152 Section 23.853(a) as well as the commuter category requirements of § 23.853(d)(3).
g. The Small Airplane Directorate has determined there is a need for guidance concerning the installation of electrical wire in small airplanes regarding the applicability of AC 43.13-1B, Change 1 for flammability of electrical wire used in part 23 aircraft. Electrical wire listed in section 7 of AC 43.13-1B, Change 1 complies with §§ 23.853 and 23.1359 and is acceptable for use in part 23 aircraft without further testing.
h. Coaxial cable flammability
Summary
This guidance clarifies FAA certification policy on 14 CFR part 23 and the Airship Design Criteria (ADC). Coaxial cables with Type IX jackets, MIL-C-17/60, /93, /94, /113, /127, and /128, have been tested and found to comply with 14 CFR part 25, § 25.869(a)(4) and applicable section of Appendix F, part I (a)(3) for selfextinguishing. The self-extinguishing requirements in part 23 for the average burn length and the average flame time of the insulation and droppings are the same as part
25. Therefore, this coaxial cable meets or exceeds the part 23 requirements in Subparts D & F and may be installed in part 23 aircraft and airships without further flammability testing.
Applicability
This guidance pertains to part 23, §§ 23.853, 23.855, 23.863 and 23.1359 for installing coaxial cable in part 23 aircraft. It applies to normal, utility, acrobatic, and commuter category airplanes. It also applies to non-rigid airships (ADC sections
4.39, 4.40 and 6.21) certificated in the normal category (14 CFR part 21, § 21.17(b)) with nine passenger seats or less.
Guidance
This guidance applies to the coaxial cables with Type IX jackets (extruded fluorinated ethylene propylene (FEP)) listed below:
MIL-C-17/60 (RG142) MIL-C-17/93 (RG178) MIL-C-17/94 (RG179) MIL-C-17/113 (RG316) MIL-C-17/127 (RG393) MIL-C-17/128 (RG400)
These coaxial cables can be installed in part 23 aircraft and airships without further flammability testing. The coaxial cables have been tested and found to comply with
153 part 25, § 25.869(a)(4) and applicable section of Appendix F, part I (a)(3) for selfextinguishing. Part 25, Appendix F, part I (a)(3) requires insulation on electrical wire or cables be self-extinguishing when subjected to the 60 degree test. The average burn length may not exceed 3 inches, and the average flame time after removal of the flame source may not exceed 30 seconds. Droppings from the test specimen may not continue to flame for more than the average of 3 seconds after falling.
The self-extinguishing requirements in part 23 for the average burn length and the average flame time of insulation and droppings are the same as part 25. Therefore, this coaxial cable meets or exceeds the part 23 requirements for self-extinguishing flammability for electrical wire and cables in Subparts D & F of part 23.
Other MIL-C-17 coaxial cable not listed in this guidance must be flammability tested per the applicable part 23 or ADC requirement.
MIL-C-17 includes some cables with Polyvinyl Chloride (PVC) jackets. These cables should not be used in new installations due to the toxicity, corrosiveness, and flammability characteristics of PVC by-products from burning.
Applicants should expect that the certificating officials will consider this information when making findings of compliance relevant to new certificate actions. Also, as with all advisory material, this policy statement identifies one means, but not the only means, of compliance.
Section 23.1359 is the most severe test requirement for part 23 aircraft. It has the same test procedure, burn length, and flame times as part 1 of Appendix F of part 25.
Therefore, in meeting § 25.869(a)(4), wire in AC 43.13-1B, Change 1 meets the most severe requirement in part 23 and exceeds the earlier flammability requirement of flame resistant. For normal, utility and acrobatic categories prior to amendment 23-49, all parts including wiring are required to be flame-resistant per § 23.853 (as defined in 14 CFR, part 1).
For commuter category prior to amendment 23-49, all materials including wiring must be self-extinguishing per § 23.853 and part 23, Appendix F.
For all part 23 categories with an amendment level of 23-49 and subsequent, § 23.1359 and part 23, Appendix F, requires self-extinguishing insulation on electrical wires and cables.
The applicability of this guidance is to normal, utility, acrobatic and commuter category airplanes (§§ 23.853, 23.855, 23.863 and 23.1359) and to non-rigid airships (ADC sections 4.39, 4.40 and 6.21) certificated in the normal category (14 CFR, part 21, § 21.17(b)) with nine passenger seats or less.
154 Amendment 23-14 and Subsequent
Notice 71-13 explains this amendment level as follows: “The proposal makes provision for illuminated signs in airplanes having separate compartments. Because of increased complexity of systems carrying flammable fluids, the regulations must provide protection.”
Amendment 23-23 and Subsequent
Requirements for materials on the cabin side of the firewall were added because of this amendment. The following explanation in NPRM 75-26 states: “There have been instances where cabin upholstery has been ignited by engine fires even though the flame did not penetrate the firewall. This proposal would broaden Sec. 23.853 to require materials located on or adjacent to the cabin side of the firewall to be selfextinguishing or otherwise protected to prevent fire within the cabin due to engine fire.”
Amendment 23-25 and Subsequent
The proposed revision to NPRM 75-10 changed the “No Smoking” requirement. The following explanation states: “The purpose of this proposal and the similar proposals to Secs. 25.853(c), 27.853(c) and 29.853(c) is to update and make consistent the certification requirements necessary to permit smoking in aircraft.”
Amendment 23-34 and Subsequent
This change added requirements for commuter category airplanes. The explanation in NPRM 83-17 states the following: “SFAR 41, Sec. 7(b) and (c), and Secs. 91.56 and
135.170 of the FAR.”
Amendment 23-62 and Subsequent
In Docket No. FAA-2009-0738, the Discussion of the Regulatory Amendments stated: Previous, § 23.853(d)(2) required placards for commuter category airplanes to have red letters at least ½ inch high on a white background at least 1 inch high. The letter size is not a requirement for either part 23 normal category or for part 25 transport category aircraft. FAA removed the letter size requirement from this section. FAA also removed the ashtray requirement from this section since smoking is no longer allowed in parts 121 and 135 operations. FAA changed § 23.853(d)(2) of this section to read “Lavatories must have ‘No Smoking’ or ‘No Smoking in Lavatory’ placards located conspicuously on each side of the entry door.”
This amendment removes the letter size requirement and the requirement to provide ashtrays for commuter category airplanes. This removes the need for an equivalent level of safety. The Final Rule is adopted as proposed.
Change 1 AC 23-17C 7/16/2012
23.855 Cargo and baggage compartment fire protection
The corresponding rule in CAR 3 is CAR 3.392.
There is no corresponding airworthiness criteria in the Airship Design Criteria.
Amendment 23-49 and Subsequent
A proposed revision in NPRM 94-21 explains this amendment as follows:
“Proposed paragraph (a) would require all sources of heat within each cargo and baggage compartment that are capable of igniting the compartment contents to be shielded and insulated to prevent such ignition.
Proposed paragraph (b) would require cargo and baggage compartments to be constructed of materials that meet the appropriate provisions of Sec. 23.853(d)(3).
Currently these requirements apply to commuter category airplanes and to the materials used in the compartments of these airplanes. The proposed new requirement would expand this applicability to the cargo and baggage compartments of all part 23 airplanes. In effect, the proposed new requirement would require materials that are self-extinguishing rather than flame resistant as currently required under Sec. 23.787(d).
Proposed new paragraph (c) would add new fire protection requirements for cargo and baggage compartments for commuter category airplanes. The proposed rule would require on of the following alternatives: (1) Either the compartment must be located where pilots seated at their duty station would easily discover the fire or the compartment must be equipped with a smoke or fire detector system to warn the pilot's station. The compartment must also provide access to the compartment with a fire extinguisher. (2) The compartment may be inaccessible, but must be equipped with a fire detector system that warns the pilot station, and the compartment must have ceiling and sidewall floor panels constructed of materials that have been subjected to and meet the vertical self-extinguishing tests of Appendix F of this part.
(3) The compartment must be constructed and sealed to contain any fire.
The proposed new section is necessary for several reasons. The proposals for additional requirements for commuter category airplane cargo and baggage compartments were developed after an examination of reported incidents of inflight fires and their causes. Although most of these incidents of inflight fires occurred on transport category airplanes, the reported sources of the fires showed that the fires originate from sources, such as matches in the pockets of clothing, that are as likely to be found on part 23 airplanes as on transport category airplanes. The same potential for inflight fires exists on commuter category airplanes and adequate protection should be provided.”
This rule applies to all baggage and cargo compartments including those that are simply extensions of the cabin area.
The subparagraphs §§ 23.855(c)(2) and (c)(3) are applicable to commuter category aircraft compartments that are not accessible in flight. For these installations, continued safe flight and landing must be assured by extinguishing or containing a fire. To contain a fire, the compartment has to be fireproof which may be shown by compliance with AC 23-2A or by use of a material from 23.1191(h).
See guidance for § 23.853.
All-Cargo or Combination Passenger/Cargo Operations
Special conditions will be required for airplanes approved for all-cargo or combination passenger/cargo operations because 14 CFR, part 23, does not have applicable airworthiness standards for these operations.
23.856 Thermal/Acoustic Insulation Materials
Amendment 23-62 and Subsequent
In Docket No. FAA-2009-0738, the Discussion of the Regulatory Amendments stated: FAA upgraded flammability standards for thermal and acoustic insulation materials used in part 23 airplanes. The current standards did not realistically address situations in which thermal or acoustic insulation materials may contribute to the propagating of a fire. The changes FAA proposes are based on the requirements in § 25.856(a), which were adopted following accidents involving part 25 airplanes, such as the Swissair MD-11. FAA believes the revised standards will enhance safety by reducing the incidence and severity of cabin fires, particularly those in inaccessible areas where thermal and acoustic insulation materials are installed.
The proposed standards include new flammability tests and criteria that address flame propagation, which would apply to thermal/acoustic insulation material installed in the fuselage of part 23 airplanes. Certification tests would consist of samples of thermal/acoustic insulation that would be exposed to a radiant heat source and a propane burner flame for 15 seconds. The insulation must not propagate flame more than 2 inches away from the burner. The flame time after removal of the burner must not exceed 3 seconds on any specimen. (See proposed Part II, Appendix F to part 23 for more details.)
Current flammability requirements focus almost exclusively on materials located in occupied compartments (§ 23.853) and cargo compartments (§ 23.855). The potential for an in-flight fire is not limited to those specific compartments. Thermal/acoustic insulation can be installed throughout the fuselage in other areas, such as electrical/electronic compartments or surrounding air ducts, where the potential also exists for materials to spread fire. New § 23.856 accounts for insulation installed within a specific compartment in areas the regulations might not otherwise cover.
Proposed § 23.856 would be applicable to all part 23 airplanes, regardless of size or passenger capacity. Advisory material describing test sample configurations to address design details (e.g., tapes and hook-and-loop fasteners) is available in DOT/FAA/AR-00/12, Aircraft Materials Fire Test Handbook, dated April 2000.
Insulation is usually constructed in what is commonly referred to as a “blanket.”
Insulation blankets typically consist of two things: (1) a batting of a material generically referred to as fiberglass (i.e., glass fiber or glass wool), and (2) a film covering to contain the batting and to resist moisture penetration, usually metalized or non-metalized polyethylene terephthalate (PET), or metalized polyvinyl fluoride (PVF). Polyimide, a heat-resistant fiber used in insulation and adhesive, is another film used on certain airplanes. Regardless of the film type used, there are variations associated with its assembly for manufacture that result in performance differences from a fire safety standpoint. These variations include the density of the film, the type and fineness of the scrim bonded to the film, and the adhesive used to bond the scrim to the film. The scrim resembles a screen, and the mesh can vary in fineness.
Change 1 AC 23-17C 7/16/2012
158 The scrim is usually constructed of either nylon or polyester and is bonded to the backside of the film to add shape and strength to the surface area. The adhesive used to bond the scrim to the film also varies. However, the type of adhesive used is important because fire retardant is frequently concentrated in the adhesive of the assembled sheet.
This new rule imposes the requirements from Part 23, Appendix F, Part II, for any Part 23 airplane that installs thermo/acoustic insulation materials in the fuselage.
Section 23.856 is adopted as proposed.
23.859 Combustion heater fire protection
The corresponding rule in CAR 3 is CAR 3.388.
There is no corresponding airworthiness criteria in the Airship Design Criteria.
Amendment 23-5 and Subsequent
A proposed revision in NPRM 65-43 explains this amendment as follows:
“Secs. 23.859, 25.859, 27,859, and 29,859 would be amended to clarify, without changing, the conditions under which the "means independent of the components provided for the normal continuous control of combustion heater air temperature, airflow, and fuel flow" must be provided. The intent of this requirement is to require independent means of control when any one of the listed conditions exists.”
Amendment 23-27 and Subsequent
This rule was changed with the following explanation in Docket 20052: “The design complexity and operational altitude and weather capability of current Part 23 pistonpowered airplanes may necessitate installation of combustion heaters for occupant survival and airplane heating to counteract windshield icing conditions. Part 25 presently contains updated type certification requirements for combustion heater fire protection that are applicable regardless of the size of airplane in which the heater is installed. Among these requirements are those for fireproof air ducts and protection of the ventilating airstream from backfire and reverse burning, as recommended by the NTSB for inclusion in Part 23. In addition, Part 25 designates fire zones, requires fire detection means, contains heater control requirements, sets forth air intake location standards, gives heater exhaust requirements, and provides for fuel system protection and drainage. These requirements constitute the necessary minimum safety standards for combustion heater fire protection for any highperformance airplane.
Because of the increasing sophistication of normal category small airplanes and the expanded operating environment for which they are designed and used, the FAA has determined that more stringent type certification fire protection and detection standards are needed for combustion heaters when such heaters are installed in these airplanes. In view of the technical similarities between these airplanes and airplanes designed to Part 25 standards, the Part 25 standards for combustion heater fire protection are substantially adopted as type certification requirements for Part 23.”
23.863 Flammable fluid fire protection
There is no corresponding rule in CAR 3.
The corresponding airworthiness criteria is section 4.40, Airship Design Criteria, FAA-P-8110-2, Change 2.
See § 23.853 guidance in this AC.
Amendment 23-23 and Subsequent
Those areas where ignition sources and flammable fluids are present must be designated as flammable fluid zones, and measures must be taken to minimize the likelihood of ignition sources and leakage being present. This is followed by a means to minimize the effects once a fire has occurred by extinguishing, ventilation, isolation, and drainage. The rule does not go so far to make the entire airplane a “designated fire zone.”
Where fire detection and extinguishing means might be impractical, the back up provisions could, for example, consist of a means to limit fluid leakage and fireproofing or isolation of critical parts. Therefore, compliance with § 23.863 could be accomplished with a means to limit fluid leakage, minimizing the likelihood of ignition, fireproofing or isolating critical parts. Minimization of ignition requires that equipment where a single failure can cause flammable fluid leakage be tested to the explosion proof standards in RTCA/DO-160F.
If a finding is made that either flammable fluids or vapors cannot escape into an area containing a potential ignition source, or if the fluids are nonflammable, this rule would not apply to that area. Design measures could support the finding such as either: (1) shrouding (sealing off) of all potential ignition sources, or (2) shrouding or sealing off all flammable fluid/vapor sources. In either case, it should be discovered the means would continue to serve its function following any single failure of the system or component it is isolating from the area.
23.865 Fire protection of flight controls, engine mounts, and other flight structure
There is no corresponding rule in CAR 3.
The corresponding airworthiness criteria is section 4.41, Airship Design Criteria, FAA-P-8110-2, Change 2.
Amendment 23-14 and Subsequent
A proposed revision in NPRM 71-13 explains this amendment as follows:
“Experience has indicated the need to ensure that flight controls and flight structure in powerplant fire zones remains operable in the event of a fire. The proposal requires this.”
Amendment 23-45 and Subsequent
A proposed revision in NPRM 90-18 added “engine mounts” to the amendement with the following explanation: “This proposal clarifies existing Section 23.865 by excluding those portions of the engine mount certificated with the engine from this section. Additionally, a clarification is provided to address the allowable damage expected on engine isolators.”
The engine mounts refer to the aircraft structure for mounting the engine and not the mount pads or attachment points, which are integral parts of the engine.
The intent of the regulations on engine mounts is the engine remains in place with a fire heating an engine mount. FAA does not intend to cover the case of a general conflagration where the entire engine compartment is burning. Therefore, an applicant should design enough load paths for the engine to remain in place with a localized fire.
For purposes of this rule, landing gears are not considered to be flight structures, so fireproofing or shielding landing gears are at the option of the manufacturer.
Shielding made from fireproof materials in part 23, § 23.1191(h), may be used without flame testing. While the shielding may be made of fireproof materials that do not require testing, means of installing the shielding such as sealers and adhesives should be shown not to reduce the efficacy of the shielding. Shielding materials subject to corrosion should be appropriately protected. Shielding need not be fireproof if it protects the enclosed structure to an extent equivalent to the enclosed structure being fireproof by itself.
The effectiveness of such shielding or fireproof materials should be determined by subjecting the shielded or fireproof structure, or control, to flammability testing as defined in AC 23-2A, “Flammability Tests.” Before removal of the flame at the end
Change 1 AC 23-17C 7/16/2012
162 of the test, loads should be applied to the shielded structure or control to show that it can withstand the loads expected to occur during completion of the flight. These loads can be treated as ultimate loads. Without a more rationale determination of the expected flight loads, a load factor of 70 percent of maneuver load or 40 percent of gust load is superposed with the loads from the engine thrust and torque for maximum continuous power. After five minutes and until the end of 15 minutes the engine may be assumed to be shutdown.
Amendment 23-48 and Subsequent
Policy on compliance of 14 CFR, part 23, § 23.865 at Amendment 23-48 for Structures in Adjacent Areas Subjected to Effects of Fire in Designated Fire Zones
The revision of 14 CFR, part 23, § 23.865 at Amendment 23-48 includes:
1. changing the words “engine compartment” to “designated fire zones” for consistency with §§ 23.1181 and 23.1203; and
2. adding the phrases “adjacent areas that woul d be subjected to the effects of fire in the designated fire zones.”
The intent of this section in the rules is to require the materials and components, in the designated fire zone, that are essential to flight safety: 1) be fabricated either from a material meeting defining fireproof under Title 14, part 1.1, or 2) be shown capable of maintaining their integrity or performing their function under the conditions of fire at least as well as steel. The intent of this section is also to require that materials and components, in adjacent areas to a designated fire zone, that are essential to flight safety, be capable of: 1) maintaining their integrity or 2) performing their function under the conditions of fire in the designated fire zone.
The fire condition characterized by a 2000-degree Fahrenheit (F) flame can be treated as a failure condition that should not prevent continued safe flight and landing for at least 15 minutes. The rule requires the structures (composite and metallic) behind the firewall and subjected to the heat effects of the fire be able to withstand the flight loads expected to occur during completion of the flight. It also requires these flight loads to not be less than the gust loads expected to be encountered during the completion of the flight. These loads can be treated as ultimate loads. Design features, including multiple load path arrangement, can be considered when establishing the remaining structural capacity. Freedom from flutter and whirl mode should also be shown.
Compliance with this requirement must be shown by tests, or by analysis supported by tests. Assessing heat effects needs to include all heat transf er mechanisms that may occur. For composite structure, the long-term environmental effects that may degrade the mechanical properties of the structures also need to be considered. These may include the effects due to moisture and steam pressure.
163 EASA AMC effective February 12, 2009, AMC 23.865 is acceptable for FAA certification.