub- responding to the point direction of the part C of part 97 of this chapter. particular beam which radiates the sig- (d) The downward extended straight nal. Each of the effective beam posi- portion of the ISMLS glide path must tions must be illuminated in sequence pass through the ISMLS reference for a short time interval. The scan rate datum at a height ensuring safe guid- must be synchronous with the 90 and ance over obstructions and safe and ef- 150 Hz tone base. The modulation im- ficient use of the runway served. The pressed on each beam must be a sample height of the ISMLS reference datum of the combined 90 Hz and 150 Hz wave- must be in accordance with subpart C form appropriate for that particular of part 97 of this chapter. beam direction and time slot. The ac- (e) The glide path equipment must tual modulation must be accomplished operate in the band 5220 MHz to 5250 by appropriately varying the length of MHz. The frequency tolerance may not time the carrier is radiated during each exceed ± 0.0001 percent. beam illumination interval.

(f) The emission from the glide path (k) The nominal depth of modulation equipment must be vertically polar- of the radio frequency carrier due to ized.

each of the 90 Hz and 150 Hz tones must (g) The glide path equipment must be 40 percent along the ISMLS glide provide signals sufficient to allow sat- path. The depth of modulation may not isfactory operation of a typical aircraft deviate outside the limits of 37.5 per- installation insectors of 8 degrees on cent to 42.5 percent.

each side of the centerline of the (l) The following tolerances apply to ISMLS glide path, to a distance of at the frequencies of the modulating least 10 nautical miles up to 1.75 q and tones: down to 0.45 q above the horizontal or to (1) The modulating tones must be 90 such lower angle at which 0.22 DDM is Hz and 150 Hz within 2.5 percent.

realized.

(2) The total harmonic content of the (h) To provide the coverage for glide 90 Hz tone may not exceed 10 percent.

path performance specified in para- (3) The total harmonic content of the graph (g) of this section, the minimum 150 Hz tone may not exceed 10 percent.

peak field strength within this cov- (m) At every half cycle of the com- erage sector must be ¥ 82 dBW/m . The bined 90 Hz and 150 Hz wave form, the peak field strength must be provided modulation must be phase-locked so on the glide path down to a height of 30 that, within the ISMLS half glide path meters (100 feet) above the horizontal sector, the demodulated 90 Hz and 150 plane containing the threshold.

Hz wave forms pass through zero in the (i) Bends in the glide path may not same direction within 20 degrees of have amplitudes which exceed the fol- phase relative to the 150 Hz component.

lowing: However, the phase need not be meas- ured within the ISMLS half glide path Amplitude sector.

(DDM) (95 Zone pct. prob- (n) The nominal angular displace- ability) ment sensitivity must correspond to a Outer limit of coverage to ISMLS point ‘‘C.’’ ..... 0.035.

DDM of 0.0875 at an angular displace- ment above and below the glide path of The amplitude referred to is the DDM 0.12 q . The glide path angular displace- due to bends as realized on the mean ment sensitivity must be adjusted and ISMLS glide path correctly adjusted. maintained within ± 25 percent of the In regions of the approach where nominal value selected. The upper and ISMLS glide path curvature is signifi- lower sectors must be as symmetrical cant, bend amplitude is calculated as practicable within the limits pre- from the mean curved path, and not scribed in this paragraph.

the downward extended straight line. (o) The DDM below the ISMLS glide (j) Guidance modulation must be im- path must increase smoothly for de- pressed on the microwave carrier of the creasing angle until a value of 0.22 radiated glide slope signal in the form DDM is reached. This value must be VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00861 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.267 achieved at an angle not less than 0.30 q § 171.271 Installation requirements.

above the horizontal. However, if it is (a) The ISMLS facility must be per- achieved at an angle above 0.45 q , the manent in nature, located, con- DDM value may not be less than 0.22 at structed, and installed according to ac- least down to an angle of 0.45 q .

cepted good engineering practices, ap- plicable electric and safety codes, FCC [Docket 14120, 40 FR 36110, Aug. 19, 1975; 40 FR 41093, Sept. 5, 1975; 40 FR 43719, Sept. 23, licensing requirements, and paragraphs 1975] (a) and (c) of § 171.261.

(b) The ISMLS facility must have a § 171.267 Glide path automatic mon- reliable source of suitable primary itor system.

power, either from a power distribution (a) The ISMLS glide path equipment system or locally generated. Adequate must provide an automatic monitor power capacity must be provided for system that transmits a warning to the operation of test and working designated local and remote control equipment of the ISMLS.

points when any of the following oc- (c) The ISMLS facility must have a curs: continuously engaged or floating bat- (1) A shift of the mean ISMLS glide tery power source for the ground sta- path angle equivalent to more than tion for continued normal operation if 0.075 q .

the primary power fails. A trickle (2) For glide paths in which the basic charge must be supplied to recharge functions are provided by the use of a the batteries during the period of avail- single frequency system, a reduction of able primary power. Upon loss and sub- power output to less than 50 percent. sequent restoration of power, the bat- (3) A change of the angle between the teries must be restored to full charge glide path and the line below the glide within 24 hours. When primary power is path (150 Hz predominating), at which a applied, the state of the battery charge DDM of 0.0875 is realized by more than may not affect the operation of the ± 0.0375 q . ISMLS ground station. The battery (4) Lowering of the line beneath the must permit continuation of normal ISMLS glide path at which a DDM of operation for at least two hours under 0.0875 is realized to less than 0.75 q from the normal operating conditions. The equipment must meet all specification the horizontal.

(5) Failure of any part of the monitor requirements with or without batteries itself. Such failure must automatically installed.

produce the same results as the mal- (d) There must be a means for deter- functioning of the element being mon- mining, from the ground, the perform- itored. ance of the equipment including anten- (b) At glide path facilities where the nae, both initially and periodically.

selected nominal angular displacement (e) The facility must have, or be sup- sensitivity corresponds to an angle plemented by, ground-air or landline below the ISMLS glide path, which is communications services. At facilities close to or at the maximum limits within or immediately adjacent to con- specified, an adjustment to the mon- trolled airspace and that are intended itor operating limits may be made to for use as instrument approach aids for protect against sector deviations below an airport, there must be ground-air 0.75 q from the horizontal. communications or reliable commu- (c) Within 10 seconds of the occur- nications (at least a landline tele- rence of any of the conditions pre- phone) from the airport to the nearest scribed in paragraph (a) of this section, Federal Aviation Administration air including periods of zero radiation, traffic control or communication facil- glide path signal radiation must cease. ity. Compliance with this paragraph need not be shown at airports where an § 171.269 Marker beacon performance adjacent Federal Aviation Administra- requirements.

tion facility can communicate with ISMLS marker beacon equipment aircraft on the ground at the airport must meet the performance require- and during the entire proposed instru- ments prescribed in subpart H of this ment approach procedure. In addition, part. at low traffic density airports within VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00862 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.273 or immediately adjacent to controlled (3) FCC licensing requirements for airspace, and where extensive delays operations and maintenance personnel.

are not a factor, the requirements of (4) Posting of licenses and signs.

this paragraph may be reduced to reli- (5) Relation between the facility and able communications (at least a FAA air traffic control facilities, with landline telephone) from the airport to a description of the boundaries of con- the nearest Federal Aviation Adminis- trolled airspace over or near the facil- tration air traffic control or commu- ity, instructions for relaying air traffic nications facility, if an adjacent Fed- control instructions and information, eral Aviation Administration facility if applicable, and instructions for the can communicate with aircraft during operation of an air traffic advisory the proposed instrument approach pro- service if the facility is located outside cedure, at least down to the minimum of controlled airspace.

en route altitude for the controlled (6) Notice to the Administrator of area. any suspension of service.

(f) Except where no operationally (7) Detailed and specific maintenance harmful interference will result, at lo- procedures and servicing guides stating cations where two separate ISMLS fa- the frequency of servicing.

cilities serve opposite ends of a single (8) Air-ground communications, if runway, an interlock must ensure that provided, expressly written or incor- only the facility serving the approach porating appropriate sections of FAA direction in use can radiate.

manuals by reference.

(9) Keeping of station logs and other [Docket 14120, 40 FR 36110, Aug. 19, 1975, as technical reports, and the submission amended by Amdt. 171–16, 56 FR 65665, Dec.

of reports required by § 171.275.

17, 1991] (10) Monitoring of the ISMLS facil- § 171.273 Maintenance and operations ity.

requirements.

(11) Inspections by United States per- sonnel.

(a) The owner of the facility must es- (12) Names, addresses, and telephone tablish an adequate maintenance sys- numbers of persons to be notified in an tem and provide qualified maintenance emergency.

personnel to maintain the facility at (13) Shutdowns for periodic mainte- the level attained at the time it was nance and issue of ‘‘Notices to Airmen’’ commissioned. Each person who main- for routine or emergency shutdowns.

tains a facility must meet at least the (14) Commissioning of the ISMLS fa- Federal Communications Commission’s cility.

licensing requirements and show that (15) An acceptable procedure for he has the special knowledge and skills amending or revising the manual.

needed to maintain the facility, includ- (16) An explanation of the kinds of ing proficiency in maintenance proce- activities (such as construction or dures and the use of specialized test grading) in the vicinity of the ISMLS equipment.

facility that may require shutdown or (b) In the event of out-of-tolerance recertification of the ISMLS facility conditions or malfunctions, as evi- by FAA flight check.

denced by receiving two successive (17) Procedures for conducting a pilot reports, the owner must close the ground check of the localizer course facility be ceasing radiation, and issue alignment, width, and clearance, glide a ‘‘Notice to Airman’’ (NOTAM) that path elevation angle and course width, the facility is out of service.

(c) The owner must prepare, and ob- and marker beacon power, and modula- tain approval of, an operations and tion.

maintenance manual that sets forth (18) The following information con- mandatory procedures for operations, cerning the ISMLS facility: periodic maintenance, and emergency (i) Facility component locations with maintenance, including instructions on respect to airport layout, instrument each of the following: runways, and similar areas.

(1) Physical security of the facility. (ii) The type, make, and model of the (2) Maintenance and operations by basic radio equipment that provides authorized persons. the service.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00863 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.275 (iii) The station power emission and that unsafe operating conditions do not frequencies of the ISMLS localizer, exist.

glide path, beacon markers, and associ- (m) Monitoring of the ISMLS radi- ated compass locators, if any. ated signal must ensure a high degree of integrity and minimize the require- (iv) The hours of operation.

ments for ground and flight inspection.

(v) Station identification call letters The monitor must be checked periodi- and method of station identification cally during the in-service test evalua- and the time spacing of the identifica- tion period for calibration and sta- tion.

bility. These tests and ground checks (vi) A description of the critical parts of glide slope, localizer, and marker that may not be changed, adjusted, or beacon radiation characteristics must repaired without an FAA flight check be conducted in accordance with the to confirm published operations.

maintenance requirements of this sec- (d) The owner or his maintenance tion.

representative must make a ground check of the ISMLS facility periodi- § 171.275 Reports.

cally in accordance with procedures ap- The owner of the ISMLS facility or proved by the FAA at the time of com- his maintenance representative must missioning, and must report the results make the following reports at the indi- of the checks as provided in § 171.275.

cated time to the appropriate FAA Re- (e) Modifications to an ISMLS facil- gional Office where the facility is lo- ity may be made only after approval by cated.

the FAA of the proposed modification (a) Facility Equipment Performance and submitted by the owner.

Adjustment Data ( FAA Form 198 ). The (f) The owner or the owner’s mainte- FAA Form 198 shall be filled out by the nance representative must participate owner or his maintenance representa- in inspections made by the FAA.

tive with the equipment adjustments (g) Whenever it is required by the and meter readings as of the time of fa- FAA, the owner must incorporate im- cility commissioning. One copy must provements in ISMLS maintenance.

be kept in the permanent records of the (h) The owner or his maintenance facility and two copies must be sent to representative must provide a suffi- the appropriate FAA Regional Office.

cient stock of spare parts, including The owner or his maintenance rep- solid state components, or modules to resentative must revise the FAA Form make possible the prompt replacement 198 data after any major repair, mod- of components or modules that fail or ernization, or retuning to reflect an ac- deteriorate in service.

curate record of facility operation and (i) FAA approved test instruments adjustment. In the event the data are must be used for maintenance of the revised, the owner or his maintenance ISMLS facility.

representative shall notify the appro- (j) The mean corrective maintenance priate FAA Regional Office of such re- time of the ISMLS equipment may not visions, and forward copies of the revi- exceed 0.5 hours, with a maximum cor- sions to the appropriate FAA Regional rective maintenance time of not great- Office.

er than 1.5 hours. This measure applies (b) Facility Maintenance Log ( FAA to failures of the monitor, transmitter Form 6030 – 1 ). FAA Form 6030–1 is a per- and associated antenna assemblies, manent record of all the activities re- limited to unscheduled outage and out- quired to maintain the ISMLS facility.

of-tolerance conditions.

The entries must include all malfunc- (k) The mean time between failures tions met in maintaining the facility of the ISMLS equipment may not be including information on the kind of less than 1,500 hours. This measure ap- work and adjustments made, equip- plies to unscheduled outages, out-of- ment failures, causes (if determined) tolerance conditions, and failures of and corrective action taken. In addi- the monitor, transmitter, and associ- tion, the entries must include comple- ated antenna assemblies.

tion of periodic maintenance required (l) Inspection consists of an examina- to maintain the facility. The owner or tion of the ISMLS equipment to ensure his maintenance representative must VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00864 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.303 keep the original of each form at the and in the vertical plane for the ele- facility and send a copy to the appro- vation function.

priate FAA Regional Office at the end Clearance guidance sector means the of each month in which it is prepared.

volume of airspace, inside the coverage However, where an FAA approved re- sector, within which the azimuth guid- mote monitoring system is installed ance information provided is not pro- which precludes the need for periodic portional to the angular displacement maintenance visits to the facility, of the aircraft, but is a constant fly- monthly reports from the remote mon- left or fly-right indication of the direc- itoring system control point must be tion relative to the approach course forwarded to the appropriate FAA Re- the aircraft should proceed in order to gional Office, and a hard copy retained enter the proportional guidance sector.

at the control point.

Control Motion Noise (CMN) means (c) Technical Performance Record ( FAA those fluctuations in the guidance Form 418 ). FAA Form 418 contains a which affect aircraft attitude, control record of system parameters, recorded surface motion, column motion, and on each scheduled visit to the facility.

wheel motion. Control motion noise is The owner or his maintenance rep- evaluated by filtering the flight error resentative shall keep the original of record with a band-pass filter which each month’s record at the facility and has corner frequencies at 0.3 radian/sec send a copy of the form to the appro- and 10 radians/sec for azimuth data and priate FAA Regional Office.

0.5 radian/sec and 10 radians/sec for ele- vation data.

Subpart J—Microwave Landing Data rate means the average number System (MLS) of times per second that transmissions occur for a given function.

S OURCE : Docket 20669, 51 FR 33177, Sept. 18, Differential Phase Shift Keying (DPSK) 1986, unless otherwise noted.

means differential phase modulation of the radio frequency carrier with rel- § 171.301 Scope.

ative phase states of 0 degree or 180 de- This subpart sets forth minimum re- grees.

quirements for the approval, installa- Failure means the inability of an tion, operation and maintenance of item to perform within previously non-Federal Microwave Landing Sys- specified limits.

tem (MLS) facilities that provide the Guard time means an unused period of basis for instrument flight rules (IFR) time provided in the transmitted signal and air traffic control procedures.

format to allow for equipment toler- ances.

§ 171.303 Definitions.

Integrity means that quality which As used in this subpart: relates to the trust which can be placed Auxiliary data means data trans- in the correctness of the information mitted in addition to basic data that supplied by the facility.

provide ground equipment siting infor- Mean corrective time means the aver- mation for use in refining airborne po- age time required to correct an equip- sition calculations and other supple- ment failure over a given period, after mentary information.

a service technician reaches the facil- Basic data means data transmitted by ity.

the ground equipment that are associ- Mean course error means the mean ated directly with the operation of the value of the azimuth error along a landing guidance system.

specified radial of the azimuth func- Beam center means the midpoint be- tion.

tween the ¥ 3 dB points on the leading Mean glide path error means the mean and trailing edges of the scanning value of the elevation error along a beam main lobe.

specified glidepath of the elevation Beamwidth means the width of the function.

scanning beam main lobe measured at the ¥ 3 dB points and defined in angu- Mean-time-between-failures (MTBF) lar units on the boresight, in the hori- means the average time between equip- zontal plane for the azimuth function ment failures over a given period.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00865 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.305 Microwave Landing System (MLS) § 171.305 Requests for IFR procedure.

means the MLS selected by ICAO for (a) Each person who requests an IFR international standardization.

procedure based on an MLS facility Minimum glidepath means the lowest which that person owns must submit angle of descent along the zero degree the following information with that re- azimuth that is consistent with pub- quest: lished approach procedures and obsta- (1) A description of the facility and cle clearance criteria.

evidence that the equipment meets the MLS Approach Reference Datum is a performance requirements of §§ 171.309, point at a specified height located 171.311, 171.313, 171.315, 171.317, 171.319, vertically above the intersection of the and 171.321 and is fabricated and in- runway centerline and the threshold.

stalled in accordance with § 171.323.

MLS back azimuth reference datum (2) A proposed procedure for oper- means a point 15 meters (50 feet) above ating the facility.

the runway centerline at the runway (3) A proposed maintenance organiza- midpoint.

tion and a maintenance manual that MLS datum point means a point de- meets the requirements of § 171.325.

fined by the intersection of the runway (4) A statement of intent to meet the centerline with a vertical plane perpen- requirements of this subpart.

dicular to the centerline and passing (5) A showing that the facility has an through the elevation antenna phase acceptable level of operational reli- center.

ability and an acceptable standard of Out of coverage indication (OCI) means performance. Previous equivalent oper- a signal radiated into areas outside the ational experience with a facility with intended coverage sector, where re- identical design and operational char- quired, to specifically prevent invalid acteristics will be considered in show- removal of an airborne warning indica- ing compliance with this subparagraph.

tion in the presence of misleading guid- (b) FAA inspects and evaluates the ance information.

MLS facility; it advises the owner of Path Following Error (PFE) means the the results, and of any required guidance perturbations which could changes in the MLS facility or in the cause aircraft displacement from the maintenance manual or maintenance desired course or glidepath. It is com- organization. The owner must then posed of the path following noise and of correct the deficiencies, if any, and op- the mean course error in the case of erate the MLS facility for an in-service azimuth functions, or the mean glide- evaluation by the FAA.

path error in the case of elevation functions. Path following errors are § 171.307 Minimum requirements for evaluated by filtering the flight error approval.

record with a second order low pass fil- (a) The following are the minimum ter which has a corner frequency at 0.5 requirements that must be met before radian/sec for azimuth data or 1.5 radi- the FAA approves an IFR procedure for ans/sec for elevation data.

a non-Federal MLS facility: Path following noise (PFN) means that (1) The performance of the MLS facil- portion of the guidance signal error ity, as determined by flight and ground which could cause displacement from inspection conducted by the FAA, must the actual mean course line or mean meet the requirements of §§ 171.309, glidepath as appropriate.

171.311, 171.313, 171.315, 171.317, 171.319, Split-site ground station means the and 171.321.

type of ground station in which the azi- (2) The fabrication and installation of muth portion of the ground station is the equipment must meet the require- located near the stop end of the run- ments of § 171.323.

way, and the elevation portion is lo- cated near the approach end. (3) The owner must agree to operate Time division multiplex (TDM) means and maintain the MLS facility in ac- that each function is transmitted on cordance with § 171.325.

the same frequency in time sequence, (4) The owner must agree to furnish with a distinct preamble preceding operational records as set forth in each function transmission. § 171.327 and agree to allow the FAA to VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00866 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.309 inspect the facility and its operation (2) A wider proportional guidance whenever necessary. sector which exceeds the minimum (5) The owner must assure the FAA specified in §§ 171.313 and 171.317.

that he will not withdraw the MLS fa- (3) Precision DME, associated mon- cility from service without the permis- itor, remote control and indicator sion of the FAA. equipment.

(6) The owner must bear all costs of (4) VHF marker beacon (75 MHz), as- meeting the requirements of this sec- sociated monitor, remote control and tion and of any flight or ground inspec- indicator equipment.

tion made before the MLS facility is (5) The MLS signal format will ac- commissioned.

commodate additional functions (e.g., (b) [Reserved] flare elevation) which may be included as desired. Remote controls for para- § 171.309 General requirements.

graphs (b) (1), (3) and (4) of this section The MLS is a precision approach and must include as a minimum on/off and landing guidance system which pro- reset capabilities, and may be inte- vides position information and various grated in the same equipment.

ground-to-air data. The position infor- (6) Provisions for the encoding and mation is provided in a wide coverage transmission of additional auxiliary sector and is determined by an azimuth data words, associated monitor, remote angle measurement, an elevation angle control and indicator equipment.

measurement and a range (distance) (c) MLS ground equipment must be measurement.

designed to operate on a nominal 120/ (a) An MLS constructed to meet the 240 volt, 60 Hz, 3-wire single phase AC requirements of this subpart must in- power source and must meet the fol- clude: lowing service conditions: (1) Approach azimuth equipment, as- (1) AC line parameters, DC voltage, sociated monitor, remote control and elevation and duty: indicator equipment.

120 VAC nominal value—102 V to 138 V ( ± 1 (2) Approach elevation equipment, as- V)* sociated monitor, remote control and 240 VAC nominal value—204 V to 276 V ( ± 2 indicator equipment.

V)* (3) A means for the encoding and 60 Hz AC line frequency—57 Hz to 63 Hz ( ± 0.2 transmission of essential data words, Hz)* associated monitor, remote control and *N OTE : Where discrete values of the above indicator equipment. Essential data frequency or voltages are specified for test- are basic data words 1, 2, 3, 4, and 6 and ing purposes, the tolerances given in paren- auxiliary data words A1, A2 and A3. theses indicated by an asterisk apply to the test instruments used to measure these pa- (4) Distance measuring equipment rameters.

(DME), associated monitor, remote control and indicator equipment. Elevation—0 to 3000 meters (10,000 feet) above sea level (5) Remote controls for paragraphs Duty—Continuous, unattended (a) (1), (2), (3), and (4) of this section must include as a minimum on/off and (2) Ambient conditions within the reset capabilities and may be inte- shelter for electronic equipment in- grated in the same equipment.

stalled in shelters are: (6) At locations where a VHF marker Temperature, ¥ 10 ° C to + 50 ° C beacon (75 MHz) is already installed, it Relative humidity, 5% to 90% may be used in lieu of the DME equip- ment.

(3) Ambient conditions for electronic (b) In addition to the equipment re- equipment and all other equipment in- quired in paragraph (a) of this section stalled outdoors (for example, antenna, the MLS may include: field detectors, and shelters): (1) Back azimuth equipment, associ- Temperature, ¥ 50 ° C to + 70 ° C ated monitor, remote control and indi- Relative humidity, 5% to 100% cator equipment. When Back Azimuth is provided, a means for transmission (4) All equipment installed outdoors of Basic Data Word 5 and Auxiliary must operate satisfactorily under the Data Word A4 shall also be provided. following conditions: VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00867 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.311 Wind Velocity: The ground equipment shall The signal format must meet the fol- remain within monitor limits with wind lowing minimum requirements: velocities of up to 70 knots from such di- (a) Frequency assignment. The ground rections that the velocity component components (except DME/Marker Bea- perpendicular to runway centerline does con) must operate on a single fre- not exceed 35 knots. The ground equip- quency assignment or channel, using ment shall withstand winds up to 100 knots from any direction without dam- time division multiplexing. These com- age.

ponents must be capable of operating Hail Stones: 1.25 centimeters ( ⁄ 2 inch) diame- on any one of the 200 channels spaced ter.

300 KHz apart with center frequencies Rain: Provide required coverage with rain from 5031.0 MHz to 5090.7 MHz and with falling at a rate of 50 millimeters (2 channel numbering as shown in Table inches) per hour, through a distance of 9 1a. The operating radio frequencies of kilometers (5 nautical miles) and with rain falling at the rate of 25 millimeters all ground components must not vary (1 inch) per hour for the additional 28 kil- by more than ± 10 KHz from the as- ometers (15 nautical miles).

signed frequency. Any one transmitter Ice Loading: Encased in 1.25 centimeters ( ⁄2 frequency must not vary more than ± 50 inch) radial thickness of clear ice.

Hz in any one second period. The MLS Antenna Radome De-Icing: Down to ¥ 6 ° C (20 angle/data and DME equipment must ° F) and wind up to 35 knots.

operate on one of the paired channels (d) The transmitter frequencies of an as shown in Table 1b.

MLS must be in accordance with the frequency plan approved by the FAA.

T ABLE 1a—F REQUENCY C HANNEL P LAN (e) The DME component listed in Fre- paragraph (a)(4) of this section must Channel No. quency comply with the minimum standard (MHz) performance requirements specified in 500 ........................................................................... 5031.0 subpart G of this part.

501 ........................................................................... 5031.3 (f) The marker beacon components 502 ........................................................................... 5031.6 listed in paragraph (b)(4) of this section 503 ........................................................................... 5031.9 504 ........................................................................... 5032.2 must comply with the minimum stand- 505 ........................................................................... 5032.5 ard performance requirements specified 506 ........................................................................... 5032.8 in subpart H of this part.

507 ........................................................................... 5033.1 508 ........................................................................... 5033.4 509 ........................................................................... 5033.7 § 171.311 Signal format requirements.

510 ........................................................................... 5034.0 The signals radiated by the MLS 511 ........................................................................... 5034.3 must conform to the signal format in * * * * * 598 ........................................................................... 5060.4 which angle guidance functions and 599 ........................................................................... 5060.7 data functions are transmitted sequen- 600 ........................................................................... 5061.0 tially on the same C-band frequency.

601 ........................................................................... 5061.3 * * * * * Each function is identified by a unique 698 ........................................................................... 5090.4 digital code which initializes the air- 699 ........................................................................... 5090.7 borne receiver for proper processing.

T ABLE 1b—C HANNELS Channel pairing DME parameters Interrogation Reply Pulse codes VHF freq. MLS angle MLS Ch.

DME No.

MHz freq. MHz No. Freq.

DME/P Mode MHz DME/N Freq. Pulse codes μ s MHz μ s IA μ s FA μ s * 1X .................... .................... .................... .............. 1025 12 .............. .............. 962 12 ** 1Y .................. .................... .................... .............. 1025 36 .............. .............. 1088 30 * 2X .................... .................... .................... .............. 1026 12 .............. .............. 963 12 ** 2Y .................. .................... .................... .............. 1026 36 .............. .............. 1089 30 * 3X .................... .................... .................... .............. 1027 12 .............. .............. 964 12 ** 3Y .................. .................... .................... .............. 1027 36 .............. .............. 1090 30 * 4X .................... .................... .................... .............. 1028 12 .............. .............. 965 12 ** 4Y .................. .................... .................... .............. 1028 36 .............. .............. 1091 30 * 5X .................... .................... .................... .............. 1029 12 .............. .............. 966 12 VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00868 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.311 T ABLE 1b—C HANNELS —Continued Channel pairing DME parameters Interrogation Reply Pulse codes VHF freq. MLS angle MLS Ch.

DME No.

MHz freq. MHz No. Freq.

DME/P Mode MHz DME/N Freq. Pulse codes μ s MHz μ s IA μ s FA μ s ** 5Y .................. .................... .................... .............. 1029 36 .............. .............. 1092 30 * 6X .................... .................... .................... .............. 1030 12 .............. .............. 967 12 ** 6Y .................. .................... .................... .............. 1030 36 .............. .............. 1093 30 * 7X .................... .................... .................... .............. 1031 12 .............. .............. 968 12 ** 7Y .................. .................... .................... .............. 1031 36 .............. .............. 1094 30 * 8X .................... .................... .................... .............. 1032 12 .............. .............. 969 12 ** 8Y .................. .................... .................... .............. 1032 36 .............. .............. 1095 30 * 9X .................... .................... .................... .............. 1033 12 .............. .............. 970 12 ** 9Y .................. .................... .................... .............. 1033 36 .............. .............. 1096 30 * 10X .................. .................... .................... .............. 1034 12 .............. .............. 971 12 ** 10Y ................ .................... .................... .............. 1034 36 .............. .............. 1097 30 * 11X .................. .................... .................... .............. 1035 12 .............. .............. 972 12 ** 11Y ................ .................... .................... .............. 1035 36 .............. .............. 1098 30 * 12X .................. .................... .................... .............. 1036 12 .............. .............. 973 12 ** 12Y ................ .................... .................... .............. 1036 36 .............. .............. 1099 30 * 13X .................. .................... .................... .............. 1037 12 .............. .............. 974 12 ** 13Y ................ .................... .................... .............. 1037 36 .............. .............. 1100 30 * 14X .................. .................... .................... .............. 1038 12 .............. .............. 975 12 ** 14Y ................ .................... .................... .............. 1038 36 .............. .............. 1101 30 * 15X .................. .................... .................... .............. 1039 12 .............. .............. 976 12 ** 15Y ................ .................... .................... .............. 1039 36 .............. .............. 1102 30 * 16X .................. .................... .................... .............. 1040 12 .............. .............. 977 12 ** 16Y ................ .................... .................... .............. 1040 36 .............. .............. 1103 30 S 17X ................. 108.00 .................... .............. 1041 12 .............. .............. 978 12 17Y .................... 108.05 5043.0 540 1041 36 36 42 1104 30 17Z .................... .................... 5043.3 541 1041 .............. 21 27 1104 15 18X .................... 108.10 5031.0 500 1042 12 12 18 979 12 18W ................... .................... 5031.3 501 1042 .............. 24 30 979 24 18Y .................... 108.15 5043.6 542 1042 36 36 42 1105 30 18Z .................... .................... 5043.9 543 1042 .............. 21 27 1105 15 19X .................... 108.20 .................... .............. 1043 12 .............. .............. 980 12 19Y .................... 108.25 5044.2 544 1043 36 36 42 1106 30 19Z .................... .................... 5044.5 545 1043 .............. 21 27 1106 15 20X .................... 108.30 5031.6 502 1044 12 12 18 981 12 20W ................... .................... 5031.9 503 1044 .............. 24 30 981 24 20Y .................... 108.35 5044.8 546 1044 36 36 42 1107 30 20Z .................... .................... 5045.1 547 1044 .............. 21 27 1107 15 21X .................... 108.40 .................... .............. 1045 12 .............. .............. 982 12 21Y .................... 108.45 5045.4 548 1045 36 36 42 1108 30 21Z .................... .................... 5045.7 549 1045 .............. 21 27 1108 15 22X .................... 108.50 5032.2 504 1046 12 12 18 983 12 22W ................... .................... 5032.5 505 1046 .............. 24 30 983 24 22Y .................... 108.55 5046.0 550 1046 36 36 42 1109 30 22Z .................... .................... 5046.3 551 1046 .............. 21 27 1109 15 23X .................... 108.60 .................... .............. 1047 12 .............. .............. 984 12 23Y .................... 108.65 5046.6 552 1047 36 36 42 1110 30 23Z .................... .................... 5046.9 553 1047 .............. 21 27 1110 15 24X .................... 108.70 5032.8 506 1048 12 12 18 985 12 24W ................... .................... 5033.1 507 1048 .............. 24 30 985 24 24Y .................... 108.75 5047.2 554 1048 36 36 42 1111 30 24Z .................... .................... 5047.5 555 1048 .............. 21 27 1111 15 25X .................... 108.80 .................... .............. 1049 12 .............. .............. 986 12 25Y .................... 108.85 5047.8 556 1049 36 36 42 1112 30 25Z .................... .................... 5048.1 557 1049 .............. 21 27 1112 15 26X .................... 108.90 5033.4 508 1050 12 12 18 987 12 26W ................... .................... 5033.7 509 1050 .............. 24 30 987 24 26Y .................... 108.95 5048.4 558 1050 36 36 42 1113 30 26Z .................... .................... 5048.7 559 1050 .............. 21 27 1113 15 27X .................... 109.00 .................... .............. 1051 12 .............. .............. 988 12 27Y .................... 109.05 5049.0 560 1051 36 36 42 1114 30 27Z .................... .................... 5049.3 561 1051 .............. 21 27 1114 15 28X .................... 109.10 5034.0 510 1052 12 12 18 989 12 28W ................... .................... 5034.3 511 1052 .............. 24 30 989 24 28Y .................... 109.15 5049.6 562 1052 36 36 42 1115 30 28Z .................... .................... 5049.9 563 1052 .............. 21 27 1115 15 VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00869 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.311 T ABLE 1b—C HANNELS —Continued Channel pairing DME parameters Interrogation Reply Pulse codes VHF freq. MLS angle MLS Ch.

DME No.

MHz freq. MHz No. Freq.

DME/P Mode MHz DME/N Freq. Pulse codes μ s MHz μ s IA μ s FA μ s 29X .................... 109.20 .................... .............. 1053 12 .............. .............. 990 12 29Y .................... 109.25 5050.2 564 1053 36 36 42 1116 30 29Z .................... .................... 5050.5 565 1043 .............. 21 27 1116 15 30X .................... 109.30 5034.6 512 1054 12 12 18 991 12 30W ................... .................... 5034.9 513 1054 .............. 24 30 991 24 30Y .................... 109.35 5050.8 566 1054 36 36 42 1117 30 30Z .................... .................... 5051.1 567 1054 .............. 21 27 1117 15 31X .................... 109.40 .................... .............. 1055 12 .............. .............. 992 12 31Y .................... 109.45 5051.4 568 1055 36 36 42 1118 30 31Z .................... .................... 5051.7 569 1055 .............. 21 27 1118 15 32X .................... 109.50 5035.2 514 1056 12 12 18 993 12 32W ................... .................... 5035.5 515 1056 .............. 24 30 993 24 32Y .................... 109.55 5052.0 570 1056 36 36 42 1119 30 32Z .................... .................... 5052.3 571 1056 .............. 21 27 1119 15 33X .................... 109.60 .................... .............. 1057 12 .............. .............. 994 12 33Y .................... 109.65 5052.6 572 1057 36 36 42 1120 30 33Z .................... .................... 5052.9 573 1057 .............. 21 27 1120 15 34X .................... 109.70 5035.8 516 1058 12 12 18 995 12 34W ................... .................... 5036.1 517 1058 .............. 24 30 995 24 34Y .................... 109.75 5053.2 574 1058 36 36 42 1121 30 34Z .................... .................... 5053.5 575 1058 .............. 21 27 1121 15 35X .................... 109.80 .................... .............. 1059 12 .............. .............. 996 12 35Y .................... 109.85 5053.8 576 1059 36 36 42 1122 30 35Z .................... .................... 5054.1 577 1059 .............. 21 27 1122 15 36X .................... 109.90 5036.4 518 1060 12 12 18 997 12 36W ................... .................... 5036.7 519 1060 .............. 24 30 997 24 36Y .................... 109.95 5054.4 578 1060 36 36 42 1123 30 36Z .................... .................... 5054.7 579 1060 .............. 21 27 1123 15 37X .................... 110.00 .................... .............. 1061 12 .............. .............. 998 12 37Y .................... 110.05 5055.0 580 1061 36 36 42 1124 30 37Z .................... .................... 5055.3 581 1061 .............. 21 27 1124 15 38X .................... 110.10 5037.0 520 1062 12 12 18 999 12 38W ................... .................... 5037.3 521 1062 .............. 24 30 999 24 38Y .................... 110.15 5055.6 582 1062 36 36 42 1125 30 38Z .................... .................... 5055.9 583 1062 .............. 21 27 1125 15 39X .................... 110.20 .................... .............. 1063 12 .............. .............. 1000 12 39Y .................... 110.25 5056.2 584 1063 36 36 42 1126 30 39Z .................... .................... 5056.5 585 1063 .............. 21 27 1126 15 40X .................... 110.30 5037.6 522 1064 12 12 18 1001 12 40W ................... .................... 5037.9 523 1064 .............. 24 30 1001 24 40Y .................... 110.35 5056.8 586 1064 36 36 42 1127 30 40Z .................... .................... 5057.1 587 1064 .............. 21 27 1127 15 41X .................... 110.40 .................... .............. 1065 12 .............. .............. 1002 12 41Y .................... 110.45 5057.4 588 1065 36 36 42 1128 30 41Z .................... .................... 5057.7 589 1065 .............. 21 27 1128 15 42X .................... 110.50 5038.2 524 1066 12 12 18 1003 12 42W ................... .................... 5038.5 525 1066 .............. 24 30 1003 24 42Y .................... 110.55 5058.0 590 1066 36 36 42 1129 30 42Z .................... .................... 5058.3 591 1066 .............. 21 27 1129 15 43X .................... 110.60 .................... .............. 1067 12 .............. .............. 1004 12 43Y .................... 110.65 5058.6 592 1067 36 36 42 1130 30 43Z .................... .................... 5058.9 593 1067 .............. 21 27 1130 15 44X .................... 110.70 5038.8 526 1068 12 12 18 1005 12 44W ................... .................... 5039.1 527 1068 .............. 24 30 1005 24 44Y .................... 110.75 5059.2 594 1068 36 36 42 1131 30 44Z .................... .................... 5059.5 595 1068 .............. 21 27 1131 15 45X .................... 110.80 .................... .............. 1069 12 .............. .............. 1006 12 45Y .................... 110.85 5059.8 596 1069 36 36 42 1132 30 45Z .................... .................... 5060.1 597 1069 .............. 21 27 1132 15 46X .................... 110.90 5039.4 528 1070 12 12 18 1007 12 46W ................... .................... 5039.7 529 1070 .............. 24 30 1007 24 46Y .................... 110.95 5060.4 598 1070 36 36 42 1133 30 46Z .................... .................... 5060.7 599 1070 .............. 21 27 1133 15 47X .................... 111.00 .................... .............. 1071 12 .............. .............. 1008 12 47Y .................... 111.05 5061.0 600 1071 36 36 42 1134 30 VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00870 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.311 T ABLE 1b—C HANNELS —Continued Channel pairing DME parameters Interrogation Reply Pulse codes VHF freq. MLS angle MLS Ch.

DME No.

MHz freq. MHz No. Freq.

DME/P Mode MHz DME/N Freq. Pulse codes μ s MHz μ s IA μ s FA μ s 47Z .................... .................... 5061.3 601 1071 .............. 21 27 1134 15 48X .................... 111.10 5040.0 530 1072 12 12 18 1009 12 48W ................... .................... 5040.3 531 1072 .............. 24 30 1009 24 48Y .................... 111.15 5061.6 602 1072 36 36 42 1135 30 48Z .................... .................... 5061.9 603 1072 .............. 21 27 1135 15 49X .................... 111.20 .................... .............. 1073 12 .............. .............. 1010 12 49Y .................... 111.25 5062.2 604 1073 36 36 42 1136 30 49Z .................... .................... 5062.5 605 1073 .............. 21 27 1136 15 50X .................... 111.30 5040.6 532 1074 12 12 18 1011 12 50W ................... .................... 5040.9 533 1074 .............. 24 30 1011 24 50Y .................... 111.35 5062.8 606 1074 36 36 42 1137 30 50Z .................... .................... 5063.1 607 1074 .............. 21 27 1137 15 51X .................... 111.40 .................... .............. 1075 12 .............. .............. 1012 12 51Y .................... 111.45 5063.4 608 1075 36 36 42 1138 30 51Z .................... .................... 5063.7 609 1075 .............. 21 27 1138 15 52X .................... 111.50 5041.2 534 1076 12 12 18 1013 12 52W ................... .................... 5041.5 535 1076 .............. 24 30 1013 24 52Y .................... 111.55 5064.0 610 1076 36 36 42 1139 30 52Z .................... .................... 5064.3 611 1076 .............. 21 27 1139 15 53X .................... 111.60 .................... .............. 1077 12 .............. .............. 1014 12 53Y .................... 111.65 5064.6 612 1077 36 36 42 1140 30 53Z .................... .................... 5064.9 613 1077 .............. 21 27 1140 15 54X .................... 111.70 5041.8 536 1078 12 12 18 1015 12 54W ................... .................... 5042.1 537 1078 .............. 24 30 1015 24 54Y .................... 111.75 5065.2 614 1078 36 36 42 1141 30 54Z .................... .................... 5065.5 615 1078 .............. 21 27 1141 15 55X .................... 111.80 .................... .............. 1079 12 .............. .............. 1016 12 55Y .................... 111.85 5065.8 616 1079 36 36 42 1142 30 55Z .................... .................... 5066.1 617 1079 .............. 21 27 1142 15 56X .................... 111.90 5042.4 538 1080 12 12 18 1017 12 56W ................... .................... 5042.7 539 1080 .............. 24 30 1017 24 56Y .................... 111.95 5066.4 618 1080 36 36 42 1143 30 56Z .................... .................... 5066.7 619 1080 .............. 21 27 1143 15 57X .................... 112.00 .................... .............. 1081 12 .............. .............. 1018 12 57Y .................... 112.05 .................... .............. 1081 36 .............. .............. 1144 30 58X .................... 112.10 .................... .............. 1082 12 .............. .............. 1019 12 58Y .................... 112.15 .................... .............. 1082 36 .............. .............. 1145 30 59X .................... 112.20 .................... .............. 1083 12 .............. .............. 1020 12 59Y .................... 122.25 .................... .............. 1083 36 .............. .............. 1146 30 ** 60X ................ .................... .................... .............. 1084 12 .............. .............. 1021 12 ** 60Y ................ .................... .................... .............. 1084 36 .............. .............. 1147 30 ** 61X ................ .................... .................... .............. 1085 12 .............. .............. 1022 12 ** 61Y ................ .................... .................... .............. 1085 36 .............. .............. 1148 30 ** 62X ................ .................... .................... .............. 1086 12 .............. .............. 1023 12 ** 62Y ................ .................... .................... .............. 1086 36 .............. .............. 1149 30 ** 63X ................ .................... .................... .............. 1037 12 .............. .............. 1024 12 ** 63Y ................ .................... .................... .............. 1087 36 .............. .............. 1150 30 ** 64X ................ .................... .................... .............. 1088 12 .............. .............. 1151 12 ** 64Y ................ .................... .................... .............. 1088 36 .............. .............. 1025 30 ** 65X ................ .................... .................... .............. 1089 12 .............. .............. 1152 12 ** 65Y ................ .................... .................... .............. 1089 36 .............. .............. 1026 30 ** 66X ................ .................... .................... .............. 1090 12 .............. .............. 1153 12 ** 66Y ................ .................... .................... .............. 1090 36 .............. .............. 1027 30 ** 67X ................ .................... .................... .............. 1091 12 .............. .............. 1154 12 ** 67Y ................ .................... .................... .............. 1091 36 .............. .............. 1028 30 ** 68X ................ .................... .................... .............. 1092 12 .............. .............. 1155 12 ** 68Y ................ .................... .................... .............. 1092 36 .............. .............. 1029 30 ** 69X ................ .................... .................... .............. 1093 12 .............. .............. 1156 12 ** 69Y ................ .................... .................... .............. 1093 36 .............. .............. 1030 30 70X .................... 112.30 .................... .............. 1094 12 .............. .............. 1157 12 ** 70Y ................ 112.35 .................... .............. 1094 36 .............. .............. 1031 30 71X .................... 112.40 .................... .............. 1095 12 .............. .............. 1158 12 ** 71Y ................ 112.45 .................... .............. 1095 36 .............. .............. 1032 30 72X .................... 112.50 .................... .............. 1096 12 .............. .............. 1159 12 ** 72Y ................ 112.55 .................... .............. 1096 36 .............. .............. 1033 30 VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00871 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.311 T ABLE 1b—C HANNELS —Continued Channel pairing DME parameters Interrogation Reply Pulse codes VHF freq. MLS angle MLS Ch.

DME No.

MHz freq. MHz No. Freq.

DME/P Mode MHz DME/N Freq. Pulse codes μ s MHz μ s IA μ s FA μ s 73X .................... 112.60 .................... .............. 1097 12 .............. .............. 1160 12 ** 73Y ................ 112.65 .................... .............. 1097 36 .............. .............. 1034 30 74X .................... 112.70 .................... .............. 1098 12 .............. .............. 1161 12 ** 74Y ................ 112.75 .................... .............. 1098 36 .............. .............. 1035 30 75X .................... 112.80 .................... .............. 1099 12 .............. .............. 1162 12 ** 75Y ................ 112.85 .................... .............. 1099 36 .............. .............. 1036 30 76X .................... 112.90 .................... .............. 1100 12 .............. .............. 1163 12 ** 76Y ................ 112.95 .................... .............. 1100 36 .............. .............. 1037 30 77X .................... 113.00 .................... .............. 1101 12 .............. .............. 1164 12 ** 77Y ................ 113.05 .................... .............. 1101 36 .............. .............. 1038 30 78X .................... 113.10 .................... .............. 1102 12 .............. .............. 1165 12 ** 78Y ................ 113.15 .................... .............. 1102 36 .............. .............. 1039 30 79X .................... 113.20 .................... .............. 1103 12 .............. .............. 1166 12 ** 79Y ................ 113.25 .................... .............. 1103 36 .............. .............. 1040 30 80X .................... 113.30 .................... .............. 1104 12 .............. .............. 1167 12 80Y .................... 113.35 5067.0 620 1104 36 36 42 1041 30 80Z .................... .................... 5067.3 621 1104 .............. 21 27 1041 15 81X .................... 113.40 .................... .............. 1105 12 .............. .............. 1168 12 81Y .................... 113.45 5067.6 622 1105 36 36 42 1042 30 81Z .................... .................... 5067.9 623 1005 .............. 21 27 1042 15 82X .................... 113.50 .................... .............. 1106 12 .............. .............. 1169 12 82Y .................... 113.55 5068.2 624 1106 36 36 42 1043 30 82Z .................... .................... 5068.5 625 1106 .............. 21 27 1043 15 83X .................... 113.60 .................... .............. 1107 12 .............. .............. 1170 12 83Y .................... 113.65 5068.8 626 1107 36 36 42 1044 30 83Z .................... .................... 5069.1 627 1107 .............. 21 27 1044 15 84X .................... 113.70 .................... .............. 1108 12 .............. .............. 1171 12 84Y .................... 113.75 5069.4 628 1108 36 36 42 1045 30 84Z .................... .................... 6069.7 629 1108 .............. 21 27 1045 15 85X .................... 113.80 .................... .............. 1109 12 .............. .............. 1172 12 85Y .................... 113.85 5070.0 630 1109 36 36 42 1046 30 85Z .................... .................... 5070.3 631 1109 .............. 21 27 1046 15 86X .................... 113.90 .................... .............. 1110 12 .............. .............. 1173 12 86Y .................... 113.95 5070.6 632 1110 36 36 42 1047 30 86Z .................... .................... 5070.9 633 1110 .............. 21 27 1047 15 87X .................... 114.00 .................... .............. 1111 12 .............. .............. 1174 12 87Y .................... 114.05 5071.2 634 1111 36 36 42 1048 30 87Z .................... .................... 5071.5 635 1111 .............. 21 27 1048 15 88X .................... 114.10 .................... .............. 1112 12 .............. .............. 1175 12 88Y .................... 114.15 5071.8 636 1112 36 36 42 1049 30 88Z .................... .................... 5072.1 637 1112 .............. 21 27 1049 15 89X .................... 114.20 .................... .............. 1113 12 .............. .............. 1176 12 89Y .................... 114.25 5072.4 638 1113 36 36 42 1050 30 89Z .................... .................... 5072.7 639 1113 .............. 21 27 1050 15 90X .................... 114.30 .................... .............. 1114 12 .............. .............. 1177 12 90Y .................... 114.35 5073.0 640 1114 36 36 42 1051 30 90Z .................... .................... 5073.3 641 1114 .............. 21 27 1051 15 91X .................... 114.40 .................... .............. 1115 12 .............. .............. 1178 12 91Y .................... 114.45 5073.6 642 1115 36 36 42 1052 30 91Z .................... .................... 5073.9 643 1115 .............. 21 27 1052 15 92X .................... 114.50 .................... .............. 1116 12 .............. .............. 1179 12 92Y .................... 114.55 5074.2 644 1116 36 36 42 1053 30 92Z .................... .................... 5074.5 645 1116 .............. 21 27 1053 15 93X .................... 114.60 .................... .............. 1117 12 .............. .............. 1180 12 93Y .................... 114.65 5074.8 646 1117 36 36 42 1054 30 93Z .................... .................... 5075.1 647 1117 .............. 21 27 1054 15 94X .................... 114.70 .................... .............. 1118 12 .............. .............. 1181 12 94Y .................... 114.75 5075.4 648 1118 36 36 42 1055 30 94Z .................... .................... 5075.7 649 1118 .............. 21 27 1055 15 95X .................... 114.80 .................... .............. 1119 12 .............. .............. 1182 12 95Y .................... 114.85 5076.0 650 1119 36 36 42 1056 30 95Z .................... .................... 5076.3 651 1119 .............. 21 27 1056 15 96X .................... 114.90 .................... .............. 1120 12 .............. .............. 1183 12 96Y .................... 114.95 5076.6 652 1120 36 36 42 1057 30 96Z .................... .................... 5076.9 653 1120 .............. 21 27 1057 15 VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00872 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.311 T ABLE 1b—C HANNELS —Continued Channel pairing DME parameters Interrogation Reply Pulse codes VHF freq. MLS angle MLS Ch.

DME No.

MHz freq. MHz No. Freq.

DME/P Mode MHz DME/N Freq. Pulse codes μ s MHz μ s IA μ s FA μ s 97X .................... 115.00 .................... .............. 1121 12 .............. .............. 1184 12 97Y .................... 115.05 5077.2 654 1121 36 36 42 1058 30 97Z .................... .................... 5077.5 655 1121 .............. 21 27 1058 15 98X .................... 115.10 .................... .............. 1122 12 .............. .............. 1185 12 98Y .................... 115.15 5077.8 656 1122 36 36 42 1059 30 98Z .................... .................... 5078.1 657 1122 .............. 21 27 1059 15 99X .................... 115.20 .................... .............. 1123 12 .............. .............. 1186 12 99Y .................... 115.25 5078.4 658 1123 36 36 42 1060 30 99Z .................... .................... 5078.7 659 1123 .............. 21 27 1060 15 100X .................. 115.30 .................... .............. 1124 12 .............. .............. 1187 12 100Y .................. 115.35 5079.0 660 1124 36 36 42 1061 30 100Z .................. .................... 5079.3 661 1124 .............. 21 27 1061 15 101X .................. 115.40 .................... .............. 1125 12 .............. .............. 1188 12 101Y .................. 115.45 5079.6 662 1125 36 36 42 1062 30 101Z .................. .................... 5079.9 663 1125 .............. 21 27 1062 15 102X .................. 115.50 .................... .............. 1126 12 .............. .............. 1189 12 102Y .................. 115.55 5080.2 664 1126 36 36 42 1063 30 102Z .................. .................... 5080.5 665 1126 .............. 21 27 1063 15 103X .................. 115.60 .................... .............. 1127 12 .............. .............. 1190 12 103Y .................. 115.65 5080.B 666 1127 36 36 42 1064 30 103Z .................. .................... 5081.1 667 1127 .............. 21 27 1064 19 104X .................. 115.70 .................... .............. 1128 12 .............. .............. 1191 12 104Y .................. 115.75 5081.4 668 1128 36 36 42 1065 30 104Z .................. .................... 5081.7 669 1128 .............. 21 27 1065 19 105X .................. 115.80 .................... .............. 1129 12 .............. .............. 1192 12 105Y .................. 115.85 5082.0 670 1129 36 36 42 1066 30 105Z .................. .................... 5082.3 671 1129 .............. 21 27 1066 15 106X .................. 115.90 .................... .............. 1130 12 .............. .............. 1193 12 106Y .................. 115.95 5082.6 672 1130 36 36 42 1067 30 106Z .................. .................... 5082.9 673 1130 .............. 21 27 1067 15 107X .................. 116.00 .................... .............. 1131 12 .............. .............. 1194 12 107Y .................. 116.05 5083.2 674 1131 36 36 42 1068 30 107Z .................. .................... 5083.5 675 1131 .............. 21 27 1068 15 108X .................. 116.10 508 .............. 1132 12 .............. .............. 1195 12 108Y .................. 116.15 5083.8 676 1132 36 36 42 1069 30 108Z .................. .................... 5084.1 677 1132 .............. 21 27 1069 15 109X .................. 116.20 .................... .............. 1133 12 .............. .............. 1196 12 109Y .................. 116.25 5084.4 678 1133 36 36 42 1070 30 109Z .................. .................... 5084.7 679 1133 .............. 21 27 1070 15 110X .................. 116.30 .................... .............. 1134 12 .............. .............. 1197 12 110Y .................. 116.35 5085.0 680 1134 36 36 42 1071 30 110Z .................. .................... 5085.3 681 1134 .............. 21 27 1071 15 111X .................. 116.40 .................... .............. 1135 12 .............. .............. 1198 12 111Y .................. 116.45 5086.6 682 1135 36 36 42 1072 30 111Z .................. .................... 5085.9 683 1135 .............. 21 27 1072 15 112X .................. 116.50 .................... .............. 1136 12 .............. .............. 1199 12 112Y .................. 116.55 5086.2 684 1136 36 36 42 1073 30 112Z .................. .................... 5086.5 685 1136 .............. 21 27 1073 15 113X .................. 116.60 .................... .............. 1137 12 .............. .............. 1200 12 113Y .................. 116.65 5086.8 686 1137 36 36 42 1074 30 113Z .................. .................... 5087.1 687 1137 .............. 21 27 1074 15 114X .................. 116.70 .................... .............. 1138 12 .............. .............. 1201 12 114Y .................. 116.75 5087.4 688 1138 36 36 42 1075 30 114Z .................. .................... 5087.7 689 1138 .............. 21 27 1075 15 115X .................. 116.80 .................... .............. 1139 12 .............. .............. 1202 12 115Y .................. 116.85 5088.0 690 1139 36 36 42 1076 30 115Z .................. .................... 5088.3 691 1139 .............. 21 27 1076 15 116X .................. 116.90 .................... .............. 1140 12 .............. .............. 1203 12 116Y .................. 116.95 5088.6 692 1140 36 36 42 1077 30 116Z .................. .................... 5088.9 693 1140 .............. 21 27 1077 15 117X .................. 117.00 .................... .............. 1141 12 .............. .............. 1204 12 117Y .................. 117.05 5089.2 694 1141 36 36 42 1078 30 117Z .................. .................... 5089.5 695 1141 .............. 21 27 1078 15 118X .................. 117.10 .................... .............. 1142 12 .............. .............. 12.5 12 118Y .................. 117.15 5089.8 696 1142 36 36 42 1079 30 VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00873 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.311 T ABLE 1b—C HANNELS —Continued Channel pairing DME parameters Interrogation Reply Pulse codes VHF freq. MLS angle MLS Ch.

DME No.

MHz freq. MHz No. Freq.

DME/P Mode MHz DME/N Freq. Pulse codes μ s MHz μ s IA μ s FA μ s 118Z .................. .................... 5090.1 697 1142 .............. 21 27 1079 12 119X .................. 117.20 .................... .............. 1143 12 .............. .............. 1206 12 119Y .................. 117.25 5090.4 698 1143 36 36 42 1080 30 119Z .................. .................... 5090.7 699 1143 .............. 21 27 1080 15 120X .................. 117.30 .................... .............. 1144 12 .............. .............. 1207 12 120Y .................. 117.35 .................... .............. 1144 36 .............. .............. 1081 30 121X .................. 117.40 .................... .............. 1145 12 .............. .............. 1208 12 121Y .................. 117.45 .................... .............. 1145 36 .............. .............. 1082 30 122X .................. 117.50 .................... .............. 1146 12 .............. .............. 1209 12 122Y .................. 117.55 .................... .............. 1146 36 .............. .............. 1083 30 123X .................. 117.60 .................... .............. 1147 12 .............. .............. 1210 12 123Y .................. 117.65 .................... .............. 1147 36 .............. .............. 1084 30 124X .................. 117.70 .................... .............. 1148 12 .............. .............. 1211 12 ** 124Y .............. 117.75 .................... .............. 1148 36 .............. .............. 1085 30 125X .................. 117.80 .................... .............. 1149 12 .............. .............. 1212 12 ** 125Y .............. 117.85 .................... .............. 1149 36 .............. .............. 1086 30 126X .................. 117.90 .................... .............. 1150 12 .............. .............. 1213 12 ** 126Y .............. 117.95 .................... .............. 1150 36 .............. .............. 1087 30 Notes: * These channels are reserved exclusively for national allotments.

** These channels may be used for national allotment on a secondary basis. The primary reason for reserving these channels is to provide protection for the secondary Surveillance Radar (SSR) system.

S 108.0 MHz is not scheduled for assignment to ILS service. The associated DME operating channel No. 17X may be as- signed to the emergency service.

(b) Polarization. (1) The radio fre- of DPSK and continuous wave (CW) quency emissions from all ground modulations of the RF carrier which equipment must be nominally have the following characteristics.

vertically polarized. Any horizontally (1) DPSK. The DPSK signal must polarized radio frequency emission have the following characteristics: component from the ground equipment bit rate .............................. 15.625 KHz must not have incorrectly coded angle bit length ........................... 64 microseconds information such that the limits speci- logic ‘‘0’’ ............................ no phase transition fied in paragraphs (b) (2) and (3) of this logic ‘‘1’’ ............................ phase transition phase transition ................ less than 10 microseconds section are exceeded.

phase tolerance ................ ± 10 degrees (2) Rotation of the receiving antenna thirty degrees from the vertically po- The phase shall advance (or retard) larized position must not cause the monotonically throughout the transi- path following error to exceed the al- tion region. Amplitude modulation lowed error at that location.

during the phase transition period (c) Modulation requirements. Each shall not be used.

function transmitter must be capable VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00874 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.311 (2) CW. The CW pulse transmissions (f) Transmission rates. Angle guidance and the CW angle transmissions as may and data signals must be transmitted be required in the signal format of any at the following average repetition function must have characteristics rates: such that the requirements of para- Average graph (d) of this section are met.

Function data rate (d) Radio frequency signal spectrum.

(Hertz) The transmitted signal must be such Approach Azimuth ................................................. 13 ± 0.5 that during the transmission time, the High Rate Approach Azimuth ................................ 39 ± 1.5 mean power density above a height of Approach Elevation ............................................... 39 ± 1.5 600 meters (2000 feet) does not exceed Back Azimuth ......................................................... 6.5 ± 0.25 ¥ 100.5 dBW/m for angle guidance and 2 Basic Data ............................................................. ( ) ¥ 95.5 dBW/m for data, as measured in Auxiliary Data ........................................................ ( ) a 150 KHz bandwidth centered at a fre- The higher rate is recommended for azimuth scanning an- quency of 840 KHz or more from the as- tennas with beamwidths greater than two degrees. It should be noted that the time available in the signal format for addi- signed frequency.

tional functions is limited when the higher rate is used.

(e) Synchronization. Synchronization Refer to Table 8a.

Refer to Table 8c.

between the azimuth and elevation components is required and, in split- (g) Transmission sequences. Sequences site configurations, would normally be of angle transmissions which will gen- accomplished by landline interconnec- erate the required repetition rates are tions. Synchronization monitoring shown in Figures 2 and 3.

must be provided to preclude function overlap.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00875 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 EC15SE91.005</GPH> jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.311 VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00876 Fmt 8010 Sfmt 8006 Y:\SGML\268049.XXX 268049 EC15SE91.006</GPH> jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.311 (h) TDM cycle. The time periods be- such combination of sequences is tween angle transmission sequences shown in Figure 4 which forms a full must be varied so that exact repeti- multiplex cycle. Data may be trans- tions do not occur within periods of mitted during suitable open times less than 0.5 second in order to protect within or between the sequences.

against synchronous interference. One VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00877 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 EC15SE91.007</GPH> jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.311 (i) Function Formats (General). Each organized as shown in Figure 5a. Each angle function must contain the fol- data function must contain a preamble lowing elements: a preamble; sector and a data transmission period orga- signals; and a TO and FRO angle scan nized as shown in Figure 5b.

(1) Preamble format. The transmitted mission followed by a receiver synchro- angle and date functions must use the nization code and a function identifica- preamble format shown in Figure 6.

tion code. The preamble timing must This format consists of a carrier acqui- be in accordance with Table 2.

sition period of unmodulated CW trans- EC15SE91.009</GPH> VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00878 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 EC15SE91.008</GPH> jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.311 (i) Digital codes. The coding used in T ABLE 2—P REAMBLE T IMING —Continued the preamble for receiver synchroni- Event time slot begins at— zation is a Barker code logic 11101. The Event 15.625 kHz time of the last phase transition mid- Time (milli- clock pulse seconds) point in the code shall be the receiver (number) reference time (see Table 2). The func- END PREAMBLE ................. 25 1.600 tion identification codes must be as Applies to all functions transmitted.

shown in Table 3. The last two bits (I Reference time for receiver synchronization for all function and I ) of the code are parity bits timing.

obeying the equations: T ABLE 3—F UNCTION I DENTIFICATION C ODES I + I + I + I + I + I = Even 6 7 8 9 10 11 Code I + I + I + I = Even 6 8 10 12 Function I 6 I 7 I 8 I 9 I 10 I 11 I 12 (ii) Data modulation. The digital code portions of the preamble must be Approach azimuth .................... 0 0 1 1 0 0 1 High rate approach azimuth ..... 0 0 1 0 1 0 0 DPSK modulated in accordance with Approach elevation .................. 1 1 0 0 0 0 1 § 171.311(c)(1) and must be transmitted Back azimuth ............................ 1 0 0 1 0 0 1 throughout the function coverage vol- Basic data 1 ............................. 0 1 0 1 0 0 0 ume. Basic data 2 ............................. 0 1 1 1 1 0 0 Basic data 3 ............................. 1 0 1 0 0 0 0 (2) Angle function formats. The timing Basic data 4 ............................. 1 0 0 0 1 0 0 of the angle transmissions must be in Basic data 5 ............................. 1 1 0 1 1 0 0 accordance with Tables 4a, 4b, and 5. Dasic data 6 ............................. 0 0 0 1 1 0 1 Auxiliary data A ........................ 1 1 1 0 0 1 0 The actual timing of the TO and FRO Auxiliary data B ........................ 1 0 1 0 1 1 1 scans must be as required to meet the Auxiliary data C ........................ 1 1 1 1 0 0 0 accuracy requirements of §§ 171.313 and 171.317.

(ii) Sector signals. In all azimuth for- (i) Preamble. Must be in accordance mats, sector signals must be trans- with requirements of § 171.311(i)(1).

mitted to provide Morse Code identi- fication, airborne antenna selection, T ABLE 2—P REAMBLE T IMING and system test signals. These signals are not required in the elevation for- Event time slot begins at— mats. In addition, if the signal from an Event 15.625 kHz Time (milli- installed ground component results in clock pulse seconds) (number) a valid indication in an area where no valid guidance should exist, OCI signals Carrier acquisition: must be radiated as provided for in the (CW transmission) ............... 0 0 Receiver reference time code: signal format (see Tables 4a, 4b, and 5).

I 1 = 1 .................................... 13 0.832 The sector signals are defined as fol- I 2 = 1 .................................... 14 0.896 lows: I 3 = 1 .................................... 15 0.960 (A) Morse Code. DPSK transmissions I 4 = 0 .................................... 16 1.024 I 5 = 1 .................................... 17 1.088 that will permit Morse Code facility Function identification: identification in the aircraft by a four I 6 ........................................... 18 1.152 letter code starting with the letter I 7 ........................................... 19 1.216 I 8 ........................................... 20 1.280 ‘‘M’’ must be included in all azimuth I 9 ........................................... 21 1.344 functions. They must be transmitted I 10 (see table 1) .................... 22 1.408 and repeated at approximately equal I 11 ......................................... 23 1.472 intervals, not less than six times per I 12 ......................................... 24 1.536 VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00879 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 EC15SE91.010</GPH> jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.311 minute, during which time the ground T ABLE 4b—H IGH R ATE A PPROACH A ZIMUTH AND subsystem is available for operational B ACK A ZIMUTH F UNCTION T IMING use. When the transmissions of the Event time slot ground subsystem are not available, begins at— the identification signal must be sup- Event 15.625 Time pressed. The audible tone in the air- kHz clock (milli- pulse sec- craft is started by setting the Morse (number) onds) Code bit to logic ‘‘1’’ and stopped by a Preamble ............................................... 0 0 logic ‘‘0’’ (see Tables 4a and 4b). The Morse Code ........................................... 25 1.600 identification code characteristics Antenna select ....................................... 26 1.664 must conform to the following: the dot Rear OCI ............................................... 32 2.048 Left OCI ................................................. 34 2.176 must be between 0.13 and 0.16 second in Right OCI ............................................... 36 2.304 duration, and the dash between 0.39 and To test ................................................... 38 2.432 0.48 second. The duration between dots 1 To scan ................................................ 40 2.560 Pause .................................................... ................ 6.760 and/or dashes must be one dot plus or Midscan point ........................................ ................ 7.060 minus 10%. The duration between char- FRO scan ............................................ ................ 7.360 acters (letters) must not be less than FRO test pulse ...................................... ................ 11.560 three dots. When back azimuth is pro- End function (airborne) .......................... ................ 11.688 End guard time; end function (ground) ................ 11.900 vided, the code shall be transmitted by The actual commencement and completion of the TO and the approach azimuth and back azi- the FRO scan transmissions are dependent on the amount of muth within plus or minus 0.08 seconds.

proportional guidance provided. The time slots provided will accommodate a maximum scan of plus or minus 42.0 de- (B) Airborne antenna selection. A sig- grees. Scan timing shall be compatible with accuracy nal for airborne antenna selection shall requirements.

be transmitted as a ‘‘zero’’ DPSK sig- (C) OCI. Where OCI pulses are used, nal lasting for a six-bit period (see Ta- they must be: (1) greater than any bles 4a and 4b).

guidance signal in the OCI sector; (2) at least 5 dB less than the level of the T ABLE 4a—A PPROACH A ZIMUTH F UNCTION scanning beam within the proportional TIMING guidance sector; and (3) for azimuth functions with clearance signals, at Event time slot begins at— least 5 dB less than the level of the left (right) clearance pulses within the left Event 15.625 Time kHz clock (milli- (right) clearance sector.

pulse sec- (number) onds) T ABLE 5—A PPROACH E LEVATION FUNCTION Preamble ............................................... 0 0 T IMING Morse code ............................................ 25 1.600 Antenna select ....................................... 26 1.664 Event time slot begins at: Rear OCI ............................................... 32 2.048 Left OCI ................................................. 34 2.176 Event 15.625 Time Right OCI ............................................... 36 2.304 kHz clock (milli- pluse sec- To test ................................................... 38 2.432 (number) onds) To scan ................................................ 40 2.560 Pause .................................................... ................ 8.760 Preamble ............................................... 0 0 Midscan point ........................................ ................ 9.060 Processor pause .................................... 25 1.600 FRO scan ............................................ ................ 9.360 OCI ........................................................ 27 1.728 FRO test ................................................ ................ 15.560 To scan ................................................ 29 1.856 End Function (Airborne) ........................ ................ 15.688 Pause .................................................... ................ 3.406 Midscan point ........................................ ................ 3.606 End guard time; end function (ground) ................ 15.900 FRO scan ............................................ ................ 3.806 AA The actual commencement and completion of the TO End function (airborne) .......................... ................ 5.356 and the FRO scan transmissions are dependent on the End guard time; end function (ground) ................ 5.600 amount of proportional guidance provided. The time slots pro- vided shall accommodate a maximum scan of plus or minus The actual commencement and completion of the TO and 62.0 degrees. Scan timing shall be compatible with accuracy FRO scan transmissions are dependent upon the amount of requirements.

proportional guidance provided. The time slots provided will accommodate a maximum scan of ¥ 1.5 degrees to + 29.5 degrees. Scan timing shall be compatible with accuracy requirements.

The duration of each pulse measured at the half amplitude point shall be at least 100 microseconds, and the rise and VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00880 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.311 fall times shall be less then 10 micro- proportional coverage sector first in seconds. It shall be permissible to se- one direction (the TO scan) and then in quentially transmit two pulses in each the opposite direction (the FRO scan).

out-of-coverage indication time slot. Angular information must be encoded Where pulse pairs are used, the dura- by the amount of time separation be- tween the beam centers of the TO and tion of each pulse shall be at least 50 FRO scanning beam pulses. The TO and microseconds, and the rise and fall FRO transmissions must be symmetri- times shall be less then 10 microsec- cally disposed about the midscan point onds. The transmission of out-of-cov- listed in Tables 4a, 4b, 5, and 7. The erage indication pulses radiated from midscan point and the center of the antennas with overlapping coverage time interval between the TO and FRO patterns shall be separated by at least scan transmissions must coincide with 10 microseconds.

a tolerance of ± 10 microseconds. Angu- N OTE : If desired, two pulses may be sequen- lar coding must be linear with angle tially transmitted in each OCI time slot.

and properly decoded using the for- Where pulse pairs are used, the duration of mula: each pulse must be 45 ( ± 5) microseconds and the rise and fall times must be less than 10 V microseconds.

θ = T t −

( )

(D) System test. Time slots are pro- vided in Tables 4a and 4b to allow radi- where: ation of TO and FRO test pulses. How- q = Receiver angle in degrees.

ever, radiation of these pulses is not re- V = Scan velocity in degrees per micro- quired since the characteristics of second.

these pulses have not yet been stand- T = Time separation in microseconds be- tween TO and FRO beam centers cor- ardized.

responding to zero degrees.

(iii) Angle encoding. The encoding t = Time separation in microseconds between must be as follows: TO and FRO beam centers.

(A) General. Azimuth and elevation angles are encoded by scanning a nar- The timing requirements are listed in row beam between the limits of the Table 6 and illustrated in Figure 7.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00881 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 EC15SE91.011</MATH> jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.311 (B) Azimuth angle encoding. Each erage. Elevation angles are defined guidance angle transmitted must con- from the horizontal plane containing sist of a clockwise TO scan followed by the antenna phase center; positive an- a counterclockwise FRO scan as viewed gles are above the horizontal and zero from above the antenna. For approach angle is along the horizontal.

azimuth functions, increasing angle (iv) Clearance guidance. The timing of values must be in the direction of the the clearance pulses must be in accord- TO scan; for the back azimuth func- ance with Figure 8. For azimuth ele- tion, increasing angle values must be ments with proportional coverage of in the direction of the FRO scan. The less than ± 40 degrees ( ± 20 degrees for antenna has a narrow beam in the back azimuth), clearance guidance in- plane of the scan direction and a broad formation must be provided by trans- beam in the orthogonal plane which mitting pulses in a TO and FRO format fills the vertical coverage. adjacent to the stop/start times of the (C) Elevation angle encoding. The radi- scanning beam signal. The fly-right ation from elevation equipment must clearance pulses must represent posi- produce a beam which scans from the tive angles and the fly-left clearance horizon up to the highest elevation pulses must represent negative angles.

angle and then scans back down to the The duration of each clearance pulse horizon. The antenna has a narrow must be 50 microseconds with a toler- beam in the plane of the scan direction ance of ± 5 microseconds. The trans- and a broad beam in the orthogonal mitter switching time between the plane which fills the horizontal cov- clearance pulses and the scanning VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00882 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 EC15SE91.012</GPH> jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.311 beam transmissions must not exceed 10 Where used, clearance pulses shall be microseconds. The rise time at the transmitted adjacent to the scanning edge of each clearance pulse must be beam signals at the edges of propor- less than 10 microseconds. Within the tional coverage as shown in Figure 8.

fly-right clearance guidance section, The proportional coverage boundary the fly-right clearance guidance signal shall be established at one beamwidth shall exceed scanning beam antenna inside the scan start/stop angles, such sidelobes and other guidance and OCI that the transition between scanning signals by at least 5 dB; within the fly- beam and clearance signals occurs out- left clearance guidance sector, the fly side the proportional coverage sector.

left clearance guidance signal shall ex- When clearance pulses are provided in ceed scanning beam antenna sidelobes conjunction with a narrow beamwidth and all other guidance and OCI signals (e.g., one degree) scanning antenna, the by at least 5 dB; within the propor- scanning beam antenna shall radiate tional guidance sector, the clearance for 15 microseconds while stationary at guidance signals shall be at least 5dB the scan start/stop angles.

below the proportional guidance signal. (3) Data function format. Basic data Optionally, clearance guidance may be words provide equipment characteris- provided by scanning throughout the tics and certain siting information.

approach guidance sector. For angles Basic data words must be transmitted outside the approach azimuth propor- from an antenna located at the ap- tional coverage limits as set in Basic proach azimuth or back azimuth site Data Word One (Basic Data Word 5 for which provides coverage throughout back azimuth), proper decode and dis- the appropriate sector. Data function play of clearance guidance must occur timing must be in accordance with to the limits of the guidance region. Table 7a.

T ABLE 6—A NGLE S CAN T IMING C ONSTANTS Max Pause V(deg/ T m Function value of T (usec) time T (usec) o t usec) (usec) (usec) (usec) t Approach azimuth ..................................................................... 13,000 6,800 0.02 7,972 600 13,128 High rate approach azimuth ...................................................... 9,000 4,800 0.02 5,972 600 9,128 Approach elevation ................................................................... 3,500 3,350 0.02 2,518 400 N/A Back azimuth ............................................................................. 9,000 4,800 ¥ 0.02 5,972 600 9,128 T ABLE 7a—B ASIC D ATA F UNCTION T IMING T ABLE 7b—A UXILIARY D ATA F UNCTION T IMING— (D IGITAL )—Continued Event time slot begins at: Event time slot begins at: Event 15.625 Time kHz clock (milli- Event 15.625 Time pulse sec- kHz clock (milli- (number) onds) pulse sec- (number) onds) Preamble ............................................... 0 0 Data transmission (bits I 13 –I 30 ) .............. 25 1.600 Parity transmission (bits I 70 –I 76 ) ............ 82 5.248 Parity transmission (bits I 31 –I 32 ) ............ 43 2.752 End function (airborne) .......................... 89 5.696 End function (airborne) .......................... 45 2.880 End guard time; end function (ground) ................ 5.900 End guard time: end function (ground) ................ 3.100 The previous event time slot ends at this time.

T ABLE 7c—A UXILIARY D ATA F UNCTION T IMING— T ABLE 7b—A UXILIARY D ATA F UNCTION T IMING— (A LPHANUMERIC ) (D IGITAL ) Event time slot begins at: Event time slot begins at: Event 15.615 Time kHz clock (milli- Event 15.625 Time pulse sec- kHz clock (milli- (number) onds) pulse sec- (number) onds) Preamble ............................................... 0 0 Address transmission (bits I 13 –I 20 ) ........ 25 1.600 Preamble ............................................... 0 0 Address transmission (bits I –I ) ........ 25 1.600 Data transmission: (bits I –I .............. 33 2.112 13 20 21 76 Data transmission: (bits I –I ) ............. 33 2.112 End function (airborne) .......................... 89 5.696 21 69 VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00883 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.311 T ABLE 7c—A UXILIARY D ATA F UNCTION T IMING— (j) Basic Data word requirements. Basic (A LPHANUMERIC )—Continued Data shall consist of the items speci- fied in Table 8a. Basic Data word con- Event time slot tents shall be defined as follows: begins at: (1) Approach azimuth to threshold dis- Event 15.615 Time kHz clock (milli- tance shall represent the minimum dis- pulse sec- tance between the Approach Azimuth (number) onds) antenna phase center and the vertical End guard time; (end function ground) ................ 5.900 plane perpendicular to the centerline which contains the landing threshold.

(i) Preamble. Must be in accordance (2) Approach azimuth proportional cov- with requirements of § 171.311(i)(1).

erage limit shall represent the limit of (ii) Data transmissions. Basic data the sector in which proportional ap- must be transmitted using DPSK mod- proach azimuth guidance is trans- ulation. The content and repetition mitted.

rate of each basic data word must be in (3) Clearance signal type shall rep- accordance with Table 8a. For data resent the type of clearance when used.

containing digital information, binary number 1 must represent the lower Pulse clearance is that which is in ac- range limit with increments in binary cordance with § 171.311 (i) (2) (iv). Scan- steps to the upper range limit shown in ning Beam (SB) clearance indicates Table 8a. Data containing digital infor- that the proportional guidance sector mation shall be transmitted with the is limited by the proportional coverage least significant bit first.

limits set in basic data.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00884 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.311 VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00885 Fmt 8010 Sfmt 8006 Y:\SGML\268049.XXX 268049 EC15SE91.013</GPH> jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.311 T ABLE 8a—B ASIC D ATA W ORDS T ABLE 8a—B ASIC DATA W ORDS —Continued Data bit LSB Data bit Data bit LSB Data bit Data item definition Data item definition # value value # value value Basic Data Word No. 1 17 .......................................... ............ 1.6 ° 18 .......................................... ............ 3.2 ° 1 Preamble ......................... N/A 1 19 .......................................... ............ 6.4 ° 20 Back azimuth status ........ ............ see note 4 21 DME status ...................... ............ see note 6 22 .......................................... ............

23 Approach azimuth status ............ see note 4 24 Approach azimuth status ............ see note 4 25 Spare ............................... ............ Transmit zero 26 ......do ............................... ............ Do.

27 ......do ............................... ............ Do.

28 ......do ............................... ............ Do.

13 Approach azimuth to 100m 100m 29 ......do ............................... ............ Do.

threshold distance 30 ......do ............................... ............ Do.

(Om ¥ 630m).

31 Parity: (13 + 14 + 15. . . N/A N/A 14 .......................................... ............ 200m + 30 + 31) = odd).

15 .......................................... ............ 400m 32 Parity: (14 + 16 + 18. . . N/A N/A 16 .......................................... ............ 800m + 30 + 32 = odd).

17 .......................................... ............ 1600m Note 1: Transmit throughout the Approach Azimuth guidance 18 .......................................... ............ 3200m sector at intervals of 0.16 seconds or less.

19 Approach azimuth propor- 2 ° ¥ 2 ° Note 2: The all zero state of the data field represents the tional coverage limit lower limit of the absolute range of the coded parameter (negative limit) (0 ° to unless otherwise noted.

¥ 62 ° ).

20 .......................................... ............ ¥ 4 ° Basic Data Word No. 3 21 .......................................... ............ ¥ 8 ° 22 .......................................... ............ ¥ 16 ° 1 Preamble ......................... N/A 1 23 .......................................... ............ ¥ 32 ° 24 Approach azimuth propor- 2 ° 2 ° tional coverage limit (positive limit) (0 ° to + 62 ° ).

25 .......................................... ............ 4 ° 26 .......................................... ............ 8 ° 27 .......................................... ............ 16 ° 28 .......................................... ............ 32 ° 29 Clearance signal type ...... N/A 0 = pulse; 1 = SB 30 Spare ............................... ............ Transmit zero 13 Approach azimuth beam- 0.5 ° 0.5 ° 31 Parity: (13 + 14 + 15. . . N/A N/A width (0.5 ° ¥ 4.0 ° ) See + 30 + 31 = odd).

note 7.

32 Parity: (14 + 16 + 18. . . N/A N/A 14 .......................................... ............ 1.0 ° + 30 + 32 = odd).

15 .......................................... ............ 2.0 ° Note 1: Transmit throughout the Approach Azimuth guidance 16 Approach elevation 0.5 ° 0.5 ° sector at intervals of 1.0 seconds or less.

beamwidth (0.5 ° to Note 2: The all zero state of the data field represents the 2.5 ° ) See note 7.

lower limit of the absolute value of the coded parameter 17 .......................................... ............ 1.0 ° unless otherwise noted.

18 Note: values greater than ............ 2.0 ° 2.5 ° are invalid.

Basic Data Word No. 2 19 DME distance (Om to 12.5m 12.5m 6387.5m.

1 Preamble ......................... N/A 1 20 .......................................... ............ 25.0m 21 .......................................... ............ 50.0m 22 .......................................... ............ 100.0m 23 .......................................... ............ 200.0m 24 .......................................... ............ 400.0m 25 .......................................... ............ 800.0m 26 .......................................... ............ 1600.0m 27 .......................................... ............ 3200.0m 28 Spare ............................... ............ Transmit zero 12 .......................................... ............ 0 29 ......do ............................... ............ Do.

13 Minimum glide path (2.0 ° 0.1 ° 0.1 ° 30 ......do ............................... ............ Do.

to 14.7 ° ). 31 Parity: (13 + 14 + 15. . . ............

14 .......................................... ............ 0.2 ° + 30 + 31 = odd).

15 .......................................... ............ 0.4 ° 32 Parity: (14 + 16 + 18. . . N/A N/A 16 .......................................... ............ 0.8 ° + 30 + 32 = odd).

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00886 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.311 T ABLE 8a—B ASIC D ATA W ORDS —Continued T ABLE 8a—B ASIC DATA W ORDS —Continued Data bit LSB Data bit Data bit LSB Data bit Data item definition Data item definition # value value # value value Note 1: Transmit throughout the Approach Azimuth guidance 16 .......................................... ............ ¥ 16 ° 17 .......................................... ............ ¥ 32 ° sector at intervals of 1.0 seconds or less.

18 Back azimuth proportional 2 ° 2 ° Note 2: The all zero state of the data field represents the coverage positive limit lower limit of the absolute range of the coded parameter (0 ° to + 42 ° ).

unless otherwise noted.

19 .......................................... ............ 4 ° Basic Data Word No. 4 20 .......................................... ............ 8 ° 21 .......................................... ............ 16 ° 1 Preamble ......................... N/A 1 22 .......................................... ............ 32 ° 23 Back azimuth beamwidth 0.5 ° 0.5 ° (0.5 ° to 4.0 ° ) See note 7.

24 .......................................... ............ 1.0 ° 25 .......................................... ............ 2.0 ° 26 Back azimuth status ........ ............ See Note 10 8 .......................................... ............ 0 27 ......do ............................... ............ Do.

28 ......do ............................... ............ Do.

29 ......do ............................... ............ Do.

30 ......do ............................... ............ Do.

31 Parity: (13 + 14 + 15. . . N/A N/A 13 Approach azimuth mag- 1 ° 1 ° + 30 + 31 = odd).

netic orientation (0 ° to 32 Parity: (14 + 16 + 18. . . N/A N/A 359 ° ).

+ 30 + 32 = odd).

14 .......................................... ............ 2 ° Note 1: Transmit only when Back Azimuth guidance is pro- 15 .......................................... ............ 4 ° vided. See note 9.

16 .......................................... ............ 8 ° Note 2: The all zero state of the data filed represents the 17 .......................................... ............ 16 ° lower limit of the absolute range of the coded parameter 18 .......................................... ............ 32 ° unless otherwise noted.

19 .......................................... ............ 64 ° 20 .......................................... ............ 128 ° Basic Data Word No. 6 21 .......................................... ............ 256 ° 22 Back azimuth magnetic 1 ° 1 ° 1 Preamble ......................... N/A 1 orientation (0 ° to 359 ° ).

23 .......................................... ............ 2 ° 24 .......................................... ............ 4 ° 25 .......................................... ............ 8 ° 26 .......................................... ............ 16 ° 27 .......................................... ............ 32 ° 28 .......................................... ............ 64 ° 29 .......................................... ............ 128 ° 30 .......................................... ............ 256 ° 31 Parity: (13 + 14 + 15. . . N/A N/A + 30 + 31 = odd).

32 Parity: (14 + 16 + 18. . . N/A N/A (13– MLS ground equipment ............

+ 30 + 32 = odd).

30) identification (Note 3).

Note 1: Transmit at intervals of 1.0 second or less through- 13 Character 2 ...................... N/A B1 out the Approach Azimuth guidance sector, except when 14 .......................................... ............ B2 Back Azimuth guidance is provided. See Note 8.

15 .......................................... ............ B3 Note 2: The all zero state of the data field represents the 16 .......................................... ............ B4 lower limit of the absolute range of the coded parameter 17 .......................................... ............ B5 unless otherwise noted.

18 .......................................... ............ B6 19 Character 3 ...................... N/A B1 Basic Data Word No. 5 20 .......................................... ............ B2 21 .......................................... ............ B3 1 Preamble ......................... N/A 1 22 .......................................... ............ B4 23 .......................................... ............ B5 24 .......................................... ............ B6 25 Character 4 ...................... N/A B1 26 .......................................... ............ B2 27 .......................................... ............ B3 28 .......................................... ............ B4 29 .......................................... ............ B5 30 .......................................... ............ B6 31 Parity: (13 + 14 + 15. . . N/A N/A + 30 + 31 = odd).

32 Parity: (14 + 16 + 18. . . N/A N/A 13 Back azimuth proportional 2 ° ¥ 2 ° + 30 + 32 = odd).

coverage negative limit (0 ° to ¥ 42 ° ).

Note 1: Transmit at intervals of 1.0 second or less through- 14 .......................................... ............ ¥ 4 ° out the Approach Azimuth guidance sector, except when Back 15 .......................................... ............ ¥ 8 ° Azimuth guidance is provided. See note 8.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00887 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.311 ured angle shall be at the approach azi- Note 3: Characters are encoded using the International Al- muth antenna phase center.

phabet Number 5, (IA–5): Note 4: Coding for status bit: 0 = Function not radiated, or radiated in test mode (not reli- N OTE : For example, this data item would able for navigation).

be encoded 090 for an approach azimuth an- 1 = Function radiated in normal mode (for Back Azimuth, tenna serving runway 27 (assuming the mag- this also indicates that a Back Azimuth transmission follows).

Note 5: Date items which are not applicable to a particular netic heading is 270 degrees) when sited such ground equipment shall be transmitted as all zeros.

that the zero degree radial is parallel to cen- Note 6: Coding for status bits: terline.

I I 21 22 0 0 DME transponder inoperative or not available.

(12) Back azimuth magnetic orientation 1 0 Only IA mode or DME/N available.

shall represent the angle measured in 0 0 FA mode, Standard 1, available.

the horizontal plane clockwise from 1 1 FA mode, Standard 2, available.

Note 7: The value coded shall be the actual beamwidth (as Magnetic North to the zero-degree defined in § 171.311 (j)(9) rounded to the nearest 0.5 degree.

angle guidance radial originating from Note 8: When back Azimuth guidance is provided, Data the Back Azimuth antenna. The vertex Words 4 and 6 shall be transmitted at intervals of 1.33 sec- onds or less throughout the Approach Azimuth coverage and of the measured angle shall be at the 4 seconds or less throughout the Back Azimuth coverage.

Back Azimuth antenna phase center.

Note 9: When Back Azimuth guidance is provided, Data Word 5 shall be transmitted at an interval of 1.33 seconds or less throughout the Back Azimuth coverage sector and 4 sec- N OTE : For example, this data item would onds or less throughout the Approach Azimuth coverage sec- be encoded 270 for a Back Azimuth Antenna tor.

serving runway 27 (assuming the magnetic Note 10: Coding for status bit: 0 = Function not radiated, or radiated in test mode (not reli- heading is 270 degrees) when sited such that able for navigation).

the zero degree radial is parallel to center- 1 = Function radiated in normal mode.

line.

(4) Minimum glidepath the lowest (13) Back azimuth proportional cov- angle of descent along the zero degree erage limit shall represent the limit of azimuth that is consistent with pub- the sector in which proportional back lished approach procedures and obsta- azimuth guidance is transmitted.

cle clearance criteria.

(14) MLS ground equipment identifica- (5) Back azimuth status shall represent tion shall represent the last three char- the operational status of the Back Azi- acters of the system identification muth equipment.

specified in § 171.311(i)(2). The char- (6) DME status shall represent the acters shall be encoded in accordance operational status of the DME equip- with International Alphabet No. 5 (IA– ment.

5) using bits b through b .

1 6 (7) Approach azimuth status shall rep- N OTE : Bit b 7 of this code may be recon- resent the operational status of the ap- structed in the airborne receiver by taking proach azimuth equipment.

the complement of bit b 6 .

(8) Approach elevation status shall rep- resent the operational status of the ap- (k) Residual radiation. The residual proach elevation equipment. radiation of a transmitter associated (9) Beamwidth the width of the scan- with an MLS function during time in- ning beam main lobe measured at the tervals when it should not be transmit- ¥ 3 dB points and defined in angular ting shall not adversely affect the re- units on the antenna boresight, in the ception of any other function. The re- horizontal plane for the azimuth func- sidual radiation of an MLS function at tion and in the vertical plane for the times when another function is radi- elevation function. ating shall be at least 70 dB below the (10) DME distance shall represent the level provided when transmitting.

minimum distance between the DME (l) Symmetrical scanning. The TO and antenna phase center and the vertical FRO scan transmissions shall be sym- plane perpendicular to the runway cen- metrically disposed about the mid-scan terline which contains the MLS datum point listed in Tables 4a, 4b and 5. The point. mid-scan point and the center of the (11) Approach azimuth magnetic ori- time interval between the TO and FRO entation shall represent the angle meas- scan shall coincide with a tolerance of ured in the horizontal plane clockwise plus or minus 10 microseconds.

from Magnetic North to the zero-de- (m) Auxiliary data —(1) Addresses.

gree angle guidance radial originating Three function identification codes are from the approach azimuth antenna reserved to indicate transmission of phase center. The vertex of the meas- Auxiliary Data A, Auxiliary Data B, VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00888 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.313 and Auxiliary Data C. Auxiliary Data (vi) MLS datum point to threshold dis- A contents are specified below, Auxil- tance shall represent the distance iary Data B contents are reserved for measured along the runway centerline future use, and Auxiliary Data C con- from the MLS datum point to the run- tents are reserved for national use. The way threshold.

(vii) Approach elevation antenna address codes of the auxiliary data height shall represent the height of the words shall be as shown in Table 8b.

elevation antenna phase center rel- (2) Organization and timing. The orga- ative to the height of the MLS datum nization and timing of digital auxiliary point.

data must be as specified in Table 7b.

(viii) DME offset shall represent the Data containing digital information minimum distance between the DME must be transmitted with the least sig- antenna phase center and the vertical nificant bit first. Alphanumeric data plane containing the runway center- characters must be encoded in accord- line.

ance with the 7-unit code character set (ix) DME to MLS datum point distance as defined by the American National shall represent the minimum distance Standard Code for Information Inter- between the DME antenna phase center change (ASCII). An even parity bit is and the vertical plane perpendicular to added to each character. Alphanumeric the centerline which contains the MLS data must be transmitted in the order datum point.

in which they are to be read. The serial (x) Back azimuth antenna offset shall transmission of a character must be represent the minimum distance be- with the lower order bit transmitted tween the back azimuth antenna phase first and the parity bit transmitted center and the vertical plane con- last. The timing for alphanumeric aux- taining the runway centerline.

iliary data must be as shown in Table (xi) Back azimuth to MLS datum point 7c.

distance shall represent the minimum (3) Auxiliary Data A content: The data distance between the Back Azimuth items specified in Table 8c are defined antenna and the vertical plane perpen- as follows: dicular to the centerline which con- (i) Approach azimuth antenna offset tains the MLS datum point.

shall represent the minimum distance (xii) Back azimuth antenna alignment between the Approach Azimuth an- with runway centerline shall represent tenna phase center and the vertical the minimum angle between the back plane containing the runway center- azimuth antenna zero-degree guidance line.

plane and the runway centerline.

(ii) Approach azimuth to MLS datum § 171.313 Azimuth performance re- point distance shall represent the min- quirements.

imum distance between the Approach Azimuth antenna phase center and the This section prescribes the perform- vertical plane perpendicular to the cen- ance requirements for the azimuth terline which contains the MLS datum equipment of the MLS as follows: point. (a) Approach azimuth coverage require- (iii) Approach azimuth alignment with ments. The approach azimuth equip- runway centerline shall represent the ment must provide guidance informa- minimum angle between the approach tion in at least the following volume of azimuth antenna zero-degree guidance space (see Figure 9): plane and the runway certerline.

T ABLE 8b—A UXILIARY D ATA W ORD A DDRESS (iv) Approach azimuth antenna coordi- C ODES nate system shall represent the coordi- nate system (planar or conical) of the No. I I I I I I I I 13 14 15 16 17 18 19 20 angle data transmitted by the ap- 1. 0 0 0 0 0 1 1 1 proach azimuth antenna.

2. 0 0 0 0 1 0 1 0 (v) Approach elevation antenna offset 3. 0 0 0 0 1 1 0 1 4. 0 0 0 1 0 0 1 1 shall represent the minimum distance 5. 0 0 0 1 0 1 0 0 between the elevation antenna phase 6. 0 0 0 1 1 0 0 1 center and the vertical plane con- 7. 0 0 0 1 1 1 1 0 taining the runway centerline. 8. 0 0 1 0 0 0 1 0 VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00889 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.313 T ABLE 8b—A UXILIARY D ATA W ORD ADDRESS T ABLE 8b—A UXILIARY D ATA W ORD A DDRESS C ODES —Continued C ODES —Continued No. I I I I I I I I No. I I I I I I I I 13 14 15 16 17 18 19 20 13 14 15 16 17 18 19 20 9. 0 0 1 0 0 1 0 1 41. 1 0 1 0 0 1 1 1 10. 0 0 1 0 1 0 0 0 42. 1 0 1 0 1 0 1 0 11. 0 0 1 0 1 1 1 1 43. 1 0 1 0 1 1 0 1 12. 0 0 1 1 0 0 0 1 44. 1 0 1 1 0 0 1 1 13. 0 0 1 1 0 1 1 0 45. 1 0 1 1 0 1 0 0 14. 0 0 1 1 1 0 1 1 46. 1 0 1 1 1 0 0 1 15. 0 0 1 1 1 1 0 0 47. 1 0 1 1 1 1 1 0 16. 0 1 0 0 0 0 1 1 48. 1 1 0 0 0 0 0 1 17. 0 1 0 0 0 1 0 0 49. 1 1 0 0 0 1 1 0 18. 0 1 0 0 1 0 0 1 50. 1 1 0 0 1 0 1 1 19. 0 1 0 0 1 1 1 0 51. 1 1 0 0 1 1 0 0 20. 0 1 0 1 0 0 0 0 52. 1 1 0 1 0 0 1 0 21. 0 1 0 1 0 1 1 1 53. 1 1 0 1 0 1 0 1 22. 0 1 0 1 1 0 1 0 23. 0 1 0 1 1 1 0 1 54. 1 1 0 1 1 0 0 0 24. 0 1 1 0 0 0 0 1 55. 1 1 0 1 1 1 1 1 25. 0 1 1 0 0 1 1 0 56. 1 1 1 0 0 0 1 1 26. 0 1 1 0 1 0 1 1 57. 1 1 1 0 0 1 0 0 27. 0 1 1 0 1 1 0 0 58. 1 1 1 0 1 0 0 1 28. 0 1 1 1 0 0 1 0 59. 1 1 1 0 1 1 1 0 29. 0 1 1 1 0 1 0 1 60. 1 1 1 1 0 0 0 0 30. 0 1 1 1 1 0 0 0 61. 1 1 1 1 0 1 1 1 31. 0 1 1 1 1 1 1 1 62. 1 1 1 1 1 0 1 0 32. 1 0 0 0 0 0 1 0 63. 1 1 1 1 1 1 0 1 33. 1 0 0 0 0 1 0 1 64. 0 0 0 0 0 0 0 0 34. 1 0 0 0 1 0 0 0 35. 1 0 0 0 1 1 1 1 36. 1 0 0 1 0 0 0 1 N OTE 1: Parity bits I and I are chosen to 19 20 37. 1 0 0 1 0 1 1 0 satisfy the equations: 38. 1 0 0 1 1 0 1 1 I + I + I + I + I + I + I = EVEN 13 14 15 16 17 18 19 39. 1 0 0 1 1 1 0 0 40. 1 0 1 0 0 0 0 0 I + I + I + I = EVEN 14 16 18 20 T ABLE 8 C—A UXILIARY D ATA Maximun Least Word time be- sig- Type Bits (See Data content tween trans- Range of values nifi- of data used note 6) missions cant (Seconds) bit A1 ...... Preamble ..................................................... Digital 1.0 12 ...................................................... .........

Address ........................................................ ........... .................... 8 ...................................................... .........

Approach azimuth antenna offset ............... ........... .................... 10 ¥ 511 m to + 511 m (See note 3) 1 m Approach azimuth to MLS datum point dis- ........... .................... 13 0 m to 8 191 m ............................ 1 m tance.

Approach azimuth antenna alignment with ........... .................... 12 ¥ 20.47 ° to 20.47 ° (See note 3) .. 0.01 ° runway centerline.

Approach azimuth antenna coordinate sys- ........... .................... 1 (See note 2) ................................. .........

tem.

Spare ........................................................... ........... .................... 13 ...................................................... .........

Parity ............................................................ ........... .................... 7 (See note 1) ................................. .........

A2 ...... Preamble ..................................................... Digital 1.0 12 ...................................................... .........

Address ........................................................ ........... .................... 8 ...................................................... .........

Approach elevation antenna offset .............. ........... .................... 10 ¥ 511 m to + 511 m (See note 3) 1 m MLS datum point to threshold distance ...... ........... .................... 10 0 m to 1 023 m ............................ 1 m Approach elevation antenna height ............. ........... .................... 7 ¥ 6.3 m to + 6.3 m (See note 3) 0.1 m Spare ........................................................... ........... .................... 22 ...................................................... .........

Parity ............................................................ ........... .................... 7 (See note 1) ................................. .........

A3 ...... Preamble ..................................................... Digital (See note 4) 12 ...................................................... .........

Address ........................................................ ........... .................... 8 ...................................................... .........

DME offset ................................................... ........... .................... 10 ¥ 511 m to + 511 m .................... 1 m DME to MLS datum point distance ............. ........... .................... 14 ¥ 8 191 m to + 8 191 m (See 1 m note 3).

Spare ........................................................... ........... .................... 25 ...................................................... .........

Parity ............................................................ ........... .................... 7 (See note 1) ................................. .........

A4 ...... Preamble ..................................................... Digital (See note 5) 12 ...................................................... .........

Address ........................................................ ........... .................... 8 ...................................................... .........

Back azimuth antenna ................................. ........... .................... 10 ¥ 511 m to + 511 m (See note 3) 1 m Back azimuth to MLS datum point distance ........... .................... 11 0 m to 2 047 m ............................ 1 m VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00890 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.313 T ABLE 8 C—A UXILIARY D ATA—Continued Maximun Least Word time be- sig- Type Bits (See Data content tween trans- Range of values nifi- of data used note 6) missions cant (Seconds) bit Back azimuth antenna alignment with run- ........... .................... 12 ¥ 20.47 ° to 20.47 ° (See note 3) .. 0.01 ° way centerline.

Spare ........................................................... ........... .................... 16 ...................................................... .........

Parity ............................................................ ........... .................... 7 (See note 1) ................................. .........

N OTE 1: Parity bits I to I are chosen to N OTE 3: The convention for the coding of 70 76 satisfy the equations which follow: negative numbers is as follows: ¥ MSB is the sign bit; 0 = + ; 1 = ¥ .

For BIT I : + ... + I ) + I + I + I + I Even = (I 13 18 20 22 24 25 —Other bits represent the absolute value.

+ I + I + I + I + I + I + I + I + I 28 29 31 32 33 35 36 38 41 The convention for the antenna location is + I + I + I + I + (I + ... + I ) + I + 44 45 46 50 52 55 58 as follows: As viewed from the MLS approach I + I + I + I 60 64 65 70 reference datum looking toward the datum For BIT I : 71 point, a positive number shall represent a lo- Even = (I + ... + I ) + I + I + I + I 14 19 21 23 25 26 cation to the right of the runway centerline + I + I + I + I + I + I + I + I + I 29 30 32 33 34 36 37 39 42 (lateral offset) or above the runway (vertical + I 45 + I 46 + I 47 + I 51 + (I 53 + ... + I 56 ) + I 59 + offset), or towards the stop end of the run- + I + I + I I 61 65 66 71 way (longitudinal distance).

For BIT I : The convention for the antenna alignment Even = (I + ... + I ) + I + I + I + I 15 20 22 24 26 27 is as follows: As viewed from above, a posi- + I + I + I + I + I + I + I + I + I 30 31 33 34 35 37 38 40 43 tive number shall represent clockwise rota- + I + I + I + I + (I + ... + I ) + I + 46 47 48 52 54 57 60 tion from the runway centerline to the re- I + I + I + I 62 66 67 72 spective zero-degree guidance plane.

For BIT I 73 : N OTE 4: Data Word A3 is transmitted at in- Even = (I + ... + I ) + I + I + I + I 16 21 23 25 27 28 tervals of 1.0 seconds or less throughout the + I + I + I + I + I + I + I + I + I 31 32 34 35 36 38 39 41 44 approach Azimuth coverage sector, except + I + I + I + I + (I + ... + I ) + I + 47 48 49 53 55 58 61 when back Azimuth guidance is provided.

I + I + I + I 63 67 68 73 Where back Azimuth is provided transmit at For BIT I : intervals of 1.33 seconds or less throughout Even = (I + ... + I ) + I + I + I + I 17 22 24 26 28 29 the approach Azimuth sector and 4.0 seconds + I 32 + I 33 + I 35 + I 36 + I 37 + I 39 + I 40 + I 42 + I 45 or less throughout the back Azimuth cov- + I + I + I + (I + ... + I ) + I + + I 48 49 50 54 56 59 62 erage sector.

I + I + I + I 64 68 69 74 N OTE 5: When back Azimuth guidance is For BIT I : provided, transmit at intervals of 1.33 sec- Even = (I + ... + I ) + I + I + I + I 13 17 19 21 23 24 onds or less throughout the back Azimuth + I + I + I + I + I + I + I + I + I 27 28 30 31 32 34 35 37 40 coverage sector and 4.0 seconds or less + I + I + I + I + (I + ... + I ) + I + 43 44 45 49 51 54 57 throughout the approach Azimuth coverage I + I + I + I + I 59 63 64 69 75 sector.

For BIT I : N OTE 6: The designation ‘‘A1’’ represents Even = I + I + ... + I + I 13 14 75 76 the function identification code for ‘‘Auxil- N OTE 2: Code for I is: 0 = conical; 1 = iary Data A’’ and address code number 1.

planar.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00891 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.313 (1) Horizontally within a sector plus way centerline. Clearance signals must or minus 40 degrees about the runway be used to provide the balance of the centerline originating at the datum required coverage, where the propor- point and extending in the direction of tional sector is less than plus or minus the approach to 20 nautical miles from 40 degrees. When intervening obstacles the runway threshold. The minimum prevent full coverage, the ± 40 ° guidance proportional guidance sector must be sector can be reduced as required. For plus or minus 10 degrees about the run- systems providing ± 60 ° lateral guidance VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00892 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 EC15SE91.014</GPH> jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.313 the coverage requirement is reduced to the approach region. This requirement 14 nm beyond ± 40 ° . does not apply to offset azimuth instal- (2) Vertically between: lations.

(i) A conical surface originating 2.5 (ii) Vertically between a horizontal meters (8 feet) above the runway cen- surface which is 2.5 meters (8 feet) terline at threshold inclined at 0.9 de- above the farthest point of runway cen- gree above the horizontal.

terline which is in line of sight of the (ii) A conical surface originating at azimuth antenna, and in a conical sur- the azimuth ground equipment antenna face originating at the azimuth ground inclined at 15 degrees above the hori- equipment antenna inclined at 20 de- zontal to a height of 6,000 meters (20,000 grees above the horizontal up to a feet).

height to 600 meters (2,000 feet). This (iii) Where intervening obstacles pen- requirement does not apply to offset etrate the lower surface, coverage need azimuth installations.

be provided only to the minimum line (4) Within the approach azimuth cov- of sight.

erage sector defined in paragraphs (a) (3) Runway region: (1), and (2) and (3) of this section, the (i) Proportional guidance hori- power densities must not be less than zontally within a sector 45 meters (150 those shown in Table 9 but the equip- feet) each side of the runway centerline ment design must also allow for: beginning at the stop end and extend- ing parallel with the runway centerline (i) Transmitter power degradation in the direction of the approach to join from normal by ¥ 1.5 dB; T ABLE 9—M INIMUM P OWER D ENSITY W ITHIN C OVERAGE B OUNDARIES ( DBW/ M ) Angle signals for various antenna Data beamwidths Clearance Function signals signals 1 ° 1.5 ° 2 ° 3 ° Approach azimuth ....................................................................... ¥ 89.5 ¥ 88 .......... ¥ 85.5 ¥ 82 ¥ 88 High rate approach azimuth ........................................................ ¥ 89.5 ¥ 88 .......... ¥ 88 ¥ 86.5 ¥ 88 Back azimuth ............................................................................... ¥ 89.5 ¥ 88 .......... ¥ 85.5 ¥ 82 ¥ 88 Approach elevation ..................................................................... ¥ 89.5 ¥ 88 ¥ 88 ¥ 88 .............. ....................

(ii) Rain loss of ¥ 2.2 dB at the longi- (6) Be installed on frangible mounts tudinal coverage extremes. or beyond the 300 meter (1,000 feet) light bar.

(b) Siting requirements. The approach (c) On runways where limited terrain azimuth antenna system must, except prevents the azimuth antenna from as allowed in paragraph (c) of this sec- being positioned on the runway center- tion: line extended, and the cost of the land (1) Be located on the extension of the fill or a tall tower antenna support is centerline of the runway beyond the prohibitive, the azimuth antenna may stop end; be offset.

(2) Be adjusted so that the zero de- (d) Antenna coordinates. The scanning gree azimuth plane will be a vertical beams transmitted by the approach plane which contains the centerline of azimuth equipment within ± 40 ° of the the runway served; centerline may be either conical or (3) Have the minimum height nec- planar.

essary to comply with the coverage re- (e) Approach azimuth accuracy. (1) The quirements prescribed in paragraph (a) system and subsystem errors shall not of this section; exceed those listed in Table 10 at the approach reference datum.

(4) Be located at a distance from the At the approach reference datum, stop end of the runway that is con- temporal sinusoidal noise components sistent with safe obstruction clearance shall not exceed 0.025 degree peak in practices; the frequency band 0.01 Hz to 1.6 Hz, (5) Not obscure any light of an ap- and the CMN shall not exceed 0.10 de- proach lighting system; and gree. From the approach reference VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00893 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.313 The system PFN component must not exceed ± 3.5 meters datum to the coverage limit, the PFE, (11.5 feet).

PFN and CMN limits, expressed in an- The mean (bias) error component contributed by the ground equipment should not exceed ± 10 feet.

gular terms, shall be allowed to lin- The system control motion noise must not exceed 0.1 de- early increase as follows: gree.

The airborne subsystem angular errors are provided for in- (i) With distance along the runway formation only.

centerline extended, by a factor of 1.2 (3) Antenna alignment. The antenna for the PFE and PFN limits and to must be equipped with suitable optical, ± 0.10 degree for the CMN limits.

electrical or mechanical means or any (ii) With azimuth angle, by a factor combination of the three, to bring the of 1.5 at the ± 40 degree and a factor of zero degree azimuth radial into coinci- 2.0 at the ± 60 degree azimuth angles for dence with the approach reference the PFE, PFN and CMN limits.

datum (for centerline siting) with a (iii) With elevation angle from + 9 de- maximum error of 0.02 degree. Addi- grees to + 15 degrees, by a factor of 1.5 tionally, the azimuth antenna bias ad- for the PFE and PFN limits.

justment must be electronically steer- (iv) Maximum angular limits. The able at least to the monitor limits in PFE limits shall not exceed ± 0.25 de- steps not greater than 0.005 degree.

gree in any coverage region below an (4) Antenna far field patterns in the elevation angle of + 9 degrees nor ex- plane of scan. On boresight, the azi- ceed ± 0.50 degree in any coverage re- muth antenna mainlobe pattern must gion above that elevation angle. The conform to Figure 10, and the beam- CMN limits shall not exceed ± 0.10 de- width must be such that, in the in- gree in any coverage region within ± 10 stalled environment, no significant lat- degrees of runway centerline extended eral reflections of the mainlobe exist nor exceed ± 0.20 degree in any other re- along the approach course. In any case gion within coverage.

the beamwidth must not exceed three N OTE : It is desirable that the CMN not ex- degrees. Anywhere within coverage the ceed ± 0.10 degree throughout the coverage.

¥ 3 dB width of the antenna mainlobe, (f) Approach azimuth antenna char- while scanning normally, must not be acteristics are as follows: less than 25 microseconds (0.5 degree) (1) Drift. Any azimuth angle as en- or greater than 250 microseconds (5 de- coded by the scanning beam at any grees). The antenna mainlobe may be point within the proportional coverage allowed to broaden from the value at must not vary more than ± 0.07 degree boresight by a factor of 1/cos q , where q over the range of service conditions is the angle off boresight. The sidelobe specified in § 171.309(d) without the use levels must be as follows: of internal environmental controls.

(i) Dynamic sidelobe levels. With the Multipath effects are excluded from antenna scanning normally, the dy- this requirement.

namic sidelobe level that is detected by (2) Beam pointing errors. The azimuth a receiver at any point within the pro- angle as encoded by the scanning beam portional coverage sector must be at any point within ± 0.5 degree of the down at least 10 dB from the peak of zero degree azimuth must not deviate the main beam. Outside the coverage from the true azimuth angle at that sector, the radiation from the scanning point by more than ± .05 degree.

beam antenna must be of such a nature Multipath and drift effects are ex- that receiver warning will not be re- cluded from this requirement.

moved or suitable OCI signals must be provided.

T ABLE 10—A PPROACH A ZIMUTH A CCURACIES AT (ii) Effective sidelobe levels. With the THE A PPROACH R EFERENCE D ATUM antenna scanning normally, the sidelobe levels in the plane of scan Angular error (degrees) must be such that, in the installed en- Error type System Ground Airborne vironment, the CMN contributed by subsystem subsystem sidelobe reflections will not exceed the 1 2 3 PFE ........ ± 20 ft. (6.1m) ± 0.118 ° .. ± 0.017 ° angular equivalent of 9 feet at ap- 1 2 4 CMN ...... ± 10.5 ft. (3.2m) ± 0.030 ° .... ± 0.050 ° proach reference datum over the re- Notes: quired range of aircraft approach Includes errors due to ground and airborne equipment and propagation effects.

speeds.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00894 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.313 (5) Antenna far field pattern in the coverage requirements and the spu- vertical plane. The azimuth antenna rious radiation requirement.

(6) Data antenna. The data antenna free space radiation pattern below the must have horizontal and vertical pat- horizon must have a slope of at least terns as required for its function.

¥ 8 dB/degree at the horizon and all (g) Back azimuth coverage require- sidelobes below the horizon must be at ments. The back azimuth equipment least 13 dB below the pattern peak. The where used must provide guidance in- antenna radiation pattern above the formation in at least the following vol- horizon must satisfy both the system ume of space (see Figure 11): VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00895 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 EC15SE91.015</GPH> jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.313 (1) Horizontally within a sector ± 40 proach at least to 20 nautical miles degrees about the runway centerline from the runway stop end. The min- originating at the back azimuth imum proportional guidance sector ground equipment antenna and extend- must be ± 10 degrees about the runway ing in the direction of the missed ap- centerline. Clearance signals must be VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00896 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 EC15SE91.016</GPH> jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.313 used to provide the balance of the re- (ii) Rain loss of ¥ 2.2 dB at the longi- quired coverage where the proportional tudinal coverage extremes.

sector is less than ± 40 degrees. (h) Back azimuth siting. The back azi- (2) Vertically in the runway region muth equipment antenna must: between: (1) Normally be located on the exten- (i) A horizontal surface 2.5 meters (8 sion of the runway centerline at the feet) above the farthest point of run- threshold end; way centerline which is in line of sight (2) Be adjusted so that the vertical of the azimuth antenna, and, plane containing the zero degree course (ii) A conical surface originating at line contains the back azimuth ref- the azimuth ground equipment antenna erence datum; inclined at 20 degrees above the hori- (3) Have minimum height necessary zontal up to a height of 600 meters (2000 to comply with the course require- feet). ments prescribed in paragraph (g) of (3) Vertically in the back azimuth re- this section; gion between: (4) Be located at a distance from the (i) A conical surface originating 2.5 threshold end that is consistent with meters (8 feet) above the runway stop safe obstruction clearance practices; end, included at 0.9 degree above the (5) Not obscure any light of an ap- horizontal, and, proach lighting system; and (ii) A conical surface orginating at (6) Be installed on frangible mounts the missed approach azimuth ground or beyond the 300 meter (1000 feet) light equipment antenna, inclined at 15 de- bar.

grees above the horizontal up to a (i) Back azimuth antenna coordinates.

height of 1500 meters (5000 feet). The scanning beams transmitted by (iii) Where obstacles penetrate the the back azimuth equipment may be ei- lower coverage limits, coverage need be ther conical or planar.

provided only to minimum line of (j) Back azimuth accuracy. The re- sight. quirements specified in § 171.313(e) (4) Within the back azimuth coverage apply except that the reference point is sector defined in paragraph (q) (1), (2), the back azimuth reference datum.

and (3) of this section the power den- (k) Back azimuth antenna characteris- sities must not be less than those tics. The requirements specified in shown in Table 9, but the equipment § 171.313(f) apply.

design must also allow for: (l) Scanning conventions. Figure 12 (i) Transmitter power degradation shows the approach azimuth and back from normal ¥ 1.5 dB. azimuth scanning conventions.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00897 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.313 EC15SE91.018</GPH> VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00898 Fmt 8010 Sfmt 8006 Y:\SGML\268049.XXX 268049 EC15SE91.017</GPH> jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.315 equivalent of ± 10 ft. at the approach ref- (m) False guidance. False courses erence datum. This will limit the electrical which can be acquired and tracked by component of the mean course error to ± 10 an aircraft shall not exist anywhere ei- ft. The field monitor alarm limit should be ther inside or outside of the MLS cov- set such that with the mean course error at erage sector. False courses which exist the alarm limit the total allowed PFE is not outside of the minimum coverage sec- exceeded on any commissioned approach tor may be suppressed by the use of course from the limit of coverage to an alti- OCI. tude of 100 feet.

N OTE : False courses may be due to (but not (2) There are errors in two consecu- limited to) MLS airborne receiver acquisi- tive transmissions of Basic Data Words tion of the following types of false guidance: 1, 2, 4 or 5.

reflections of the scanning beam, scanning (3) There is a reduction in the radi- beam antenna sidelobes and grating lobes, ated power to a level not less than that and incorrect clearance.

specified in §§ 171.313(a)(4) or 171.313(g)(4) for a period of more than § 171.315 Azimuth monitor system re- quirements. one second.

(4) There is an error in the preamble (a) The approach azimuth or back DPSK transmissions which occurs azimuth monitor system must cause more than once in any one second pe- the radiation to cease and a warning riod.

must be provided at the designated (5) There is an error in the time divi- control point if any of the following sion multiplex synchronization of a conditions persist for longer than the particular azimuth function that the periods specified: requirement specified in § 171.311(e) is (1) There is a change in the ground not satisfied and if this condition per- equipment contribution to the mean sists for more than one second.

course error component such that the (6) A failure of the monitor is de- path following error at the reference tected.

datum or in the direction of any azi- (b) Radiation of the following muth radial, exceeds the limits speci- fuctions must cease and a warning pro- fied in §§ 171.313(e)(1) or 171.313(j) for a vided at the designated control point if period of more than one second.

there are errors in 2 consecutive trans- N OTE : The above requirement and the re- missions: quirement to limit the ground equipment (1) Morse Code Identification, mean error to ± 10 ft. can be satisfied by the (2) Basic Data Words 3 and 6, following procedure. The integral monitor alarm limit should be set to the angular (3) Auxiliary Data Words.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00899 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 EC15SE91.019</GPH> jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.317 (c) The period during which erro- (1) Laterally within a sector origi- neous guidance information is radiated nating at the datum point which is at must not exceed the periods specified least equal to the proportional guid- in § 171.315(a). If the fault is not cleared ance sector provided by the approach within the time allowed, the ground azimuth ground equipment.

equipment must be shut down. After (2) Longitudinally from 75 meters (250 shutdown, no attempt must be made to feet) from the datum point to 20 nau- restore service until a period of 20 sec- tical miles from threshold in the direc- onds has elapsed. tion of the approach.

(3) Vertically within the sector § 171.317 Approach elevation perform- bounded by: ance requirements.

(i) A surface which is the locus of This section prescribes the perform- points 2.5 meters (8 feet) above the run- ance requirements for the elevation way surface; equipment components of the MLS as (ii) A conical surface originating at follows: the datum point and inclined 0.9 degree (a) Elevation coverage requirements. above the horizontal and, The approach elevation facility must (iii) A conical surface originating at provide proportional guidance informa- the datum point and inclined at 15.0 de- tion in at least the following volume of grees above the horizontal up to a space (see Figure 13): height of 6000 meters (20,000 feet).

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00900 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.317 Where the physical characteristics of section, guidance need not be provided the approach region prevent below a conical surface originating at theachievement of the standards under the elevation antenna and inclined 0.9 paragraphs (a) (1), (2), and (3) of this degree above the line of sight.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00901 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 EC15SE91.020</GPH> jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.317 (4) Within the elevation coverage sec- and PFN limits and by a factor of 2.0 tor defined in paragraphs (a) (1), (2) and for the CMN limits; (3) of this section, the power densities (iii) With increasing elevation angles must not be less than those shown in from + 3 degrees to + 15 degrees, by a Table 9, but the equipment design must factor of 2.0 for the PFE and PFN lim- its; also allow for: (i) Transmitter power degradation T ABLE 13—E LEVATION A CCURACIES AT THE from normal by ¥ 1.5 dB.

A PPROACH R EFERENCE D ATUM (ii) Rain loss of ¥ 2.2 dB at the cov- erage extremes.

Angular error (degrees) (b) Elevation siting requirements. The Error type System Ground sub- Airborne Elevation Antenna System must: system subsystem (1) Be located as close to runway cen- 1 2 3 PFE .................... ± 0.133 ( ) ± 0.017 terline as possible (without violating CMN .................. ± 0.050 ± 0.020 ± 0.010 obstacle clearance criteria).

Notes: (2) Be located near runway threshold Includes errors due to ground and airborne equipment and such that the asymptote of the min- propagation effects.

The system PFN component must not exceed ± 0.087 de- imum glidepath crosses the threshold gree.

of the runway at the Approach Ref- 3 The mean (bias) error component contributed by the ground equipment should not exceed ± 0.067 degree.

erence Datum height. Normally, the The airborne subsystem angular errors are provided for in- minimum glidepath should be 3 degrees formation only.

and the Approach Reference Datum (iv) With decreasing elevation angle height should be 50 feet. However, from + 3 degrees (or 60% of the min- there are circumstances where other imum glide path angle, whichever is glideslopes and reference datum less) to the coverage extreme, by a fac- heights are appropriate. Some of these tor of 3 for the PFE, PFN and CMN instances are discussed in FAA Order limits; and 8260.34 (Glide Slope Threshold Crossing (v) Maximum angular limits. the Height Requirements) and Order 8260.3 CMN limits shall not exceed ± 0.10 de- (IFR Approval of MLS.)

gree in any coverage region within ± 10 (3) Be located such that the MLS Ap- degrees laterally of runway centerline proach Reference Datum and ILS Ref- extended which is above the elevation erence Datum heights are coincident angle specified in (iv) above.

within a tolerance of 3 feet when MLS is installed on a runway already served N OTE : It is desirable that the CMN not ex- by an ILS. This requirement applies ceed ± 0.10 degree throughout the coverage re- gion above the elevation angle specified in only if the ILS glide slope is sited such paragraph (d)(1)(iv) of this section.

that the height of the reference datum meets the requirements of FAA Order (2) The system and ground subsystem 8260.34.

accuracies shown in Table 13 are to be (c) Antenna coordinates. The scanning demonstrated at commissioning as beams transmitted by the elevation maximum error limits. Subsequent to subsystem must be conical.

commissioning, the accuracies are to (d) Elevation accuracy. (1) The accura- be considered at 95% probability limits.

cies shown in Table 13 are required at (e) Elevation antenna characteristics the approach reference datum. From are as follows: the approach reference datum to the (1) Drift. Any elevation angle as en- coverage limit, the PFE, PFN and CMN coded by the scanning beam at any limits shall be allowed to linearly in- point within the coverage sector must crease as follows: not vary more than 0.04 degree over the (i) With distance along the runway range of service conditions specified in centerline extended at the minimum § 171.309(d) without the use of internal glide path angle, by a factor of 1.2 for environmental controls. Multipath ef- the PFE and PFN limits and to ± 0.10 fects are excluded from this require- degree for the CMN limits; ment.

(ii) With azimuth angle, from runway (2) Beam pointing errors. The elevation centerline extended to the coverage ex- angle as encoded by the scanning beam treme, by a factor of 1.2 for the PFE at any point within the coverage sector VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00902 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.319 must not deviate from the true ele- size the signal away from antenna vation angle at that point by more boresight. Typically, the horizontal than ± 0.04 degree for elevation angles pattern should be reduced by at least 3 from 2.5 ° to 3.5 ° . Above 3.5 ° these errors dB at 20 degrees off boresight and by at may linearly increase to ± 0.1 degree at least 6 dB at 40 degrees off boresight.

Depending on the actual multipath 7.5 ° . Multipath and drift effects are ex- conditions, the horizontal radiation cluded from this requirement.

patterns may require more or less de- (3) Antenna alignment. The antenna emphasis.

must be equipped with suitable optical, (6) Data antenna. The data antenna electrical, or mechanical means or any must have horizontal and vertical pat- combination of the three, to align the terns as required for its function.

lowest operationally required glidepath (f) False guidance. False courses to the true glidepath angle with a max- which can be acquired and tracked by imum error of 0.01 degree. Addition- an aircraft shall not exist anywhere ei- ally, the elevation antenna bias adjust- ther inside or outside of the MLS cov- ment must be electronically steerable erage sector. False courses which exist at least to the monitor limits in steps outside of the minimum coverage sec- not greater than 0.005 degrees.

tor may be suppressed by the use of (4) Antenna far field patterns in the OCI.

plane of scan. On the lowest operation- ally required glidepath, the antenna N OTE : False courses may be due to (but not mainlobe pattern must conform to Fig- limited to) MLS airborne receiver acquisi- ure 10, and the beamwidth must be tion of the following types of false guidance: reflections of the scanning beam and scan- such that in the installed environment, ning beam antenna sidelobes and grating no significant ground reflections of the lobes.

mainlobe exist. In any case, the beam- width must not exceed 2 degrees. The § 171.319 Approach elevation monitor antenna mainlobe may be allowed to system requirements.

broaden from the value at boresight by (a) The monitor system must act to a factor of 1/cos q , where q is the angle ensure that any of the following condi- of boresight. Anywhere within cov- tions do not persist for longer than the erage, the ¥ 3 dB width of the antenna periods specified when: mainlobe, while scanning normally, (1) There is a change in the ground must not be less than 25 microseconds component contribution to the mean (0.5 degrees) or greater than 250 micro- glidepath error component such that seconds (5 degrees). The sidelobe levels the path following error on any glide- must be as follows: path exceeds the limits specified in (i) Dynamic sidelobe levels. With the § 171.317(d) for a period of more than antenna scanning normally, the dy- one second.

namic sidelobe level that is detected by N OTE : The above requirement and the re- a receiver at any point within the pro- quirement to limit the ground equipment portional coverage sector must be mean error to ± 0.067 degree can be satisfied down at least 10 dB from the peak of by the following procedure. The integral the mainlobe. Outside the proportional monitor alarm limit should be set to ± 0.067 coverage sector, the radiation from the degree. This will limit the electrical compo- scanning beam antenna must be of nent of mean glidepath error to ± 0.067 degree.

such a nature that receiver warnings The field monitor alarm limit should be set will not be removed or a suitable OCI such that with the mean glidepath error at the alarm limit the total allowed PFE is not signal must be provided.

exceeded on any commissioned glidepath (ii) Effective sidelobe levels. With the from the limit of coverage to an altitude of antenna scanning normally, the 100 feet.

sidelobe levels in the plane of scan must be such that, when reflected from (2) There is a reduction in the radi- the ground, the resultant PFE along ated power to a level not less than that any glidepath does not exceed 0.083 de- specified in § 171.317(a)(4) for a period of grees. more than one second.

(5) Antenna far field pattern in the hor- (3) There is an error in the preamble izontal plane. The horizontal pattern of DPSK transmission which occurs more the antenna must gradually de-empha- than once in any one second period.

VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00903 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR 14 CFR Ch. I (1–1–26 Edition) § 171.321 (4) There is an error in the time divi- Commission (FCC) licensing require- sion multiplex synchronization of a ments and siting requirements of particular elevation function such that §§ 171.313(b) and 171.317(b).

the requirement specified in § 171.311(e) (b) The MLS facility components is not satisfied and this condition per- must utilize solid state technology ex- sists for more than one second.

cept that traveling wave tube ampli- (5) A failure of the monitor is de- fiers (TWTA) may be used. A maximum tected.

level of common modularity must be (b) The period during which erro- provided along with diagnostics to fa- neous guidance information is radiated cilitate maintenance and trouble- must not exceed the periods specified shooting.

in § 171.319(a). If the fault is not cleared (c) An approved monitoring capa- within the time allowed, radiation bility must be provided which indicates shall cease. After shutdown, no at- the status of the equipment at the site tempt must be made to restore service and at a remotely located maintenance until a period of 20 seconds has elapsed.

area, with monitor capability that pro- vides pre-alarm of impending system § 171.321 DME and marker beacon per- failures. This monitoring feature must formance requirements.

be capable of transmitting the status (a) The DME equipment must meet and pre-alarm over standard phone the performance requirements pre- lines to a remote section. In the event scribed in subpart G of the part. This the sponsor requests the FAA to as- subpart imposes requirements that per- sume ownership of the facility, the formance features must comply with monitoring feature must also be capa- International Standards and Rec- ble of interfacing with FAA remote ommended Practices, Aeronautical monitoring requirements. This require- Telecommunications, Vol. I of Annex ment may be complied with by the ad- 10 to ICAO. It is available from ICAO, dition of optional software and/or hard- Aviation Building, 1080 University ware in space provided in the original Street, Montreal 101, Quebec, Canada, equipment.

Attention: Distribution Officer and (d) The mean corrective maintenance also available for inspection at the Na- time of the MLS equipment must be tional Archives and Records Adminis- equal to or less than 0.5 hours with a tration (NARA). For information on maximum corrective maintenance time the availability of this material at not to exceed 1.5 hours. This measure NARA, call 202–741–6030, or go to: http:// applies to correction of unscheduled www.archives.gov/federal _ register/ failures of the monitor, transmitter code _ of _ federal _ regulations/ibr _ loca- and associated antenna assemblies, tions.html.

limited to unscheduled outage and out (b) MLS marker beacon equipment of tolerance conditions.

must meet the performance require- (e) The mean-time-between-failures ments prescribed in subpart H of this of the MLS angle system must not be part. This subpart imposes require- less than 1,500 hours. This measure ap- ments that performance features must plies to unscheduled outage, out-of-tol- comply with International Standards erance conditions, and failures of the and Recommended Practices, Aero- monitor, transmitter, and associated nautical Telecommuncations, Vol. I of antenna assemblies.

Annex 10 to ICAO.

(f) The MLS facility must have a reli- able source of suitable primary power, [Docket 5034, 29 FR 11337, Aug. 6, 1964, as amended at 69 FR 18803, Apr. 9, 2004] either from a power distribution sys- tem or locally generated. Adequate § 171.323 Fabrication and installation power capacity must be provided for requirements.

the operation of the MLS as well as the (a) The MLS facility must be perma- test and working equipment of the nent and must be located, constructed, MLS.

and installed in accordance with best (g) The MLS facility must have a commercial engineering practices, continuously engaged or floating bat- using applicable electric and safety tery power source for the continued codes and Federal Communications normal operation of the ground station VerDate Sep<11>2014 10:01 Aug 27, 2026 Jkt 268049 PO 00000 Frm 00904 Fmt 8010 Sfmt 8010 Y:\SGML\268049.XXX 268049 jgilmore on DSK4WB1RN3PROD with CFR Federal Aviation Administration, DOT § 171.325 operation if the primary power fails. A (j) The location of the phase center trickle charge must be supplied to re- for all antennas must be clearly marked on the antenna enclosures.

charge the batteries during the period (k) The latitude, longitude and mean of available primary power. Upon loss sea level elevation of all MLS anten- and subsequent restoration of power, nas, runway threshold and runway stop the battery must be restored to full end must be determined by survey with charge within 24 hours. When primary an accuracy of ± 3 meters ( ± 10 feet) lat- power is applied, the state of the bat- erally and ± 0.3 meter ( ± 1.0 foot) tery charge must not affect the oper- vertically. The relative lateral and ation of the MLS ground station. The vertical offsets of all antenna phase battery must allow continuation of centers, and both runway ends must be normal operation of the MLS facility determined with an accuracy of ± 0.3 for at least 2 hours without the use of meter ( ± 1.0 foot) laterally and ± 0.03 additional sources of power. When the meter ( ± 0.1 foot) vertically. The owner system is operating from the battery must bear all costs of the survey. The supply without prime power, the ra- results of this survey must be included dome deicers and the environmental in the ‘‘operations and maintenance’’ system need not operate. The equip- manual required by section 171.325 of ment must meet all specification re- this subpart and will be noted on FAA quirements with or without batteries Form 198 required by § 171.327.

installed.

[Docket 20669, 51 FR 33177, Sept. 18, 1986, as (h) There must be a means for deter- amended by Amdt. 171–16, 56 FR 65665, Dec.

mining, from the ground, the perform- 17, 1991] ance of the system including antenna, both initially and periodically. § 171.325 Maintenance and operations requirements.

(i) The facility must have, or be sup- plemented by, ground, air, or landline (a) The owner of the facility must es- communications services. At facilities tablish an adequate maintenance sys- within or immediately adjacent to con- tem and provide MLS qualified mainte- trolled airspace, that are intended for nance personnel to maintain the facil- use as instrument approach aids for an ity at the level attained at the time it airport, there must be ground air com- was commissioned. Each person who maintains a facility must meet the munications or reliable communica- FCC licensing requirements and dem- tions (at least a landline telephone) onstrate that he has the special knowl- from the airport to the nearest FAA edge and skills needed to maintain an air traffic control or communication MLS facility, including proficiency in facility. Compliance with this para- maintenance procedures and the use of graph need not be shown at airports specialized test equipment.

where an adjacent FAA facility can (b) In the event of out-of-tolerance communicate with aircraft on the conditions or malfunctions, as evi- ground at the airport and during the denced by receiving two successive entire proposed instrument approach pilot reports, the owner must close the procedure. In addition, at low traffic facility by encasing radiation, and density airports within or immediately issue a ‘‘Notice to Airmen’’ (NOTAM) adjacent to controlled airspace, and that the facility is out of service.

where extensive delays are not a fac- (c) The owner must prepare, and ob- tor, the requirements of this paragraph tain approval of, an operations and may be reduced to reliable communica- maintenance manual that sets forth tions from the airport to the nearest mandatory procedures for operations, FAA air traffic control or communica- periodic maintenance, and emergency tions facility. If the adjacent FAA fa- maintenance, including instructions on cility can communicate with aircraft each of the following: during the proposed instrument ap- (1) Physical security of the facility.

proach procedure down to the airport (2) Maintenance and operations by surface or at least down to the min- authorized persons.

imum en route altitude, this would re- (3) FCC licensing requirements for quire at least a landline telephone. operations and maintenance personnel.

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trolled airspace over or near the facil- (vi) A description of the critical parts ity, instructions for relaying air traffic that may not be changed, adjusted, or control instructions and information, repaired without an FAA flight check if applicable, and instructions for the to confirm published operations.

operation of an air traffic advisory (d) The owner or his maintenance service if the facility is located outside representative must make a ground of controlled airspace.

check of the MLS facility periodically (6) Notice to the Administrator of in accordance with procedures ap- any suspension of service.

proved by the FAA at the time of com- (7) Detailed and specific maintenance missioning, and must report the results procedures and servicing guides stating of the checks as provided in § 171.327.

the frequency of servicing.

(e) The only modifications permitted (8) Air-ground communications, if are those that are submitted to FAA provided, expressly written or incor- for approval by the MLS equipment porating appropriate sections of FAA manufacturer. The owner or sponsor of manuals by reference.

the facility must incorporate these (9) Keeping the station logs and other modifications in the MLS equipment.

technical reports, and the submission Associated changes must also be made of reports required by § 171.327.

to the operations and maintenance (10) Monitoring of the MLS facility.

manual required in paragraph (c) of (11) Inspections by United States per- this section. This and all other correc- sonnel.

tions and additions to this operations (12) Names, addresses, and telephone and maintenance manual must also be numbers of persons to be notified in an submitted to FAA for approval.

emergency.

(f) The owner or the owner’s mainte- (13) Shutdowns for periodic mainte- nance representative must participate nance and issuing of NOTAM for rou- in inspections made by the FAA.

tine or emergency shutdowns.

(g) The owner must ensure the avail- (14) Commissioning of the MLS facil- ability of a sufficient stock of spare ity.

parts, including solid state compo- (15) An acceptable procedure for nents, or modules to make possible the amending or revising the manual.

prompt replacement of components or (16) An explanation of the kinds of modules that fail or deteriorate in activities (such as construction or service.

grading) in the vicinity of the MLS fa- (h) FAA approved test instruments cility that may require shutdown or re- must be used for maintenance of the certification of the MLS facility by MLS facility.

FAA flight check.

(i) Inspection consists of an examina- (17) Procedures for conducting a tion of the MLS equipment to ensure ground check of the azimuth and ele- that unsafe operating conditions do not vation alignment.

exist.

(18) The following information con- cerning the MLS facility: (j) Monitoring of the MLS radiated (i) Facility component locations with signal must ensure a high degree of in- respect to airport layout, instrument tegrity and minimize the requirements runways, and similar areas. for ground and flight inspection. The (ii) The type, make and model of the monitor must be checked daily during basic radio equipment that provides the in-service test evaluation period (96 the service including required test hour burn in) for calibration and sta- equipment. bility. These tests and ground checks (iii) The station power emission, or azimuth, elevation, DME, and mark- channel, and frequency of the azimuth, er beacon radiation characteristics elevation, DME, marker beacon, and must be conducted in accordance with associated compass locators, if any. the maintenance requirements of this (iv) The hours of operation. section.

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ment failures, causes (if determined) The owner of the MLS facility or his and corrective action taken. In addi- maintenance representative must sub- tion, the entries must include comple- mit the following operational records tion of periodic maintenance required at the indicated time to the appro- to maintain the facility. The owner or priate FAA regional office where the his maintenance representative must facility is located.

keep the original of each form at the (a) Facility Equipment Performance & facility and send a copy to the appro- Adjustment Data (FAA Form 198). The priate FAA regional office at the end of FAA Form 198 shall be filled out by the each month in which it is prepared.

owner or his maintenance representa- However, where an FAA approved re- tive with the equipment adjustments mote monitoring system is installed and meter readings as of the time of fa- which precludes the need for periodic cility commissioning. One copy must maintenance visits to the facility, be kept in the permanent records of the monthly reports from the remote mon- facility and two copies must be sent to itoring system control point must be the appropriate FAA regional office.

forwarded to the appropriate FAA re- The owner or his maintenance rep- gional office, and a hard copy retained resentative must revise the FAA Form at the control point.

198 data after any major repair, mod- (c) Technical Performance Record (FAA ernization, or retuning to reflect an ac- Form 6830 (formerly FAA Form 418)). This curate record of facility operation and form contains a record of system pa- adjustment.

rameters as specified in the manufac- (b) Facility Maintenance Log (FAA turer’s equipment manual. This data Form 6030–1). FAA Form 6030–1 is per- will be recorded on each scheduled visit manent record of all the activities re- to the facility. The owner or his main- quired to maintain the MLS facility. tenance representative shall keep the The entries must include all malfunc- original of each record at the facility tions met in maintaining the facility and send a copy of the form to the ap- including information on the kind of propriate FAA regional office.

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