Certification of Transport Airplane Mechanical Systems

3/14/2000 AC 25-22 Section 2. INSTRUMENTS: INSTALLATION 52. SECTION 25.1325 - STATIC PRESSURE SYSTEMS.

a. Rule Text.

(a) Each instrument with static air case connections must be vented to the outside atmosphere through an appropriate piping system.

(b) Each static port must be designed and located in such manner that the static pressure system performance is least affected by airflow variation, or by moisture or other foreign matter, and that the correlation between air pressure in the static pressure system and true ambient atmospheric static pressure is not changed when the airplane is exposed to the continuous and intermittent maximum icing conditions defined in Appendix C of this Part.

(c) The design and installation of the static pressure system must be such that- (1) Positive drainage of moisture is provided; chafing of the tubing and excessive distortion or restriction at bends in the tubing is avoided; and the materials used are durable, suitable for the purpose intended, and protected against corrosion; and (2) It is airtight except for the port into the atmosphere. A proof test must be conducted to demonstrate the integrity of the static pressure system in the following manner: (i) Unpressurized airplanes. Evacuate the static pressure system to a pressure differential of approximately 1 inch of mercury or to a reading on the altimeter, 1,000 feet above the airplane elevation at the time of the test. Without additional pumping for a period of 1 minute, the loss of indicated altitude must not exceed 100 feet on the altimeter.

(ii) Pressurized airplanes. Evacuate the static pressure system until a pressure differential equivalent to the maximum cabin pressure differential for which the airplane is type certificated is achieved. Without additional pumping for a period of 1 minute, the loss of indicated altitude must not exceed 2 percent of the equivalent altitude of the maximum cabin differential pressure or 100 feet, whichever is greater.

(d) Each pressure altimeter must be approved and must be calibrated to indicate pressure altitude in a standard atmosphere, with a minimum practicable calibration error when the corresponding static pressures are applied.

(e) Each system must be designed and installed so that the error in indicated pressure altitude, at sea level, with a standard atmosphere, excluding instrument calibration error, does not result in an error of more than +/- 30 feet per 100 knots speed for the appropriate configuration in the speed range between 1.3 Vso with flaps extended and 1.8 Vs1 with flaps retracted. However, the error need not be less than +/- 30 feet.

3/14/2000 AC 25-22 (f) If an altimeter system is fitted with a device that provides corrections to the altimeter indication, the device must be designed and installed in such manner that it can be bypassed when it malfunctions, unless an alternate altimeter system is provided. Each correction device must be fitted with a means for indicating the occurrence of reasonably probable malfunctions, including power failure, to the flight crew. The indicating means must be effective for any cockpit lighting condition likely to occur.

(g) Except as provided in paragraph (h) of this section, if the static pressure system incorporates both a primary and an alternate static pressure source, the means for selecting one or the other source must be designed so that- (1) When either source is selected, the other is blocked off; and (2) Both sources cannot be blocked off simultaneously.

(h) For unpressurized airplanes, paragraph (g)(1) of this section does not apply if it can be demonstrated that the static pressure system calibration, when either static pressure source is selected, is not changed by the other static pressure source being open or blocked.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-5, 30 FR 8261, Jun. 29, 1965; Amdt. 25-12, 32 FR 7587, May 24, 1967; Amdt. 25- 41, 42 FR 36970, Jul. 18, 1977] b. Intent of Rule. This rule provides minimum design and certification requirements for static pressure systems to ensure proper static system operation in varying operating conditions.

c. Background. Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the Civil Air Regulations (CAR). Many of the requirements in § 4b.612(b) of the CAR were carried over essentially unchanged to § 25.1325 of 14 CFR.

(1) Amendment 25-5 (June 29, 1965) added requirements for (1) operation in icing conditions and (2) devices that provide corrections to the altimeter indication.

(2) Amendment 25-12 (May 24, 1967) added requirements for static system proof testing for pressurized and unpressurized airplanes.

(3) Amendment 25-41 (July 18, 1977) added standards for static pressure systems, which incorporate the ability to select one or the other of primary and alternate static systems.

d. Policy/Compliance Methods. For policy and guidance on compliance with this requirement, refer to Advisory Circular (AC) 25-XX, Electrical Systems Handbook.

e. References. None.

3/14/2000 AC 25-22 Section 3. SAFETY EQUIPMENT 53. SECTION 25.1419 ICE PROTECTION.

a. Rule Text.

If certification with ice protection provisions is desired, the airplane must be able to safely operate in the continuous maximum and intermittent maximum icing conditions of appendix C. To establish that the airplane can operate within the continuous maximum and intermittent maximum conditions of appendix C: (a) An analysis must be performed to establish that the ice protection for the various components of the airplane is adequate, taking into account the various airplane operational configurations; and (b) To verify the ice protection analysis, to check for icing anomalies, and to demonstrate that the ice protection system and components are effective, the airplane or its components must be flight tested in the various operational configurations, in measured natural atmospheric icing conditions and, as found necessary, by one or more of the following means: (1) Laboratory dry air or simulated icing tests, or a combination of both, of the components or models of the components.

(2) Flight dry air tests of the ice protection system as a whole, or of its individual components.

(3) Flight tests of the airplane or its components in measured simulated icing conditions.

(c) Caution information, such as an amber caution light or equivalent, must be provided to alert the flightcrew when the anti-ice or de-ice system is not functioning normally.

(d) For turbine engine powered airplanes, the ice protection provisions of this section are considered to be applicable primarily to the airframe. For the powerplant installation, certain additional provisions of Subpart E of this Part may be found applicable.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-23, 35 FR 5680, Apr. 8, 1970; Amdt. 25-72, 55 FR 29785, Jul. 20, 1990] b. Intent of Rule . This rule provides standards for certification of an airplane with ice protection provisions. Certification for flight in icing conditions is optional at the discretion of the applicant. If the airplane is not certificated for flight in icing condition, appropriate limitations shall be placed in the type certificate data sheet and the airplane flight manual.

c. Background . Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the Civil Air Regulations (CAR). Many of the provisions in section 4b.640 of the CAR were carried over with minor word changes to § 25.1419 of 14 CFR. However, the intent of the CAR 4b.640 was unchanged.

3/14/2000 AC 25-22 Amendment 25-23 revised paragraph (c) to require flight tests in measured natural atmospheric icing conditions. Prior to Amendment 25-23 flight tests in measured natural atmospheric icing conditions were optional.

(1) Amendment 25-23 (April 8, 1970) added the requirements for flight testing in natural icing conditions contained in § 25.1419(c).

(2) Amendment 25-72 (July 20, 1990) rearranged the sub-paragraphs and inserted a new paragraph (c), which requires caution information when the anti-ice or de-ice system is not functioning normally. Prior to this amendment, a means to determine that a pneumatic de-icing boot system was working normally was required by § 25.1416. Section 25.1416 was removed to allow for the concept of the "dark cockpit.” (The term “dark cockpit” is descriptive language that refers to the absence of annunciation lights in the cockpit unless a system is operating abnormally.)

d. Policy/Compliance Methods . For guidance on compliance with this requirement, refer to the preamble of this rule and AC 20-73 and AC 25.1419-1.

e. References. The addresses for ordering the latest revision of advisory circulars, and other referenced documents listed below can be found in the Appendix to this AC.

AC 20-73, Aircraft Ice Protection.

AC 23.1419-2, Certification of Part 23 Airplanes for Flight in Icing Conditions.

AC 25.1419-1, Certification of Transport Category Airplanes for Flight in Icing Conditions.

Report No. DOT/FAA/CT-88/8-1 - Aircraft Icing Handbook (three volumes) FAA Technical Report ADS-4 - Engineering summary of Airframe Icing Technical Data, December 1963. (Although most of the information contained in this report is still valid, some is outdated, and more usable information is now available through recent research and experience and is included in the Aircraft Icing Handbook.)

54 - 58. [RESERVED] 3/14/2000 AC 25-22 Section 4. MISCELLANEOUS EQUIPMENT 59. SECTION 25.1433 - VACUUM SYSTEMS.

a. Rule Text.

There must be means, in addition to the normal pressure relief, to automatically relieve the pressure in the discharge lines from the vacuum air pump when the delivery temperature of the air becomes unsafe.

[Amdt. 25-72, 55 FR 29785, Jul. 20, 1990] b. Intent of Rule. This rule provides minimum design and certification requirements for vacuum systems, specifically to require automatic pressure relief in the presence of high delivery air temperatures.

c. Background. Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the Civil Air Regulations (CAR). The requirements in section 4b.658 of the CAR were carried over essentially unchanged to § 25.1433 of 14 CFR.

(1) Amendment 25-72 (July 20, 1990) moved §§ 25.1433(b) and 25.1443(c), which dealt with fire protection for vacuum air systems, to § 25.869, Fire protection: Systems.

d. Policy/Compliance Methods. There is no existing written policy or guidance related to this subject in our files.

e. References . None.

60. SECTION 25.1435 - HYDRAULIC SYSTEMS.

a. Rule Text.

(a) Design.

(1) Each element of the hydraulic system must be designed to withstand, without deformation that would prevent it from performing its intended function, the design operating pressure loads in combination with limit structural loads which may be imposed.

(2) Each element of the hydraulic system must be able to withstand, without rupture, the design operating pressure loads multiplied by a factor of 1.5 in combination with ultimate structural loads that can reasonably occur simultaneously. Design operating pressure is maximum normal operating pressure, excluding transient pressure.

3/14/2000 AC 25-22 (b) Tests and analysis.

(1) A complete hydraulic system must be static tested to show that it can withstand 1.5 times the design operating pressure without a deformation of any part of the system that would prevent it from performing its intended function. Clearance between structural members and hydraulic system elements must be adequate and there must be no permanent detrimental deformation. For the purpose of this test, the pressure relief valve may be made inoperable to permit application of the required pressure.

(2) Compliance with 25.1309 for hydraulic systems must be shown by functional tests, endurance tests, and analyses. The entire system, or appropriate subsystems, must be tested in an airplane or in a mockup installation to determine proper performance and proper relation to other aircraft systems. The functional tests must include simulation of hydraulic system failure conditions. Endurance tests must simulate the repeated complete flights that could be expected to occur in service. Elements which fail during the tests must be modified in order to have the design deficiency corrected and, where necessary, must be sufficiently retested. Simulation of operating and environmental conditions must be completed on elements and appropriate portions of the hydraulic system to the extent necessary to evaluate the environmental effects. Compliance with 25.1309 must take into account the following: (i) Static and dynamic loads including flight, ground, pilot, hydrostatic, inertial and thermally induced loads, and combinations thereof.

(ii) Motion, vibration, pressure transients, and fatigue.

(iii) Abrasion, corrosion, and erosion.

(iv) Fluid and material compatibility.

(v) Leakage and wear.

(c) Fire protection. Each hydraulic system using flammable hydraulic fluid must meet the applicable requirements of 25.863, 25.1183, 25.1185, and 25.1189.

[Amdt. 25-13, 32 FR 9154, Jun. 28, 1967, as amended by Amdt. 25-41, 42 FR 36971, Jul. 18, 1977; Amdt. 25-72, 55 FR 29786, Jul. 20, 1990] b. Intent of Rule. The intent of this rule is to provide minimum design, performance, and safety requirements for transport category airplane hydraulic systems addressing the following aspects of component design and qualification, subsystem/system design, and system integration: (1) Design operating loads in combination with limit and ultimate structural loads.

(2) Pressure transients and cyclic pressures.

(3) Environmental conditions.

(4) Fatigue and endurance life.

(5) Single and multiple failure modes.

3/14/2000 AC 25-22 (6) Indication and warning.

(7) Installation and support.

(8) Pump/engine interface.

(9) Fire protection.

(10) Continued safe flight and landing .

c. Background. Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the Civil Air Regulations (CAR). Sections 4b.653, 4b.654, and 4b.655 respectively became §§ 25.1435(a), 25.1435(b), and 25.1435(c) of 14 CFR for hydraulic systems. Since then, § 25.1435 has been revised under Amendment 25-13, Amendment 25-41, and Amendment 25-72 to make the regulations more comprehensive and to delete redundancies.

(1) Amendment 25-13 (June 28, 1967) prescribed more comprehensive design and test requirements by requiring (1) cockpit indication of system fluid quantity, (2) a means to prevent harmful or hazardous concentrations of the fluid or vapors in the crew or passenger compartments during flight due to hydraulic fluid leakage/release, and (3) compliance with § 25.1309 by functional tests, endurance tests, and analysis of the entire system or appropriate subsystems tested in an airplane or in a mockup installation to determine proper performance and proper relation to other aircraft systems.

(a) Regarding compliance with § 25.1435(b)(2), the preamble to the final rule states in part that, "the FAA agrees that the proposed environmental testing of the assembled system is not necessary in order to achieve a reasonable and effective testing program for improving hydraulic system reliability." The final rule was changed to allow applicants to meet endurance test requirements by performing endurance testing on components as long as the test program was representative of the airplane installation and environment.

(b) Applicants have shown compliance to the endurance testing requirements of § 25.1435 by conducting endurance tests on components or subassemblies using fixtures that represent the airplane installation and environmental conditions. The FAA normally accepts endurance test programs that vary hydraulic fluid temperature during endurance testing. The other environmental conditions are usually tested independent of the endurance test program.

3/14/2000 AC 25-22 The regulation does not specify the number of repeated cycles to meet endurance test requirements. As a minimum, the applicant must show that the reliability of components will meet the airplane system reliability requirements of § 25.1309.

(2) Amendment 25-23 (April 8, 1970) expanded § 25.1435(a)(4) to require means to ensure that no pressure will exceed a safe limit above design operating pressure by specifying pressure variation tolerances of +/- 10% on the pump discharge pressures and an upper limit of 125% of the design operating pressure for transients. These tolerances were based on in-service experience with such systems.

(3) Amendment 25-41 (July 18, 1977) clarified under § 25.1435(a)(2) that the pressure and quantity indication requirement was applicable to systems performing a function that is essential for continued safe flight and landing, or requiring corrective crew action when a system malfunction has occurred. It also recognized that means other than gages (e.g., warning lights) were an acceptable means of compliance. Sections 25.1435(a)(7) and 25.1435(a)(8) were added to allow certain transient pressures to exceed prescribed limits under (a)(4)(ii), provided the resulting fatigue strength was accounted for, and to require pump design such that loss of fluid condition could not create a hazard preventing continued safe flight and landing.

(4) Amendment 25-72 (July 20, 1990). Prior to this amendment, § 25.1435(b) was labeled "Tests," and contained references to a hydraulic system proof test, which was needed in order to comply with § 25.1309. Under Amendment 25-72, the general requirements of the old §§ 25.1435(a)(2) through 25.1435(a)(8), relative to indication, system pressures, transients, volumetric changes, pump discharge pressure limits, ripple damping devices, vibration, abrasion, corrosion, mechanical damage, inertia loads, hazardous vapors, relative motion, differential vibration, transient pressures, fatigue strength and loss of fluid to the pumps, were consolidated under a general listing as "Tests and Analyses" in the new § 25.1435(b)(2).

(5) Exemptions . In October 1993, pursuant to the authority contained in §§ 313(a) and 601(c) of the Federal Aviation Act of 1958, an applicant was granted an exemption (refer to exemption 5758A) from § 25.1435(b)(1) of Title 14, Code of Federal Regulations (14 CFR) to the extent necessary to permit type certification of a new airplane by testing of the complete hydraulic system at the system relief pressure, but not less than 3400 psig, in lieu of 1.5 times the design operating pressure (4500 psig). Additional similar exemptions have been granted (Refer to Exemptions 6086, 6504, and 6577).

3/14/2000 AC 25-22 (6) Harmonization . This regulation is the subject of a Federal Aviation Regulations/Joint Aviation Requirements (FAR/JAR) harmonization effort under the Aviation Rulemaking Advisory Committee (ARAC). The ARAC working group has recommended revisions to § 25.1435 and a new Advisory Circular (AC) 25.1435-1. The harmonized rule will reflect the exemptions granted, see (5) above. The notice of proposed rulemaking (NPRM 96-6) and accompanying proposed AC 25.1435-1, were published in the Federal Register on July 3, 1996 (61 FR 35056) and public comments were invited. The final rule is at the FAA headquarters for a regulatory evaluation. The final rule and AC are expected to be adopted in 2000.

d. Policy/Compliance Methods. For guidance on compliance with this requirement, refer to the preamble of this rule and the following information.

(1) Hydraulic Fluid Contamination. The following was extracted from an FAA letter to the National Transportation Safety Board (NTSB), dated June 29, 1998, and related correspondence. The NTSB accepted the FAA-Industry (Society of Automotive Engineers Committee A-6) task force resolution concerning the NTSB safety recommendation, A-96-116.

(a) Background. Following the crash of the USAir flight 427, a Boeing 737-300, on September 8, 1994, an NTSB investigation team found hydraulic fluid with a high particulate count in the main rudder power control unit (PCU). While the effect of contaminated hydraulic fluid on the different aircraft systems was not known at that time, it was examined as a potential factor. In October 1996, the NTSB made safety recommendation, A-96-116, which recommended that the FAA define and implement standards for in-service hydraulic fluid cleanliness and sampling intervals for all transport-category aircraft.

(b) Discussion. An April 1995, FAA study concluded that the existing standard, NAS 1638, was adequate for classifying the particulate contamination levels for aircraft hydraulic fluid. At the FAA's request, an industry task force formed by the Society of Automotive Engineers (SAE) Committee A-6 studied the fluid contamination issues. The industry task force concluded that (i) flight control servoactuators had demonstrated operation at contamination levels up to NAS 1638 class 17 and higher and, (ii) an in-service limit of NAS 1638 class 9 prescribed by the majority of current airframe manufacturers was conservative, adequate, and the maximum recommended limit. The task force also studied chemical contamination effects and provided in-service limits for fluid properties such as specific gravity, moisture content, viscosity, and chlorine content.

(c) Chemical Sensitivity. Actuation systems are insensitive to chemical contamination within normal in-service operational limits (see tabulation below). Gross contamination with other fluids is prohibited.

3/14/2000 AC 25-22 Chemical Quality Recommendations for In-Service Hydraulic Fluid Analysis Limit Reason Appearance No cloudiness or phase Particulate and/or chemical separation or contamination precipitation Moisture 1.0 percent maximum Corrosion, fluid stability (acidity), low temperature pumpability Neutralization number 1.5 mg KOH/gm Corrosion, deposit formation maximum Kinematic viscosity @ 6.0 - 12.5cs Lubricity 100ºF/38ºC Chlorine contamination* 200 ppm maximum Fluid purity, erosion * This limitation is in addition to the amount already contained in the base stock.

(d) Sensitivity Methods. The task force recognized that the inconsistencies in the existing hydraulic fluid sampling procedures gave wide variations in the measured levels of particulate contamination. As a result, an Aerospace Recommended Practice ARP-5376, "Methods, Locations and Criteria for System Sampling and Measuring the Solid Particle Contamination of Hydraulic Fluids," was developed and published in September 1998.

(e) Sampling. The fluid sampling interval requirement for particulate contamination check is the same as the current one for checking chemical contamination.

Typical fluid sampling intervals used by airlines are on-condition, C-check, and 2C-check. In addition, manufacturers recommend fluid sampling when a suspected hydraulic contamination may exist (for example, due to or indicated by excessive component wear or deterioration).

(f) In summary. The FAA has identified an existing industry standard, NAS 1638, that defines fluid cleanliness levels as Classes 00 to 12; has defined NAS 1638 class 9, as the in- service limit, verified that the manufacturers already recommend these limits in their maintenance manuals including a sampling interval, and helped develop an SAE ARP document for sampling and testing techniques. The intent of the safety recommendation has been met and no regulatory corrective action is deemed necessary.

(2) Certification of Hydraulic Lines for Temporary Repairs. The following was extracted from an FAA letter dated April 23, 1992, which addresses certification of hydraulic lines for use as temporary repairs.

(a) It is not clear from the applicant's letter whether the hydraulic tubing assemblies being discussed are rigid or flexible, but it is assumed that the discussion involves various lengths of flexible hydraulic hose assemblies which can be joined together to replace 3/14/2000 AC 25-22 rigid or flexible hydraulic lines that have become unserviceable. There is an FAA Technical Standard Order (TSO) which provides minimum airworthiness requirements for hydraulic hose assemblies intended for use on transport category airplanes. Technical Standard Order TSO- C75, Hydraulic Hose Assemblies, and the accompanying Federal Aviation Standard should be considered. It should be noted that while the TSO provides an authorization for manufacturing a part that meets certain standards, it does not automatically approve the part for a specific installation.

(b) Section 43.13(a) requires that repairs must be accomplished in accordance with the manufacturers' maintenance manuals. However, air carriers are supposed to follow their Air Carrier Manual approved under part 121.

(c) The only mechanism available for certification of these repair systems by a manufacturer other than the type certificate holder would be a Supplemental Type Certificate (STC). An STC, issued for each installation on every model of airplane on which the applicant desired approval, would be a daunting task. Major airframe manufacturers, because they have all the pertinent data regarding design parameters for the hydraulic systems on their airplanes, can issue appropriate instructions in their maintenance manuals for installation of temporary repairs.

Airlines should use the manufacturer's manuals per § 43.13(a).

(d) One of the ways a manufacturer, other than the type certificate holder who wishes to manufacture parts for a certificated airplane, can apply for a Parts Manufacturing Authorization (PMA) is to show that the parts it makes are identical to those produced by the original manufacturer. Unless the applicant has original drawings complete with all necessary standards and specifications, it is difficult to show identicality. The cognizant FAA Manufacturing Inspection District Office can provide insight into the appropriate PMA application procedures, reference Order 8110.42A.

(3) Use of Hydraulic Lines for Temporary Repairs. The following was extracted from an FAA memorandum dated January 25, 1988, which addresses the use of flexible hydraulic hoses as temporary repairs for unserviceable hydraulic tubing.

(a) The use of flexible hydraulic hoses as temporary repairs for unserviceable hydraulic tubing has been commonplace on transport category airplanes for a number of years.

The lack of adverse service history indicates that this practice can be a viable method of repair, when used with the proper cautions. Strictly speaking, such substitution of hoses for rigid tubing would cause the airplane to be not in compliance with its type design; however, the provisions of Part 43 allow repairs and alterations to be made, provided the work is done in accordance with the methods, techniques, and practices in the current manufacturer's maintenance manual. With respect to multiple repairs, the FAA has concluded that they would be acceptable, provided that each one is individually performed in accordance with an approved procedure, and, collectively, the repairs will not interfere with each other or with any structure, or with the operation or performance of any system on the airplane.

3/14/2000 AC 25-22 (b) The key issue is the length of time that these temporary repairs may be allowed to exist on the airplane. Only by limiting the exposure can the repair be considered to be a safe alternative to the original design, much in the same manner that the Minimum Equipment List allows operation of the airplane for a short time with certain items of equipment inoperative.

Since a temporary repair would not have been evaluated and certificated in the same manner as the original system, it would not be proper to allow the repair to become, in any way, a permanent part of the type design. It has been suggested by one manufacturer that these repairs be replaced at the next "C" check, which in some cases may be a year in the future. The FAA has concluded that this much time is unwarranted, and may seriously compromise the safety of the repair. An interval of 300 to 350 hours would, in most cases, allow for the ordering and delivery of any needed parts and the scheduling of the airplane for restoration of the system to the original configuration. Also, limiting the time in this manner will reduce the problem of multiple repairs on the system. Any time limit would be largely arbitrary, but this figure, which represents approximately a month of operations, appears to be a good compromise between the economic interests of the operators, and the need for a short exposure to the temporary repair.

(4) Hydraulic System Certification Philosophy. The following was extracted from an FAA letter dated March 5, 1982, which addresses guidance concerning compliance with § 25.1435(b)(2), 14 CFR.

(a) The FAA has not been requested to accept endurance and reliability data based solely on flight test. This is because it is impractical, within a given certification time frame, to conduct the number of test cycles required to comply with § 25.1435(b)(2). The FAA would have no objection to using flight test data in addition to simulated functional endurance and reliability data, provided the manufacturer establishes that the flights are representative of expected service cycles.

(b) It is normal practice, for certification purposes, to comply with the requirements of § 25.1435(b)(2) by the use of simulators such as an "iron bird." The simulators are intended to be representative of the aircraft systems. Mounting brackets, hydraulic and electrical system flight controls, and control surfaces are all the same as the actual airplane. For practical purposes, simulation may be broken into functional subsystems, i.e., wing, rudder, gear, etc. Deviations from actual simulation have been allowed where the deviation will not interfere with the intent of establishing endurance and reliability. Deviation cases have to be ruled on in a case by case basis.

(c) The FAA would not accept compliance with § 25.1435(b)(2) based on only vendor component tests and flight tests. Functional tests and endurance tests, either using an airplane or mock-up (iron bird, simulator) at the system or subsystem level, are required.

Functional tests are required prior to first flight test.

(d) The manufacturer will develop load data through analysis, wind tunnel data, flight test experience, and/or any combination of these (spoilers and slots require flight test data, § 25.459). This load data is submitted to the FAA in the form of a loads document. The loads document is usually approved by FAA designated engineering representatives (DER) and 3/14/2000 AC 25-22 submitted to the FAA for a spot check review when and where it is considered necessary. Flight test load verification is not required when the methods used in determining those loading conditions are shown to be reliable (§ 25.301(b)). Most manufacturers go beyond FAA requirements and check the loads with strain gauges during flight tests.

(e) The airframe manufacturer (type design applicant) identifies the loading spectrum (amplitude and cycles) for the hydraulic systems based on the loads document and expected service. The FAA will be involved only indirectly in most cases, through the loads DER’s.

(f) The manufacturer subjects components and systems or the aircraft to the selected load/cycle spectrum in demonstrating compliance with the endurance requirements of § 25.1435(b)(2). Normally, vendor testing will be used for verification of the components for endurance as well as other requirements, such as environmental qualifications, fatigue, etc. The airframe manufacturer's simulator (iron bird) or simulators will be used for endurance tests and functional tests. The qualification reports documenting these tests are reviewed by FAA DER’s and approved or submitted to the FAA with a recommendation for approval. This option is designated by the FAA.

(5) Interpretation of § 25.1435(a)(4) of 14 CFR. The following was extracted from an FAA memorandum dated September 14, 1978, which addresses interpretation of § 25.1435(a)(4), Amendment 25-41.

(a) Section 25.1435(a)(4)(i) states: "There must be a means to keep hydraulic system pressures within +/- 10 percent of the pressure at the discharge of the pump outlet or the transient pressure dampening device, if provided."

(b) This rule was originally established to cover pump ripple pressure variations.

It can be seen that, under extreme system loading (high flow) conditions, the pump average discharge pressure can decrease as much as 25 percent. Apparently, the system pressure tolerance of +/- 10 percent mentioned above would then apply to this reduced pump average discharge pressure, decreased due to high flow conditions.

(c) Section 25.1435(a)(4)(ii) states: "Except as provided in Paragraph (a)(7) of this section, system pressures will not exceed 125 percent of the design operating pressure, excluding pressure at the pump outlet or dampening device. Design operating pressure is defined as the maximum steady operating pressure."

(d) The FAA has determined that Paragraph (4)(i) covers pressure variations due to pump ripple and high flow conditions while Paragraph (4)(ii) covers variations due to pressure transients. Note the use of "pump average discharge pressure" in (4)(i) and "design operating pressure" in (4)(ii).

3/14/2000 AC 25-22 e. References. The addresses for ordering the latest revision of advisory circulars, technical standard orders, and other referenced documents listed below can be found in the Appendix to this AC.

AC 25.1309-1A - System Design and Analysis.

AC 120-42A - Extended Range Operation with Two Engine Airplanes.

AC 20-128 - Design Considerations for Minimizing Hazards Caused by Uncontained Turbine Engine and Auxiliary Power Unit Rotor and Fan Blade Failures.

TSO-C47 - Pressure Instruments-Fuel, Oil, and Hydraulic.

TSO-C75 - Hydraulic Hose Assemblies.

SAE AS-595B - Civil Type Aircraft and Variable Delivery Hydraulic Pump.

SAE ARP-763 - Accumulators, Ground, Hydropneumatic Pressure.

SAE AIR-4150 - Inspection of In-Service Airborne Accumulators.

SAE AIR-1047C - A Guide for Selection of Quick Disconnect Couplings for Aerospace Fluid Systems.

SAE ARP-1709 - Coupling Assembly, Hydraulic Self Sealing, Quick Disconnect.

SAE AIR-786A - Elastomer Compatibility Considerations Relative to O-Ring and Sealant Selection.

SAE AS-1241B - Fire Resistant Phosphate Ester Hydraulic Fluid for Aircraft.

SAE AIR-1116 - Fluid Properties.

SAE ARP-1084 - Hydraulic External Leakage for In-service Components.

SAE AIR-1362 - Physical Properties of Hydraulic Fluids.

SAE ARP-1832 - Color Identification for O-Ring Seals.

SAE AIR-737E - Hydraulic and Pneumatic Specifications and Standards.

SAE ARP-994 - Design of Tubing Installations for Aerospace Fluid Power Systems.

SAE AIR-4003 - Turbine Engine Containment.

SAE AIR-1083B - Airborne Hydraulic and Control System Survivability for Military Aircraft.

SAE AIR-1899 - Aircraft Hydraulic System Characteristics.

SAE AIR-1918 - Comparison of Hydraulic System Cleanliness Procedures and Requirements for Ten Aerospace Companies.

SAE ARP-24B - Determination of Hydraulic Pressure Drop.

SAE ARP-490E - Electro-Hydraulic Servovalves.

SAE ARP-1280A - Aerospace Application Guide for Hydraulic Power Transfer Units.

SAE ARP-1281B - Actuators: Aircraft Flight Controls, Power Operated, Hydraulic, General Specification.

SAE ARP-4379 - Accumulator, Hydraulic, Cylindrical Aircraft.

SAE ARP-4752 - Aerospace - Design and Installation of Commercial Transport Aircraft Hydraulic Systems.

FAA Order 8000.40D - Maintenance of Pressure Cylinders in Use as Aircraft Equipment.

61. SECTION 25.1438 PRESSURIZATION AND PNEUMATIC SYSTEMS.

3/14/2000 AC 25-22 a. Rule Text.

(a) Pressurization system elements must be burst pressure tested to 2.0 times, and proof pressure tested to 1.5 times, the maximum normal operating pressure.

(b) Pneumatic system elements must be burst pressure tested to 3.0 times, and proof pressure tested to 1.5 times, the maximum normal operating pressure.

(c) An analysis, or a combination of analysis and test, may be substituted for any test required by paragraph (a) or (b) of this section if the Administrator finds it equivalent to the required test.

[Amdt. 25-41, 42 FR 36971, Jul. 18, 1977] b. Intent of Rule. This rule provides standards for the tests that must be conducted to demonstrate that pneumatic and pressurization ducting and components will not fail in normal operation. The rule was originated to address the pneumatic system, from the engine bleed port(s) to the pressure regulating and/or shut-off valve, and the pressurization system, which comprises all ducting and components of the air distribution system downstream of the above- mentioned valve.

c. Background. This subject was not addressed in either part 4b of the Civil Air Regulations (CAR) or part 25 of Title 14, Code of Federal Regulations (14 CFR) when it was originally codified. The reason for proposing the new standards was: "Components (such as ducts and couplings) of pressurization and pneumatic systems have failed at an unacceptable rate in service. The proposed standards for these components have been effective in preventing design deficiencies in the past."

(1) Harmonization. This regulation is the subject of a Federal Aviation Regulations/Joint Aviation Requirements (FAR/JAR) harmonization effort under the Aviation Rulemaking Advisory Committee (ARAC). The ARAC working group may recommend a revised § 25.1438/JAR 25.1438 and JAR 25X1436, and may develop an accompanying new advisory circular.

d. Policy/Compliance Methods. For guidance on compliance with this requirement, refer to the preamble of this rule and the following information.

(1) Pneumatic Versus Pressurization System Identification: The following policy was extracted from an FAA letter dated October 19, 1993, in response to questions regarding § 24.1438 and the difference between pressurization system elements and pneumatic system elements.

(a) Section 25.1438(a) states: "Pressurization system elements must be burst pressure tested to 2.0 times, and proof pressure tested to 1.5 times, the maximum normal operating pressure," and § 25.1438(b) states: "Pneumatic system elements must be burst pressure tested to 3.0 times, and proof pressure tested to 1.5 times, the maximum normal operating pressure."

3/14/2000 AC 25-22 (b) The FAA considers the pneumatic system to include all air supply elements from the bleed port on the engine to the pressure regulating and shutoff valve. Pressurization system elements are all other elements in the air distribution system.

(c) The burst pressure test requirement for pneumatic and pressure system elements has been used to demonstrate that high pressure air will be contained within the system or element. The element is not required to function during or after the burst pressure test, but pressurized air must be contained within the element or system. The proof pressure test is used to demonstrate that pneumatic and pressure system elements can function after a higher than normal pressure (1.5 times the maximum normal operating pressure) is introduced into the element or system.

(d) Section 25.1438(c) allows the applicant to use an analysis as a method of showing compliance to the burst and proof pressure test requirement in §§ 25.1438(a) & (b).

e. References . None.

62. SECTION 25.1439 PROTECTIVE BREATHING EQUIPMENT.

a. Rule Text.

(a) If there is a class A, B, or E cargo compartment, protective breathing equipment must be installed for the use of appropriate crewmembers. In addition, protective breathing equipment must be installed in each isolated separate compartment in the airplane, including upper and lower lobe galleys, in which crewmember occupancy is permitted during flight for the maximum number of crewmembers expected to be in the area during any operation.

(b) For protective breathing equipment required by paragraph (a) of this section or by any operating rule of this chapter, the following apply: (1) The equipment must be designed to protect the flight crew from smoke, carbon dioxide, and other harmful gases while on flight deck duty and while combating fires in cargo compartments.

(2) The equipment must include- (i) Masks covering the eyes, nose, and mouth; or (ii) Masks covering the nose and mouth, plus accessory equipment to cover the eyes.

(3) The equipment, while in use, must allow the flight crew to use the radio equipment and to communicate with each other, while at their assigned duty stations.

(4) The part of the equipment protecting the eyes may not cause any appreciable adverse effect on vision and must allow corrective glasses to be worn.

(5) The equipment must supply protective oxygen of 15 minutes duration per crewmember at a pressure altitude of 8,000 feet with a respiratory minute volume of 30 liters per minute BTPD. If a demand oxygen system is used, a supply of 300 3/14/2000 AC 25-22 o F. and 760 mm. Hg. pressure is considered to be of liters of free oxygen at 70 15-minute duration at the prescribed altitude and minute volume. If a continuous flow protective breathing system is used (including a mask with a standard rebreather bag) a flow rate of 60 liters per minute at 8,000 feet (45 liters per o minute at sea level) and a supply of 600 liters of free oxygen at 70 F. and 760 mm. Hg. pressure is considered to be of 15-minute duration at the prescribed altitude and minute volume. BTPD refers to body temperature conditions (that is, o 37 C., at ambient pressure, dry).

(6) The equipment must meet the requirements of paragraphs (b) and (c) of § 25.1441.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-38, 41 FR 55468, Dec. 20, 1976] b. Intent of Rule . The intent of this rule is for the protective breathing equipment (PBE) provisions to protect crewmembers from the effects of hazardous gasses and smoke, either while on flight deck duty or combating a fire, if there is a class A, B, or E cargo compartment or an isolated compartment in which crewmembers are permitted access during flight. This rule does not address passenger protective breathing equipment. Section 25.1439(b) contains wording that requires PBE if required "by any operating rule of this chapter. . . " There are two technical standard orders (TSO) providing standards for approval of PBE. Technical Standard Order, TSO-C99, provides standards for use by flight crewmembers while on flight deck duty. Per the TSO, the PBE must provide eye protection in addition to preventing inspiration of smoke/fumes.

The flightcrew supplemental oxygen system can provide this via a full face mask with a setting that provides a positive pressure differential between the mask and ambient pressure in the cockpit to prevent smoke/fumes from entering the mask. If the crew supplemental oxygen system is equipped with an oro-nasal type mask (covers nose and mouth only) rather than a full mask, the eye protection can be achieved via a pair of goggles located within easy reach. This type of equipment is intended for use by flight crewmembers at their stations for a prolonged length of time. It would not generally be acceptable for firefighting since the crewmember's ability to reach the fire would be limited by the amount of extra oxygen tubing provided by the stationary system. TSO-C116 provides standards for PBE to be used by crewmembers while locating and fighting a fire. Per the TSO, it also provides head and shoulder protection from "drippings," and typically provides protective oxygen for 15 minutes. This type of PBE would not be suitable for use by the flightcrew at their stations.

c. Background . Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the Civil Air Regulations (CAR). Many of the requirements in section 4b.651 of the CAR were carried over essentially unchanged to § 25.1439 of 14 CFR. Part 25 standards state that PBE must be installed “if there is a class A, B, or E cargo compartment.” (1) Amendment 25-38 (December 20, 1976) added the requirement that PBE be installed in each isolated separate compartment, including upper and lower lobe galleys, in which crewmember occupancy is permitted during flight for the maximum number of crewmembers expected to be in the area.

3/14/2000 AC 25-22 d. Policy/Compliance Methods . For guidance on compliance with this requirement, refer to the preamble of this rule and the following information.

(1) Protective Breathing Equipment Usage When Approved Under TSO-C99 and TSO-C116. The following policy, extracted from an FAA letter dated May 13, 1993, clarifies compliance with the requirements of § 25.1439 using equipment of the "smoke hood" variety approved under TSO-C116.

(a) The FAA letter clarified whether smoke hood type PBE would be acceptable for meeting the requirements of § 25.1439. The FAA is not aware of any smoke hood type PBE being approved as meeting the requirements of § 25.1439(b)(3), which relates to the use of radio equipment by the flight crew. The FAA would consider a smoke hood type PBE if compliance with § 25.1439(b)(3) is demonstrated.

(b) The FAA letter also clarified that a finding of equivalent safety would be required if an applicant wishes to use a “breathable gas,” in lieu of providing oxygen as specified in § 25.1439(b)(5).

(c) The FAA letter also addressed § 25.1439(b)(6), which specifies that there must be a means provided to allow the crew to readily determine the quantity of oxygen available.

PBE approved in accordance with TSO-C116 may or may not have such features. The FAA does not grant exemptions for the cases where the PBE is used by the flight crewmembers while on flight deck duty. When the PBE is intended for use in locating and combating a fire, the FAA will approve equipment which, when the container is intact, is considered to have a full charge of oxygen or, for chemical oxygen generation, the canister has not been activated. The container is "tamper evident" and the crewmember can readily determine that the equipment is fully charged and ready for use. This PBE would not be suitable for approval in meeting the flight crewmember requirements addressed by § 25.1439.

(d) The letter provided an FAA position on PBE requirements for the first and second observers. The FAA treats the first observer and second observer differently. The first observer must have the same protection, i.e., the same equipment, as the flight crewmembers.

The second observer may be supplied with oxygen equipment suitable for passengers. Again, the first observer must have the same protection (including the ability to communicate on the crewmember interphone) that is provided for the flight crewmembers; the second observer may be provided with passenger-type oxygen equipment.

(2) Protective Breathing Equipment Serviceability. The following policy was extracted from an FAA memorandum dated March 9, 1990, to provide guidance regarding the approval of PBE which met the requirements of § 121.337 and FAA Action Notice 8150.2.

(a) Section 121.337 was revised in 1987 and, in part, incorporated the intent of § 25.1439 and expanded on those requirements. This revision resulted in a new type of PBE for 3/14/2000 AC 25-22 use by any crewmember while combating fires on board an airplane. The approval basis was contained in Action Notice A8150.2, dated September 1, 1987, in advance of TSO-C116.

(b) Section 121.337 clearly intends that any crewmember PBE be immediately ready to perform its intended function during an emergency. In fact, the rule requires that each certificate holder's operations manual designate at least one crewmember to check that each PBE unit is properly stowed and serviceable prior to the first-flight of the day.

(c) The approval basis (TSO-C116) for crewmember PBE requires that the equipment has a means to indicate the serviceability of the unit in its stowed condition. Some manufacturers of the crewmember PBE designs approved by the FAA have elected to use a vacuum sealed envelope as a means of protecting the PBE, and the loss of vacuum has been accepted as an indicator that the PBE is not serviceable.

(d) One manufacturer recommended that when the vacuum is lost the PBE need not be replaced immediately, since ambient moisture will not deactivate the potassium superoxide in the atmosphere regenerating system for a number of days. This may well be correct, but it is only one consideration. Since the cause of the loss of vacuum will most likely not be known to the crewmember making the inspection, and the extent of damage to the PBE itself may not be evident, the PBE should be considered not serviceable. Another consideration is that a design, which includes a protective envelope material that can readily be damaged, may not perform its intended function.

(e) Based on the above information, ACO's should ensure that the manufacturer submits operating, installation, and maintenance instructions with limitations, warnings, or cautions for FAA approval. The information being provided the end user should be in accord with the safety intent of § 121.337.

(3) Protective Breathing Equipment on the Flight Deck. The following policy was extracted from an FAA memorandum dated December 19, 1988, and provided additional guidance on protective breathing equipment for use on the flight deck.

(a) Section 121.337 specifies provisions for protective breathing equipment with the airplane both pressurized and unpressurized. Section 25.1439 makes no such distinction.

The part 25 rule specifies that protective breathing equipment must be installed as part of the type design if certain types of cargo compartments or isolated, occupied compartments are installed. If these specified compartments are not installed on the airplane, then protective breathing equipment is not required as part of the type design.

(b) For an unpressurized part 25 airplane certified without these specified compartments and operated under Part 121, however, the decision to require protective breathing equipment should be based on an evaluation of the hazard. Section 25.831(d) states that if accumulation of hazardous quantities of smoke in the cockpit area is reasonably probable, smoke evacuation must be readily accomplished, starting with full pressurization and without depressurizing beyond safe limits. This capability must be demonstrated for certification under 3/14/2000 AC 25-22 any normal operating condition, including unpressurized flight; and smoke clearance must be accomplished within three minutes (Advisory Circular 25-9A, or latest revision, explains a test procedure in detail). Section 25.831 also specifies limits for carbon dioxide and carbon monoxide, but does not define unsafe levels of any other gas, vapor, or fume. Since the toxicity of smoke or fumes generated by a fire is unknown, the FAA has required that there be essentially no penetration of smoke into an occupied compartment. Since it is likely that smoke of unknown composition would be generated within the cockpit, and may be present for up to three minutes prior to its removal, installation of protective breathing equipment would be appropriate, unless the applicant can show that it is not necessary.

(4) Definition of Terms Used in § 25.1439. The following policy was extracted from an FAA memorandum dated February 26, 1985, that responded to a request for the meaning of the words "isolated separate compartment," as used in § 25.1439.

(a) The preamble to the Notice 75-10, item 2-91, read: "The proposal would require protective breathing equipment for crewmembers expected in isolated areas." Item 2-91 was based on the First Biennial Airworthiness Review of 1974-1975, proposal No. 812 that read: "(a) Protective breathing equipment must be installed for each required crewmember in isolated separate compartments, such as upper or lower lobe galleys, in which occupancy is permitted during flight."

(b) Based on the intent of the background quoted above, the FAA concluded that the crew rest area, not being part of the main cabin, is similar in location to a lower lobe galley and, therefore, is an isolated separate compartment. However, as crewmembers are not required in the crew rest area except to fight a fire, only sufficient protective breathing equipment need be provided in the crew rest area for that function. It is also noted that, as long as the lavatory is located next to the flight deck door, there is little chance that a crewmember may be isolated there by a fire. The crew lavatory need not be considered isolated.

3/14/2000 AC 25-22 e. References. The address for ordering the latest revision of the technical standard orders listed below can be found in the Appendix to this AC.

TSO-C99, Protective Breathing Equipment.

TSO-C116, Crewmember Protective Breathing Equipment.

63. SECTION 25.1441 - OXYGEN EQUIPMENT AND SUPPLY.

a. Rule Text .

(a) If certification with supplemental oxygen equipment is requested, the equipment must meet the requirements of this section and 25.1443 through 25.1453.

(b) The oxygen system must be free from hazards in itself, in its method of operation, and in its effect upon other components.

(c) There must be a means to allow the crew to readily determine, during flight, the quantity of oxygen available in each source of supply.

(d) The oxygen flow rate and the oxygen equipment for airplanes for which certification for operation above 40,000 feet is requested must be approved.

b. Intent of Rule . This rule is intended to ensure that, if supplemental oxygen equipment is to be included in the type design of an airplane, the oxygen dispensing equipment will protect passengers and crewmembers from the effects of hypoxia. Many of the oxygen system requirements are addressed in §§ 25.1443 through 25.1453, which are incorporated by reference.

c. Background . Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the Civil Air Regulations (CAR). The requirements in section 4b.651(a) of the CAR for oxygen systems were carried over essentially unchanged to § 25.1441 of 14 CFR.

d. Policy/Compliance Methods . For guidance on compliance with this requirement, refer to the preamble of this rule and the following information.

(1) Compliance with §§ 25.1309(c) and 25.1441(c). The following policy was extracted from an FAA memorandum dated February 23, 1994, and provides an FAA position on the requirements of § 25.1309(c) as related to a Passenger Gaseous Oxygen System that could erroneously indicate oxygen is available.

(a) Section 25.1309(c) states: "Warning information must be provided to alert the crew to unsafe system operating conditions, and to enable them to take appropriate corrective action. Systems, controls, and associated monitoring and warning means must be designed to minimize crew errors which could create additional hazards." Section 25.1441(c) states: "There must be a means to allow the crew to readily determine, during flight, the quantity of oxygen 3/14/2000 AC 25-22 available in each source of supply." An applicant proposed a passenger oxygen system where the means is provided through an indication available to the flight crew of the oxygen pressure in the oxygen system plumbing between the oxygen bottles and the flow control valves. There are several bottles, each with its own shut-off valve, manifolded together. If, during maintenance, the valves on all the bottles are turned off and left in that position, but the tubing between the bottles and the flow control valve is not disturbed, the pressure in the lines will continue to read the same value that would be measured if the bottle valves were open. Therefore, the reading in the cockpit will erroneously indicate that oxygen is available. A concern arises because the flightcrew will dispatch believing that passenger oxygen is available. If a depressurization event occurs, the passengers will not have supplemental oxygen available as required by the regulations. Passengers will be at risk during the emergency descent due to lack of available oxygen.

(b) The non-availability of passenger supplemental oxygen presents a hazard if a depressurization occurs. In most cases of depressurization, the flightcrew executes an emergency descent and the cabin altitude does not exceed safe limits. This is not, of course, always the case; loss of consciousness or more serious injury, and even death, could occur for some passengers if oxygen is not available after depressurization. There is usually no risk to the airplane itself because the flightcrew has a separate oxygen system and, assuming they act properly, the airplane will quickly descend to a safe altitude and proceed to the nearest airport.

For these reasons, passenger supplemental oxygen being unavailable is not an immediate threat to continued safe flight and landing. However, one of the design principles suggested in Advisory Circular (AC) 25.1309-1A for ensuring fail-safe design concepts is error tolerance to allow for possible adverse effects of foreseeable errors during the airplane's design, test, manufacture, operation, and maintenance. This system does not appear to adhere to that principle. In addition, the AC also notes that a warning is required for a failure which makes it necessary for the flightcrew to make an unscheduled landing to reduce exposure to a more hazardous failure condition that would result from subsequent failures or operational conditions, or if the failure must be corrected before a subsequent flight. In conclusion, a warning to the flightcrew for non-availability of passenger oxygen is the type of warning addressed in the first sentence of § 25.1309(c).

(c) The system installed to provide the crew with an indication of the amount of oxygen available does not appear to meet the requirement contained in the second sentence of § 25.1309(c). The false indication of oxygen pressure resulting from the oxygen trapped between the shut off valves and the flow control valves will continue indefinitely, leading to dispatch after dispatch with no means to detect the problem until either a depressurization occurs or some maintenance action leads to the discovery that the oxygen bottle valves are closed. If the crew were aware of the situation, they would not dispatch or, if the problem were discovered in flight, they would immediately divert to an alternate airport. Clearly, the indication system is not designed to minimize crew errors that could create additional hazards.

(d) It is not acceptable to use probability of the event (depressurization) to demonstrate the probability of the unsafe condition (decompression combined with passenger oxygen being unavailable). In this case, the unsafe condition is not catastrophic so it is not 3/14/2000 AC 25-22 necessary to show that it is extremely improbable. As noted in the earlier advisory material regarding System Design Analysis (AC 25.1309-1), "If a quantitative analysis is used to help show compliance with Federal Aviation Regulations for equipment which is installed and required only for a specific operating condition for which the airplane is thereby approved, credit may not be taken for the fact that the operating condition does not always exist." While this note does not appear in AC 25.1309-1A, the basic philosophy has not changed.

(2) Guidance, Availability of Flightcrew Oxygen. The following policy was extracted from an FAA memorandum dated May 11, 1992, in response to an FAA Safety Recommendation regarding annunciation that oxygen is available for use by the flightcrew when in actuality there is no oxygen available.

(a) On a recent twin-engine transport airplane flight, the crew elected to divert after the first officer donned his oxygen mask and discovered he had no oxygen available. After landing, the crew oxygen bottle valve was found turned to the closed position. Prior to the flight, maintenance had started to replace the bottle due to low pressure, and the valve located at the bottle was turned off. When the bottle pressure was found to be acceptable, the bottle was reinstalled but the valve was left turned off and safety wired in that position. The maintenance crew checked the bottle pressure on the airplane Engine Indication and Crew Alerting System (EICAS) status page and because the EICAS displays the pressure in the line downstream of the valve, the residual pressure in the line resulted in a displayed pressure that was within limits.

(b) The existing system on this airplane measures the oxygen pressure in the line to the flightcrew regulator. If the shutoff valve at the pressure bottle is shut off, there is sufficient pressure remaining in the line to indicate a pressure high enough for dispatch. Even when the crew checks the masks, only a small amount of oxygen is allowed to escape, and there are currently no means to determine that the valve is off. Further, the oxygen pressure, and therefore the quantity, is observable on EICAS only when the crew selects the status page.

(c) The FAA determined that this is unacceptable for the following reasons: 1 . Section 25.1441(c) requires that the crew be able to determine the quantity of oxygen available . When the valve is in the "OFF" position, the oxygen is not available , but the indication on EICAS (the residual pressure in the line) is that oxygen is available if needed.

The pressure measurement gives information about quantity only when the valve is open. If the valve is inadvertently left closed, the information provided is misleading.

2 . Section 25.1309(c) states: “Warning information must be provided to alert the crew to unsafe system operating conditions, and to enable them to take appropriate corrective action. Systems, controls, and associated monitoring and warning means must be designed to minimize crew errors which could create additional hazards.” It is clear that the existing design gives misleading information to the flightcrew, which could lead them into an unsafe operation. If depressurization takes place at a significant altitude, and oxygen is not available to the crew, an unsafe condition exists.

3/14/2000 AC 25-22 3 . Further, § 121.333(c)(4) states: "Before the takeoff of a flight, each flight crewmember shall personally preflight his oxygen equipment to insure that the oxygen mask is functioning, fitted properly, and connected to appropriate supply terminals, and that the oxygen supply and pressure are adequate for use." In theory, adherence to this rule should ensure that the oxygen supply is available.

(d) In order for the scenario discussed above to be a hazard, four separate events would have to occur: 1 There would have to be maintenance performed on the airplane oxygen system that required the valve, located on the oxygen bottle, to be turned off for some reason.

The airplane maintenance manual contains both visual and operational checks to ensure that the oxygen valve is open and the pressure is adequate. These procedures were not followed in the case of interest because the bottle was never removed.

2 The flightcrew check of their oxygen equipment would have to fail to indicate that oxygen is not available. This is possible with the present preflight procedure, but the procedure is being changed.

3 A decompression would have to occur that required the use of oxygen by the flightcrew.

4 Event 3 would have to occur before the flightcrew had attempted to use supplemental oxygen (which would demonstrate no oxygen available) or checked the EICAS Status Page, which would indicate low oxygen pressure. In either case, airline procedures and Federal Aviation Regulations require that the crew divert to fix the problem.

(e) The manufacturer of the airplane involved in the incident which prompted this memorandum is changing their operational procedures, which are used by the airlines for their Operations Manuals, to describe an acceptable procedure to verify that adequate oxygen is available at the pilots mask. This procedure involves two separate flow tests (Normal and 100 percent), followed by a pressure check on EICAS. As all flightcrew masks must be tested (at least two on any transport category airplane), there will be ample tests and pressure checks to identify a problem prior to dispatch. Based on the above considerations, the FAA has determined an adequate level of safety is achieved through the existing and proposed procedures with the certificated design. However, this mechanization is not considered to meet the requirements of § 25.1309(c).

(f) Flightcrew oxygen systems should be reviewed to ensure that on future certification programs, a system design that can lead to misinformation is not allowed.

(3) Oxygen Installation for Medical Use. The following policy was extracted from an FAA facsimile message dated January 3, 1991, that was written in response to a request for policy relative to the installation of shutoff valves, pressure relief devices and overboard vent lines installed on oxygen bottles for medical use.

3/14/2000 AC 25-22 (a) There is no current written FAA policy relative to the installation of manifolded oxygen systems other than Civil Aeronautics Manual (CAM) 4b.651-1. CAM 4b.651-1 recommends that low pressure oxygen systems have a pressure relief device to prevent over pressurization during the filling operation.

(b) Department of Transportation (DOT) regulation (49 CFR, § 173.34(d)) requires that all pressure cylinders be provided with a safety device (a rupture disc) to prevent explosion of the bottle if the bottle is subjected to over-pressure or excessive heat. The pressure relief device may be installed on the bottle or on the valve of the bottle (on the pressure side of the valve).

(c) To meet the requirements of § 25.1441(b) and § 1451(c) (note: Amendment 25-72 deleted § 25.1451 and moved the requirements to § 25.869(c)), aircraft manufacturers have been installing oxygen systems that have a pressure relief that vents through a vent line, normally stainless steel, to the outside of the aircraft. A colored blowout plug is installed at the end of the vent line on the surface of the aircraft to indicate if the rupture disc has blown.

(d) The inquiring FAA office indicated that they may have approved single high pressure bottle (air ambulance) installations that do not have the overboard drain line. Further, these single bottle installations are filled off the airplane. There may be other installations without a vent line because there doesn't appear to be a written policy on this subject.

(e) To determine if a vent line is needed to comply with §§ 25.1441(b) and § 25.869(c)(3) (formerly 25.1451(c)), the consequences of the pressure relief device venting the total contents of the bottle or bottles (if manifolded together) into the compartment should be considered, i.e., overpressurizing the compartment; exposure to grease, flammable fluids and ignition sources.

(f) All the installations, which the FAA is aware of, have a high pressure shutoff valve located on the bottle to isolate the bottle from the oxygen system. On a manifolded system, these valves normally are lockwired in the open position. However, the bottle shutoff valve is downstream of the pressure relief device in order that the pressure relief device will protect the bottle from exploding if the bottle is isolated (valve shut) from the system and is exposed to heat or over- pressurization.

(g) The FAA is not aware of any objection to having a common high pressure manifold without the bottle shutoff valves as long as there is a manifold system shutoff valve and a pressure relief device between the bottles and the shutoff valve.

(h) One objection might be exposing the airplane and maintenance personnel to the hazards of a fully pressurized vented bottle or bottles if someone tries to remove a bottle from the system. The total system has to be depressurized before the bottle can be removed as opposed to the manifold system where each bottle shutoff valve can be closed, and an individual bottle with its valve can be removed.

3/14/2000 AC 25-22 (i) In general, industry practice has been to separate and isolate the oxygen system from sources of ignition. Ignition sources include pumps, motors, and electrical equipment associated with the medical installations as well as the aircraft equipment. Further, the manufacturers normally install a pressure relief device with an overboard vent line.

e. Reference . The address for ordering the document listed below can be found in the Appendix to this AC.

The Society of Automotive Engineers (SAE) has aerospace committees that prepare documents reflecting industry standards and practices. The SAE A-10 Committee, Aircraft Oxygen Equipment, has prepared a handbook, “1992 SAE Aircraft Oxygen Equipment Handbook,” containing all Aerospace Standards, Aerospace Recommended Practices, and Aerospace Information Reports related to oxygen equipment published by SAE. While not regulatory in nature, this handbook contains information that may be of interest to an applicant.

64. SECTION 25.1443 - MINIMUM MASS FLOW OF SUPPLEMENTAL OXYGEN.

a. Rule Text .

(a) If continuous flow equipment is installed for use by flight crewmembers, the minimum mass flow of supplemental oxygen required for each crewmember may not be less than the flow required to maintain, during inspiration, a mean tracheal oxygen partial pressure of 149 mm. Hg. when breathing 15 liters per minute, BTPS, and with a maximum tidal volume of 700 cc. with a constant time interval between respirations.

(b) If demand equipment is installed for use by flight crewmembers, the minimum mass flow of supplemental oxygen required for each crewmember may not be less than the flow required to maintain, during inspiration, a mean tracheal oxygen partial pressure of 122 mm. Hg., up to and including a cabin pressure altitude of 35,000 feet, and 95 percent oxygen between cabin pressure altitudes of 35,000 and 40,000 feet, when breathing 20 liters per minute BTPS. In addition, there must be means to allow the crew to use undiluted oxygen at their discretion.

(c) For passengers and cabin attendants, the minimum mass flow of supplemental oxygen required for each person at various cabin pressure altitudes may not be less than the flow required to maintain, during inspiration and while using the oxygen equipment (including masks) provided, the following mean tracheal oxygen partial pressures: (1) At cabin pressure altitudes above 10,000 feet up to and including 18,500 feet, a mean tracheal oxygen partial pressure of 100 mm. Hg. when breathing 15 liters per minute, BTPS, and with a tidal volume of 700 cc. with a constant time interval between respirations.

(2) At cabin pressure altitudes above 18,500 feet up to and including 40,000 feet, a mean tracheal oxygen partial pressure of 83.8 mm. Hg. when breathing 30 liters 3/14/2000 AC 25-22 per minute, BTPS, and with a tidal volume of 1,100 cc. with a constant time interval between respirations.

(d) If first-aid oxygen equipment is installed, the minimum mass flow of oxygen to each user may not be less than four liters per minute, STPD. However, there may be a means to decrease this flow to not less than two liters per minute, STPD, at any cabin altitude. The quantity of oxygen required is based upon an average flow rate of three liters per minute per person for whom first-aid oxygen is required.

(e) If portable oxygen equipment is installed for use by crewmembers, the minimum mass flow of supplemental oxygen is the same as specified in paragraph (a) or (b) of this section, whichever is applicable.

b. Intent of Rule . The requirements of this rule provide standards to ensure that oxygen dispensing equipment will protect passengers and crewmembers from the effects of hypoxia.

The requirements for flight crewmembers are provided in terms of mean tracheal partial pressure of oxygen, which is not easily measured in certification testing. Dispensing equipment is, however, designed to provide the required oxygen flow. This equipment is, in most cases, approved through the technical standard order system. Requirements for passenger and cabin crewmember equipment are expressed in terms of oxygen flow rates.

c. Background . Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the Civil Air Regulations (CAR). The requirements in § 4b.651(b) of the CAR were carried over essentially unchanged to § 25.1443 of 14 CFR.

d. Policy/Compliance Methods . There is no written policy or guidance in our files.

e. Reference . The address for ordering the document listed below can be found in the Appendix to this AC.

The Society of Automotive Engineers (SAE) has aerospace committees that prepare documents reflecting industry standards and practices. The SAE A-10 Committee, Aircraft Oxygen Equipment, has prepared a handbook containing all Aerospace Standards, Aerospace Recommended Practices, and Aerospace Information Reports related to oxygen equipment published by SAE. While not regulatory in nature, this handbook contains valuable information that may be of interest to an applicant.

3/14/2000 AC 25-22 65. SECTION 25.1445 - EQUIPMENT STANDARDS FOR THE OXYGEN DISTRIBUTING SYSTEM.

a. Rule Text .

(a) When oxygen is supplied to both crew and passengers, the distribution system must be designed for either- (1) A source of supply for the flight crew on duty and a separate source for the passengers and other crewmembers; or (2) A common source of supply with means to separately reserve the minimum supply required by the flight crew on duty.

(b) Portable walk-around oxygen units of the continuous flow, diluter-demand, and straight demand kinds may be used to meet the crew or passenger breathing requirements.

b. Intent of Rule . This rule addresses the oxygen distribution system and does not address oxygen dispensing equipment (masks), the standards for which are addressed in § 25.1447.

c. Background . Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the Civil Air Regulations (CAR). The requirements in § 4b.651(c) of the CAR were carried over essentially unchanged to § 25.1445 of 14 CFR, except for the standards on potable walk-around units that are found in § 25.1445(b).

d. Policy/Compliance Methods . There is no written policy or guidance in our files.

e. Reference . The address for ordering the document listed below can be found in the Appendix to this AC.

The Society of Automotive Engineers (SAE) has aerospace committees that prepare documents reflecting industry standards and practices. The SAE A-10 Committee, Aircraft Oxygen Equipment, has prepared a handbook, “1992 SAE Aircraft Oxygen Equipment Handbook,” containing all Aerospace Standards, Aerospace Recommended Practices, and Aerospace Information Reports related to oxygen equipment published by SAE. While not regulatory in nature, this handbook contains information that may be of interest to an applicant.

66. SECTION 25.1447 - EQUIPMENT STANDARDS FOR OXYGEN DISPENSING UNITS.

a. Rule Text .

If oxygen dispensing units are installed, the following apply: (a) There must be an individual dispensing unit for each occupant for whom supplemental oxygen is to be supplied. Units must be designed to cover the nose and mouth and must be equipped with a suitable means to retain the unit in 3/14/2000 AC 25-22 position on the face. Flight crew masks for supplemental oxygen must have provisions for the use of communication equipment.

(b) If certification for operation up to and including 25,000 feet is requested, an oxygen supply terminal and unit of oxygen dispensing equipment for the immediate use of oxygen by each crewmember must be within easy reach of that crewmember. For any other occupants, the supply terminals and dispensing equipment must be located to allow the use of oxygen as required by the operating rules in this chapter.

(c) If certification for operation above 25,000 feet is requested, there must be oxygen dispensing equipment meeting the following requirements: (1) There must be an oxygen dispensing unit connected to oxygen supply terminals immediately available to each occupant, wherever seated, and at least two oxygen dispensing units connected to oxygen terminals in each lavatory. The total number of dispensing units and outlets in the cabin must exceed the number of seats by at least 10 percent. The extra units must be as uniformly distributed throughout the cabin as practicable. If certification for operation above 30,000 feet is requested, the dispensing units providing the required oxygen flow must be automatically presented to the occupants before the cabin pressure altitude exceeds 15,000 feet. The crew must be provided with a manual means of making the dispensing units immediately available in the event of failure of the automatic system.

(2) Each flight crewmember on flight deck duty must be provided with a quick- donning type oxygen dispensing unit connected to an oxygen supply terminal.

This dispensing unit must be immediately available to the flight crewmember when seated at his station, and installed so that it: (i) Can be placed on the face from its ready position, properly secured, sealed, and supplying oxygen upon demand, with one hand, within five seconds and without disturbing eyeglasses or causing delay in proceeding with emergency duties; and (ii) Allows, while in place, the performance of normal communication functions.

(3) The oxygen dispensing equipment for the flight crewmembers must be: (i) The diluter demand or pressure demand (pressure demand mask with a diluter demand pressure breathing regulator) type, or other approved oxygen equipment shown to provide the same degree of protection, for airplanes to be operated above 25,000 feet.

(ii) The pressure demand (pressure demand mask with a diluter demand pressure breathing regulator) type with mask-mounted regulator, or other approved oxygen equipment shown to provide the same degree of protection, for airplanes operated at altitudes where decompressions that are not extremely improbable may expose the flightcrew to cabin pressure altitudes in excess of 34,000 feet.

(4) Portable oxygen equipment must be immediately available for each cabin attendant.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-41, 42 FR 36971, Jul. 18, 1977; Amdt. 25-87, 61 FR 28696, Jun. 5, 1996] 3/14/2000 AC 25-22 b. Intent of Rule . This rule addresses the oxygen dispensing units, including oxygen masks and regulators, and do not address oxygen distributing systems , the standards for which are addressed in § 25.1445.

c. Background . Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the Civil Air Regulations (CAR). Many of the requirements in § 4b.651(d) of the CAR for oxygen dispensing units were carried over essentially unchanged to § 25.1447 of 14 CFR.

(1) Amendment 25-41 (July 18, 1977) added requirements for a manual means for the crew to make the dispensing units available in the event of a failure of the automatic means, and that the masks for use by the flight crewmembers be of the quick donning type.

(2) Amendment 25-87 (June 5, 1996) added flightcrew oxygen equipment requirements for a pressure demand type with mask-mounted regulator, or other approved equipment, for airplanes operated at altitudes where decompressions that are not extremely improbable may expose the flightcrew to cabin pressure altitudes in excess of 34,000 feet.

d. Policy/Compliance Methods . For guidance on compliance with this requirement, refer to the preamble of this rule and the following information.

(1) Oxygen Equipment for Forward Observer's Position. The following policy was extracted from an FAA memorandum dated February 1, 1988, that was written to provide guidance for certification of forward observer's oxygen equipment.

(a) The requirements for a forward observer's seat are contained in § 25.785(k), § 121.581(a), § 125.317(b), and § 135.75(b). In parts 121, 125, and 135 of 14 CFR, there is no specific list of required equipment for the first observer's seat, but rather a general statement that the required equipment would be "determined by the Administrator." The FAA considers a representative of the Administrator, occupying the first observer's seat and performing official duties, to be a required crewmember. This designation also applies to a company check airman, or other person performing official duties relating to the performance of the crew or operation of the airplane. This person would be expected to interact with the captain and other flight crewmembers, in addition to his or her normal duties relating to enroute inspection and surveillance. For these reasons, it is important that the occupant of the observer seat be provided with the equipment necessary to perform his or her function, e.g., oxygen, protective breathing equipment, and communication via a radio and interphone panel which is the same type equipment provided to the flightcrew.

(b) Section 25.785(l) does not specify what type of equipment must be provided at the observer seat as part of the type design. The rule states, “Each forward observer’s seat required by the operating rules must be shown to be suitable for use in conducting the necessary enroute inspection.” Section 25.785(l) has been interpreted to allow the use of passenger-type oxygen equipment, provided that the airplane in question is not to be used in Part 121, 125, or 135 operation. If the airplane is to be so used, the oxygen, communication, and protective 3/14/2000 AC 25-22 breathing requirements stated above must be provided. If the airplane is not to be used in parts 121, 125, or 135 operation (i.e., in Part 91 operation), installation of either type of oxygen equipment at the first observer's seat is adequate to show compliance with the requirements of § 25.1441, Oxygen Equipment and Supply, and installation of communication equipment and protective breathing equipment would be optional.

(c) The duration of oxygen supply should be commensurate with the crew supply, since protection may be necessary due to a delayed descent following decompression, protective breathing requirements, or other extended usage.

e. References . The addresses for ordering the latest revision of technical standard orders and other referenced documents listed below can be found in the Appendix to this AC.

TSO-C64a, Oxygen Mask Assembly Continuous Flow, Passenger (For Air Carrier Aircraft).

TSO-C78, Crewmember Demand Oxygen Masks.

TSO-C89, Oxygen Regulators, Demand.

TSO-C99, Protective Breathing Equipment.

TSO-C116, Crewmember Protective Breathing Equipment.

The Society of Automotive Engineers (SAE) has aerospace committees which prepare documents reflecting industry standards and practices. The SAE A-10 Committee, Aircraft Oxygen Equipment, has prepared a handbook, “1992 SAE Aircraft Oxygen Equipment Handbook,” containing all Aerospace Standards, Aerospace Recommended Practices, and Aerospace Information Reports related to oxygen equipment published by SAE. While not regulatory in nature, this handbook contains information that may be of interest to an applicant.

67. SECTION 25.1449 - MEANS FOR DETERMINING USE OF OXYGEN.

a. Rule Text .

There must be a means to allow the crew to determine whether oxygen is being delivered to the dispensing equipment.

b. Intent of Rule . The standards in this section ensure that the flightcrew is able to determine that oxygen is being dispensed properly.

c. Background . Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the Civil Air Regulations (CAR). The requirement in § 4b.651(e) of the CAR that there be a means for the crew to determine that oxygen is being delivered to the dispensing equipment (masks) were carried over essentially unchanged to § 25.1449 of 14 CFR.

d. Policy/Compliance Methods . For guidance on compliance with this requirement, refer to the preamble of this rule and the following information. Compliance with this section is usually 3/14/2000 AC 25-22 accomplished by the use of flow indicators in the oxygen regulators (for flight crewmembers) and in the oxygen tubes leading to the masks (for passenger equipment).

(1) Oxygen Equipment for Observer Position. The following policy was extracted from an FAA letter dated April 19, 1996, in response to an inquiry concerning the requirement for supplemental oxygen flow indication at the observers' stations.

(a) An applicant proposed installing mask-mounted regulators without flow indication at the observers' stations. This configuration has been certified for previous versions of the same airplane model. It was the applicant’s position that the FAA exempts mask-mounted regulators from the § 25.1449 flow indication requirement. They cited FAA Technical Standard Order (TSO) C-89, which exempts mask-mounted regulators from the TSO requirement to provide a means to indicate oxygen flow from the regulator outlet. Although the TSO allows omission of flow indicators for mask-mounted regulators, it is not an authorization to install such items on transport airplanes. However, the FAA reviewed the original certification data for the airplane model in question, and the background of § 25.1449. Based on this review, the FAA determined that installation of the mask-mounted regulators without flow indicators at the observers' stations meets the intent of § 25.1449.

(b) The background for § 25.1449 is found in the FAA Civil Aeronautics Manual (CAM) 4b. Section 25.1449 states: "There must be a means to allow the crew to determine whether oxygen is being delivered to the dispensing equipment." Similarly, § 4b.651 of the Civil Air Regulation (CAR) states: "Means shall be provided to enable the crew to determine whether oxygen is being delivered to the dispensing units." Although flow indicators for each individual passenger or flight crew station represent one method of compliance, policy guidance provided in § 4b.651-10 of the CAR (for crew systems) and § 4b.651-11 of the CAR (for passenger systems) allows operators to establish procedures for checking the oxygen flow to individual oxygen users. For passenger diluter-demand systems, § 4b.651-11 of the CAR states that the procedure may be "checking of the oxygen flow by a trained crewmember by momentarily moving the regulator lever to Automix ‘OFF’ (100% OXYGEN) while the mask is being worn."

Lack of oxygen flow would be "immediately evidenced by the user's inability to inhale while wearing his mask."

(c) The FAA is satisfied that § 25.1449 does not specifically require flow indicators at each mask. Although these indicators are generally provided, other methods of flow indication are not precluded. Therefore, the FAA is satisfied that flow indicators are not required at the observers' stations for certification, provided that the applicant incorporates suitable design features and procedures to ascertain flow at the observers' stations. On the model in question, supplemental oxygen for the flightcrew and the observers' stations is provided by a common source. Flow of oxygen from the source is split between the flight crew and observers' stations by a "T" fitting. Under normal operations, all cockpit masks are set for "100% OXYGEN." At this setting, lack of flow would be immediately detected by the user. The FAA is requiring incorporation of a preflight check of the observers' masks in the airplane flight manual (AFM).

In addition, a positive indication of flow at the flightcrew stations by the flow indicators installed at those stations would indicate that oxygen is also flowing to the observers' stations. The FAA 3/14/2000 AC 25-22 is satisfied that the system design, the preflight inspection procedure, and flow indicators at the flightcrew stations are adequate to meet the intent of § 25.1449.

(2) Determination of Passenger Oxygen Supply. The following policy was extracted from an FAA memorandum dated January 8, 1996, which addresses compliance with § 25.1449 for a design that will determine, from the flightdeck, that oxygen is flowing to the passenger supplemental oxygen masks. It is noted that 14 CFR does not require a means for the flight crew to make this determination while on flight deck duty. A number of airplanes have gaseous supplemental oxygen systems which do not have a specific indication of oxygen flow on the flight deck. Compliance with 14 CFR requirements is usually shown through use of a flow indicating device in the oxygen mask tubing. Technical Standard Order TSO-C64a, and the associated Society of Automotive Engineers Aerospace Standard SAE-AS 8025, require a means for the crew to determine that oxygen is flowing. This is usually accomplished with a small device that provides a green indication when the flow rate exceeds 0.5 liters per minute. A cabin crewmember verifies from the indicator whether or not oxygen is flowing. If there are no cabin crewmembers, this would require a flight crewmember to leave their station and check. The FAA has determined that this would not be a viable option during an emergency such as a decompression.

e. References . None.

68. SECTION 25.1450 - CHEMICAL OXYGEN GENERATORS.

a. Rule Text .

(a) For the purpose of this section, a chemical oxygen generator is defined as a device which produces oxygen by chemical reaction.

(b) Each chemical oxygen generator must be designed and installed in accordance with the following requirements: (1) Surface temperature developed by the generator during operation may not create a hazard to the airplane or to its occupants.

(2) Means must be provided to relieve any internal pressure that may be hazardous.

(c) In addition to meeting the requirements in paragraph (b) of this section, each portable chemical oxygen generator that is capable of sustained operation by successive replacement of a generator element must be placarded to show- (1) The rate of oxygen flow, in liters per minute; (2) The duration of oxygen flow, in minutes, for the replaceable generator element; and (3) A warning that the replaceable generator element may be hot, unless the element construction is such that the surface temperature cannot exceed 100 degrees F.

[Amdt. 25-41, 42 FR 36971, Jul. 18, 1977] 3/14/2000 AC 25-22 b. Intent of Rule . The standards in this rule ensure that chemical oxygen generators safely provide oxygen.

c. Background . The standards in this section address chemical oxygen generators. This subject was not addressed in either part 4b of the CAR or part 25 when it was originally codified.

This section was added at Amendment 25-41, July 18, 1977.

d. Policy/Compliance Methods . There is no written policy or guidance in our files.

e. Reference . The address for ordering the latest revision of the document listed below can be found in the Appendix to this AC.

The Society of Automotive Engineers (SAE) has aerospace committees that prepare documents reflecting industry standards and practices. The SAE A-10 Committee, Aircraft Oxygen Equipment, has prepared a handbook, “1992 SAE Aircraft Oxygen Equipment Handbook,” containing all Aerospace Standards, Aerospace Recommended Practices, and Aerospace Information Reports related to oxygen equipment published by SAE. While not regulatory in nature, this handbook contains information that may be of interest to an applicant.

69. SECTION 25.1453 PROTECTION OF OXYGEN EQUIPMENT FROM RUPTURE.

a. Rule Text.

Oxygen pressure tanks, and lines between tanks and the shutoff means, must be- (a) Protected from unsafe temperatures; and (b) Located where the probability and hazards of rupture in a crash landing are minimized.

b. Intent of Rule. This rule ensures that the oxygen equipment is not exposed to unsafe temperatures and minimizes the possibility of rupture in the event of a crash landing.

c. Background . Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the Civil Air Regulations (CAR). The requirements in § 4b.651(g) of the CAR were carried over essentially unchanged to § 25.1453 of 14 CFR.

d. Policy/Compliance Methods . For guidance on compliance with this requirement, refer to the preamble of this rule and the following information.

(1) Flexible Plastic Oxygen Lines. The following policy was extracted from an FAA memorandum dated December 27, 1983, to provide guidance regarding the use of flexible plastic tubing for oxygen distribution lines. While this guidance was generated for Part 23 airplanes, it is equally applicable for part 25 airplanes.

3/14/2000 AC 25-22 (a) The FAA has determined that the use of plastic lines for an oxygen distribution system that is operating under continuous pressure is not acceptable for certification in Part 23 airplanes.

(b) Lines constructed of combustible materials, including nylon, polyvinylchloride (PVC) and Teflon, may be used in oxygen lines which are pressurized only when cabin depressurization occurs. The following precautions should be taken when using such lines in the oxygen system: 1 Swaged metal type end fittings should be used to prevent leakage from cold flow.

2 Lines should be protected from abrasion by use of a reinforcing sleeving of fabric braid.

3 Precautions should be taken to route such lines away from areas where they might be subjected to elevated temperatures, electrical arcing (relays and switches) and flammable fluids.

4 Refer to Advisory Circular (AC) 43.13-2A, Chapter 6, for additional guidance material.

(2) Use of Plastic Oxygen Lines. The following policy was extracted from an FAA memorandum dated October 28, 1983, and addresses the use of plastic or nylon tubing as oxygen lines.

(a) Tubing in the fuselage for high or low pressure oxygen systems that are located behind liners or in the walls of the fuselage are typically made of rigid stainless steel (for high pressure) or aluminum (for low pressure). Synthetic flexible lines connecting the oxygen mask to the oxygen distribution system have been accepted. Swaged metal end fitted PVC tubing, covered with a synthetic braid (for abrasion resistance and strength), should be used between the aluminum low pressure distribution line and the passenger service unit manifold of many large transports. These tubes and aluminum line do not contain oxygen until a depressurization occurs. Then, the pressure is low and for a short duration. These hoses meet the interior burn requirements.

(b) Synthetic lines such as plastic or nylon cannot be recommended for oxygen high or low pressure lines that will be exposed to a continuous pressure (i.e., as opposed to pressurized when needed). These materials can cold flow. Care must be taken in the selection of the fitting design for exposures of even short duration.

(c) In addition to cold flow, polyethylene and nylon will lose strength with increasing temperature. These materials are much more susceptible to combustion in the presence of oxygen than either stainless steel or aluminum. For these reasons, the FAA 3/14/2000 AC 25-22 considers polyethylene or nylon tubing inappropriate and unsafe for oxygen lines that are subjected to continuous oxygen pressure.

e. Reference. The address for ordering the document listed below can be found in the Appendix to this AC.

The Society of Automotive Engineers (SAE) has aerospace committees that prepare documents reflecting industry standards and practices. The SAE A-10 Committee, Aircraft Oxygen Equipment, has prepared a handbook, “1992 SAE Aircraft Oxygen Equipment Handbook,” containing all Aerospace Standards, Aerospace Recommended Practices, and Aerospace Information Reports related to oxygen equipment published by SAE. While not regulatory in nature, this handbook contains information that may be of interest to an applicant.

70. SECTION 25.1455 - DRAINING OF FLUIDS SUBJECT TO FREEZING .

a. Rule Text.

If fluids subject to freezing may be drained overboard in flight or during ground operation, the drains must be designed and located to prevent the formation of hazardous quantities of ice on the airplane as a result of the drainage.

[Amdt. 25-23, 35 FR 5680, Apr. 8, 1970] b. Intent of Rule. This rule addresses fluids subject to freezing that normally drain from the airplane either in flight or during ground operation. The intent is to prevent damage to the airplane when the ice disengages and falls free. This section addresses "gray" water from the sinks and drains in galleys and lavatories. Section 25.1455 does not apply to lavatory drain systems that are normally drained when the airplane is parked, rather than being in "ground operation." This requirement is usually met by designing the drain masts (usually heated to prevent the fluid from freezing) so that the fluid does not impact the airframe or engines when it is draining.

c. Background. Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the Civil Air Regulations (CAR). The requirements in section 4b.660 of the CAR were carried over to § 25.1455 of 14 CFR.

(1) Amendment 25-23 (April 8, 1970) changed the intent of the rule from preventing the formation of ice to preventing the formation of hazardous quantities of ice on the airplane as a result of drainage.

d. Policy/Compliance Methods. There is no written policy or guidance in our files.

e. Reference . The address for ordering the latest revision of the advisory circular listed below can be found in the Appendix to this AC.

3/14/2000 AC 25-22 AC 25.1455-1, Waste Water/Potable Water Drain System Certification Testing.

71. SECTION 25.1461 - EQUIPMENT CONTAINING HIGH ENERGY ROTORS.

a. Rule Text.

(a) Equipment containing high energy rotors must meet paragraph (b), (c), or (d) of this section.

(b) High energy rotors contained in equipment must be able to withstand damage caused by malfunctions, vibration, abnormal speeds, and abnormal temperatures.

In addition- (1) Auxiliary rotor cases must be able to contain damage caused by the failure of high energy rotor blades; and (2) Equipment control devices, systems, and instrumentation must reasonably ensure that no operating limitations affecting the integrity of high energy rotors will be exceeded in service.

(c) It must be shown by test that equipment containing high energy rotors can contain any failure of a high energy rotor that occurs at the highest speed obtainable with the normal speed control devices inoperative.

(d) Equipment containing high energy rotors must be located where rotor failure will neither endanger the occupants nor adversely affect continued safe flight.

[Amdt. 25-41, 42 FR 36971, Jul. 18, 1977] b. Intent of Rule. This rule ensures that failures of high energy rotating equipment will not adversely affect systems, structure, or occupants in the event that the rotating components fail at high speeds. Some of the equipment that contains high energy rotors are turbine engine starters, air cycle machines, air driven hydraulic pumps, cooling fans for galley equipment and electronic bays, cabin ventilation recirculation fans, and high speed electrically driven hydraulic pumps.

This section does not pertain to equipment covered by Subpart E, Propulsion, such as engines and auxiliary power units, which are covered by the provisions of § 25.903(d).

3/14/2000 AC 25-22 c. Background.

(1) Amendment 4b-8 of the Civil Air Regulations (CAR) . This subject was first addressed in part 4b of the CAR under Amendment 4b-8, effective May 17, 1958. A new § 4b.659 was included which required appropriate protection of the airplane against failure of high energy rotors when such rotors were incorporated in any equipment on the airplanes.

Section 4b.659 read "Equipment incorporating high energy rotors shall be demonstrated as capable of containing a failed rotor or shall be so located that failure will not affect the ability of the airplane to continue safe flight."

(2) Amendment 4b-12 of the Civil Aeronautics Manual (CAM) . Amendment 4b-12, effective May 13, 1962, deleted § 4b.659 because it was surmised that its substance was covered by the provisions of § 4b.606 (which later became § 25.1309) which is concerned with the reliability of all equipment, systems, and installations.

(3) Amendment 25-41 . Amendment 25-41 added § 25.1461 as a result of an Airworthiness Review Program conducted in 1975. This new section added requirements for protection against the failure of equipment containing high energy rotors. Experience had demonstrated that failures which release the energy stored in these rotors may result in engine or structural damage, fires, or injury to occupants.

d. Policy/Compliance Methods. Compliance to §25.1461(c) is accomplished if it can be shown by test that equipment containing high-energy rotors can contain any failure of the rotor that occurs at the highest speed obtainable with normal speed control devices inoperative. In general, three phase induction motor driven fans do not have speed control devices. Fan speed is a function of the input power frequency supplied to the device.

(1) Because of the absence of speed controls, these fans can be treated as an extension of the aircraft power generating system. To comply with § 25.1461(c), the minimum test speed would be at the highest speed obtainable with power generating system speed control devices inoperative (speed control device is the mechanical system that governs generator shaft speed).

In the event of such a failure, generating system controls will limit frequency. Exceeding those limits would require further multiple failures. These higher order failures do not have to be considered to comply with § 25.1461(c).

(2) For external ground power operation, the same frequency limits are applicable. The cart (or other) providing power must fail, the cart protective overfrequency protection must fail, and the airplane protective systems must fail to trip the external power contactor. In addition, an uncontained fan rotor burst on the ground is classified differently as it is not a safety of flight issue.

e. References . None.

3/14/2000 AC 25-22 Chapter 4. OPERATING LIMITATIONS AND INFORMATION Section 1. OPERATING LIMITATIONS 72. SECTION 25.1529 - INSTRUCTIONS FOR CONTINUED AIRWORTHINESS.

a. Rule Text .

The applicant must prepare instructions for Continued Airworthiness in accordance with Appendix H to this Part that are acceptable to the Administrator.

The instructions may be incomplete at type certification if a program exists to [Amdt. 25-54, 45 FR 60173, Sep. 11, 1980] ensure their completion prior to delivery of the first airplane for issuance of a standard certificate of airworthiness, whichever occurs later.

H25.4 Airworthiness Limitations section.

The Instructions for Continued Airworthiness must contain a section titled Airworthiness Limitations that is segregated and clearly distinguishable from the rest of the document. This section must set forth each mandatory replacement time, structural inspection interval, and related structural inspection procedures approved under § 25.571. If the Instructions for Continued Airworthiness consist of multiple documents, the section required by this paragraph must be included in the principal manual. This section must contain a legible statement in a prominent location that reads: "The Airworthiness Limitations section is FAA approved and specifies maintenance required under §§ 43.16 and 91.403 of the Federal Aviation Regulations unless an alternative program has been FAA approved."

[Amdt. 25-54, 45 FR 60173, Sep. 11, 1980; Amdt. 25-68, 54 FR 34329, Aug. 18, 1989] b. Intent of Rule . The purpose of this rule is to ensure continued airworthiness of the airplane by requiring that inspections, checks, and replacement of parts are performed in accordance with the requirements established for type certification.

c. Background . This subject was not addressed in either section 4b of the Civil Air Regulations (CAR) or part 25 of Title 14, Code of Federal Regulations (14 CFR). This rule was added, along with Appendix H, by Amendment 25-54.

3/14/2000 AC 25-22 d. Policy/Compliance Methods . For guidance on compliance with this requirement, refer to the preamble of this rule and the airworthiness limitations document.

e. Reference . The address for ordering the latest revision of the advisory circular listed below can be found in the Appendix to this AC.

Advisory Circular 25-19, Certification Maintenance Requirements.

3/14/2000 AC 25-22 APPENDIX 1, CROSS REFERENCE FOR SELECTED SECTIONS OF PART 25, CAR 4b/CAM 4b DISTRIBUTION TABLE Revised Section Former Section Revised Former Section Section 25.671 4b.320 (less (b)) 25.869(b) 25.1443(b) & (c) [4b.658] 25.672 not applicable 25.869(c) 25.1451 [4b.651(f)] 25.699 4b.323(e) & (f) 25.1001 4b.437 (less (e) (last sent.)) 25.701 4b.324 25.1183 4b.333, 4b.483 25.703 not applicable 25.1185 4b.481 25.729 4b.334, -2 25.1189 4b.382 25.731 4b.335(a) & (b) 25.1301 4b.600, 4b.601 25.733 4b.336 25.1309 4b.606 25.735 4b.335 less (a), (b) 25.1416 not applicable 4b.337, -4 (1st sent.) 25.1419 4b.640 (less intro, 3rd sent.

25.771 4b.350 25.1431 4b.650 25.773 4b.351 25.1433 4b.658 25.775 4b.352 25.1435 4b.653, 4b.654, 4b.655 25.777 4b.353 25.1438 not applicable 25.783 4b.356, -1(last sent) 25.1439 4b.651 (less (a)-(g) 4b.356-2(a)/1st sent 25.1441 4b.651(a) 25.831 4b.371, 4b.371-1 25.1443 4b.651(b) 25.832 not applicable 25.1445 4b.651(c), 4b.651-5a 25.833 4b.372 25.1147 4b.651(d) 25.841 4b.374, 4b.375, -1 25.1449 4b.651(e) 25.843 4b.376 25.1450 not applicable 25.851 4b.380 (less (c)), 4b.383 25.1453 4b.651(g) (2nd sent. of (a) & (b)(3) 25.854 not applicable 25.1455 4b.660 25.855 4b.382, 4b.384 25.1461 not applicable 25.857 not applicable 25.858 not applicable 25.863 4b.385 3/14/2000 AC 25-22 APPENDIX 2, GLOSSARY OF ACRONYMS AC Advisory Circular ACO Aircraft Certification Office AD Airworthiness Directive AFM Airplane Flight Manual AIA Aerospace Industries Association AIR Aircraft Certification Service ARAC Aviation Rulemaking Advisory Committee ARP Aerospace Recommended Practice (SAE) BTMS Aircraft Brake Temperature Monitor System CAA Civil Aeronautics Administration (US) CAR Civil Air Regulations CAM Civil Aeronautics Manual CFR Code of Federal Regulations DER Designated Engineering Representative ECS Environmental Control System EICAS Engine Indication and Crew Alerting System FAR Federal Aviation Regulations IIDSS Inflight Ice Detection Sensing Systems JAA Joint Aviation Authorities JAR Joint Airworthiness Requirements KE Kinetic Energy NOE Non-original Equipment NTSB National Transportation Safety Board OAT Outside Air Temperature OBOGS On-Board Oxygen Generating System OEM Original Equipment Manufacturer PBE Protective Breathing Equipment PMA Parts Manufacturer Approval PPM Parts Per Million PPMV Parts Per Million by Volume QTR Qualification Test Report R&D Research & Development RTO Rejected Take-off SAE Society of Automotive Engineers SLD Supercooled Large Droplets SLE Sea Level Equivalent STC Supplemental Type Certificate TAD Transport Airplane Directorate TAT Total Air Temperature TC Type Certificate TSO Technical Standard Order TWA Time-Weighted-Average 3/14/2000 AC 25-22 APPENDIX 3, INDEX OF ADVISORY CIRCULAR REFERENCES The advisory circulars listed below contain information relevant to the approval of mechanical systems on transport category airplanes. They can be obtained from the U.S. Department of Transportation, Subsequent Distribution Office, SVC-121.23, Ardmore East Business Center, 3341 Q 75th Avenue, Landover, MD 20785, USA.

AC No. Title Section Reference 20-32B Carbon Monoxide (CO) Contamination in Aircraft- 25.831 Detection and Prevention, November 24, 1972, or latest revision, ACE-110 20-33B Technical Information Regarding Civil Aeronautics All sections Manuals 1, 3, 4a, 4b, 5, 6, 7, 8, 9, 13 and 14, May 1, 1975, or latest revision, AIR-200 20-34D Prevention of Retractable Landing Gear Failures, 25.729 August 8, 1980, or latest revision, AFS-340 20-36S Index of Articles (Materials, Parts, Processes and All sections Appliances) Certified Under the Technical Standard Order System, September 1, 1993, or latest revision, AFS-613 20-41A Substitute Technical Standard Order (TSO) Aircraft All sections Equipment, April 5, 1977, or latest revision, AIR-120 20-42C Hand Fire Extinguishers for use in Aircraft, 25.851 March 7, 1984, or latest revision, ACE-110 20-62D Eligibility, Quality, and Identification of Approved All sections Aeronautical Replacement Parts, May 24, 1996, or latest revision, AFS-340 20-73 Aircraft Ice Protection, April 21, 1971, or latest revision, 25.1419 AIR-120 20-97A High-Speed Tire Maintenance and Operational Practices, 25.733 May 13, 1987, or latest revision, AFS-340 3/14/2000 AC 25-22 20-99 Antiskid and Associated Systems, May 27, 1977, or 25.735 latest revision, ANM-100 20-110J Index of Aviation Technical Standard Orders, All sections May 30, 1997, or latest revision, AIR-120 20-117 Hazards Following Ground Deicing and Ground 25.1419 Operations in Conditions Conducive to Aircraft Icing, December 17, 1982; Chg. 1, April 15, 1983, or latest revision, AFS-200 20-128A Design Considerations for Minimizing Hazards Caused 25.1435 by Uncontained Turbine Engine and Auxiliary Power Unit Rotor and Fan Blade Failures, March 25, 1997, or latest revision, ANM-114 21-16C Radio Technical Commission for Aeronautics (now called All sections RTCA Inc.) Document DO-160C, February 14, 1990, or latest revision, AIR-120 21-23 Airworthiness Certification of Civil Aircraft Engine, 25.735 Propellers, and Related Products, July 7, 1987, or latest revision, AIR-4 23.729-1 Landing Gear Doors and Retraction Mechanism, March 26, 23.729 1984, or latest revision, ACE-110. For information only.

23-1419-2 Certification of Part 23 Airplanes for Flight in Icing 23.1419 Conditions, January 3, 1992, or latest revision, ACE-100 25-7A Flight Test Guide for Certification of 25.729, 25.731 Transport Category Airplanes, March 31, 1998, or 25.733, 25.735 latest revision, ANM-110 25.773 25-9A Smoke Detection, Penetrating, and Evacuation Tests and 25.831, 25.854 Related Flight Manual Emergency Procedures, 25.855, 25.858 January 6, 1994, or latest revision, ANM-110 25-14 High Lift and Drag Devices, May 4, 1988, or latest 25.699, 25.703 revision, ANM-112 25.671, 25.672 25-16 Electrical Fault and Fire Prevention and Protection, 25.869 April 5, 1991, or latest revision, ANM-111 25-17 Transport Airplane Cabin Interiors Crashworthiness 25.773, 25.857 Handbook, July 15, 1991, or latest revision, ANM-114 25.858, 25.869 3/14/2000 AC 25-22 25-18 Transport Category Airplanes Modified for Cargo Service, 25.857 January 6, 1994, or latest revision, ANM-114 25-19 Certification Maintenance Requirements, November 28, 25.1309 1994, or latest revision, ANM-113 25-20 Pressurization, Ventilation, and Oxygen Systems 25.831, 25.841 Assessment for Subsonic Flight Including High Altitude Operation, September 10, 1996, or latest revision, ANM-111 25-21 Certification of Transport Airplane Structure, 25.671, 25.672 September 1, 1999, ANM-110 25.701 25.672-1 Active Flight Controls, November 15, 1983, or latest 25.672 revision, ANM-110B 25.703-1 Takeoff Configuration Warning Systems, March 17, 1993, 25.703 or latest revision, ANM-111 25.773-1 Pilot Compartment View for Transport Category Airplanes, 25.773 January 8, 1993, or latest revision, ANM-111 25.783-1 Fuselage Doors, Hatches, and Exits, December 10, 1986, 25.783 or latest revision, ANM-110 25.963--1 Fuel Tank Access Covers, July 29, 1992, or latest 25.729 revision, ANM-112 25.1309-1A System Design Analysis, June 21, 1988, or latest 25.1309, 25.1435 revision, ANM-112 25.1419-1 Certification of Transport Category Airplanes for 25.1419 Flight in Icing Conditions, August 18, 1999, or latest revision, ANM-112 25.1455-1 Waste Water/Potable Water Drain System Certification 25.1455 Testing, March 11, 1985, or latest revision, ANM-112 27-1A Certification of Normal Category Rotorcraft, dated 25.731 July 30, 1997, or latest revision, ASW-111 3/14/2000 AC 25-22 29-2B Certification of Transport Category Rotorcraft, July 30, 1997, 25.731 or latest revision, ASW-111 43.13-1A Acceptable Methods, Techniques and Practices 25.729, 25.731, Aircraft Inspection and Repair (with Errata Sheet), dated 25.733, 25.735 April 17, 1972, or latest revision, AFS-600 43.13-2A Acceptable Methods, Techniques, and Practices Aircraft All sections Alterations, includes Chg. 1, dated June 9, 1977; Chg. 2, dated Oct. 30, 1989, or latest revision, AFS 340 91-6A Water, Slush, and Snow on the Runway, May 24, 1978, 25.109, 25.735 or latest revision, AFS-430 91-13C Cold Weather Operation of Aircraft, July 24, 1979, 25.109, 25.735 or latest revision, AFS-806 91-51A Effect of Icing on Aircraft Control and Airplane De-ice and 25.1419 Anti-Ice Systems, July 19, 1996, or latest revision, AFS-820 120-38 Transport Category Airplanes Cabin Ozone Concentrations, October 10, 1980, or latest revision, AFS-260 25.832 120-39 Hazards of Waste Water Ice Accumulation Separating From 25.1455 Aircraft in Flight, October 31, 1980, or latest revision, AFS-331 120-42A Extended Range Operation with Two Engine Airplanes 25.1435 (ETOPS), December 30, 1988, or latest revision, AFS-400 120-58 Pilot Guide for Large Aircraft Ground Deicing, September 30, 25.1419 1992, or latest revision, AFS-420 121.195-1A Operational Landing Distances for Wet Runways: Transport 25.109, 25.735 Category Airplanes, June 19, 1990, or latest revision, AFS-430 145-4 Inspection, Retread, Repair and Alterations of Aircraft Tires, September 27, 1982, or latest revision, AFS-340 25.733 3/14/2000 AC 25-22 *25-XX Cargo Compartment Fire Extinguishing or Suppression Systems, date TBD 25.857 *25-XX Class B and F Cargo Compartments, date TBD 25.857 *25-XX Propulsion Systems Handbook 25.863, 25.943, (Mega AC) date TBD 25.1001, 25.1183, 25.1185, 25.1189 *25-XX Electrical Systems Handbook (Mega AC) 25.1301, 25.1309, date TBD 25.1325 *NOTE : The designation "25-XX" means that a draft AC exists for the subject. Upon approval, the "XX" will be replaced with a numerical reference identification code.

3/14/2000 AC 25-22 APPENDIX 4, INDEX OF INCORPORATED GUIDANCE MATERIAL AND REFERENCES 1. FAA Memorandums and Letters Referenced in this AC: Copies of the memorandums and letters are available from the FAA Transport Airplane Directorate, 1601 Lind Ave. SW, Renton, WA 98055, USA.

SectionSubject Date 25.729 Protection of Equipment in Wheel Wells, Dec. 4, 1997 § 25.729(f)(1) 25.729 Landing Gear Position Indication System - July 12, 1988 “Backup Requirement” - Section 25.729(e) 25.729 Flap System/Landing Gear Warning System Dec. 19, 1983 Tie-In 25.729 Landing Gear Position Indication System June 3, 1983 25.729 Landing Gear Slush Tests April 22, 1983 25.733 Approval of Retreaded Tires by Similarity March 1, 1995 25.733 Approval of Nonretreadable Tires - August 18, 1988 Qualification Testing 25.733 Approval Method for Substitute Tires April 14, 1988 25.733 Replacement of Bias Ply Tires with Radial Feb. 7, 1984 Ply Tires 25.733 Certification Program for Replacing Bias Jan. 12, 1984 Tires with Radial Tires, Part 25 Transports; All Weight Categories 25.733 Certification of Radial Tire Installation March 28, 1984 25.733 Critical Conditions & Maximum Ramp Jan. 26, 1981 Weight Definitions 25.735 Carbon Brake Refurbishment April 11, 1996 (redensification) 25.735 Parts Manufacturer Approval for a April 9, 1996 Non-U.S. Location: § 21.303(g) 25.735 Certification of Replacement Brakes: May 19, 1992 Non-U.S. Location 25.735 Parking Brake Testing March 20, 1992, 25.735 Worn Brake Requirements for Non- Feb. 18, 1992 Original-Equipment Parts (letter) 25.735 Determination of Allowable Feb. 23, 1990, Mar. 2, 1990 Worn Brake Limits 25.735 Credit for Reverse Thrust in Worn April 28, 1989 Brake Testing 3/14/2000 AC 25-22 25.735 Certification of Brake Replacement Mar. 16, 1989, Dec. 27, 1988, Components - Performance and March 16, 1988 25.735 Ground Equipment-Brake Cooling Unit Dec. 27, 1988 25.735 Certification Requirements for Asbestos- Dec. 16, 1987 Free Brake Linings 25.735 Determination of Certification Requirements Oct. 26, 1987 for Brake Components - Performance 25.735 Approval of Brake Components Utilizing July 27, 1987 New Brake Friction Material 25.735 Maximum Quick Turnaround Times August 19, 1983 25.735 Dynamometer Test Guidelines to Establish March 2, 1990 Brake Wear Limits (letter) 25.831 Ventilation During Takeoff with the May 20, 1983 Environmental Control System Turned Off 25.831 Fresh Air and Normal Operating Conditions Sept. 10, 1997 25.831 Cabin Altitude Limit; § 25.841(a) Jan. 12, 1994 25.832 Use of Operational Limitations March 31, 1997 25.832 Meaning of the Term Time-Weighted Average Oct. 26, 1987 in § 25.832 of the FAR 25.833 Standards for Certification of Combustion March 14, 1948 Heaters 25.841 Rapid Equalization of Pressure June 21, 1982 25.841 Access to a Pressurized Cargo Compartment June 25, 1986 in the Engine Burst Zone During High Altitude Operation 25.841 Cabin Altitude Limit; § 25.841(a) Jan. 12, 1994 25.843 Pressure Tests for Compliance with 25.843(a) Feb. 21, 1990 25.854 Approval of Lavatory Smoke Detectors Oct. 28, 1991 25.854 Approval of Lavatory Fire Extinguishers March 31, 1997 Containing Agents Other Than Halon 25.857 Main Deck Cargo Compartment Fire June 6, 1997 Protection Certification Procedures 25.857 Cargo Compartments Sept. 13, 1988 25.857 Class A Cargo Compartments February 8, 1996 25.857 Class E Cargo Compartments March 21, 1991 25.857 Class E Cargo Compartments July 3, 1990 25.858 Smoke Detection Certification Testing June 18, 1997 25.858 Smoke Detection Certification Testing Feb. 11, 1993 25.858 Smoke Detection Certification Testing Dec. 3, 1992, Dec. 15, 1992 25.1419 Inflight Ice Detection Systems Jan. 13, 1998 25.1419 Aircraft Mounted Ground Ice Detection Oct. 10, 1996 Systems 25.1419 Roll Control in Supercooled Large Droplets July 23, 1997 25.1435 Hydraulic Fuel Contamination April 20, 1995 3/14/2000 AC 25-22 25.1435 Certification of Hydraulic Lines for April 23, 1992 Temporary Repairs 25.1435 Use of Hydraulic Lines for Temporary Repairs Jan. 25, 1988 25.1435 Hydraulic System Certification Philosophy March 5, 1982 25.1435 Interpretation of 25.1425(a)(4) of the FAR Sept. 14, 1978 25.1438 Pneumatic Versus Pressurization System Oct. 19, 1993 Identification 25.1439 Protective Breathing Equipment Usage May 13, 1993 When Approved Under TSO-C99 and TSO-C116 25.1439 Protective Breathing Equipment March 9, 1990 Serviceability 25.1439 Protective Breathing Equipment on the Dec. 19, 1988 Flight Deck 25.1439 Definition of Terms Used in § 25.1439 Feb. 26, 1985 25.1441 Certification of On-Board Oxygen Jan. 31, 1996 Generation Systems 25.1441 Compliance with §§ 25.1309(c) and 25.1441(c) Feb. 23, 1994 25.1441 Guidance Availability of Flightcrew Oxygen May 11, 1992 25.1441 Oxygen Installation for Medical Use Jan. 3, 1991 25.1445 Isolation of Flight Crewmember Oxygen Jan. 8, 1996 Supply 25.1447 Oxygen Equipment for Forward Observer’s Feb. 1, 1988 Position 25.1447 Oxygen Equipment for Observer Position Jan. 24, 1983 25.1449 Oxygen Equipment for Observer Position April 19, 1996 25.1450 Life Limit on Solid State Oxygen Aug. 15, 1983 25.1453 Use of Plastic Oxygen Lines Dec. 27, 1983 25.1453 Use of Plastic Oxygen Lines Oct. 28, 1983 3/14/2000 AC 25-22 APPENDIX 4 2. FAA Technical Standard Orders (TSO) Referenced in this AC.

The Technical Standard Orders listed below contain information relevant to mechanical system components installed on transport category airplanes. They can be obtained from the U.S.

Department of Transportation, Subsequent Distribution Office, SVC-121.23, Ardmore East Business Center, 3341 Q 75th Avenue, Landover, MD 20785, USA.

TSO Date Title Section Reference TSO-C1c July 10, 1987 Cargo and Baggage Compartment Smoke 25.854 Detection Instruments TSO-C19b Portable Water-Solution Type Fire 25.851 Extinguishers TSO-C20 Combustion Heaters 25.833 TSO-C26 Mar. 15, 1952 25.731 TSO-C26a June 1, 1961 25.731 TSO C26b 1962 Aircraft Tires 25.733 TSO-C26b Jan. 21, 1971 25.731 TSO-C26c Dec. 31, 1979 Aircraft Tires 25.731 TSO-C26c May 18, 1984 Aircraft Wheels and Wheel-Brake 25.731, 25.735 Assemblies, with Addendum I TSO-C45a Feb. 28, 1995 Manifold Pressure Indicating Instruments 25.869 TSO-C47 Pressure Instruments - Fuel, Oil, and 25.1435 Hydraulic TSO-C48 Carbon Monoxide Detector Instruments 25.831 TSO C62c Dec. 31, 1979 Aircraft Tires 25.733 TSO-C62c Sept. 12, 1984 Aircraft Tires, with Addendum 1 25.733 TSO-C62d Sept. 7, 1990 Aircraft Tires 25.733 TSO-C64a Aug. 25, 1989 Oxygen Mask Assembly Continuous 25.1445, 25.1447 Flow, Passenger (for air carrier aircraft) TSO-C75 Hydraulic Hose Assemblies 25.1435 TSO-C78 Crewmember Demand Oxygen Masks 25.1447 TSO-C89 Oxygen Regulators, Demand 25.1447, 25.1449 TSO-C99 June 27, 1983 Protective Breathing Equipment 25.1439 TSO-116 March 1, 1990 Crewmember Protective Breathing 25.1439, 25.1447 Equipment 3/14/2000 AC 25-22 APPENDIX 4 3. FAA Orders Referenced in this AC.

The FAA Orders listed below contain information relevant to mechanical system components installed on transport category airplanes. They can be obtained from the U.S. Department of Transportation, Subsequent Distribution Office, SVC-121.23, Ardmore East Business Center, 3341 Q 75th Avenue, Landover, MD 20785, USA.

Number Title Section Reference 8000.40D Maintenance of Pressure Cylinders In Use As 25.857, 25.1435 Aircraft Equipment, Dec. 26, 1995, AFS-350 8000.54 Process Specifications for Retreading Tires and 25.733 Inspection Procedures Manuals for Tire Retreaders, Nov. 2, 1982, AFS-350 8000.64 Qualification of Aircraft Radial Tires for Use on 25.733 Aircraft and for Retreading, Dec. 4, 1986, AFS-350 8110.4A Type Certification Process, March 2, 1995, AIR-110 21.11 to 21.53 8110.8 Engineering Flight Test Guide for Transport Category 25.729, 25.735 Airplanes, Chg. 5, July 17, 1986. This order was canceled by AC 25-7A, March 31, 1998, ANM-100 8150.1A Technical Standard Order Procedures, Sept. 21, 1987, 21.60 to 21.621 AIR-120 4. FAA Videos Referenced in this AC: These videos are available from the William J. Hughes (FAA) Technical Center, Atlantic City International Airport, Atlantic City, NJ 08405, USA.

Title Section Reference FAA’s Tire Approval Process Video, MTS 422/422.1, 42:15 minutes, September, 1994 25.733 FAA’s Wheels & Brakes Approval Process Videos, Parts 1 & 2, September, 1994 25.735 FAA’s Smoke Quantities to Certify Smoke Detection Systems in 25.858 Cargo Areas, June, 1997 3/14/2000 AC 25-22 APPENDIX 4 5. SAE Documents Referenced in this AC.

The Society of Automotive Engineers (SAE) has aerospace committees that prepare documents reflecting industry standards and practices. While not regulatory in nature, this handbook contains information that may be of interest to an applicant. These documents provide additional information, guidance, and/or standards, and are available from the Society of Automotive Engineers, Inc., 400 Commonwealth Drive, Warrendale, PA 15096-0001, USA.

Number Title Section Reference SAE AIR-737E Hydraulic and Pneumatic Specifications and Standards, 25.1435 May 1995 SAE AIR-786A Elastomer Compatibility Considerations Relative to 25.1435 O-Ring and Sealant Selection, July 1992 SAE AIR-811B Disposition of Wheels which have been Overheated, 25.731 April 1, 1996 SAE AIR-1047C A Guide for Selection of Quick Disconnect Couplings for 25.1435 Aerospace Fluid Systems, April 1994 SAE AIR-1064C Brake Dynamics, March 1, 1993 25.735 SAE AIR-1083B Airborne Hydraulic and Control System Survivability 25.1435 for Military Aircraft, June 1994 SAE AIR-1116 Fluid Properties, July 1992 25.1435 SAE AIR-1362 Physical Properties of Hydraulic Fluids, Nov. 1991 25.1435 SAE AIR-1739 Information on Antiskid Systems, March 1, 1993 25.735 SAE AIR-1899 Aircraft Hydraulic System Characteristics, Nov. 1991 25.1435 SAE AIR-1904 Tire Spray Suppression-Airplane, Design Consideration 25.733 and Testing, Jan. 1, 1997 SAE AIR-1918 Comparison of Hydraulic System Cleanliness Procedures 25.1435 and Requirements for Ten Aerospace Companies, Nov. 1991 SAE AIR-1934A Use of Carbon Heat Sink Brakes on Aircraft, March 1, 1995 25.735 SAE AIR-4003 Turbine Engine Containment, Jan. 1991 25.1435 SAE AIR-4150 Inspection of In-Service Airborne Accumulators, Feb. 1993 25.1435 SAE AIR-4566 Crashworthiness Landing Gear Design, July 1992 25.729 SAE ARP-24B Determination of Hydraulic Pressure Drop, Nov. 1991 25.1435 SAE ARP-219 Procedure and Method for Conducting Test of Hydraulic 25.1435 Components in Contamination Controlled System SAE ARP-490E Electro-Hydraulic Servovalves, Sept. 1993 25.1435 SAE ARP 507C Wheels and Brakes, Supplementary Criteria for Design 25.735 Endurance-Civil Transport Aircraft SAE ARP-597C Wheels and Brakes, Supplementary Criteria for Design 25.735 Endurance, Civil Transport Aircraft, April 1, 1996 SAE ARP-598B The Determination of Particulate Contamination in Liquids 25.1435 3/14/2000 AC 25-22 by the Particle Count Method SAE ARP-763 Accumulators, Ground, Hydropneumatic Pressure, 25.1435 Oct. 15, 1962 SAE ARP-785 Procedure for the Determination of Particulate 25.1435 Contamination in Hydraulic Fluids by the Control Filter Gravimetric Procedure SAE ARP 813A Maintainability Recommendations for Aircraft Wheels 25.735 and Brakes SAE ARP-813B Maintainability Recommendations for Aircraft Wheels 25.735 and Brakes, April 1, 1993 SAE ARP-862A Skid Control Performance, April 1, 1996 25.735 SAE ARP-994 Design of Tubing Installations for Aerospace Fluid 25.1435 Power Systems, Nov. 1991 SAE ARP 1064B Brake Dynamics 25.735 SAE ARP-1070B Design and Testing of Antiskid Brake Control, 25.735 April 1, 1996 SAE ARP-1084 Hydraulic External Leakage for In-Service Components, 25.1435 November 1991 SAE ARP-1280A Aerospace Application Guide for Hydraulic Power 25.1435 Transfer Units, July 1994 SAE ARP-1281B Actuators: Aircraft Flight Controls, Power Operated, 25.1435 Hydraulic, General Specification, May, 1993 SAE ARP-1311A Landing Gear - Aircraft, January 1995 25.729 SAE-ARP 1322 Overpressurization Release Devices, March 1, 1992 25.731, 25.733 SAE ARP-1619 Replacement and Modified Brakes and Wheels, 25.735 April 1, 1993 SAE APR-1709 Coupling Assembly, Hydraulic Self Sealing, Quick 25.1435 Disconnect, April 1994 SAE ARP-1786 Wheel Roll on Rim Criteria for Aircraft Application, 25.731 July 1, 1994 SAE ARP-1832 Color Identification for O-Ring Seals, Dec. 1992 25.1435 SAE-ARP-1907 Automatic Braking Systems Requirements, April 1, 1993 25.735 SAE ARP-4379 Accumulator, Hydraulic, Cylindrical Aircraft, June 1991 25.1435 SAE ARP-4752 Aerospace - Design and Installation of Commercial 25.1435 Transport Aircraft Hydraulic Systems, Sept. 1994 SAE-ARP-4834 Recommended Practice for Retreaded Aircraft Tires- 25.733 Radial and Bias, Nov. 1, 1995 SAE AS-483A Skid Control Equipment, March 1, 1992 25.735 SAE AS 595B Civil Type Aircraft and Variable Delivery Hydraulic 25.1435 Pump, March 1995 SAE AS-707B Thermal Sensitive Inflation Pressure Release Devices 25.731, 25.733 for Tubeless Aircraft Wheels, March 1, 1992 3/14/2000 AC 25-22 SAE AS-1145A Aircraft Brake Temperature Monitor System (BTMS), 25.735 March 1, 1992 SAE-AS-1188 Aircraft Tire Inflation-Deflation Equipment, 25.733 April 1, 1993 SAE AS-1241B Fire Resistant Phosphate Ester Hydraulic Fluid for 25.1435 Aircraft, Feb. 18, 1992 SAE AS-4059 Cleanliness Classification for Hydraulic Fluids 25.1435 SAE-AS-4833 Aircraft New Tire Standard-Bias and Radial, June 1, 1995 25.733 SAE A-6 Committee has prepared the Aerospace Fluid Power 25.1435 Actuation & Control Technologies documents, related to methods for testing and measurement of fluid contamination.

SAE A-10 Committee has prepared the Aircraft Oxygen Equipment 25.1441, 25.1443, Handbook, 1992, or latest revision, containing all Aerospace 25.1445, 25.1447, Standards, Aerospace Recommended Practices, and Aerospace 25.1453 Information Reports related to oxygen equipment published by SAE SAE publication “Aircraft Flight Control Actuation System Design,” 25.1435 by E. T. Raymond and C. C. Chenoweth 3/14/2000 AC 25-22 APPENDIX 4 6. Miscellaneous References in this AC: These documents provide additional information, guidance, and/or standards, and are available from the National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22161, USA.

Number Title Section Reference DOT/FAA/AR-96/122 Development of a Minimum Performance Standard 25.854 for Lavatory Trash Receptacle Automatic Fire Extinguishers, February 1997 DOT/FAA/CT-88/8-1 Aircraft Icing Handbook (three volumes) 25.1419 DOT/FAA/CT/83/1 FAA Technical Center Report, Analysis of 25.857 Dissipation of Gaseous Extinguisher Agents in Ventilated Compartments, May 1983 CAA Technical Development Report No. 146, Appendix I Evaluation of Flight Fire Protection Means 25.857 for Inaccessible Aircraft Baggage Compartments, June 1951 FAA Technical Report ADS-4 Engineering Summary of Airframe Icing 25.1419 Technical Data, Dec. 10, 1963 FAA Report FAA-AEQ-77-13 Ozone Concentration By Latitude, Altitude, 25.832 and Month, Near 80 ° West, August 1977 FAA Report FAA-AM-79-20 Effects of Ozone on Exercising and Sedentary 25.832 Adult Men and Women Representative of the Flight Attendant Population, October 1979 Generic Issue Paper PCARGOE.DOC, Protection of Critical Systems 25.855 & Equipment within Class E Cargo Compartments 3/14/2000 AC 25-22 NPRM 89-31 Minimum Air Flow, Requirements, Fresh Air 25.831 NPRM 93-8 Determination of Allowable Worn Brake 25.735 Limits AD-93-07-15 Class B Fire Extinguishing Methods 25.857 The Tire and Rim Association, Inc. prepares a yearbook which lists aircraft tire 25.731 and rim sizes and ratings. 25.735 The address is: Tire and Rim Association, Inc.

175 Montrose West Ave., Suite 150 Copley, OH 44321, USA.

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3/14/2000 188 AC Draft Mechanical Systems Handbook x x AC Draft Electrical Systems Handbook AC 25-22 AC Draft Crashworthin ess Handbook AC 25- 21 APPENDIX 4 AC Draft Propulsion Handbook AC 25-7A x x Order 8110.8 x x Subject Accelerate-stop distance Landing 3/14/2000 7. Cross Reference for Other Handbooks. While not regulatory in nature, these handbooks contain information that may be of interest to an applicant. These documents provide additional information, guidance, and/or standards. Copies of the handbooks are available from the FAA Transport Airplane Directorate, 1601 Lind Ave. SW, Renton, WA 98055, USA. Part 25 Airworthiness Standards: Transport Category Airplanes Mechanical Systems Subpart B - Performance Section 25.109 25.125 Subpart C - Structures AC Draft Mechanical Systems Handbook x AC Draft Mechanical Systems Handbook x x x x x x x x x AC Draft Electrical Systems Handbook AC Draft Electrical Systems Handbook AC 25-22 AC Draft Crashworthin ess Handbook AC Draft Crashworthin ess Handbook AC 25- 21 AC 25- 21 x x x x x x x AC Draft Propulsion Handbook x AC Draft Propulsion Handbook AC 25-7A AC 25-7A x x x x x Order 8110.8 Order 8110.8 x x x x Subject Lightning protection Subject General Stability augmentation Trim systems Lift and drag device ind. Flap interconnection Takeoff warning system Retracting mechanism Wheels Tires Brakes 3/14/2000 Section 25.581 Subpart D - Design and Construction Section Control Systems 25.671 25.672 25.677 25.699 25.701 25.703 Landing Gear 25.729 25.731 25.733 25.735 190 x x x x x x AC Draft Mechanical Systems Handbook x x x x AC Draft Electrical Systems Handbook AC 25-22 x AC Draft Crashworthin ess Handbook x x x x x AC 25- 21 AC Draft Propulsion Handbook x x x x AC 25-7A x Order 8110.8 Pilot compartment view Doors Ventilation Cabin ozone concentration Combustion heating systems Pressurized cabins Tests for pressurized cabins Subject Fire extinguishers Lavatory fire protection Cargo or baggage compartments Cargo compartment classification Cargo Compartment 3/14/2000 Personnel/Cargo Accommodation 25.773 25.783 Ventilation and Heating 25.831 25.832 25.833 Pressurization 25.841 25.843 Section Fire Protection 25.851 25.854 25.855 25.857 25.858 x x x AC Draft Mechanical Systems Handbook x x x AC Draft Electrical Systems Handbook AC 25-22 AC Draft Crashworthin ess Handbook x x AC 25- 21 x x AC Draft Propulsion Handbook x x AC 25-7A x x Order 8110.8 x fire detection systems Flammable fluid fire protection Fire protection of flight controls Fire protection: systems Subject Negative acceleration Fuel jettisoning system 3/14/2000 25.863 25.865 25.869 Subpart E - Powerplant Section General 25.943 Fuel System Components 25.1001 192 AC Draft Mechanical Systems Handbook x x x AC Draft Mechanical Systems Handbook x x x x x AC Draft Electrical Systems Handbook AC Draft Electrical Systems Handbook x x x x x AC 25-22 AC Draft Crashworthin ess Handbook AC Draft Crash- worthiness Handbook AC 25- 21 AC 25- 21 AC Draft Propulsion Handbook x x x AC Draft Propulsion Handbook x x AC 25-7A AC 25-7A x x Order 8110.8 Order 8110.8 x x Subject Flammable fluid- carrying components Flammable fluids Shutoff means Subject Function and installation Equipment, system, & installation System lightning protection Warning, caution, & advisory System lightning protection 3/14/2000 Section Powerplant Fire Protection 25.1183 25.1185 25.1189 Subpart F - Equipment Section General 25.1301 25.1309 25.1316 25.1322 25.1351 x x AC Draft Mechanical Systems Handbook x x x x x x x x x x AC Draft Electrical Systems Handbook x AC 25-22 AC Draft Crashworthin ess Handbook AC 25- 21 x AC Draft Propulsion Handbook AC 25-7A x Order 8110.8 x Electrical system fire & smoke protection (now 25.869) Ice protection Subject Electronic equipment Vacuum systems Hydraulic systems Pressurization & pneumatic systems Protective breathing equipment Oxygen equipment and supply Minimum mass flow of supplemental oxygen Equipment standards for oxygen distributing system Equipment standards for oxygen dispensing units Means for 3/14/2000 25.1359 Safety Equipment 25.1419 Section Miscellaneous Equipment 25.1431 25.1433 25.1435 25.1438 25.1439 25.1441 25.1443 25.1445 25.1447 25.1449 194 x x x x x x AC 25-22 determining use of oxygen Chemical oxygen generators Fire protection: oxygen equipment (now 25.869) Protection of oxygen equipment from rupture Draining of fluids subject to freezing Equipment containing high energy rotors 3/14/2000 25.1450 25.1451 25.1453 25.1455 25.1461 AC Draft Mechanical Systems Handbook x x x x AC Draft Electrical Systems Handbook AC 25-22 AC Draft Crashworthin ess Handbook AC 25- 21 AC Draft Propulsion Handbook AC 25-7A Order 8110.8 Subject Instructions for continued airworthiness Markings and placards Miscellaneous markings and placards Airplane flight manual 3/14/2000 Subpart G- Operating Limitations Section General 25.1529 25.1541 25.1557 25.1581 196 AC 25-22 THIS PAGE INTENTIONALLY LEFT BLANK.

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