U.S. Department of Transportation
Advisory Federal Aviation Administration
Circular
AC 25-22
DATE: 3/14/00
CERTIFICATION OF
TRANSPORT AIRPLANE
MECHANICAL SYSTEMS
______________________________________________ Subject: CERTIFICATION OF TRANSPORT
AIRPLANE MECHANICAL SYSTEMS Date: 3/14/00 AC No: 25-22 Initiated by ANM-110 Change:
_________________________
1. PURPOSE. This advisory circular (AC) provides methods acceptable to the Administrator for showing compliance with the type certification requirements for transport airplane mechanical systems and equipment installations. This AC is intended to provide guidance to airplane manufacturers, modifiers, foreign regulatory authorities, Federal Aviation Administration (FAA) transport airplane type certification engineers and their designees. The methods and procedures described herein have evolved over many years and represent current certification practice. Like all advisory material, these guidelines are not mandatory and do not constitute regulations. They are derived from previous FAA experience in finding compliance with the airworthiness requirements and represent methods and procedures found to be acceptable by that experience. Although mandatory terms such as “shall” and “must” are used in this AC, because the AC method of compliance is not in itself mandatory, these terms apply only to applicants who seek to demonstrate compliance by use of the specific method described in this AC.
2. CANCELLATION. Advisory Circular 25-14, High Lift and Drag Devices, dated May 4, 1988, is cancelled.
3. APPLICABILITY. This advisory circular contains guidance for the latest amendment of the regulations and applies to all transport category airplanes approved under the provisions of part 25, for which a new, amended, or supplemental type certificate is requested.
4. RELATED DOCUMENTS.
a. Related Federal Aviation Regulations. Sections which prescribe requirements for the design, substantiation, and certification of transport airplane mechanical systems are for most part in Title 14 Code of Federal Regulations (14 CFR) part 25, subpart D - Design and
Construction, and subpart F - Equipment. Additional sections (and their associated advisory circulars where applicable) that prescribe requirements which can have a significant impact on the overall design and configuration of mechanical systems are in subpart B- Performance, subpart C - Structure, subpart E - Powerplant, and subpart G - Operating Limitations and Information. Five advisory circulars are planned. Each AC will address primarily one area of regulations for transport category airplanes. They are: Certification of Transport Airplane Mechanical Systems (AC 25-XX), Certification of Electrical Equipment Installations (AC 25- XX), Transport Airplane Propulsion Engine and Auxilliary Power Unit Installation Certification Handbook - The Propulsion Mega-AC (AC 25-XX), Certification of Transport Airplane Structure (A 25-21), and Transport Airplane Cabin Interiors Handbook (AC 25-17A). Each AC will cross reference the other four AC's, as necessary, for coverage of the related regulations. A cross reference index is provided as item 7 in appendix 4 of this AC.
b. Advisory Circulars (AC’s). This AC can be found and downloaded from the Internet at http://www.faa.gov/avr/air/airhome.htm, at the link titled "Advisory Circulars."
Copies of advisory circulars referenced in this AC may be obtained from the US Department of Transportation, Subsequent Distribution Office, SVC-121.23, Ardmore East Business Center, 3341Q 75th Avenue, Landover, MD 20785. The help line number is 301-322-4961, and the fascimile number is 301-386-5394 DOT Warehouse.
5. BACKGROUND.
a In the past, advisory and guidance information applicable to transport airplane mechanical systems and equipment installations has been formally published within AC's. However, in many instances, policy has been developed and applied to specific certification projects without formal publication. This policy appeared in the form of policy memorandums and issue papers (or certification review items) which were distributed to the Aircraft Certification Offices. In many instances this information was not organized in a way that allowed easy access. This AC formalizes existing policy so that the public, FAA personnel, and their designees may have access to this information, and contains policy extracted from existing FAA communications used to provide guidance to applicants and other aircraft certification organizations.
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b. The guidance contained in this document is presented in a format that lists the regulatory text, intent of the rule, background of the rule, acceptable compliance methods, and references.
This AC is considered to be a “living document.” As such, it will be revised to maintain currency, such as with the issuance of part 25 rule changes, or the development of substantive new guidance. An index of all references listed in this AC is included as an appendix to this document.
c. The methods and procedures described in this AC are only one acceptable means of compliance. Any alternative means proposed by the applicant should be given due consideration. Applicants are encouraged to use their technical ingenuity and resourcefulness in order to develop more efficient and less costly methods of achieving the objective of part 25.
/s/ Donald L. Riggin Donald L. Riggin Acting Manager Transport Airplane Directorate Aircraft Certification Service, ANM-100
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C ONTENTS
Chapter 1. DESIGN AND CONSTRUCTION
Section 1. CONTROL SYSTEMS
1. Section 25.671 General 1 a . Rule Text 1
2. Section 25.672 Stability augmentation and automatic and power-operated systems 2 a . Rule Text 2
3. Section 25.699 Lift and drag device indicator 3 a . Rule Text 3
b. Intent of Rule 3
c. Background 3
(1) Amendment 25-23 3
d. Policy/Compliance 3
(1) Advisory Circular (AC) 25-14 4 e . Reference 7
4. Section 25.701 Flap interconnection 7 a . Rule Text 7
5. Section 25.703 Takeoff warning system 8 a . Rule Text 8
b. Intent of Rule 8
c. Background 8
d. Policy/Compliance 9 e . Reference 9 [6-10] [ RESERVED] 9
Section 2. LANDING GEAR
11. Section 25.729 Retracting mechanism 11 a . Rule Text 11
b. Intent of Rule 12
c. Background 13
(1) Amendment 25-23 13
(2) Amendment 25-42 13
(3) Amendment 25-72 13 Paragraph Page No.
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(4) Amendment 25-75 13
d. Policy/Compliance 13
(1) Protection of equipment in wheel wells 13
(2) Landing gear position indication system 14
(3) Flap system/landing gear warning system tie-in 15
(4) Landing gear position indication system 15
(5) Landing gear slush tests 16 e . References 17 f . Definitions 17
12. Section 25.731 Wheels 17 a . Rule Text 17
b. Intent of Rule 17
c. Background 17
(1) Amendment 25-72 18 ( 2) Harmonization 18
d. Policy/Compliance 18 e . References 19
13. Section 25.733 Tires 19 a . Rule Text 20
b. Intent of Rule 21
c. Background 21
(1) Amendment 25-23 21
(2) Amendment 25-38 21
(3) Amendment 25-49 21
(4) Amendment 25-52 22
(5) Amendment 25-72 22
(6) Amendment 25-78 22
d. Policy/Compliance 22
(1) Approval of retreaded tires by similarity 22
(2) Approval: nonretreadable tires - qualification testing 24
(3) Approval method for substitute tires 25
(4) Replacement of bias ply tires with radial ply tires 26
(5) Certification of radial tire installation 28
(6) Critical conditions and maximum ramp weight definitions 30 e . References 31
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14. Section 25.735 Brakes 31 a . Rule Text 31
b. Intent of Rule 33
c. Background 34
(1) Amendment 25-23 34
(2) Amendment 25-48 34
(3) Amendment 25-52 34
(4) Amendment 25-72 34
(5) Amendment 25-92 34 ( 6) Harmonization 35
d. Policy/Compliance 35
(1) Carbon brake refurbishment (redensification) 35
(2) FAA/JAA certification requirements;
steel/carbon brakes 37
(3) Certification of replacement brakes 37
(4) Parking brake testing 40
(5) Worn brake requirements, non original equipment parts 41
(6) Determination of allowable worn brake limits 41
(7) Credit for reverse thrust in worn brake testing 46
(8) Certification of brake replacement components 47
(9) Ground equipment - brake cooling unit 51
(10) Certification of asbestos-free brake linings 52
(11) Certification of brake components - performance 53
(12) Approval of brake components utilizing new brake friction material 54
(13) Maximum quick turnaround times 55 e . References 57
Section 3. PERSONNEL AND CARGO ACCOMMODATIONS
15. Section 25.773 Pilot compartment view 59 a . Rule Text 59
b. Intent of Rule 60
c. Background 60
(1) Amendment 25-23 60
(2) Amendment 25-46 60
(3) Amendment 25-72 60 ( 4) Harmonization 60
d. Policy/Compliance 60 e . References 60 [16-25] [RESERVED] 60 Paragraph Page No.
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26. Section 25.783 Doors 61 a . Rule Text 61
b. Intent of Rule 62
c. Background 62
d. Policy/Compliance 62 e . Reference 62 [27-29] [RESERVED] 62
Section 4. VENTILATION AND HEATING
30. Section 25.831 Ventilation 63 a . Rule Text 63
b. Intent of Rule 64
c. Background 64
(1) Amendment 25-41 64
(2) Amendment 25-87 65 ( 3) Harmonization 65
(4) Amendment 25-89 65
d. Policy/Compliance 65
(1) Ventilation rates 65 ( 2) Smoke evacuation 65
(3) Ventilation system design 66
(4) Airplane operation with airconditioning packs off 66
(5) Fresh air and normal operating conditions 69
(6) Ventilation during takeoff 70 e . Reference 70
31. Section 25.832 Cabin ozone concentration 71 a . Rule Text 71
b. Intent of Rule 71
c. Background 71
(1) Amendment 25-56 71 ( 2) Operating Rule 72
d. Policy/Compliance 72
(1) Sea level equivalent 72
(2) Ground test 74
(3) Use of default retention ratio 74
(4) Use of operational limitations 75
(5) Meaning of "time-weighted average" 76
(6) Example of compliance with § 25.832 77 e . References 80
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32. Section 25.833 Combustion heating systems 80 VIII
a . Rule Text 80
b. Intent of Rule 80
c. Background 80
d. Policy/Compliance 80
(1) Standards for certification of combustion heaters 80 e . Reference 83
33. Section 25.841 Pressurized cabins 83 a . Rule Text 83
b. Intent of Rule 84
c. Background 84
(1) Amendment 25-38 84
(2) Amendment 25-87 84 ( 3) Harmonization 85
d. Policy/Compliance 85
(1) Rapid equalization of pressure 85
(2) Access to a pressurized cargo compartment in the engine burst zone during high altitude operation 85
(3) Cabin altitude limit; § 25.841(a) 86 e . References 87
34. Section 25.843 Tests for pressurized cabins 88 a . Rule Text 88
b. Intent of Rule 88
c. Background 88
(1) Amendment 25-87 88 ( 2) Harmonization 88
d. Policy/Compliance 89
(1) Pressure tests for compliance with § 25.843(a) 89 e . Reference 89
Section 5. FIRE PROTECTION
35. Section 25.851 Fire extinguishers 91 a . Rule Text 91
b. Intent of Rule 92
c. Background 92
d. Policy/Compliance 92 e . References 92
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36. Section 25.854 Lavatory fire protection 92 a . Rule Text 92
b. Intent of Rule 93
c. Background 93
d. Policy/Compliance 93
(1) Approval of lavatory smoke detectors 93
(2) Approval of lavatory fire extinguishers containing a gents other than Halon 95 e . References 95
37. Section 25.855 Cargo or baggage compartments 96 a . Rule Text 96
b. Intent of Rule 96
c. Background 97
(1) Amendment 25-15 97
(2) Amendment 25-32 97
(3) Amendment 25-60 97
(4) Amendment 25-72 97
(5) Amendment 25-93 97 ( 6) Harmonization 97
d. Policy/Compliance 97
(1) Halon concentration 98
(2) Class D to class C conversion 98
(3) Protection of critical equipment in class E cargo compartments 100
e. Reference 101
38. Section 25.857 Cargo compartment classification 101
a. Rule Text 101
b. Intent of Rule 102
c. Background 102
(1) Amendment 25-32 102
(2) Amendment 25-60 102
(3) Amendment 25-93 103
(4) Harmonization 103
d. Policy/Compliance 103
(1) Main deck cargo compartment fire protection certification procedures 103
(2) Class A cargo compartments 105
(3) Class E cargo compartments 106 X
(4) Access to Class E cargo compartments 107
(5) Freighter aircraft with accessible class E compartment 107
e. References 108
39. Section 25.858 Cargo or baggage compartment smoke or fire detection systems 108
a. Rule Text 108
b. Intent of Rule 108
c. Background 108
(1) Amendment 25-93 109
d. Policy/Compliance 109
(1) Smoke detection certification testing 109
(2) Certification testing for smoke detection 110
(3) Smoke detection certification testing 111
(4) William J. Hughes Technical Center Research and Developm ent 114
e. References 114
40. Section 25.863 Flammable fluid fire protection 114
a. Rule Text 114
b. Intent of Rule 115
c. Background 115
d. Policy/Compliance 115
e. Reference 115
41. Section 25.869 Fire protection systems 115
a. Rule Text 115
b. Intent of Rule 116
c. Background 116
(1) Amendment 25-72 116
d. Policy/Compliance 116
e. References 116
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