Airworthiness Approval of Traffic Alert and Collision Avoidance Systems (TCAS II) and Mode S Transponders

AC: 20""131A

U.S. Deportmenf of TransPQrlation Federal Aviation Administration

DATE: 3/29/93

. .

Advisory .

Circular

AIRWORTHINESS APPROVAL OF TRAFFIC ALERT

AND COLLISION AVOIDANCE SYSTEMS (TCAS II)

AND MODES TRANSPONDERS

Advisory

U.S. Department of Transportation

Circular

Federal Aviation Administration Subject: AC No: Date: 3/29/93 AIRWORTHINESS APPROVAL OF 20-131A Change: Initiated by: ANM- 110 TRAFFIC ALERT ANO COLLISION AVOIDANCE SYSTEMS {TCAS II) AND MODES TRANSPONDERS 1. PURPOSE. This advisory circular (AC) provides guidance material for the airworthiness approval of Traffic Alert and Collision Avoidance Systems {TCAS II) and Mode S transponders. Like all AC material, this AC is not mandatory and does not constitute a regulation. It is issued for guidance purposes and to outline a method of compliance with the rules. In lieu of following this method without deviation, the applicant may elect to follow an alternative method, provided the alternative method is also found by the Federal Aviation Administration (FAA) to be an acceptable means of complying with the requirements of the Federal Aviation Regulations {FAR). Because the method of compliance presented in this AC is not mandatory, the terms "shall" and "must" used herein apply only to an applicant who chooses to follow this particular method without deviation.

j 2. CANCELLATION. Advisory Circular 20-131, Airworthiness Approval of Traffic Alert and Collision Avoidance Systems (TCAS II) and Mode S Transponders, dated October 3, 1988, is cancelled.

3. RELATED DOCUMENTS.

a. Related Federal Aviation Regulations. Portions of the FAR, as presently written, can be applied for the design, substantiation, certification and operational approval of TCAS II and Mode S transponders.

Sections which prescribe requirements for these types of systems include: § 25.301 Loads.

§ 25.303 Factor of safety.

§ 25.305 Strength and deformation.

§ 25.561 Emergency Landing Conditions--General.

§ 25.603 Materials.

§ 25.609 Protection of structure.

§ 25.629 Flutter, deformation, and fail-safe criteria.

§ 25.1301 Function and installation.

§ 25.1303 Flight and navigation instruments.

§ 25.1307 Miscellaneous equipment.

§ 25.1309 Equipment, systems, and installations.

§ 25 . 1321 Arrangement and visibility.

§ 25.1322 Warning, caution, and advisory lights.

§ 25.1331 Instruments using a power supply.

§ 25.1333 Instrument systems.

§ 25.1335 Flight director systems.

AC 20-131A 3/29/93 § 25.1351 Electrical Systems and Equipment: General.

§ 25.1353 Electrical equipment and installations.

§ 25.1355 Distribution system.

§ 25.1357 Circuit protective devices.

§ 25.1381 Instrument lights.

§ 25.1431 Electronic equipment.

§ 25.1541 Markings and Placards: General.

§ 25.1581 Airplane Flight Manual: General.

§ 25.1585 Operating procedures.

b. Advisory Circulars.

AC 20-llSA Radio Technical Commission for Aeronautics Document RTCA/D0-178A.

AC 25.1309-IA System Design and Analysis.

AC 25-11 Transport Category Airplane Electronic Display Systems.

AC 120-XX Procedures and Criteria for Determining the Type Rating Requirements for an Aircraft.

AC 120-55 Air Carrier Operational Approval and Use of TCAS II.

c. Technical Standard Orders.

TS0-Cll2 Air Traffic Control Radar Beacon System/Mode Select (ATCRBS/Mode S) Airborne Equipment.

TSO-CI19a Traffic Alert and Collision Avoidance System (TCAS) Airborne Equipment, TCAS II.

d. Industry Documents.

(1) Radio Technical Commission for Aeronautics (RTCA) document D0-160C, Environmental Conditions and Test Procedures for Airborne Equipment; RTCA document D0-178A, Software Considerations in Airborne Systems and Equipment Certifications; RTCA document 00-181, Minimum Operational Performance Standards for Air Traffic Control Radar Beacon System/Mode Select (ATCRBS/Mode S) Airborne Equipment; RTCA document D0-185, Minimum Operational Performance Standards for Traffic Alert and Collision Avoidance Systems (TCAS) Airborne Equipment. These documents can be obtained from the RTCA, One McPherson Square, Suite 500, 1425 Street Northwest, Washington, D.C. 20005.

II 3/29/93 AC 20-131A (2) Aerospace Recommended Practice (ARP) 926A, Fault/Failure Analysis Procedure; ARP 1834, Fault/Failure Analysis Guidelines for Digital Equipment; and ARP 1068A, Flight Deck Instrumentation, Display Criteria and Associated Controls for Transport Aircraft. These documents are available from the Society of Automotive Engineers, Inc. (SAE), 400 Commonwealth Drive, Warrendale, PA 15096.

4. DEFINITIONS. The following definitions are applicable to this AC.

a. Advisory. A message given to alert the crew of converging aircraft and/or a potential collision.

b. Air traffic control (ATC). A generic term for a joint civil/military system for controlling traffic within a specific area.

c. Air traffic control radar beacon system (ATCRBS}. A secondary surveillance radar system having ground-based interrogators and airborne transponders capable of operation on Modes A and C.

d. Alert. Indicator (aural or visual) which provides information to the flightcrew in a'timely manner about a converging aircraft or a potential collision.

e. Coast. In the event of TCAS II momentarily developing the track of an intruder, a memory feature of the traffic display causes the traffic symbol to continue to move in the same direction and at the same speed as the original target.

f. Corrective resolution advisory. A resolution advisory that advises the pilot to deviate from current vertical speed, e.g., CLIMB when the aircraft is level.

g. Discrete. A separate, complete and distinct signal.

h. Failure. The inability of a system, subsystem, unit, or part to perform within previously specified limits.

i. False advisory. An advisory caused by a false track or a TCAS malfunction.

j. Fruit. Intruder replies corrupted by the receipt of undesired transponder replies that were elicited by ground interrogators and other TCAS II interrogators.

k. Incorrect resolution advisorv . A resolution advisory which occurs when a threat is present, but, because of a failure of the installed TCAS II, Mode S transponder, or associated sensors, commands a maneuver which reduces separation to the threat.

l. Intruder. A target that has been determined by the TCAS II logic to be a converging aircraft which requires a traffic advisory.

III AC 20-131A 3/29/-93 m. Mode A. Type of secondary surveillance radar (SSR) equipment which provides a selected 4096 code reply (nonaltitude) when interrogated.

n. Mode C. Type of secondary surveillance radar (SSR) equipment which provides a reply with aircraft altitude information when interrogated.

o. Mode S. Type of secondary surveillance radar {SSR) equipment which provides replies to Mode A and Mode C interrogations and discrete address interrogations from the ground or air.

p. Other traffic. Aircraft more than± 1200 feet vertical and 6NM from your aircraft which cause neither an RA nor a TA.

q. Preventive resolution. A resolution advisory that advises the pilot to avoid certain deviations from the current vertical speed because certain vertical speed restrictions exist.

r. Proximate traffic. Nearby aircraft within± 1200 feet vertical and 6 NM which cause neither an RA nor a TA.

s. Resolution advisory (RA). Aural and visual information provided to the flightcrew to avoid a potential collision.

t. Resolution display, A display which shows vertical guidance depicting areas to "fly-to" and/or avoid above or below the TCAS equipped aircraft.

u. Sense. A direction that a resolution advisory may take: Either UP or DOWN relative to existing flight path of own aircraft.

v. Threat. A target that has satisfied the threat detection logic and thus requires a resolution advisory (RA).

w. Traffic. An aircraft within the surveillance range of TCAS.

x. Traffic advisory (TA). Information given to the pilot pertaining to the position of another aircraft in the immediate vicinity. The information contains no resolution information.

y. Traffic display. A display of the horizontal position of transponder equipped aircraft relative to the TCAS equipped aircraft.

IV 3/29/93 AC 20-131A 5. SCOPE. The material provided in this AC addresses the design aspects, characteristics, mechanization, testing, and the criticality of system failure cases for TCAS II and Mode S transponders. The guidance material is directed at systems which provide traffic advisories and resolution advisories in the vertical axis only (TCAS II) and where the operational performance standards are defined in technical documents that were developed by a joint air transport industry/government group (RTCA Special Committee SC-147).

irector, Aircraft Cert fic~tion Service V (and VI) 3/29/93 AC 20-131A CONTENTS PAGE PARAGRAPH . . . . .

BACKGROUND 1.

2. SYSTEM DESCRIPTION .

3. AIRWORTHINESS CONSIDERATIONS

. 2

. . . . . . .

Certification Program . .

a.

. . . 2

. .

b. Certification Plan .

Equipment Installation 2 c.

(1) Mode S Transponder (2) Pilot Control . . .

. 4 (3) . . . . . . .

Antennas .

(4) The TCAS II Processor.

(5) Equipment Compatibility .

(6) Aircraft Performance .

. . . . . . . . . . 11

(7) Aircraft Interfaces .

. .

(8) Traffic Display . .

(9) Resolution Display .

.

(10) Caution/Warning Lights . . . . . 16

( lJ.) Aural Alerts . . .

d. Software Verification and Validation .

System Safety Analysis . . . . . . 20

e.

Approval) f. Test and Evaluation (Initial

. 20

(I) Basic Ground Tests . . . . . .

. . . . 22 (2) Basic Flight Tests . .

Planned Encounter Flight Tests . . . . . . . . . . . . 23

(3) (4) Mode S Transponder Flight Tests .

(STC or Amended TC) 26 g. Follow-On Approvals . . . . . .

(1) Ground Tests . .

. . . . . . . . 27

(2) Flight Tests . . . .

28 Supplement (AFMS) h. Airplane Flight Manual . . . . . . . . .

4. OPERATIONAL APPROVAL .

VII AC 20-131A 3/29/93 CONTENTS (cont'd) PARAGRAPH PAGE APPENDIX 1 AIRPLANE FLIGHT MANUAL SUPPLEMENT (Example) Figure 1 TCAS/Transponder Control Panel (Example) .

Figure 2 TCAS II - Traffic Display (Example) .... . .

. 5

Figure 3 TCAS II Instantaneous Vertical Speed Indicator (Example) ... .

Figure 4 TCAS Examples - Preventive ... .

Figure 5 TCAS Examples - Corrective ........ .

APPENDIX 2 SUPPLEMENTAL INITIAL CERTIFICATION FLIGHT TESTS ...

I APPENDIX 3 TRANSPONDER TESTS ....... .

VII I AC 20-131A 3/29/93 1. BACKGROUND. The airline industry has been working through the Air Transport Association since 1955 to find a workable collision avoidance system. It was not until the mid-1970s, however, that research centered upon the use of signals from ATCRBS airborne transponders as the cooperative element of a collision avoidance system. This technical approach allows a collision avoidance capability on the flightdeck which is independent of the ground system. In 1981, the FAA announced its decision to proceed with the implementation of an aircraft collision avoidance concept called the Traffic Alert and Collision Avoidance System (TCAS). The concept is based upon agency and industry development efforts in the areas of beacon-based collision avoidance systems and air-to-air discrete address communications techniques utilizing Mode S airborne transponder message formats.

A short time later, prototypes of TCAS II were installed on two Piedmont Airlines B-727 aircraft, and were flown on regularly scheduled flights.

Although the displays were located outside the view of the flightcrew and were seen only by trained observers, these tests did provide valuable information on the frequency and circumstances of alerts and their potential for interaction with the ATC system. On a follow-on phase II program, a later version of TCAS II was installed on a single Piedmont Airlines B-727, and the system was certified in April 1986 and subsequently approved for operational evaluation in early 1987. Since the equipment was not developed to full standards, the system was only operated in visual meteorological conditions.

Although the flightcrew operated the system, the evaluation was primarily for the purpose of data collection and its correlation with flightcrew and observer observation and response.

Later versions of TCAS II manufactured by Bendix/King Air Transport Avionics Division were installed and approved on United Airlines airplanes in early 1988. Similar units manufactured by Honeywell were installed and approved on Northwest Airlines airplanes in late 1988. This Limited Installation Program operated TCAS II units approved for operation as a full time system in both visual and instrument meteorological conditions on three different aircraft types. The operational evaluation programs continued through 1988 to validate the operational suitability of the systems.

2. SYSTEM DESCRIPTION. The TCAS II is an airborne traffic alert and collision avoidance system that interrogates ATC transponders in nearby aircraft and uses computer processing to identify and display potential and predicted collision threats. The system is designed to protect a volume of airspace around the TCAS II equipped aircraft. The system will provide appropriate aural and visual advisories to the flightcrew, to take action so as to ensure adequate separation, when the computer analysis of the intruding aircraft transponder replies predict a penetration of the protected airspace.

The system provides two types of advisories. Traffic advisories indicate the Par 1 AC 20-131A 3/29/93 relative positions of intruding aircraft that are approximately 40 seconds from the closest point of approach and may a short time later require a resolution advisory. They also provide the flightcrew the opportunity to visually acquire the intruding aircraft. A resolution advisory will provide a vertical avoidance maneuver that will increase separation when the computer predicts the threat aircraft is within approximately 25 seconds from the closest point of approach.

The system provides two types of flightdeck displays. A traffic display indicates the relative position of ATC transponder equipped aircraft. A resolution display for each pilot indicates the appropriate vertical maneuver to avoid a threat. The TCAS II aircraft must be equipped with a Mode S ATC transponder which provides air-to-air communications for coordinating the resolution maneuvers between TCAS equipped aircraft. The Mode S transponder also provides discrete address replies to interrogations from ground stations and other TCAS II equipped aircraft.

The TCAS II system can only generate resolution advisories for intruders equipped with responding Mode Sor Mode C transponders, which provide information on the altitude of the threat aircraft. Traffic advisories can be generated for aircraft with operative Mode S, Mode C or Mode A transponders.

The TCAS II equipment is viewed as a supplement to the pilot who, with the aid of the ATC system, has the primary responsibility for avoiding mid-air collisions. The TCAS II system provides no indication of aircraft without operative transponders.

3. AIRWORTHINESS CONSIDERATIONS.

a. Certification Program. This AC provides guidance for the installation of TCAS II equipment and Mode S transponders. The system displays information and provides advisories in a number of formats. The degree of system integration to perform these functions is extensive and as a result, the applicant's program must be directed toward airworthiness approval through the type certification or supplemental type certification process.

b. Certification Plan. A comprehensive certification plan should be developed by the applicant. It should include how the applicant plans to comply with the applicable certification requirements and should provide a listing of the substantiating data and necessary tests. Also, a system description and an estimated time schedule should be included. A well developed plan will be of significant value both to the applicant and the FAA.

c. Equipment Installation.

(1) Mode S Transponder. A Mode S transponder is required for TCAS II operation. It is an enhanced version of existing ATCRBS transponders that is interoperative and compatible with the current ATCRBS system. Each aircraft equipped with a Mode S transponder is assigned a discrete address code.

Mode S also provides the air-to - air data link between TCAS II equipped aircraft to coordinate resolution maneuver s . This ensures that the resolution advisory displayed in one TCAS II equipped aircraft is compatible with the maneuver displayed in the other TCAS II equipped aircraft. It has the capability to provide a data link between the equipped aircraft and the Par 2

AC 20-131A 3/29/93 relative positions of intruding aircraft that are approximately 40 seconds from the closest point of approach and may a short time later require a resolution advisory. They also provide the flightcrew the opportunity to visually acquire the intruding aircraft. A resolution advisory will provide a vertical avoidance maneuver that will increase separation when the computer predicts the threat aircraft is within approximately 25 seconds from the closest point of approach.

The system provides two types of flightdeck displays. A traffic display indicates the relative position of ATC transponder equipped aircraft. A resolution display for each pilot indicates the appropriate vertical maneuver to avoid a threat. The TCAS II aircraft must be equipped with a Mode S ATC transponder which provides air-to-air communications for coordinating the resolution maneuvers between TCAS equipped aircraft. The Mode S transponder also provides discrete address replies to interrogations from ground stations and other TCAS II equipped aircraft.

The TCAS II system can only generate resolution advisories for intruders equipped with responding Mode Sor Mode C transponders, which provide information on the altitude of the threat aircraft. Traffic advisories can be generated for aircraft with operative Mode S, Mode C or Mode A transponders.

The TCAS II equipment is viewed as a supplement to the pilot who, with the aid of the ATC system, has the primary responsibility for avoiding mid-air collisions. The TCAS II system provides no indication of aircraft without operative transponders.

3. AIRWORTHINESS CONSIDERATIONS.

a. Certification Program. This AC provides guidance for the installation of TCAS II equipment and Mode S transponders. The system displays information and provides advisories in a number of formats. The degree of system integration to perform these functions is extensive and as a result, the applicant's program must be directed toward airworthiness approval through the type certification or supplemental type certification process.

b. Certification Plan. A comprehensive certification plan should be developed by the applicant. It should include how the applicant plans to comply with the applicable certification requirements and should provide a listing of the substantiating data and necessary tests. Also, a system description and an estimated time schedule should be included. A well developed plan will be of significant value both to the applicant and the FAA.

c. Equipment Installation.

(1) Mode S Transponder. A Mode S transponder is required for TCAS II operation. It is an enhanced version of existing ATCRBS transponders that is interoperative and compatible with the current ATCRBS system. Each aircraft equipped with a Mode S transponder is assigned a discrete address code.

Mode S also provides the air-to - air data link between TCAS II equipped aircraft to coordinate resolution maneuver s . This ensures that the resolution advisory displayed in one TCAS II equipped aircraft is compatible with the maneuver displayed in the other TCAS II equipped aircraft. It has the capability to provide a data link between the equipped aircraft and the Par 2 AC 20-131A 3/29/93 ground, and performs all the functions of current Mode A and C transponders.

A Mode S transponder may be installed independently or in conjunction with a TCAS II installation. The performance standard for Mode Sis provided in paragraph (a)(l), Minimum Performance Standard, of TS0-Cll2. The discrete aircraft address for the Mode S transponder must be obtained from the appropriate airworthiness authorities of the country in which the aircraft is registered for each aircraft in which a Mode S transponder is installed. For U.S. registered aircraft the discrete aircraft address may be obtained from the Federal Aviation Administration, Mike Monroney Aeronautical Center, Aircraft Registration Information, AVN-450, P.O. Box 25082, Oklahoma City, OK 73125, Telephone: (405) 680-3116.

(2) Pilot Control.

(i) A means to select the following modes of operation must be provided: (A) Operation of the Mode S transponder only.

(B) Operation of the TCAS II in the TA/RA mode and Mode S transponder simultaneously.

(C) Operation of the ATCRBS transponder only, if installed.

It must not be possible to operate the TCAS II and ATCRBS transponder or the Mode Sand ATCRBS transponder simultaneously.

(D) Operation of TCAS II in the TA mode and Mode s transponder simultaneously.

( E} Operation of TCAS II in the standby mode.

(ii ) The foll owing add it ion al features must also be provided: (A) A means to select the assigned ATCRBS code.

(B} A means to initiate the transponder "IDENT" function.

(C} A means to initiate the TCAS II self-test.

altitude reporting.

(D) A means to suppress transponder controls may be provided: (iii) The following optional (A) Selection of the weather radar only.

(B) Control to select the display of traffic within selected altitude bands.

(C) Selection of the weather radar and traffic display simultaneously.

{D) Selection of actual/flight-level (FL) or relative altitude of traffic.

Par 3 3/29/93 AC 20-131A (3) Antennas. The active Mode S transponder shall have a top and bottom omni-directional antenna. The TCAS II shall have a top directional antenna and a bottom omni-directional or directional antenna.

(i) Directional antennas. For an aircraft installation, the TCAS II directional antenna should be located on the top forward fuselage as close to the centerline as possible. If more than one directional antenna is provided, locate the second antenna in a similar manner on the lower fuselage.

The TCAS II antennas should be mounted on the aircraft with at least 20 db.

isolation from other L-band frequency antennas. Since the antenna diameter may be large, sorae structural considerations may be necessary and a centerline offset resulting in an angular offset of up to 5 degrees is acceptable. The maximum height of the directional antenna is expected to be approximately I inch, and therefore is not considered susceptible to icing effects in the general area of the proposed installation. Otherwise, anti-icing provisions should be considered. Section 3 of Volume I of RTCA document D0-185 provides antenna selection and performance criteria. For propeller driven aircraft, the location and performance of the directional antenna must be investigated for minimum blockage and to ensure that the propellers do not interfere with system operation.

(ii) Omni-directional antennas. The TCAS II antennas should be mounted on the aircraft with at least 20 db. isolation from other L-band frequency antennas. The Mode S transponder antennas shall be mounted at locations chosen for adequate isolation and signal coverage. These antennas may be standard ATCRBS transponder antennas.

(iii) Structural analysis. A structural analysis of the antenna installations showing compliance with the applicable FAR should be submitted to the FAA. This includes the structural provisions for a beam steering unit {if installed) if it is not mounted in a standard avionics rack.

(4) The TCAS II Processor. The TCAS II processor unit computes information to identify and to display potential and predicted collision threats, and to issue resolution advisories to avoid the threat aircraft. The TCAS II processor unit must comply with the environmental requirements and minimum performance standards specified in TS0-Cll9a. A manufacturer of TSO equipment may obtain authorization to produce equipment which deviates from the detailed criteria of the TSO. The FAA aircraft certification office which is approving the initial installation of the TCAS II equipment must verify that the TCAS II processor design does not differ from the criteria specified in RTCA document D0-185, Volumes I and II, Changes I through 6, Minimum Operational Performance Standards for Traffic Alert and Collision Avoidance System {TCAS) Airborne Equipment.

Par 3 3/29/93 AC 20-131A (5) Equipment Compatibility. An evaluation should be made to show that the TCAS II system will communicate with other approved TCAS II systems made by other manufacturers. This evaluation should include a TCAS II to TCAS II coordination demonstration, or equivalent, with at least one other manufacturer's approved TCAS II system. If it can be shown for a specific design that communication link failures are no more hazardous than encouritering a Mode C intruder, then these tests are not necessary. Also, after completing mature bench tests, future certification experience may show that these tests are no longer necessary.

(6) Aircraft Performance.

(i) This paragraph, along with Table I, provides guidance on considerations and analysis to evaluate the need to inhibit TCAS II CLIMB and/or INCREASE CLIMB RAs because of inadequate aircraft climb performance.

The collision avoidance maneuvers posted as RAs by TCAS II assume an aircraft's ability to safely achieve them. If it is likely they are beyond the capability of the aircraft, then TCAS II must know beforehand so it can change its strategy and issue an alternative RA. These performance limits shall be provided to TCAS II from the aircraft interface and discretes relative to altitude and/or configuration. However, the need to inhibit TCAS II CLIMB or INCREASE CLIMB RAs should be carefully considered since the alternative RAs will not provide the optimum solution to the encounter.

Inhibiting these RAs will increase the likelihood of TCAS II (a) issuing crossing maneuvers (crossing through an intruder's altitude) increasing the probability that an RA may be thwarted by the intruder maneuvering, (b) causing an increase in DESCEND RAs at low altitude, and (c) providing no RAs if below the descend inhibit altitude of 1200 feet AGL during takeoff and 1000 feet AGL on approach.

(ii) The configuration interface may need switches or sensors besides the basic airplane flap position switches to prevent unnecessary TCAS II inhibits. For example, if CLIMB RAs need to be inhibited for the maximum takeoff flap only, and no switch exists to sense that position, an additional switch should be installed in lieu of simply using one that may exist at lesser flap angles.

(iii) Because of the limited number of inputs to TCAS II for airplane performance inhibits, in some instances where inhibiting RAs would be appropriate it is not possible to do so. In these cases, TCAS II may command maneuvers which may significantly reduce stall margins or result in stall warning. Conditions where this may occur include bank angles greater than 15°, weight/altitude/temperature combinations outside the envelope shown in Table I, initial speeds below those shown in Table I, one engine inoperative, leaving configuration fixed for climb RA on landing transition to go-around, and abnormal configurations such as landing gear not retractable. The Airplane Flight Manual (AFM) or Airplane Flight Manual Supplement (AFMS) should provide information concerning this aspect of TCAS so that flightcrews may take appropriate action.

Par 3 AC 20-131A 3/29/93 (iv) An aircraft's low altitude climb capability during takeoff, approach, or landing is significantly affected by the aircraft's configuration, initial climb true airspeed available to safely trade if needed for climb rate, and the initial airspeed margin from the current stall speed.

Table I, Conditions 1-3 apply for the takeoff and initial climb configuration analysis. Conditions 4-6 apply for the approach flap configuration analysis when operating in the terminal area with the flaps set at less than the landing flaps. Conditions 7-9 apply for the landing flight regime analysis.

To be consistent with normal operation, the AFM or AFMS should indicate that when a climb RA occurs with the aircraft in the landing configuration, the pilot should initiate the normal go-around procedure when complying with the TCAS II RA. Therefore, it may be assumed that the flaps are being retracted from the landing position to the go-around position when evaluating Conditions 7-9.

(v) To prevent very unlikely combinations of events, e.g., weight/altitude/temperature limiting conditions, in conjunction with low airspeed, high drag configurations, unusual encounter geometries, etc., causing climb inhibits when generally the aircraft's performance is more than adequate, the entry and exit conditions and RAs in Table I are structured into two classes of encounters. Maneuvers A and B represent reasonably severe combinations of entry conditions and RAs, and restricts the exit conditions to l.2V~ • Maneuver C represents reasonably worst case combinations of entry conditions and RAs, and for this very unlikely event may require flying near stall warning conditions through the recovery. Airspeeds between l.2V and stall warning represent a range of usable airspeed that maybe traded for climb performance (as is currently recommended for windshear recovery) for evaluation of this low probability event. The altitude/temperature envelope represents a range of values which exist at busy airports in the continental USA. Operation routinely outside this envelope may require special crew procedures if the normal AFM weight, altitude, temperature, and configuration limitations are not sufficiently compensating, e.g., operation at Mexico City.

(vi) For those airplanes that may routinely operate at low climb airspeeds during the clean configuration en route phase of flight, e.g., propeller commuter airplanes, consideration should be given to providing a discrete to the TCAS II based on airspeed. Such an input, derived from a TCAS II interface system, would provide for climb or increase climb RA inhibits when the airplane is in the clean configuration and operating below a certain airspeed. Such a scheme would be considered appropriate in lieu of an across the-board inhibit for the clean configuration regardless of flight regime, which is not considered to provide the best overall level of safety as previously discussed.

(vii) An aircraft's climb capability when operating at or near its maximum approved operating altitude is also affected by excess thrust and true airspeed, which may be available to safely trade if needed for climb rate. Climb RAs should not be inhibited if the aircraft has adequate performance available or because it may exceed its maximum certificated altitude by several hundred feet during an RA. The configurations that should be evaluated in this flight regime are shown in Table I, Conditions 10 and 11.

If the aircraft is approved for significant alternative configurations, then the initial airspeed used for the analysis should be appropriate for them; Par 3 AC 20-131A 3/29/93 e.g., spare engine pod, gear down operation, etc. In the analysis of the aircraft's ability to accelerate and return to the initial speed and altitude following the RA, an undershoot of approximately 200 feet is permissible.

(viii) In icing conditions, the FAR limited performance weights must be debited and sometimes the operating speeds increased to account for icing system bleeds and residual ice on the unprotected surfaces. Therefore, the capability to perform the TCAS II maneuvers remains essentially unchanged, eliminating the need to provide additional RA inhibits under these circumstances. However, if a particular aircraft design shows marginal capability to operate in the icing environment, additional RA inhibits enabled by icing system activation should be considered .

. (ix) If Maneuver A causes airspeeds below the minimum in Table I, then the CLIMB RA should be inhibited. If Maneuver B or C cause airspeeds below the minimum in Table I, then the INCREASED CLIMB RA should be inhibited. However, early recovery of 1 to 2 seconds is of little or no consequence on the collision avoidance maneuver and a higher overall level of safety will be achieved if inhibits are not provided under these circumstances, as previously discussed in paragraph 3c(6)(i).

(x) System Inhibits. A summary of the inhibits (limitations) that have been programmed into the TCAS computer are given in Table II.

Par 3 TABLE I M - A AIRSPEED N E C FLIGHT WEIGHT THRUST FLAPS GEAR INITIAL MIN. u I 0 REGIME ALTITUDE V N TEMPERATURE E D R 1. Takeoff FAR s Rated All Takeoff UP V +20 1. 2 V ,4 thru RA A Ma~im¥f Clim Limit Ta eo II II It II II 2. " " B II II It II II 3.

AFM All-Engine C 15° ~ank to Stal Warni ng Takeoff Speed thru Recovery II ti 4. Approach Sr,in up to Max.

Less than 1.6 vs, 1.2 vs,4 thru RA A Go-Around Thrust Landing Durin~ Maneuver from hrust for Level F ight II II II II II II 5. " B II 11 II 6. " UP or Min. Mfneuver 15° Bank to C ON to Stall Warning ~peed ro~ Train- UP mg Proce ures thru Recovery II 7.

Landin! Spin up to Max. Trans it ion DN to VREF+lO 1. 2 V ,4 thru RA A Transi ioniag Go-Around Thrust f om Landing UP to Go-Aroun

1 Durin~ Maneuver F ap to Go

at RA from hrust Re- Around Flap auired for 3° uide Slope II ti II II II II 8.

B II II II II 9.

C 15° pank t9 Vm+ AJ qf~ed A d1 10n Stal Warn rng from Training thru Recovery Procedures 10. En Route Critical Thrust for Level UP UP Long-Range Cruise Higher of 1.2 A Wt/Alt Giv- Flt Increased to Max. Continuous

v/ H Defined ini 0.38 to

Bu fet nset if Required or Buffet Onset w 11 II 11 II II II 11. " B N

-

I ID ID 1. ~eight= Lesser of clirro limit or structural; Airport Pressure Altitude= S.L. to 5300 ft; - w Temperature= !SA+/- 50°F(10°C); Conditions t-3 evaluated 700 ft above airport; Conditions 4-9 evaluated 1700 ft above airport.

2. Vy+ 10 for nontransport category aircraft without a defined v .

3. Vy for nontransport category aircraft without a defined v .

4. 1.1 v for those airplanes where the power-on stalling speed is significantly reduced from the power-off stalling speed.

5. Vs for tho~e airplanes where the power-on stalling speed is significantly reduced from the power-off stalling speed.

3/29/93 AC 20-131A TABLE I MANEUVERS A. This maneuver is to evaluate the TCAS II CLIMB RA. From the initial steady state condition, after an expected 3-second pilot reaction time delay, rotate the aircraft at 1.25g to attain +1500 feet per minute climb. Hold until the total duration of the RA of 25 seconds has elapsed. Recover to attain the initial trim airspeed.

B. This maneuver is to evaluate the TCAS II INCREASE CLIMB RA following a CLIMB RA. From the initial steady state condition, after an expected 3 second pilot reaction time delay, rotate the aircraft at 1.25g to attain +1500 feet per minute climb. Hold until 15 seconds has elapsed from when the CLIMB RA was issued. Then, after an expected I-second pilot reaction time delay to the INCREASE CLIMB RA, rotate the aircraft again at 1.25g to attain +2500 feet per minute climb and hold until the total duration of the RA of 25 seconds has elapsed. Recover to attain the initial trim airspeed.

C. This maneuver is to evaluate a maximum duration TCAS II INCREASE CLIMB RA following a minimum duration CLIMB RA. From the initial steady state condition, after an expected 3-second pilot reaction time delay, rotate the aircraft at 1.25g targeting +1500 feet per minute climb until 6 seconds has elapsed from when the CLIMB RA was issued. Then, after an expected I-second pilot reaction time delay to the INCREASE CLIMB RA, rotate the aircraft again at 1.25g to attain +2500 feet per minute climb and hold until the total duration of the RA of 24 seconds has elapsed.

Delay recovery l second to account for expected pilot reaction time delay to the end of the encounter. Recover to attain the initial trim airspeed.

~r3 9 r AC 20-131A 3/29/93 TABLE II SYSTEM INHIBITS A summary of the inhibits (limitations) that have been programmed into the TCAS computer.

INHIBIT PARAMETERS Increase Descent RA Inhibited below 1450 ft AGL.

Inhibited below 1200 ft AGL while Descend RA climbing & inhibited below 1000 ft AGL while descending.

Inhibited below 400 ft AGL while RA & TA Voice Messages descending & inhibited below 600 ft AGL while climbing.

{TCAS automatically reverts to TA only).

Close-Range Surveillance May not function at separations of less than approximately 900 ft.

Self-Test Can be inhibited when airborne.

Can revert to TA ONLY when higher Advisory Priority priority advisories (e.g., GPWS, Windshear) occur.

Climb RA 1500 fpm can be inhibited, based upon aircraft performance capability.

2500 fpm can be inhibited, based Increase Climb RA upon aircraft performance capability.

Altitude Limit for Climb RA Can be inhibited, based upon aircraft performance capability.

10 Par 3 3/29/93 AC 20-131A (7) Aircraft Interfaces.

(i) Pressure altitude information. The pressure altitude data should be obtained from the most accurate source available in the aircraft and shall correspond to that being transmitted by the associated Mode S transponder. The accuracy of the altitude data shall be at least that specified in Appendix A of RTCA document 00-185. It shall be shown that the resolution of the altimetry source is compatible with TCAS II. The altitude source with the finest compatible resolution should be used. When available, the resolution should be in increments of 10 feet or less. Information should also be provided to indicate when the pressure altitude information is invalid.

(ii) Radio altitude information. Radio altitude information shall be provided to TCAS II to inhibit DESCEND resolution advisories below 1000 feet AGL, INCREASE DESCENT resolution advisories below 1450 feet AGL, all resolution advisories and aural traffic advisories below 400 feet AGL, to allow automatic sensitivity level selection when close to the ground, and to determine that individual targets are on the ground. Information shall also be provided to indicate when the radio altitude information is invalid.

(iii) Discrete information from aircraft configuration sensors such as flaps, slat, landing gear, etc., should be used to ensure that TCAS II appropriately inhibits climb and increased climb RAs to the airplane performance limits as described in paragraph 7c(6).

{iv) Aircraft identification. Discrete information shall be provided to the Mode S transponder for the unique aircraft Mode S identification code and its maximum airspeed capability.

{v) Attitude. Information of pitch and roll attitude may be provided to assist with stabilization of the directional antenna function to assure surveillance and TA display data remain unaffected by aircraft normal maneuvers. If attitude information is used by TCAS II, the information shall also be provided to indicate when the attitude data are invalid.

(vi) Heading. Information of aircraft heading may be provided for use of surveillance reference and for the TA display reference presentation. Information shall also be provided to indicate when the heading data are invalid.

(vii) System failure display. An indication shall be provided to indicate when resolution advisories are not possible due to failure of the TCAS II equipment or any of its sensors or displays.

Par 3 AC 20-131A 3/29/93 (8) Traffic Display.

(i) Purpose. The primary purpose of the traffic display is to aid the flightcrew in the visual acquisition of transponder equipped aircraft.

This is accomplished by displaying the intruder aircraft's horizontal and, if altitude information is available, vertical position relative to the TCAS II equipped aircraft. The TCAS II systems will provide traffic information on Mode A (no altitude data available), Mode C, and Mode S transponder equipped aircraft. A secondary purpose of the traffic display is to provide the flightcrew with confidence in proper system operation and to give them time to prepare to maneuver the aircraft in the event TCAS II issues a resolution advisory.

(ii) Description. The traffic display may take several forms.

Traffic displays may be independent, stand-alone, integrated and time-shared with digital color radar, integrated with the flightcrew's Instantaneous Vertical Speed Indicators (IVSI), or integrated with other displays such as Electronic Horizontal Situation Indicators (EHSI), navigation, or other multi-function displays. If the traffic display uses a multi-function display that is shared with other services such as ACARS, the traffic display function shall be immediately available for display by a single selection accessible to both p i1 ots.

(iii) Symbology/Feature Criteria. The FAA has worked closely with the ATA, NASA, and both the SAE S-7 and G-10 Committees in an effort to standardize TCAS II symbology and features. A consensus has been reached for TCAS II symbols and they are provided in this AC. Other symbology and features may be used provided the applicant uses human factors technology to demonstrate that a clear and substantial benefit can be derived by its use.

Otherwise, the traffic display must depict or provide the following symbology, features, or information: (A) Own Aircraft Symbol. This shall be an aircraft-like symbol. For fixed range displays, it should be located so as to provide a minimum of 2.5NM range to six o'clock position (indicating an aircraft is 2.5NM behind the TCAS II equipped aircraft) and a minimum of 6NM range to the twelve o'clock position (indicating an aircraft is 6NM in front of the TCAS II equipped aircraft). The symbol color should be white or cyan and should be the same color as the range ring.

(B) The Intruder Aircraft at the Traffic Advisory (TA) Level. This symbol shall be shaped as a circle and should be solid amber in color. This symbol must be positioned to depict its relative bearing and distance to the TCAS II aircraft. TAs and RAs must be displayed whenever the appropriate CAS Logic is satisfied, regardless of display/surveillance switch positions (above/below) intended for other traffic.

(C) The Threat Aircraft at the Resolution Advisory (RA) Level. This symbol shall be shaped as a square and it should be solid red in color. Since red is of low conspicuity, the use of other graphical techniques to enhance this symbol (such as outlining) should be evaluated, and research in this area is encouraged.

12 Par 3 AC 20-131A 3/29/93 (D) Proximate Traffic. When a TA or RA is present, a symbol shall be depicted for transponder equipped aircraft within 1200 feet relative altitude and 6NM (or the minimum range, whichever is less). This symbol shall be shaped like a diamond and colored solid white or cyan but not the same color as own aircraft symbol. It is required to display proximate traffic only when the requirements to display a TA or an RA exist. The display of proximate traffic under these circumstances will assist the pilot in the detection of the intruder aircraft. Proximate traffic may also be displayed even when no TA or RA exists.

(E) Other Traffic. Other transponder equipped traffic within+/- 9900 feet of ownship may be displayed. This symbol should be shaped as an open diamond and should be the same color as proximate traffic. The ability to display other traffic has been determined by service experience to be a significant aid to the flightcrew's situational awareness and incorporation of this feature is highly recommended.

NOTE: All transponder equipped aircraft without altitude reporting will be considered co-altitude by TCAS. Therefore, it will become a solid diamond the same color as proximate traffic when within 6NM and may represent a serious threat that cannot be resolved by TCAS.

(F) Relative Altitude Display. Relative altitude is the difference between the other aircraft's altitude and the TCAS II equipped aircraft's altitude. This should be pres.ented in a dig ita 1 format rounded off to the nearest one hundred feet. This digital information should be centered on the intruder aircraft symbol and positioned above or below the intruder symbol when the intruder aircraft is above or below the TCAS II aircraft respectively. The digital data should include a leading zero and a plus or minus sign as appropriate. For example, -05 positioned below the threat symbol (solid red square) would indicate the threat aircraft is 500 feet below the TCAS II aircraft. This digital data should conform to the color of the threat aircraft symbol. Co-altitude situations should be depicted as "00" (without the+ or - symbol}. The "00" symbol may be placed above the traffic symbol if the other aircraft closed from above, and vice versa.

(G} Displayed Traffic Range. The range of the displayed traffic is horizontal (slant range corrected) when altitude is available.

Slant range is displayed when altitude information is not available.

(H) The Range "Ring". There should be markings surrounding the own aircraft symbol at each of the twelve o'clock positions.

These markings may be small dots, small lines or indices, or asterisks.

Enhancement of the 3, 6, 9, and 12 o'clock positions is permissible. A solid range ring is not recommended due to clutter. A range ring of 2NM radius is required for small fixed range displays such as 3 ATI (ARINC Specification 408A for 3 inch Air Transport Indicator) displays and the entire range ring must be depicted. A range ring radius of 3NM has been found acceptable for all other displays. The radius must remain scaled to the range selected for variable range displays. When the traffic display is integrated with an EHSI or a Navigation Display (ND), a partial range ring is permissible for Arc or Expanded display modes. Full or partial range rings are acceptable when integrated with weather radar displays. The color should be the same as own Par 3 AC 20-131A 3/29/93 aircraft symbol. The 2 or 3NM range ring is not required when the range of the display exceeds 20NM.

(I) Off Scale Symbology. RA or TA traffic which is off scale shall be indicated by placing one half of the appropriate symbol at the edge of the active display area in the direction of the measured bearing of the traffic for fixed range displays. Data tags and appropriate vertical trend arrows shall remain fixed in the normal design position relative to the traffic symbol even if a portion of the information is masked by the edge of the active display area. An alternative method for variable range displays 11 11 would be to annunciate a message "TRAFFIC OFF-SCALE", 0FF-SCALE , or "TA(RA if appropriate) OFF-SCALE".

(J) No Bearing Display. When the TCAS II system uses a bottom omni-directional antenna and the upper directional antenna loses track on the intruder aircraft, the threat aircraft can no longer be depicted on the traffic display with the correct bearing. The relative altitude or the actual altitude or flight level (if the actual altitude mode has been selected) and range should be digitally presented. This information must be colored to conform to the threat level (amber for TAs and red for RAs). There are several acceptable formats that may be displayed depending upon the type of altitude information being displayed. Some examples are as follows: (1) "TA 1.2NM/+lli" depicting a TA intruder at 1.2NM and 1100 feet above ownship and descending at a rate greater than 500 fpm.

(2.) "RA 4.6NM/FL230" depicting an RA threat at 4.6NM at Flight Lsvel 230.

(~) "TA 8.8NM/OO" depicting a co-altitude TA intruder at 8.8NM.

(.4) "RA 3.3NM/165 depicting an RA threat at 3.3NM at a barometric altitude of 16,500 feet MSL.

(~) TA 5.5NM" depicting a mode A (no altitude reporting) TA intruder at 5.SNM.

NOTE: The TA or RA which precedes the range information in the above examples may be omitted if display space is limited.

(K) Mode A Transponder Equipped Aircraft. A data tag shall not be associated with the symbol for targets which are not reporting altitude. Note that an RA will not be generated for targets not reporting altitude.

Par 3 AC 20-131A 3/29/93 (L) Other aircraft Vertical Speed. A vertical arrow should be located immediately to the right of the other aircraft symbol display if the vertical speed of the other aircraft is equal to or greater than 500 feet per minute with the arrow pointing up for climbing traffic and down for descending traffic. The color of the tag should be the same as the symbol.

(M) TA Only Mode. The ability to inhibit the RA mode of operation should be provided to prevent the display of unwanted RAs. This feature should be pilot selectable, and suitably annunciated. In this mode of operation, all TAs (and threat aircraft that would ordinarily be displayed as RAs) will be displayed as TAs.

(iv) Optional Features/Symbology.

(A) Compass Heading. Aircraft heading and/or a compass rose may be included in the traffic display, and it should be colored white.

(B) Actual Intruder Altitude. A switch may be provided to select the display of the intruders actual barometric altitude in place of relative altitude. The display of actual barometric altitude should be displayed as a three digit number representing hundreds of feet above MSL; e.g., 007 for 700 feet MSL and 210 for 21000 feet MSL. Clear and unambiguous indication must be provided on the display that the actual intruder altitude mode has been selected. Actual altitude tags shall be positioned above or below the traffic symbol in a manner consistent with relative altitude data tags. The display of actual barometric altitude below the transition altitude (18,000 MSL in the U.S.) requires a barometric pressure correction from ownship. If barometric pressure corrections are not incorporated, the display of actual barometric altitudes below the transition altitude is considered potentially ambiguous and may be displayed by pilot selection only for approximately 15 seconds per selection.

(C) Range Selection/Reversion. Traffic displays may incorporate a variable range feature, and there must be a means to manually select each range. A feature may be provided to automatically select the optimum range when an RA/TA occurs. In addition, if a dedicated TCAS mode is provided within a multifunction display, the selection of that mode may automatically change the range of the display to a predetermined value.

(D) Maximum Number of Displayed Targets. There currently are no requirements to establish a maximum number of displayed targets when TA or RA conditions exist. (For 3 ATI displays, a maximum of 12 targets has been found acceptable.) Overlapping traffic symbols should be displayed with the appropriate information overlapped. If display technology requires prioritization of symbols, this shall be accomplished to allow the maximum display of data.

(E) Traffic Display Switch. A switch may be provided which will display all traffic within the range of the display and within 2700 feet vertically of own aircraft. This switch may be either momentary or a lock-on type of switch.

Par 3 AC 20-131A 3/29/93 (F) Extended Altitude Surveillance Switch. A switch may be provided to select the viewing of traffic from 2700 feet below own aircraft to a maximum of 9900 feet above own aircraft and the viewing of traffic from 2700 feet above own aircraft to a maximum of 9900 feet below own aircraft.

(9} Resolution Display.

(i} Purpose. The purpose of the resolution display is to provide each pilot with the information to readily correct the aircraft flight path or to prevent a maneuver that would significantly reduce the vertical separation between ownship and a threat aircraft.

(ii) Description. The resolution display may be integrated with the two primary IVSis on the flightdeck. These displays depict red arcs along the perimeter of round dial IVSis or red vertical lines on vertical tape IVSis that must be avoided in order to maintain safe vertical separation. The pilot's task is to maneuver the aircraft promptly to achieve a vertical speed just out of the illuminated red arc or line (within the green "fly to" arc or line) when presented or to maintain a vertical speed out of the illuminated red arc or line that most nearly complies with the ATC clearance.

(iii) Symbology. The resolution display must depict a red illuminated arc or line for corrective RAs. Corrective RAs should also depict a green "fly to" symbol; for example, when a climb RA is issued on a round dial IVSI, a red colored arc should be depicted (adjacent to the IVSI scale) from -6000 FPM to +1500 FPM and a green fly-to arc or line from +1500 FPM to approximately 2000 FPM. The resolution display must also depict an illuminated arc to be avoided for preventive RAs. A green "fly to" arc or line is not required in this case since the current aircraft vertical speed is satisfactory. The color of the preventive RA arc or line should be red. The same requirements for round dial RA displays are applicable to vertical tape RA displays in PFD's. Some applicants may wish to integrate the RA display within an EADI or PFD. There are several good reasons to pursue the development of this technology within PFD's and EADI's. The basic concepts of a warning area and a "fly to" area must be retained. The use of new TCAS symbology such as target pitch attitudes or flight path angles will require testing throughout the flight envelope to determine accuracy, over/undershoot tendencies, flight technical error, and potential confusion with flight director symbology. Applicants pursuing this technology should contact the appropriate FAA ACO early in the development cycle.

(iv) Failure indications must be provided for TCAS failures (TCAS unable to generate RAs). Annunciation must be provided for the TA only mode.

Electrical IVS! failures must also be annunciated.

(10) Caution/Warning Lights.

(i) Discrete caution and/or warning lights may be installed which are separate from the traffic display. The purpose of these additional indicators is to annunciate the presence of potentially threatening intruder aircraft at times when the pilot's attention may be diverted from the primary TCAS display. Two different discrete TCAS II annunciators have been used: Par 3 AC 20-131A 3/29/93 (A) A discrete amber caution annunciator which indicates the presence of a TCAS II TA. Installation of this discrete caution annunciator is optional. If installed, it must be located in each pilot's primary field of view and be inhibited below 400 feet AGL.

(B) A discrete red warning annunciator which indicates the presence of a TCAS II RA. This red warning must be located in each pilot's primary field of view and be inhibited below 400 feet AGL. An IVSI with a lighted red arc, or an alphanumeric message on the EADI is acceptable in lieu of this discrete warning annunciator.

(ii) Because of the numerous TCAS II advisories expected in service, the basic aircraft master caution and warning system should not be interfaced with these TCAS II caution/warning discretes. Overuse of the primary aircraft caution and warning system would tend to reduce its effectiveness in annunciating non-TCAS II system failures.

(iii) Discrete visual alerts should remain on until cancelled by the pilot or until the aircraft is no longer considered an intruder or a threat by TCAS II.

(11) Aural Alerts.

(i) Each TCAS II aural alert should be annunciated by a dedicated voice message over a cockpit speaker at a volume adequate for clear understanding at high cockpit noise levels, but not excessively loud at low noise levels. The evaluation includes the case where a flight crewmember is wearing a headset, covering the outboard ear when appropriate.

(ii) The TCAS II Traffic Advisories (TAs) should be annunciated by the voice message "TRAFFIC, TRAFFIC" stated once for each TA.

(iii) The TCAS II Resolution Advisories (RAs) should be annunciated by the following voice messages, as appropriate: (A) "CLIMB, CLIMB, CLIMB" (Climb at the rate depicted by the green {fly to) arc or line on the IVSI or other suitable indicator.)

(B) "DESCEND, DESCEND, DESCEND" (Descend at the rate depicted by the green (fly to) arc or line on the IVSI or other suitable indicator.)

(C) "MONITOR VERTICAL SPEED-MONITOR VERTICAL SPEED" (Spoken only once if softening from a previous corrective advisory.) Assure that vertical speed is out of the illuminated IVSI red arc or line.

(D) "REDUCE CLIMB-REDUCE CLIMB" (Reduce vertical speed to a value within the illuminated green arc or line.)

(E) "CLEAR OF CONFLICT" (Range is increasing, and separation is adequate; expeditiously return to the applicable clearance, unless otherwise directed by ATC.)

Par 3 17 AC 20-131A 3/29/93 (F) "CLIMB, CROSSING CLIMB, CLIMB, CROSSING CLIMB" (Cl irnb at the rate depicted by the green (fly to) arc or line on the IVS! or other suitable indicator.) Safe separation will best be achieved by climbing through the threat's flight path.

(G) "REDUCE DESCENT-REDUCE DESCENT" (Reduce vertical speed to a value within the illuminated green arc or line.)

(H) "DESCEND, CROSSING DESCEND, DESCEND, CROSSING DESCEND (Descend at the rate depicted by the green (fly to) arc or line on the IVS! or other suitable indicator.) Safe separation will best be achieved by descending through the threat's flight path.

(iv) The following voice messages are required to annunciate enhanced TCAS II maneuvers when the initial RA does not provide sufficient vertical separation. The tone and inflection must connote increased urgency.

(A) "INCREASE CLIMB, INCREASE CLIMB (Climb at the rate depicted by the green (fly to) arc or line on the IVSI or other suitable indicator.} Received after "CLIMB" advisory, and indicates an additional climb rate is required to achieve safe vertical separation from a maneuvering threat aircraft.

(B) "INCREASE DESCENT, INCREASE DESCENT (Descend at the rate depicted by the green (fly to) arc or line on the IVSI or other suitable indicator.) Received after "DESCEND" advisory, and indicates additional descent rate is required to achieve safe vertical separation from a maneuvering threat aircraft.

(C) "CLIMB - CLIMB NOW, CLIMB - CLIMB NOW" (Climb at the rate depicted by the green (fly to) arc or line on the IVSI or other suitable indicator}. Received after a "DESCEND" resolution advisory and indicates a reversal in sense is required to achieve safe vertical separation from a maneuvering threat aircraft.

(D) "DESCEND - DESCEND NOW, DESCEND - DESCEND NOW" (Descend at the rate depicted by the green (fly to) arc or line on the IVSI or other suitable indicator.) Received after a ucLIMB" resolution advisory and indicates a reversal in sense is required to achieve safe vertical separation from a maneuvering threat aircraft.

(v} All TCAS II aural alerts must be inhibited below 400 feet AGL.

(vi) Both increases and decreases in the threat level must be aurally annunciated. However decreases in threat level need only be annunciated once, e.g., a "monitor vertical speed" aural which follows a climb RA should only be annunciated once.

(vii) In general, other messages which are clear and unambiguous will be evaluated on an individual basis. Messages which use negatives should not be used (e.g., "DON'T CLIMB").

Par 3 3/29/93 AC 20-131A d. Software Verification and Validation. The verification and validation of TCAS II software using the procedures outlined below are required for the first installation of a manufacturer's TCAS II equipment. These procedures shall also be applied to subsequent software changes to a manufacturer's TCAS II equipment. A manufacturer may provide a design that partitions the software which affects resolution advisories from other software (level 3} such as that necessary for the traffic display. If the partitioned software is initially approved by the FAA, verification and validation for the level 3 software may be accomplished by the TCAS II manufacturer using the minor change authority of the TSO system.

(1) The verification and validation of the TCAS II software represents a unique challenge because the collision avoidance algorithms, commonly called "CAS logic," as contained in Volume II of RTCA document 00-185, represent a software design specification. However, the surveillance software necessary to establish and maintain the relative tracks of nearby transponder equipped aircraft and the software necessary to provide the interface with the Mode S transponder and with other aircraft sensors and displays must be developed by the manufacturer of the TCAS II equipment. This hybrid approach to the specification of the software requirements and design does not permit the direct application of the software criteria contained in RTCA document D0-178A. The CAS logic has been provided by Volume II of RTCA document 00-185.

(2) If software is used for the displays of TCAS II resolution advisories or in the operation of the Mode S transponder data link, the verification and validation of this software should be done to level 2, as defined in RTCA document D0-178A. These procedures should also be applied where the TCAS II manufacturer develops the software requirements for the TCAS II processor associated with functions other than surveillance or the CAS logic. Where the software design is specified by Volume II of RTCA document D0-185, the manufacturer of the TCAS II processor should conduct code walk-throughs and develop and perform module tests and module integration tests to verify that the specified software design has been implemented correctly. This includes the surveillance software necessary to establish and maintain the relative tracks of nearby transponder equipped aircraft.

(3) The functional tests required by TSO C-119a as described in Volume I of RTCA document 00-185, do not provide complete testing for the TCAS II processor software. The TCAS II manufacturer must develop additional functional tests which correspond to the detailed requirements which it develops for the TCAS II processor. The potential consequences of software errors in the TCAS II processor or resolution display require that the manufacturer provide a structural coverage analysis to show single condition test coverage of all instructions at the source code which can affect the generation and display of resolution advisories. The tests which provide this may be a combination of module tests, module integration tests and functional tests.

P ar 3 AC 20-131A 3/29/93 (4) Equipment produced in accordance with a technical standard order may have obtained FAA concurrence that the software for the equipment was produced in accordance with the criteria of RTCA document D0-178A for a particular software level. Nevertheless, it is the responsibility of the applicant who first installs a manufacturer's TCAS II equipment in an aircraft to demonstrate to the appropriate FAA ACO that the system software used for the TCAS II equipment, Mode S transponder and new sensors and displays necessary to provide resolution advisories have been developed in accordance with the criteria outlined above. Data from the TSO process may be sufficient to establish that the appropriate verification and validation have been accomplished, but the ACO may require additional tests and analysis of the software for the installed TCAS II system. Subsequent installations of the same TCAS II equipment on other aircraft types do not require any additional verification if the software is not changed.

e. System Safety Analyses. A false resolution advisory has the potential of causing a mid-air collision. Failures of the TCAS II equipment and its associated sensors and displays which could provide a false resolution advisory must be improbable. This should be established using the methods described in AC 25.1309-IA, System Design and Analysis. It is expected that a failure modes and effects analysis (FMEA) and a quantitative probability analysis of the TCAS II equipment, Mode S transponder, and altitude information source will be necessary to establish that an incorrect resolution advisory is improbable. For the purposes of a numerical analysis, the probability of an incorrect resolution advisory without a TCAS II failure indication should be on the order of 1.0 x 10-5 per flight hour in the enroute environment and 1.0 x 10-4 per flight hour in the terminal area. The frequency of encounters which would produce a resolution advisory can be assumed to be once per 200 hours in the enroute environment and once per 10 hours in the terminal area, unless the applicant can establish different frequencies based on operational data. These analyses should be provided for the first installation of a particular model of TCAS II equipment. Subsequent installations of the same equipment in other aircraft may make use of the same analyses with particular attention to the differences in own altitude sensors.

f. Test and Evaluation (Initial Approval}. Testing of the first of a manufacturer's TCAS II system for its initial approval in an aircraft should be conducted to verify that the design and installation performs its intended function under the expected operating conditions, that there are no adverse interactions between the TCAS II and existing aircraft systems, and that prior approvals of present aircraft equipment have not been compromised . The applicant should provide a test plan that includes adequate testing to perform this verification. This test plan will generally require a combination of ground tests, basic flight tests, and flight tests involving planned encounters with another TCAS II equipped aircraft. The use of other than a transport category aircraft for either the TCAS II installation or for the air-to-air cooperative flights is acceptable. The test plan should contain, as a minimum, the following elements: (1) Basic Ground Tests.

(i) Bearing Accuracy Tests. Bearing estimation accuracy of the TCAS II system shall be demonstrated as installed in the aircraft. The 20 Par 3 3/29/93 AC 20-131A bearing accuracy may be measured using a calibrated antenna range that allows precise echo-controlled, far-field, angle-of-arrival measurements at or slightly above zero degrees elevation and over 360 degrees in azimuth. The bearing accuracy may also be measured using a fixed transponder location while rotating the test aircraft on a compass-rose while measuring the bearing angles at 30 degree intervals. Alternately, the airplane is fixed and the transponder may be moved. Manual readout of the bearing estimate may be accomplished directly from a plan position display on the traffic advisory display. Alternatively, the bearing estimates may be automatically recorded or may be read from a special test display. A maximum error of± 15 degrees in azimuth is acceptable; however, larger errors are acceptable in the area of ± 45 degrees from the tail and the area is not visible from the cockpit. In this case, aircraft structure may interfere with the signal path.

(ii) Sensor failures. Simulated failures of the aircraft sensors integrated with TCAS II should be evaluated to determine that the resulting system failure state agrees with the predicted results. These tests should be part of the ground test plan.

(iii) Electromagnetic Interference (EMI). A flightdeck EMI survey should be made to determine that the TCAS II equipment is not a source of objectionable conducted or radiated interference to previously installed systems or equipment, and that operation of the TCAS II equipment is not adversely affected by conducted or radiated interference from previously installed systems and equipment. Attention should be given to possible interference with TCAS II equipment from weather radar, particularly if operating in the C-band.

(iv) Evaluate the general arrangement and operation of controls, displays, circuit breakers, annunciators, and placards of the TCAS system.

(v) Self Test. Evaluate the TCAS self test features and failure mode displays and annunciators.

(vi) Verify that the pressure altitude source and radio altimeter are properly interfaced with the TCAS equipment.

(vii) Verify that the windshear and GPWS warnings and TCAS II voice alerts are compatible. Also, verify that windshear warnings can be clearly understood when TCAS II and windshear voice announcements simultaneously occur. If TCAS II, windshear and GPWS aural warnings have been prioritized, the alert priorities should be windshear, GPWS and then TCAS II.

(viii) Verify the performance of TCAS II traffic display by observing any available area traffic.

(ix) Evaluate the TCAS II system installation for satisfactory identification, accessibility, and visibility during both day and night conditions.

(x) Determine that any configuration discretes associated with the TCAS II logic including inhibits of climb RAs, operate properly. (Changes in logic or function with aircraft configuration, altitude, or speed.)

Par 3 AC 20-131A 3/29/93 (xi) Verify that the Mode S identification code and maximum airspeed are correct.

(2) Basic Flight Tests.

(i) During all phases of flight, determine if there is any mutual interference with any other aircraft system. Weather radar should be operating during the flight test.

(ii) Evaluate TCAS II aural messages for acceptable volume and intelligibility during both low and high cockpit noise levels (idle descent at low speed and high power at VM ) with headset covering outboard ear only (when appropriate) and without headsets. If the TCAS II TEST is used to simulate voice announcements, ensure that the audio level is not changed by use of the TEST function.

(iii) Demonstrate that traffic information remains valid and usable when the aircraft is pitched± 15 degrees and rolled approximately 30 degrees of bank during normal maneuvers by observing area traffic in the traffic advisory display.

(iv) Evaluate the effective surveillance range of the traffic display, including target azimuth reasonableness and track stability. Use of targets of opportunity or a nontransport (low-speed) aircraft as a target for these tests is permissible.

(v) Determine that any configuration discretes associated with the TCAS II logic including inhibits of climb RAs, operate properly unless previously demonstrated during ground tests. (Changes in logic or function with aircraft configuration, altitude, or speed.)

(vi) Perform the additional flight tests in Appendix 2 of this AC unless previously accomplished under TS0 - C119a.

(vii) Evaluate TCAS for noninterference during coupled Autopilot and Flight Director approaches to the lowest minimums approved for the aircraft.

(viii) Prior to any cooperative flight tests at any altitude involving the TCAS II equipped aircraft and another aircraft, both aircraft should be flown in close formation to assure matched altimetry readouts.

These checks should be flown at the speeds and altitudes to be used for the tests .

(ix) Evaluate all selectable mode s of the TCAS II to determine that they perform their intended function.

Par 3 3/29/93 AC 20-131A (x) Reevaluate any previously installed aircraft systems that have required changes as a result of the TCAS II installation. (e.g., EFIS, FD, PFD, ND, IVSI, interface, etc.)

(3) Planned Encounter Flight Tests. The objective of these flight tests is to demonstrate adequate TCAS II surveillance and to verify smooth, predictable TCAS II performance. Having established appropriate safety rules, static system leak test (if necessitated by having opened the system), and altimeter correlation between the encounter aircraft and the TCAS aircraft, the following encounters between the TCAS II aircraft and a dedicated intruder aircraft should be flown to insure that the TCAS II aircraft system performs its intended function by generating TAs and RAs and is consistent with RTCA document D0-185. The intruder aircraft should be equipped with transponders capable of Mode A, Mode C, and for those tests making it necessary, Mode S, and TCAS II. These tests are also intended to expose the installed TCAS II system to a reasonable number of carefully controlled encounters which are likely in service. This matrix covers the envelope of encounter speeds, altitudes, and geometries which have in the past identified flaws in surveillance, logic, and antenna mechanization that were not detected earlier by bench tests.

(i) Intruder overtaking TCAS II aircraft {from the aft quadrants).

(ii) Head-on.

(A) Low and high closure speeds.

(B) Above climb limit, TCAS II to TCAS II.

(C) TCAS II against Mode C with TCAS II above intruder and above climb limit {intent is to force TCAS II aircraft to descend.)

(D) At 3000 feet over calm water to evaluate multipath protection.

(iii) Converging.

(iv} Crossing (intruder above TCAS II, descending or vice versa.)

(v) Evaluate the TA only mode during planned encounters.

(vi} A mix of intruder transponder modes {A, C, and S} should be evaluated, but primary emphasis should be on TCAS II to TCAS II coordination, and on Mode C replies from the intruder aircraft.

(vii) Evaluate a mix of encounters with TCAS II both above and below the intruder.

Par 3 AC 20-131A 3/29/93 (viii) If a flight test is necessary to insure compatibility with other designs, verify correct air-to-air coordination between the test TCAS II and another manufacturer's previously approved equipment (see paragraph 3c(5)).

(ix) Evaluate the effect of electrical transients (bus transfer), during encounters. The TCAS II should not experience adverse effects. No false TAs or RAs should be generated as a result of electrical transients. Normal TCAS II functions and displays should be restored within approximately three seconds.

(4) Mode S Transponder Flight Tests. The flight tests described by this section may be used to obtain the certification of a stand-alone Mode S transponder installation. These tests should also be used to evaluate a Mode S transponder which is intended for use with a TCAS II installation. The purpose of these tests is to primarily verify that the installed antenna(s) are compatible with the Mode S transponder and provide an adequate response to ground radar interrogations during normal aircraft maneuvers. In addition, the flight test is a demonstration that the Mode S transponder functions properly as installed and does not interfere with other aircraft electronic equipment. The need for a detailed flight test is reduced when the Mode S Transponder and antenna installation is identical or similar to that of previously approved ATCRBS transponder installation.

(i) If the Mode S transponder uses a top mounted antenna in addition to a bottom mounted antenna which is installed at or near the same location used by a previously approved ATCRBS transponder antenna, conduct a comprehensive ground test in accordance with Appendix 3 and conduct a functional flight test. The transponder code, altitude reporting and "!DENT" features of the transponder should be exercised during normal maneuvering.

There should be no objectionable behavior observed by the ground controller.

(ii) If a Mode S transponder is installed in an aircraft which does not have a previously approved ATCRBS transponder installation or which uses a bottom mounted antenna location which differs significantly from that used by a previously approved ATCRBS transponder antenna, the following ground and flight tests should be conducted.

(A} Conduct Ground Tests Per Appendix 3 (B) Climb and Distance Coverage. Beginning at a distance of at least IONM from, and an altitude of 2000 to 3000 feet above that of the radar facility and using a transponder code assigned by the ATC, fly on a heading that will pass the aircraft over the facility. At a distance of 5 to lONM beyond the facility, fly the aircraft at its normal maximum climb attitude to within 90 percent of the maximum altitude for which the aircraft is certificated, maintaining the aircraft at a heading within 5 degrees of the track from the radar facility. After reaching the maximum altitude for which the aircraft is certificated, fly level at the maximum altitude to 160NM for turbojet and some turboprop powered airplanes (or 80NM for most other aircraft) from the nearest radar facility. (Distance from the radar facility is a function of the airplane's maximum certificated altitude.) Communicate with the ground radar personnel for evidence of transponder dropout. During Par 3 3/29/93 AC 20-131A the flight, check the "ident" mode of the ATC transponder to assure that it is performing its intended function. There should be no dropouts (no return for two or more sweeps). Uncontrollable ringing that hinders use of the ground radar is unsatisfactory.

(C) Long Range Reception. At 90 percent of maximum certificated altitude perform left and right 360 degree turns, at bank angles of 8 to 10 degrees. The aircraft should be at least 160 (or 80)NM from the nearest radar facility. During these turns, the radar displays should be monitored and there should be no signal dropouts (no return for 2 or more sweeps).

(D) High Angle Reception. Perform two 360 degree turns, one to the right and one to the left, at bank angles of 8 to 10 degrees with the airplane at a distance of 50 to 70NM from the nearest radar facility and at an altitude of at least 35,000 feet or within 90 percent of the maximum altitude for which the aircraft is certificated. There should be no dropouts (no return for 2 or more sweeps). Switch the transponder to a code not selected by the ground controller. The aircraft secondary return should disappear from the scope. The controller should then change his control box to "common sense and a single slash should appear on the scope at the aircraft's position.

(E) High Altitude Cruise. Within 90 percent of the aircraft's maximum certificated altitude or its maximum operating altitude beginning at a point 160 (or 80)NM from the nearest radar facility fly on a course which will pass over the radar facility. There should be no transponder dropout or "ring-around".

(F) Surveillance Approach. Beginning at or above 90 percent of the maximum certificated altitude of the aircraft, perform a letdown and approach to a runway of an airport served by Airport Surveillance Radar (ASR) having an ATCRBS facility. The approach should be made at the maximum normal rate of descent and normal approach and landing configuration for the aircraft and should continue down to an altitude of 200 feet or less above the ground radar antenna elevation. Not more than one dropout should occur for any 10 sweeps during final approach. Uncontrolled ringing that hinders use of the ground radar is unsatisfactory.

(G) Holding and Orbiting Patterns.

(1) At an altitude of 2000 feet above the radar antenna or minimum obstruction clearance altitude (whichever is greater) with landing flaps and gear extended, fly left and right 360 degree turns approximately 10 miles from the radar facility. There should be no signal dropouts.

(Z) At an altitude of 2000 feet above the radar antenna or minimum obstruction clearance altitude (whichever is greater) fly 45 degree sectors of left and right 10 mile orbital patterns around a radar facility with gear and landing flaps extended. There should be no signal dropouts.

{H) Altitude Reporting. Conduct a functional test of the altitude encoder by comparison with ATC-displayed altitudes. Verify correspondence at several altitudes between ATC readings and the Captain's Par 3 AC 20-131A 3/29/93 altimeter, when set at or corrected to 29.92 inches of mercury (or equivalent).

g. Follow-On Approvals (STC or Amended TC). Flight testing of TCAS II systems for follow-on approvals (previously approved TCAS II equipment installed in a different aircraft type) should be conducted to verify that the design and installation performs its intended function under the expected operating conditions, that there are no adverse interactions between the TCAS II and existing aircraft systems, and that prior approvals of present aircraft equipment have not been compromised. The applicant should provide a flight test plan that includes adequate testing to perform this verification.

This test plan will generally require a combination of ground tests, basic flight tests, and flight tests involving planned encounters with a Mode C equipped aircraft, or the use of a suitably located fixed transponder. The test plan should contain, as a minimum, the following elements: (1) Ground Tests.

(i) Evaluate the general arrangement and operation of controls, displays, circuit breakers, annunciators, and placards of the TCAS II system.

(ii) Evaluate the TCAS II self test features and failure mode displays and annunciators.

(iii) Verify that the pressure altitude source and radio altimeter are properly interfaced with the TCAS II equipment.

(iv) Measure the performance of the directional antenna for 360 degrees coverage at 30 degree intervals, as specified under basic certification ground tests.

(v) Evaluate the TCAS II system installation for satisfactory identification, accessibility, and visibility during both day and night conditions.

(vi) Determine that any configuration discretes associated with the TCAS II logic including inhibits of climb RAs, operate properly. (Changes in logic or function with aircraft configuration, altitude, or speed.)

(vii) Verify that the Mode S identification code and maximum airspeed are correct.

(viii) Verify that the windshear and GPWS warnings and TCAS II voice alerts are compatible. Also, verify that windshear warnings can be clearly understood when TCAS II and windshear voice announcements and GPWS simultaneously occur. If TCAS II windshear and GPWS aural warnings have been prioritized the alert priorities should be windshear, GPWS and then TCAS II.

Par 3 AC 20-131A 3/29/93 (2) Flight Tests.

(i) Proper operation of the traffic display should be verified by observing proximate traffic, at least one traffic advisory and at least one resolution advisory. Confirm that the appropriate aural alerts occur correctly with the traffic advisory and resolution advisory. The advisories may be generated by: (A) Planned encounters with an intruder aircraft operating a transponder with Mode C capability.

NOTE: Prior to any cooperative flight tests at any altitude involving the TCAS II equipped aircraft and another aircraft, both aircraft should be flown in close formation to assure matched altimetry readouts. These checks should be flown at the speeds and altitudes to be used for the tests.

(B) Encounters with an operating Mode C transponder installed at a fixed ground location which reports an appropriate test altitude.

{C) Encounters with aircraft targets of opportunity.

(D) The use of suitable test equipment, during ground tests.

(ii) During all phases of flight, determine if there is any mutual interference with any other aircraft system.

(iii) Evaluate TCAS II aural messages for acceptable volume and intelligibility during both low and high cockpit noise levels (idle descent at low speed and high power at VM ) with and without headsets, covering the outboard ear where appropriate. If the TCAS II TEST is used to simulate voice announcements, ensure that the audio level is not changed by use of the TEST function.

(iv) Evaluate the effective surveillance range of the traffic display, including target azimuth reasonableness and track stability. Use of a nontransport (low-speed) Mode C equipped aircraft as a target or a fixed transponder or suitable test equipment for these tests is permissible.

(v) Evaluate the Mode S transponder air-to-ground ATCRBS function against an appropriate ground facility.

{vi) Determine that any configuration discretes associated with the TCAS II logic including inhibits of climb RAs, operate properly unless previously demonstrated during ground tests. (Changes in logic or function with aircraft configuration, altitude, or speed.)

(vii) Evaluate TCAS II for noninterference during coupled Autopilot and Flight Director approaches to the lowest minimums approved for the aircraft.

Par 3 27 3/29/93 AC 20-131A (viii) Evaluate all selectable modes of the TCAS II to determine that they perform their intended function.

{ix) Reevaluate any previously installed aircraft systems that have required changes as a result of the TCAS II installation {e.g., EFIS, FD, PFD, ND, IVS!, interface, etc.)

h. Airplane Flight Manual Supplement (AFMS). The AFMS should provide the appropriate system limitations and procedures, and a comprehensive description of all normal modes of operation including what actions are expected by the flightcrew in each case. Appendix 1 provides an example of the elements and extent of detail that may be shown by a typical AFMS (specific performance data and procedures may vary with system design and aircraft type).

4. OPERATIONAL APPROVAL. Operational approval of TCAS II is addressed by AC 120-55.

Par 3

AC 20-131A 3/29/93 Appendix 1 APPENDIX 1 Descriptive material and procedures contained in this AFMS example may, when appropriate, be replaced by reference in the AFMS to the TCAS II equipment supplier's pilot's operating guide. However, the AFMS reference to this guide must be specific; i.e., date, revision level; and not openended, e.g., "or later revision"; unless the pilot's guide is specifically FAA approved. Also, the AFMS must define the specific configuration approved from the various options contained in the pilot's guide; e.g., which model control panel, whether the pilot-initiated self-test is available in flight, range features, TA vertical display features, etc.

AIRPLANE FLIGHT MANUAL SUPPLEMENT (Example) DESCRIPTION The TCAS II is an on-board collision avoidance and traffic situation display system with computer processing to identify and display intruding and threatening collision aircraft, and issue resolution advisories in the form of vertical maneuver guidance on the pilot and copilot's instantaneous vertical speed indicators (IVSI). From the transponder replies, TCAS II determines relative altitude, range, and bearing of any ATCRBS or Mode S equipped aircraft with altitude reporting. From this, TCAS II will determine the level of advisory using standardized algorithms. The TCAS II will resolve multiple aircraft encounters. ATCRBS equipped aircraft which only reply with Mode A information will not provide altitude information; therefore, TCAS II will not issue resolution advisories for these aircraft but can issue traffic advisories. The TCAS II will not detect aircraft without transponders.

The TCAS II installation consists of one TCAS II processor, one top-mounted directional antenna, one bottom-mounted blade (or directional antenna), one Mode S transponder with control panel and top and bottom antennas, one traffic advisory display with control panel (if not combined with the IVSI/RA indicators), two resolution advisory displays, one overhead speaker for voice messages, (caution/warning lights), and associated wiring.

The TCAS II provides two levels of advisories: If the traffic gets within 25 to 45 seconds, depending upon altitude, of projected Closest Point of Approach (CPA), it is then considered an intruder, and an aural and visual traffic advisory (TA) is issued. This level calls attention to what may develop into a collision threat using the traffic advisory display and the voice message, "TRAFFIC-TRAFFIC."

It permits mental and physical preparation for a possible maneuver to follow and assists the pilot in achieving visual acquisition of the intruding aircraft.

If the intruder gets within 20 to 35 seconds, depending upon altitude, of CPA, it is considered a threat, and an aural and visual resolution advisory (RA) is issued. This level provides a recommended vertical maneuver using modified IVSis and voice messages to provide adequate vertical separation from the threat aircraft or prevents initiation of a maneuver that would place the TCAS II aircraft in jeopardy.

AC 20-131A 3/29/93 Appendix 1 The TCAS II is considered a back-up system to the "SEE-AND-AVOID" concept and the ATC radar environment.

The TCAS II resolution advisories are annunciated by the following voice messages, as appropriate, along with the expected pilot response: 11 11 (A) CLIMB, CLIMB, CLIMB (Climb at the rate depicted by the green (fly to) arc on the IVSI.)

(B) "DESCEND, DESCEND, DESCEND" (Descend at the rate depicted by the green (fly to) arc.)

{C) "MONITOR VERTICAL SPEED-MONITOR VERTICAL SPEED" (Spoken only once if softening from a previous corrective advisory.) Assure that vertical speed is out of the illuminated IVSI red arc.

(D) "REDUCE CLIMB-REDUCE CLIMB" (Reduce vertical speed to a value within the illuminated green arc.)

(E) "CLEAR OF CONFLICT" (Range is increasing, and separation is adequate; expeditiously return to the applicable ATC clearance, unless otherwise directed by ATC.)

(F) "CLIMB, CROSSING CLIMB, CLIMB, CROSSING CLIMB" (Climb at the rate depicted by the green (fly to) arc on the IVSI.) Safe separation will best be achieved by climbing through the threat's flight path.

(G) "REDUCE DESCENT-REDUCE DESCENT" (Reduce vertical speed to a value within the illuminated green arc.)

(H) "DESCEND, CROSSING DESCEND, DESCEND, CROSSING DESCEND" (Descend at the rate depicted by the green (fly to) arc on the IVSI.) Safe separation will best be achieved by descending through the intruder's flight path.

The following voice messages annunciate enhanced TCAS II maneuvers when the initial RA does not provide sufficient vertical separation. The tone and inflection connote increased urgency.

(A) "INCREASE CLIMB, INCREASE CLIMB" (Climb at the rate depicted by the green (fly to) arc on the IVSI.) Received after "CLIMB" advisory, and indicates additional climb rate required to achieve safe vertical separation from a maneuvering threat aircraft.

(B) "INCREASE DESCENT, INCREASE DESCENT" (Descend at the rate depicted by the green (fly to) arc on the IVSI.) Received after "DESCEND" advisory, and indicate~ additional descent rate required to achieve safe vertical separation from a maneuvering threat aircraft.

(C) "CLIMB - CLIMB NOW, CLIMB - CLIMB NOW" (Climb at the rate depicted by the green (fly to) arc on the IVS!.) Received after a "DESCEND" resolution advisory and indicates a reversal in sense is required to achieve safe vertical separation from a maneuvering threat aircraft.

3/29/93 AC 20-131A Appendix 1 (D) DESCEND - DESCEND NOW, DESCEND - DESCEND NOW" (Descend at the rate depicted by the green (fly to) arc on the IVSI.)

Received after a "CLIMB" resolution advisory and indicates a reversal in sense is required to achieve safe vertical separation from a maneuvering threat aircraft.

AC 20-131A 3/29/93 Appendix 1 Figure 1: TCAS/Transponder Control Panel (Example).

Warning Light (Amber) Code Indicator ALT RPTG STBY XPDR TCAS/ TEST

(Q)

Transponder _J~--- TA

IOENT Function Selector TA/RA ATCXPDR TCAS XPDR

•

FAIL Code Selectors TCAS/Transponder Function Selector TEST Holding the TCAS/Transponder function selector in TEST for 2 to 3 seconds will activate the system test sequence. In the TEST position, maintenance messages may be read on the display. Discretion must be used when selecting TEST in flight, since both TCAS II and the Transponder will be inhibited for approximately 20 seconds. The function selector is spring loaded to STBY.

STBY Activates TCAS II and XPDR warmup cycles.

XPDR Transponder is on. TCAS II is in warmup cycle.

TA Transponder is on. Only the "TRAFFIC ADVISORY", or "TA", function of the TCAS 11 is on. No "RESOLUTION ADVISORIES" will be received in this position. The written warning "TA ONLY" will appear on the display, and the yellow "RA OFF" flag will be in view on both IVSJ's TA/RA Transponder is on. All TCAS II functions are on. No TCAS flags should be present on either IVSI.

XPDR Fail Indicates a transponder system failure when the transponder is on. Comes on Light (Red) during "TEST", but goes off after approximately 3 seconds if the transponder is OK.

Code Indicates code selected with the code selectors. Warning Light (Amber) Indicator Indicates both transponders are on.

IDENT Causes the word INDENT to flash in the aircraft data block on the ATC display.

ALTRPTG Provides automatic altitude reporting of ATC.

Code Select the transponder code. Left and right selectors consist of a large knob Selectors and a small knob. Each controls one digit of the code.

3/29/93 AC 20-131A Appendix 1 Figure 2: TCAS II - Traffic Display (Example).

20nm ,,\1T11 \\ N // ,_\33.A. 3 // ' V / ' / ' +00 ·~ / ....... 30 '11111 • 6 ....... _ -

. ~··

-03:~·-· "'·1· ·.

• • • • • •I• • • • ••••• ABOVE REL ALT

NORM@

@

fl BELOW RANGE Arrows indicate that the target is climbing t or descending i at a rate of at least 500 fpm.

Relative altitude in displayed in the proximity of the aircraft symbol in hundreds of feet. A"+" preceding the relative altitude indicates the target is above you, and a"-" indicates it is below you.

Ois1;2li:!yed Aictrnl! Symb2ls (Examples) Unfilled white diamond. Non-threatening traffic without altitude reporting. If

¢

altitude reporting, the altitude data will be displayed.

Solid white diamond. Proximity traffic 700 feet above. Non-threatening, altitude reporting traffic within 1200 feet vertically and 6nm horizontally. Aircraft without +07 altitude reporting will be assumed to be co-altitude and will be displayed as a solid diamond when within 6nm even though they may not be within 1200 feet vertically.

•

Solid yellow circle. "TA", 300 feet below, descending. At least 500 FPM.

•t

~03 Solid red square. "RA", level at your altitude.

+00

•

Ownship. Airplane symbol in white just below the center of CRT. On a dedicated display or when in the TFC Mode on a combination TCAS/AADAR Display.

~

This arc Is a repeater of the Captains compass. (Not required for a TCAS II (Compass Arc) Display).

(Range 3nm - Small ring with ticks at clock positions 5 NM - Large ring made of dots.

Rings) AC 20-131A 3/29/93 Appendix 1 Figure 2: TCAS II- Traffic Display (Example) (Con't).

REL ALT ABOVE ~RT NORM@ •

@

FL BELOW OFF MAX RANGE eadtl'li SwitQb BEL AL.ILEL SwilQI] Paddle switch is spring loaded to the center position. Display shows REL REL ALT ALT in hundreds of feet above (+)or below(-) your aircraft.

Momentary contact allows display of traffic flight levels, referenced to 29.92, FL for 15 seconds. Your FL is displayed in lower left corner. Three digits are shown, except for negative flight levels which are shown as -xxx The compass arc is always set at range selected by the range knob. Ranges RANGE of 3, 5, 1O or 20 nm are selected.

Controls brightness of the displays. BAT Knob Abg:,i:eL~g[rnlBilQW Swii,ti ABOVE Displays altitude reporting traffic from 2700 feet below to 9900 feet above.

NORM Displays altitude reporting traffic from 2700 feet below to 2700 feet above.

BELOW Displays altitude reporting traffic from 2700 feet above to 9900 feet below.

3/29/93 AC 20-131A Appendix 1 Figure 2: TCAS II - Traffic Display (Example) (Cont).

OFF-SCALE TRAFFIC ADVISORY In the event that TCAS II tracks an intruder that is outside the range of the display but has entered the Caution or Warning areas, one-half of the appropriate symbol will appear at the appropriate bearing at the edge of the display area. The symbol will appear in its proper color and have its data tag displayed, providing there is room. For example, a TA intruder with a high closure rate, and which is directly ahead and is 300 feet below your airplane will appear as an amber-filled half circle at the 12 o'clock position on the edge of the display area. The data tag "-03" will appear below the half symbol. If this intruder is above your altitude, the data tag is not visible. An off-scale RA intruder will appear as a red-filled half square with data tag, if possible.

NO BEARING ADVISORIES If and when TCAS II is unable to track the bearing of an intruder, the traffic advisory will appear in the lower center of the display just below the own-airplane symbol. The advisory will present appropriate color-coded traffic information. This phenomenon usually is caused either by temporary antenna shielding caused by steep bank angles or a failure in the TCAS II bearing antenna. Up to two lines of information can be displayed. TA 5.2-06t" for example means an intruder is creating a Traffic Advisory 5.2 nautical miles away, 600 feet below, and climbing in excess of 500 FPM. "RA 0.6 00" means resolution advisory traffic is 0.6 nautical miles away at the same altitude. TCAS II's ability to compute a Traffic or Resolution Advisory is NOT degraded by lack of bearing information.

AC 20-131A 3/29/93 Appendix l Figure 3: TCAS I/ Instantaneous Vertical Speed Indicator (Example) INSTANTANEOUS VERTICAL SPEED INDICATOR. Indicates vertical speed in feet per minute. The JVSI is a normal instantaneous vertical speed indicator, and the presence of the lights or the flags will not interfere with the ability of the needle to indicate vertical speeds.

RED/GREEN EYEBROW LIGHTS. Eyebrow lights are invisible until they illuminate as part of a TCAS II "RESOLUTION ADVISORY", or system ''TEST".

These lights indicate a vertical speed regime which will provide safe traffic separation. The green lights form a wider band than the red lights.

C

IVSI Status Window Flags BLACK. Normal operation.

T C A s AMBER FLAG. Indicates unusable TCAS II information.

T C A s WHITE "RA OFP' FLAG. Always displayed when TCAS/TRANSPONDER function selector is in STBY, XPDR, or TA. Will also be displayed with selector in RA/TA in "RAs" are inhibited and/or inoperative.

AC 20-131A 3/29/93 Appendix 1 Figure 4: TCAS II Examples - Preventive.

Red .iz...

Green ~ (a) Preventive {b) Preventive MONITOR VERTICAL SPEED.

MONITOR VERTICAL SPEED.

Note: This multi-aircraft encounter is the only preventive RA that displays a green arc.

VERTICAL -{c) Preventive (d) Preventive MONITOR VERTICAL SPEED.

MONITOR VER/CAL SPEED.

AC 20-131A 3/29/93 Appendix l Figure 5: TCAS II Examples - Corrective.

Red r Z...

Green ~ (a) Corrective (b) Corrective DESCEND.

CLIMB or CLIMB, CLIMB NOW.

(c) -Corrective (d) Corrective INCREASE DESCENT.

REDUCE CLIMB.

3/29/93 AC 20-131A Appendix 1 SECTION 1 - LIMITATIONS o Pilots are authorized to deviate from their current ATC clearance to the extent necessary to comply with a TCAS II resolution advisory (RA).

SECTION II - EMERGENCY PROCEDURES o No change from basic airplane flight manual.

SECTION III - PROCEDURES 1. TCAS II Flight Procedures: o Compliance with a TCAS II resolution advisory (RA) is necessary unless the pilot considers it unsafe to do so, or unless the pilot has better information about the cause of the RA and can maintain safe separation (e.g., visual acquisition of and safe separation from a nearby aircraft, obvious TCAS II system failure, etc.).

CAUTION Once a noncrossinq RA has been issued, safe operation could be compromised if current vertical speed is changed, except as necessary to comply with the RA. This is because TCAS 11-to TCAS II coordination may be in progress with the intruder airplane, and any change in vertical speed that does not comply with the RA may negate the effectiveness of the other airplane's compliance with its RA.

* * * * *******WARNING********** - Noncompliance with a crossing RA by one airplane may result in reduced vertical separation; therefore, safe horizontal separation must also be assured by visual means.

NOTE The consequences of not following an RA may result in additional RAs in which aural alert and visual annunciations may not agree with each other.

o Because of the limited number of inputs to TCAS II for airplane performance inhibits, in some instances where inhibiting RAs may be appropriate it is not possible to do so. In these cases, TCAS II may command maneuvers which may significantly reduce stall margins or result in stall warning. Therefore, the stall warning stick shaker must be respected when following an RA. Conditions where this may occur include: AC 20-131A 3/29/93 Appendix l - Bank angle in excess of 15 degrees.

- One engine inoperative.

- Abnormal configurations such as landing gear not retractable, etc.

- Leaving airplane in inappropriate configurations when climb RA occurs.

- Operation at airports outside of O' to 5,300' MSL or temperatures outside of ISA± 50°F (27.8°C).

- Speeds below normal operating speeds.

- Buffet margin less than 0.3g.

o The TCAS II RA algorithms are based on the pilot initiating the initial .25g incremental maneuver within approximately 5 seconds, and within approximately 2 1/2 seconds if an additional corrective RA increase or reverse is issued. (The reversal is based on a .Sg incremental maneuver.)

NOTE Evasive maneuvering must be limited to the minimum required to comply with the RA. Excessive responses to RAs are not desirable or appropriate because of , other potential traffic and ATC consequences. From level flight, proper response to an RA typically results in an overall altitude deviation of 300 to 500 feet in order to successfully resolve a traffic conflict.

Preventive advisories are also posted after a corrective advisory has been satisfied and the TCAS II airplane is projected to have adequate altitude separation. The corrective RA is said to soften, indicating a gradual return to the original flight path or clearance is allowed. As the corrective advisory softens to a preventive advisory, the green arc is removed, the magnitude of the red arc decreased and MONITOR VERTICAL SPEED is announced. The new preventive RA restricts the rate (vertical speed) the pilot may use in returning to the original flight path. The RA may soften several times before "CLEAR OF CONFLICT"; "MONITOR VERTICAL SPEED" will be announced only after the initial downgrading of the corrective RA. Utilizing the softening advisory will greatly reduce the ultimate altitude deviation caused by the original corrective resolution advisory.

o If a "CLIMB" RA is issued while in the landing configuration, initiate normal go-around procedure.

AC 20-131A 3/29/93 Appendix l NOTE Initiating go-around procedure for a "CLIMB" RA does not mandate a missed approach. It is intended to assure the airplane is properly configured for the expected maneuver. In most cases, the TCAS II event will be resolved with only minor deviation to the intended flight path, and sufficient time and altitude may exist to recover safely to the desired flight path.

o The pilot should not initiate evasive maneuvers using information from the traffic display only or on a traffic advisory (TA) only without visually sighting the traffic. These displays and advisories are intended only for assistance in visually locating the traffic and lack the flight path trends necessary for use in evasive maneuvering.

However, while climbing or descending, modest changes in vertical speed based on traffic display information is not considered evasive maneuvering.

o Following a TCAS II CLEAR OF CONFLICT" advisory, the pilot should expeditiously return to the applicable ATC clearance unless otherwise directed by ATC.

NOTE There can be a case where the threat aircraft track or altitude information is lost during an RA. In this case, the RA will terminate without a "CLEAR OF CONFLICT" annunciation.

2. TCAS II OPERATION: Pilot-Initiated TCAS II Self-Test: o The TCAS II should be tested using the pilot-initiated self-test feature during cockpit preparation. A successful test is indicated by .... (provide test results from particular TCAS II system) o Use of the self-test function in flight will inhibit TCAS II operation for up to 20 seconds depending upon the number of aircraft being tracked.

o The ATC transponder will not function during some portion of the self test sequence.

Ground Operation: o The TCAS II should not be selected out of STBY to TA/RA until just prior to takeoff.

o The TCAS II should be selected to STBY immediately after clearing runway following landing.

3/29/93 AC 20-131A Appendix 1 o TA Mode: o The TA position should only be used to preclude unnecessary RAs when intentionally operating near other aircraft such as to closely spaced parallel runways (less than 2500 feet apart).

o In TA mode, RAs will not be issued.

WX-ONLY Mode: o When WX-ONLY mode is selected, traffic information, traffic advisories, and resolution advisories are inhibited on the weather radar scope.

Therefore, this mode should be used only in the event TCAS interferes with weather information.

(This example is to show the kind of procedure to be developed.

Procedures will vary depending upon installation; e.g., pop-up display modes, PFD/ND implementation, etc.)

3. TCAS II System Characteristics: o CLIMB" RAs are inhibited with flaps greater than XX degrees.

o When below 1000 feet AGL and "CLIMB RAs are inhibited with flaps greater than XX degrees, the TCAS II will go into the TA only mode.

11 11 o INCREASE CLIMB RAs are inhibited with flaps greater than XX degrees.

o "DESCEND" RAs are inhibited below 1200 feet AGL while climbing and below 1000 feet AGL while descending.

o INCREASE DESCENT" RAs are inhibited below 1450 feet AGL.

o All RA and TA voice messages are inhibited below 600 feet AGL while climbing and below 400 feet AGL while descending.

o The TCAS II surveillance may not function at distances less than 900 feet.

o During windshear and/or GPWS warnings, TCAS II switches automatically into a TA only no-voice mode. In this mode, RAs are not issued, current RAs become TAs, and TCAS II aural annunciations are inhibited.

AC 20-131A 3/29/93 Appendix 1 4. TCAS II Abnormal Procedures: o RA OFF Flag in IVSI - Verify TCAS/transponder function selector is in TA/RA position.

11 11 - If TA/RA is selected and RA OFF flag is in view, then the pilot with the operable IVSI (flag not in view) should be the pi1 ot flying.

o AMBER FLAG in IVSI - Check XPDR FAIL light.

- If OFF select other altitude source.

- If ON select alternate ATCRBS transponder. (TCAS II will no longer be available.)

o XPOR FAIL Light Illuminated - Select alternate ATCRBS transponder. (TCAS II will no longer be av a i1 ab l e . ) (These examples are to show the kinds of abnormal procedures to be developed. Procedures will vary depending upon the installation; e.g., dual Mode S, etc.)

SECTION 4 - PERFORMANCE o No change from basic airplane flight manual.

15 (and 16) AC 20-131A 3/29/93 Appendix 2 Appendix 2 SUPPLEMENTAL INITIAL CERTIFICATION FLIGHT TESTS 1. Surveillance Flight Tests. The bench tests in Section 2.4 of the TCAS II MOPS, 00-185, are designed to verify TCAS II surveillance performance under carefully controlled conditions. A surveillance flight test should be performed to completely validate a TCAS II surveillance design.

a. A flight test under environmentally stressful conditions should be performed to provide the data for a complete TCAS II Mode C surveillance design validation. The environment includes the combined effects of multipath interference, synchronous garbling and fruit interference as a result of high aircraft density, and ground interrogator interference from multiple ground interrogators.

b. A flight test should be performed for each new TCAS II surveillance design, and whenever major modifications are made to the surveillance function of a previously certified TCAS II. Subject to agreement between the applicant and the certifying office, a major modification is defined as one that is expected to impact on the ability of TCAS II to meet the surveillance performance criteria of paragraph l.k. below. The tests should be accomplished with all certifiable antenna configurations unless the applicant can demonstrate that a worst-case configuration has been evaluated. Since the surveillance functions to be evaluated by this test are sufficiently independent of installation factors such as aircraft type and specific antenna location, the flight test can be carried out using a smaller non-carrier aircraft. The results of the test are only applicable for initial certification for each manufacturers system.

c. Flight testing should be accomplished in the Los Angeles basin area, particularly in the vicinity of the Long Beach and Santa Ana airports, since previous tests of TCAS II have shown that this area provides the stressful environment necessary for proper evaluation of TCAS II surveillance. Flight paths should include a representative mixture of the following conditions.

(1) Over-land flights at altitudes between 3000 and 6000 feet, (2) Over-water flights at altitudes between 3000 and 6000 feet for a duration that is at least 20% of the total required flight duration defined in l(iv) below, and (3) Approach and departure flights to Long Beach and Santa Ana airports.

d. The flight test should be conducted on weekends between 10:00 a.m. and 3:00 p.m. when the ground visibility is greater than 5 nmi with a ceiling of at least 10,000 feet to ensure the highest peak traffic densities. Another location may be proposed by the applicant and will be considered as a suitable AC 20-131A 3/29/93 Appendix 2 alternative to the Los Angeles area if the applicant can demonstrate that the TCAS II surveillance test was conducted in an average density of at least 0.1 transponder-equipped aircraft per sq. nmi and a peak density of at least 0.2 transponder-equipped aircraft per sq. nmi. Density is defined as the number of other transponder-equipped aircraft within 5 nmi of the TCAS II test aircraft divided by the area of a circle of 5 nmi radius. Eight real aircraft target tracks occurring simultaneously within 5 nmi of the TCAS II test aircraft is equivalent to a density of 0.1 transponder-equipped aircraft per sq. nmi. The alternative location should also contain a minimum of three FAA or military secondary surveillance radars located within 30 nmi of the TCAS II aircraft in order to provide an interference environment similar to the Los Angeles area.

e. Flight testing should be of sufficient duration to record at least 10,000 seconds of target track reports on targets-of-interest. The data should be accumulated during a continuous time period not exceeding 3 hours.

A target-of-interest is defined as any target-of-opportunity that exhibits the following characteristics.

(1) within a 5 nmi range of TCAS in the forward quadrant, (2) within a 3.5 nmi range of TCAS in the right and left quadrants, (3) within a 2 nmi range of TCAS in the aft quadrant, (4) within+/- 5 deg. elevation of TCAS, and (5) is altitude reporting and airborne.

f. The number of actual flight hours necessary to collect 10,000 track seconds of data depends on the aircraft density. For example, a one hour recording in the Los Angeles basin which has a demonstrated minimum average density of 0.1 aircraft per sq.nm would result in approximately 10,000 track seconds of data on targets-of-interest. It is expected that the applicant will have prior knowledge of the density conditions and will select the flight time necessary to record the appropriate amount of data.

g. The recorded data should include as a minimum all raw reply reports prior to any duplicate reply elimination, reply merging, reply correlation, etc., processed surveillance track reports that have been declared established, traffic and resolution advisories, internal processor clock, and time-of-day. Recorded flight data should be provided to the FAA to permit an independent assessment of surveillance performance in accordance with paragraph l.h. below. Details concerning the format and data types of the tape data to be provided should be coordinated with the FAA in a timely manner (i.e., 60 days or more in advance of the availability of the recorded flight data is recommended).

h. The applicant should perform at least the following specific post flight data analyses: (1) Identify all recorded surveillance target track reports that are established and that satisfy the criteria for a target-of-interest.

AC 20-131A 3/29/93 Appendix 2 (2) Identify those established target-of-interest track reports that are associated with real aircraft.

(3) Determine the total number of aircraft-seconds associated with real aircraft and the total number of true track-seconds (i.e., those update intervals in which an established surveillance track report was either coasted or updated with a valid reply) associated with real aircraft.

(4) Determine the TCAS II surveillance track probability as the ratio of the total number of true track-seconds associated with real aircraft to the total number of aircraft-seconds associated with real aircraft. · (5) Identify those established target-of-interest track reports that are not associated with real aircraft.

(6) Determine the total number of track-seconds that are not associated with real aircraft. These are classified as false track-seconds.

(7) Determine the TCAS false track probability as the ratio of the total number of false track-seconds to the total number of aircraft-seconds associated with real aircraft.

i. The data should also be examined to determine whether any single event such as crossing targets, multipath induced image targets, the inability to maintain track at closest-point-of-approach, or a synchronously garbled target dominates the false track rate or the rate at which real targets are dropped.

If the false tracks or dropped tracks are due mostly to one type of interference mechanism or geometric condition, it could indicate a design deficiency in this area even though the overall surveillance track probability and false track ratio is acceptable. If this condition exists, the applicant should present this information and provide an evaluation summary that indicates an acceptable design.

j. An effective method of evaluating TCAS II data to determine overall surveillance statistics has been developed as a result of the initial design effort associated with TCAS II. This method uses high-resolution plots of range, altitude and bearing reply data verses time to first identify those reply reports that are associated with real aircraft. To accomplish this, the reply reports generated by TCAS II are examined visually in an attempt to recognize patterns in the reply data stream that represent real aircraft. To be effective, this technique requires experience in the analysis of TCAS II surveillance data and enough knowledge of the physical aspects of aircraft flight and of the mechanisms that cause false replies to be able to determine, with reasonable probability, whether a reply is false or real. Each of the identified real aircraft replies are then associated with a real aircraft by AC 20-131A 3/29/93 Appendix 2 manually and visually tracing through the replies to form real aircraft plots.

The real aircraft plot starts at the first observance of a real reply in the aircraft reply stream and terminates at the last observed real reply in this stream. An overlay of the manually-derived real aircraft plots on a similarly scaled plot of TCAS II processed tracks will identify the TCAS II track reports associated with real aircraft.

k. The applicant should present to the certification office sufficient data in the form of reply plots, surveillance track plots, printouts, tabulations etc. to substantiate that the Mode C surveillance performance on targets-of-interest, measured as a result of the surveillance flight test, meets or exceeds the following acceptance criteria: (1) TCAS surveillance probability for targets-of-interest >95% (2) TCAS false track rate for target-of-interest< 1.2% The applicant should also present an evaluation summary on any single dominant failure event as discussed in 1.h. above.

2. TCAS to TCAS Coordination Encounters. Planned TCAS II to TCAS II coordination encounters should be performed in order to evaluate the reliability of the overall air to air coordination data link for installed TCAS II and Mode S transponder equipments. The encounters should be flown at 3000 feet over calm water in order to increase the likelihood of multipath and in configurations that maximize the times during which a resolution advisory is present and coordination is taking place. Examples of such encounters are tail chases and side-by-side flights. If the lateral separation necessary for multipath is larger than the separation that maintains the RA, the aircraft can periodically turn in towards each other during side-by-side flights in order to continually initiate RAs. The encounters should be flown so as to involve a reasonable mix of the four quadrants of the TCAS II and transponder antennas. Each TCAS II aircraft should have sufficient recording capability to record the replies received in response to coordination interrogations .

The recorded data should include at least 2000 TCAS coordination scans. The criteria for acceptable performance is as follows: a. The probability of a single scan coordination link dropout should be no greater than 0.1%.

b. There should be no coordination link dropouts that exceed one scan in duration.

3/29/93 AC 20-131A Appendix 3 APPENDIX 3 TRANSPONDER TESTS Using a suitable calibrated transponder test set, conduct the following tests: TEST DESCRIPTION O. Mode Test Identifies modes of operation. Interrogations are made in Modes A, C, and S (uplink format 11) to determine which modes the transponder replies to.

These are the modes tested during the Auto Test sequence.

1. Reply Delay Interrogates with valid modes and verifies Reply delay minus Range delay (average of best 8 out of 13 replies) equals: 128.00 us (±0,25 us) for Mode S.

3.00 us (±0.50 us) for ATCRBS.

2. Reply Jitter Interrogates with valid modes and verifies, using best 8 out of 13 replies. Reply Jitter (changes In Reply Delay) is less than or equal to: 0.05 us for Mode S 0.06 us for Intermode (All-Call) 0.10 us for ATCRBS.

3. ATCRBS Reply Interrogates with ATCRBS (Modes A and C) interrogations and verifies: to spacing is 20.3 us (±0.10 us). F F 1 2 and Fa pulse width between the 0.5 amplitude point on the leading F and trailing edge i s 0.45 us (±0,10 us) .

4. SLS level Interrogates with valid ATCRBS Interrogations including P pulse.

Interrogations are conducted with P level at -9 dB and then again at 0 dB. Test verifies: Transponder does not reply when level is at O dB (UUT is P suppressed) .

Transponder replies when P level is at -9 dB (UUT is not suppressed) .

AC 20-131A 3/29/93 Appendix 3 5. ATCRBS Only All-Call Interrogates with an ATCRBS only All-Call and verifies: If Mode Sis valid, no reply is received from a Mode S transponder.

If no Mode S, reply is received from an ATCRBS transponder.

6. Mode S All-Call Interrogates with the ATCRBS (mode A)/Mode S All-Call. Address received in downlink format (OF) 11 is then used in an uplink formate (UF} 4 interrogation to solicit a DF4 reply. The address received is decoded and compared with the address sent.

7. Invalid Mode S Address Interrogates with Mode S interrogations using two addresses different from the address determined by the Mode S All-Call, UFll. Test verifies no reply is received. Addresses used are one greater and 256 greater than the correct address.

8. SPR On/Off Interrogates with a Mode S interrogation with the Synchronous Phase Reversal (SPR) on, verifying correct reply is received. Then same interrogation is sent again with the SPR off, verifying no reply is received.

9. Mode S UFO Interrogates with Mode S uplink format O (Short air to air surveillance, ACAS) verifying reply is received that has correct altitude (compared with Mode C altitude), address (compared with Mode Test address) and format.

10. Mode S UF4 Interrogates with Mode S uplink format 4 (Surveillance, altitude request), verifying reply is received that has correct altitude (compared with Mode C altitude), address (compared with Mode Test address) and format.

11. Mode S UF5 Interrogates with Mode S uplink format 5 (Surveillance, identity request) verifying reply is received that has correct identity (compared with Mode A identity), address (compared with Mode Test address) and format.

AC 20-131A 3/29/93 Appendix 3 12. Mode S UFII Interrogates with Mode S uplink format 11, verifying reply is received that has correct address (compared with Mode Test address) and format.

13. Mode S UF16 Interrogates with Mode S uplink format 16 (Long air to air surveillance, ACAS), verifying reply, if received, has correct altitude (compared with the Mode C altitude), address (compared with Mode Test address) and format. No reply to UF16 does not fail Mode Sin Auto Test.

14. Mode S UF20 Interrogates with Mode S uplink format 20 (Comm A, altitude request) verifying reply received has correct altitude {compared with Mode C altitude), address {compared with Mode Test address) and format. No reply to UF21 does not fail Mode Sin Auto Test.

15. Mode S UF21 Interrogates with Mode S uplink format 21 (Comm A, identity request) verifying reply received has correct identity {compared with Mode A identity), address (compared with Mode Test address) and format. No reply to UF21 does not fail Mode Sin Auto Test.

16. Squitter Verifies squitters are being received from the UUT every 0.8 to 2.4 seconds.

17. Frequency Verifies frequency of transponder is 1090 MHz{± MHz). Frequency is displayed in the Auto Test screen.

18. Diversity Verifies diversity isolation (power level difference between UUT "On" antenna squitters and "Off" antenna squitters) is greater than or equal to 20 dB. Diversity isolation is displayed in Auto Test screen.

NOTE: To insure~ 20 dB dynamic range, test must be run within 50 feet (15.24 meters) of UUT antenna being tested.

19. MTL Difference Verifies Receiver Sensitivity (MTL) to Mode A interrogations equals MTL to Mode C interrogations (±1.0 dB).

AC 20-131A 3/29/93 A[?pendix 3 20. Power Verifies transponder's: Peak output power (ERP) is greater than 48.5 dBm and less than 57.0 dBm.

Receiver sensitivity (MTL) is -73.0 dBm (±4,0 dBm).

"U.S.Govt:irnment Printing Office: 1993- 715-000/66026