SECTION 21. FIRE PROTECTION
357. § 29.851 FIRE EXTINGUISHERS.
a. Explanation.
(1) The standard concerns objective performance criteria for both handheld fire extinguishers in the crew and passenger compartments and built-in fire extinguisher systems if the system is required.
(2) Section 29.853(e) and (f) dictate the quantity and general location of the handheld fire extinguishers.
(3) Section 29.855(d) contains standards for cargo/baggage compartments.
(4) Sections 29.1541 and 29.1561 concern durable and conspicuous markings and placards for location and operation or use of the equipment.
(5) The rotorcraft flight manual should contain appropriate information as well.
(6) Advisory Circular 20-42C, Handheld Fire Extinguishers for use in Aircraft, provides an acceptable means of compliance with the standard.
b. Procedures.
(1) Advisory Circular 20-42C provides valuable information to select the type and size of the handheld extinguishers.
(2) The type design data shall contain appropriate information. One location should be used (recommended) for the crew compartment. Several locations may be selected to allow for evaluation and approval of several extinguishers and their locations in the passenger compartment.
(3) During a compliance inspection of a complete interior, the installation of required and optional extinguishers shall be checked for compliance.
(4) Whenever an extinguisher is installed, even though not required by § 29.853(f), it shall also comply with the standards.
358. § 29.853 (Amendment 29-23) COMPARTMENT INTERIORS.
a. Explanation.
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(1) Interior materials and components, windows, linings, etc., must meet certain flammability standards as set forth in Amendment 29-17. The rule refers to Part 25, Appendix F (Amendment 25-32), for procedures. Flight Standards Service Release No. 453 contained acceptable flammability standards for specified interior materials prior to adoption of Amendment 29-17.
(2) Smoking may be permitted with use of self-contained removable ashtrays as specified in § 29.853(c).
(3) Fire resistant waste containers may be used as specified.
(4) Hand fire extinguishers are required for flight crewmembers and passengers as specified. Section 29.851 and AC 20-42C, Hand Fire Extinguishers for use in Aircraft, dated March 7, 1984, contain standards for the extinguishers.
Section 29.1561(b) concerns identification and operating information signs for the safety equipment, and § 29.1411 concerns accessibility of the equipment.
(5) Amendment 29-23 adopted new flammability requirements for passenger seat and seat back cushions. Section 29.853(b) was added to require tests of "fire blockingi features of the cushions including upholstery materials. The rule refers to Part II, Appendix F, FAR Part 25 or an equivalent for the test procedures and test specimen requirements. Appendix F to Part 25, effective November 26, 1984, is the correct reference.
b. Procedures.
(1) With adoption of Amendment 29-17, materials subject to the flammability standards were significantly expanded. Acrylic windows and signs and transparencies were, for example, included. The rules list the materials and components subject to the flammability standards and refer to Appendix F of FAR Part 25 for the test procedures.
Specific burn chambers are also required for the tests. See Paragraph b(5) below for flame application time and reference to Appendix F.
(2) A placard prohibiting smoking at all times may be used if ashtrays are not provided. If ashtrays are provided, the installation must have an inner fire resistant liner to close off the ashtray cavity or receptacle when the ashtray is removed. An illuminated sign or signs must be used if prescribed. Each crewmember must be able to control illumination of the sign.
(3) Fire resistant waste containers must have self-closing lids, such as a spring-loaded lid. If a removable container is installed in the receptacle, it must meet the same fire resistant standards as the receptacle. The receptacle must not have any openings outside the galley or an opening into the rotorcraft structure. An opening may allow accumulation of trash and may allow flames and smoke to go throughout the rotorcraft in case of fire.
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(4) A fire extinguisher must be adjacent to crew seats and must be readily accessible to the crew (§§ 29.1411 and 29.853(e)). The extinguisher should be accessible to the crewmember while he is seated. Fire extinguishers are also required in the passenger compartment for seven or more passengers. If one passenger is allowed in the left forward crew seat and six passengers are allowed in the passenger compartment, an extinguisher is not required for the passenger compartment. The extinguisher specified in § 29.853(e) should be located, whenever possible, so that it is visible and convenient to the passengers. If the passenger compartment extinguisher or extinguishers (§ 29.853(f)) are not visible to the passengers when seated, locating signs will be required. See § 29.1561(b).
(5) FAR Part 25, Appendix F, Part 1, established in Amendment 25-32 (effective May 1, 1972) contains flammability test procedures that must be used when complying with § 29.853 of Amendment 29-17. Appendix F refers to sections of FAR Part 25 that do not coincide with sections of the FAR Part 29. To preclude confusion the following statements should be used to develop company test procedures that will provide for compliance with § 29.853.
Section 29.853(a)(1) materials are tested (vertically) to procedures in Appendix F, Paragraph (d), and the flame must be applied for 60 seconds and then may be removed.
(ii) Section 29.853(a)(2) materials are tested (vertically) to procedures in Appendix F, Paragraph (d), and the flame must be applied for 12 seconds and then may be removed.
(iii) Section 29.853(a)(3) and (4) materials are tested (horizontally) to procedures in Appendix F, Paragraph (e), and the flame must be applied for 15 seconds and then may be removed.
(iv) Appendix F, Paragraph (h) contains criteria for burn length measurement.
(v) Appendix F, Paragraph (f) contains a procedure that does not apply to FAR Part 29, certification rules through Amendment 29-19.
(vi) Appendix F, Paragraphs (a), (b), and (c) contain appropriate test procedures. It is noted § 29.853(a)(4) materials are equivalent to the materials specified in § 25.853(b-3).
(vii) Electrical wire and cable materials are tested in accordance with FAR 25, Appendix F, Paragraph (g). (Refer to §§ 29.1351(d)(3), 29.831, and 29.863, and possibly special conditions for some rotorcraft.)
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(6) AC 23-2, Flammability Tests, dated August 20, 1984, pertains to small airplanes and their materials. This AC includes information from Flight Standards Service Release No. 453 and may be useful in preparing a test proposal for flash-resistant, flame-resistant, fire-resistant, and fireproof materials. FAR Part 1 contains a further definition of these four terms.
(7) The "fire blocking layer" features of the seat cushions must be tested as prescribed in Appendix F, Part II, Part 25. Specific test equipment and devices are prescribed. AC No. 25.853-1, Flammability Requirements for Aircraft Seat Cushions, dated September 17, 1986, provides guidance material for demonstrating compliance with the seat cushion flammability standards.
359. § 29.855 (Amendment 29-24) CARGO AND BAGGAGE COMPARTMENTS.
a. Explanation. This section contains standards for accessible and inaccessible compartments. The rotorcraft should be able to contain a fire until it is detected and extinguished or until a safe landing and evacuation are accomplished. The cabin may be used as a cargo compartment for rotorcraft used for carriage of cargo only.
Protective breathing equipment is required (§ 29.1439) for an appropriate crewmember or crewmembers when a compartment is accessible in flight. The rule does not provide for classification of cargo compartments. Reference is made to § 29.853 for flammability standards of certain materials.
(1) The compartment must be constructed of, or lined with, materials that are at least fire resistant. Accessible and inaccessible compartments must comply.
(2) Inaccessible compartments must be sealed and designed to completely contain a compartment fire or to allow detection as stated in § 29.855(c) and (d).
(3) Inaccessible compartments must have a detector unless the compartment can contain a fire as stated. Accessible compartments must have a detector or be designed to ensure detection by a crewmember while at his station as stated in Paragraph (d). Flight evaluations assure that an inaccessible compartment is sealed and will contain smoke, gases, etc., as stated.
(4) The cabin area may be used for carriage of cargo only as stated in Paragraph (e). Crew emergency exit must be accessible; sources of heat protected, and air flow must be stopped.
(5) Section 29.853 of Amendment 29-17 provides flammability standards for cargo compartment liners, covers, cargo, baggage tiedown equipment, etc., as stated in that section. This section pertains to compartments used by passengers or crew.
Section 29.855(a) requires a fire resistant liner and is the overriding requirement.
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b. Procedures. It is intended to provide for adequate protection of the crew and passengers in the event of an in-flight fire. For Category B rotorcraft, one objective as stated in § 29.861 is that the rotorcraft should be protected for at least 5 minutes (after recognition) in the event of a fire. The correct time interval to consider for Category A or B rotorcraft may be derived from the policy stated in Paragraph 361, § 29.861.
(1) An aluminum inner skin, fire resistant liner, or closure of the compartment, whether the compartment is accessible or inaccessible is required by the rule. In the event of a compartment fire, the inner skin or liner will protect the load-carrying structure from direct flame impingement until the fire is detected and appropriate action is taken. Flight Standards Service Release No. 453 provides the standards for fire resistant materials.
(2) Inaccessible compartments, in addition to having the inner skin or liner, must be sealed to prevent entry of air and thereby contain a fire in the compartment.
Flight tests are generally necessary to assure the compartment, primarily doors, do not leak in flight. Sensitive pressure measuring equipment (range of 10 inches of H20) may be used to prove the compartment is sealed by finding no appreciable change in compartment pressure during ground and flight conditions. The appropriate tests should also be conducted to determine that no accumulation of harmful quantities of smoke, flame, extinguishing agents, or other noxious gases occur in any crew or passenger compartment. For compartments having a volume not in excess of 500 cubic feet, an airflow of not more than 1,500 cubic feet per hour is considered acceptable. For larger compartments lesser airflow may be applicable to assure fires are contained.
(3) Inaccessible compartments may have a detector as prescribed. A smoke detector is preferable in place of a fire detector. The instrument panel will have an illuminated red indicator, such as baggage/cargo, as a warning signal for the flightcrew.
Although no specific standards for the detectors are contained in FAR Part 29, the following standards are recommended. The detection system should be designed to provide a visual indication to the flightcrew within one minute after start of a fire or within 5 minutes after smoke initiation appropriate to the detector used (30 seconds is allowed under TSO C 1b, for smoke detector actuation). There should be a means to allow the crew to check in flight the functioning of each fire or smoke detector circuit.
For large compartments, the effectiveness of the detection system should be proven and the detection system should be capable of detecting a fire at a temperature significantly below the temperature at which the structural integrity of the rotorcraft would be substantially decreased.
(4) Accessible compartments must have a detector or detectors unless a crewmember can detect a fire while at his station. Flight evaluations are necessary to assure accessible compartments may be isolated from crew and passenger compartments as stated. The rule envisaged separate compartments for passengers or crew and cargo/baggage.
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(5) Insulation blankets, cargo covers, cargo and baggage tie-down equipment, including containers, bins and pallets used in accessible and inaccessible compartments should meet the flammability standards specified in § 29.853 for the same counterparts noted therein.
359A. § 29.855 (Amendment 29-30) CARGO AND BAGGAGE COMPARTMENTS.
a. Explanation. Amendment 29-30 relaxes previous requirements by allowing small, accessible cargo and baggage compartments to be lined with passenger compartment materials rather than fire resistant materials. Materials may meet the requirements in § 29.853(a)(1), (a)(2), and (a)(3) for cargo or baggage compartments if:
(1) The presence of a compartment fire would be easily discovered by a crew member while at the crew member's station;
(2) Each part of the compartment is easily accessible in flight; or
(3) The compartment has a volume of 200 cubic feet or less.
b. Procedures. The previous procedures continue to apply to Amendment 29-30 except for allowing the use of passenger compartment materials for accessible compartments.
360. § 29,859 (Amendment 29-2) COMBUSTION HEATER FIRE PROTECTION
a. Explanation. This regulation ensures that onboard combustion heating systems (of all type designs) are safe during normal and survivable emergency operations. Thus as a minimum, each combustion heater design must meet the requirements of § 29.859.
b. Definitions.
(1) Backfire. An improperly timed detonation (or explosion) of a fuel mixture which results in higher than normal temperatures and pressures.
(2) Reverse flame propagation. An event that occurs when the flame from a controlled combustion process (such as a heater) goes in an abnormal path (l.e., either a reverse or different path than the intended path) as a result of a change in internal pressure or internal pressure gradient (e.g., a backfire) from a detonation or a similar event.
(3) Safe distance. A maximum flow length dimension determined from the thermodynamics of a worst-case flow reversal (backfire) and the local heater system geometry.
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(4) Heater zone (or region). A geometric zone defined by the heater type, heater size, the location of heater system components, and the maximum safe distance determined under (3) above. The heater system components may affect the heater zone's size if they are closely located to the heat source. For example a heater fuel tank would not be part of the heater zone if it were located far away from the zone boundary; however, if it were adjacent or close to the boundary, it would be included in the heater zone.
(5) Fireproof. Fireproof is defined in § 1.1, "General Definitions."
(6) Severe Fire. The following thermodynamic definitions are based on AC 20-135, "Powerplant Installation and Propulsion System Component Fire Protection Test Methods, Standards and Criteria" and on the definitions in § 1.1 for fire resistant and fireproof materials. These definitions are provided for analytical purposes. A severe fire, when used with respect to fireproof materials, is one which reaches a steady state temperature of 2,000 150° F for at least 15 minutes. A severe fire, when used with respect to fire resistant materials, is one which reaches a steady state temperature of 2,000 ‡150° F for at least 5 minutes.
(7) Hazardous accumulation of water or ice. An accumulation of water or ice that causes a device to not perform its intended function in either normal operation or a survivable emergency situation.
c. Procedures. When suitable data is available, the heating system design should be thoroughly reviewed to determine which system components and arrangements must comply with each subsection of § 29.859. The method-of-compliance relative to each subsection of § 29.859 should then be determined. Acceptable, but not the only, methods of compliance are discussed on a section-by-section basis as follows.
(1) For compliance with § 29.859(a), combustion heater designs, their installations and their heater zones must be identified and thoroughly evaluated. The most direct method of compliance for the heater, itself, is to procure units that already have internal design features that meet the relevant requirements of this section;
otherwise, design features should be provided and evaluated during certification that meet these same requirements. Several combustion heaters are approved under TSO-C20. TSO-C20 provides the procurement sources and the detailed approval standards for these combustion heaters. Each heater, its installation and its heater zone should be reviewed against the criteria of §§ 29.1181 through 29.1191 and §§ 29.1195 through 29.1203 (reference Paragraphs 584 through 589 and 592 through 596 of this AC) to ensure compliance. Next, the fire detector installation drawings and specifications should be reviewed for each heater region. The review should consider all reasonable hazards and failure modes of the heater and the detection system, itself.
If not previously TSO approved, the detectors themselves should be evaluated and 532 Par 360
approved during the overall system certification effort. Then, the drainage and venting system for each heater installation should be reviewed to ensure that areas of fuel or fuel vapor collection are properly drained or vented. The capacity of each drain or vent should be determined and, unless impracticable, the flow capacity should be a minimum of 3-to-1 over the worst-case leakage anticipated (including the adverse effects of surface tension). Phased inspections to eliminate clogging should be considered. Finally, the drainage and ventilation systems should be reviewed to ensure that discharges do not create external hazards by entering or contacting external ignition sources such as engine inlets and hot exhausts. If an accurate determination cannot be made by a design review, ground and/or flight test work with dyed, inert fluids or vapors should be conducted to accurately display discharge patterns.
(2) For compliance with § 29.859(f), the ventilating air duct design should be reviewed to determine what ducts are routed through heater zones. Once this has been determined, each duct section running through the heater zone should be made fireproof by either using a fireproof shroud around the existing duct or by using fireproof material for the duct wall. A primary purpose of these certification measures is to eliminate any system leakage that would allow carbon monoxide (a poisonous gas) to enter occupied areas, incapacitate the crew or passengers, and cause a crash.
Regardless of the method-of-compliance chosen, periodic checks should be performed during certification using carbon monoxide detection equipment to certify the leak-free integrity of the system. Several such checks should be done during flight test, especially after rigorous maneuvers, to ensure no leakage. It is also recommended that periodic checks using a carbon monoxide detector be conducted in conjunction with phased visual inspections (typically at a less frequent interval than each visual inspection) to ensure continued airworthiness. Carbon monoxide tests are reliable and quickly accomplished without any system disassembly. Continued airworthiness considerations are very important since carbon monoxide is a colorless, odoriess, tasteless, poisonous gas that incapacitates an occupant without warning. Carbon monoxide's ability to incapacitate increases with altitude, and has long been suspected as a probable cause for many aircraft accidents. It is the subject of General Aviation Airworthiness Alert No. 137, dated December 1983.
(3) For compliance with § 29.859(c), any design using combustion air ducts should be reviewed to ensure that the ducts are either made from fireproof material or shrouded with a fireproof shroud over a safe distance (see definition). The safe distance should be determined analytically, by test, or a combination, if the analytical results are not conclusive. The design should be reviewed to ensure that combustion air ducts are not connected to the ventilating airstream, except when an informal equivalent safety finding can be made that shows backfires or reverse burning cannot induce flames or fumes into the ventilating airstream under any failure condition or malfunction of the heater or its associated components. Such a finding should require analysis, testing, or a combination for a proper determination. A hazard FMEA should be conducted to ensure that no flames or fumes can be induced under any failure mode.
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(4) For compliance with § 29.859(d), the design and installation of all standard heater control components, control tubing and safety controls should be reviewed to determine the probable points of water or ice accumulation (e.g., sumps, rough surfaces, joints, etc.). If a design review cannot accurately determine these accumulation points, then bench tests and flight tests should be conducted for proper determination. Once these points are identified, the ability of the effected part (or parts) to perform its intended function when water or ice has fully accumulated must be determined for both normal and survivable emergency operations. If the part (or parts) either has not lost its ability to function; has lost part of its ability to function; or has lost all of its ability to function; and the entire system's function is not impaired, then nothing further should be required. However, if the overall system's function is hazardously impaired or lost, as a result of water or ice accumulation on a part (or parts), then rectifying design improvements should be made prior to final approval. These improvements should either alter the part's environment (e.g., relocation, enclosure, insulation, etc.) or eliminate the hazardous accumulation of water or ice (e.g., provide drainage, better sealing, better location, different surface finish, etc.).
(5) For compliance with § 29.859(e), combustion heaters, if used, must have separate, independent safety controls from their standard controls (e.g., air temperature, air flow, fuel flow, etc.) which are remotely located in case of a heater fire, are operable by the crew and automatically shut off the ignition and fuel supply when a hazardous condition exists, (as defined by § 29.859(g)). These separate safety controls must comply with § 29.859(g) (1), must keep the heater off until restarted by the crew or ground maintenance, and must warn the crew when an essential heater is automatically shut down. The safety control system design should be thoroughly reviewed and tested to ensure that it complies and that no hazardous failure modes exist. An FMEA should be conducted to ensure proper compliance.
(6) For compliance with § 29.859(f), each combustion and ventilating air intake's location should be identified, reviewed, and tested to ensure that no flammable fluids or vapors can enter the heater system, ignite and create a fire. If a combustion or ventilating air intake's location is critical or questionable, it should be relocated, shielded, drained, or other equivalent means provided to eliminate the potential fire hazard. If engineering analysis and evaluation are not adequate to make an acceptable safety finding, testing using dyed, inert, leaked fluids or vapors should be conducted.
(7) For compliance with § 29.859(g), each heater exhaust system design should be reviewed, tested, or a combination to ensure proper compliance with § 29.1121 and § 29.1123 (reference AC Paragraphs 548 and 549, respectively). Each exhaust shroud should be sealed to ensure that leaked flammable fluids or vapors do not contact the hot exhaust and cause a fire. The seal design should be reviewed to ensure that the sealing material is fireproof, is chemically compatible with the relevant fuels and vapors, is durable and is functionally adequate. If the design review is not conclusive for compliance purposes, then the seal system should be bench tested 534 Par 360
7/30/97/ AC 29-2B under pressure while undergoing critical service loads and motions to ensure no leakage occurs. Phased seal inspections should be considered to ensure continued airworthiness. An analysis should be conducted to determine the structural effects on the exhaust system of the worse case restricted backfire (typically a shock wave analysis can be used to determine the peak internal pressure and the resultant load on the exhaust system.) If structural failure would occur, based on the analysis, either the backfire restriction should be reduced or the exhaust design should be structurally improved to eliminate the failure.
(8) For compliance with § 29.859(h), each heater's fuel system design must be reviewed to ensure compliance with the powerplant fuel system requirements of Part 29 that are necessary for safe operation to be achieved. An equivalent safety finding should be made if an application is received that requests partial compliance or non-compliance with the powerplant fuel system requirements of Part 29. The finding should ensure that the safety intent of § 29.859() is achieved. Analysis, engineering evaluation, testing, or a combination should be used to substantiate the heater fuel system design. Heater fuel system components that, by leakage or other failures, can induce flammable fluids or vapors into the ventilating air stream should be shrouded by drainable, fireproof shrouds.
(9) For compliance with § 29.859(1), the drain system design should be reviewed to identify parts that may be subjected to high temperature and parts that may be subjected to hazardous ice accumulation in service. The high temperature parts should be evaluated using the methods of compliance for heater exhausts (reference Paragraph c(7), above and Paragraph 549 of this AC). Drains that would be stopped up from ice accumulation should be protected by relocation, size, shields, heating, or a combination to ensure hazardous fluids and vapors are properly drained away.
361. § 29.861 FIRE PROTECTION OF STRUCTURE, CONTROLS, AND OTHER PARTS.
a. Explanation.
(1) As stated in the rule, a Category B rotorcraft must be controllable until landed and a Category A rotorcraft must be controllable and continue its flight after a powerplant fire. For Category B rotorcraft designs with Category A powerplant isolation or Category A rotorcraft, a powerplant fire in one engine compartment must not adversely affect the remaining engine or engines. (Refer to § 29.903(b)). A policy statement on powerplant fire protection provisions was contained in the following note that appeared after Civil Air Regulation (CAR), Part 7, § 7.480, Designated Fire Zones.
NOTE: For Category B rotorcraft, the powerplant fire protection provisions are intended to ensure that the main and auxiliary rotors and controls remain operable, that the essential rotorcraft structure remains intact, and that the Par 360 535
passengers and crew are otherwise protected for a period of at least 5 minutes after the start of an engine fire to permit a controlled autorotative landing.
(2) To achieve the objectives of the rule, each part of the rotorcraft, as stated in the rule, must be isolated from a powerplant fire by a firewall (§ 29.1191), or for
(i) Category A, must be fireproof and must also comply with § 29.903(b).
(Il) Category B, must be protected so that they can perform their essential tunctions for at least 5 minutes under any foreseeable powerplant fire condition.
Review Case No. 26 pertains to CAR, Part 6, §§ 6.384 and 6.483. These rules were replaced by §§ 27.861 and 27.1191 respectively. Even though these rules pertain to normal category rotorcraft requirements, the objective statements contained in the review case pertain to the interpretation of the time interval specified by CAR, Part 7, § 7.384(b) and the note under CAR, Part 7, § 7.480 for Category B rotorcraft. These rules have been replaced by § 29.861(b) and § 29.1191, respectively. In the review case, the FAA stated, in part, that the firewall must be fireproof, support appropriate flight and landing condition loads, and prevent flame penetration when subjected to a flame of 2000° F for 15 minutes. Essential structure and controls must be protected for the duration of time appropriate to the rotorcraft operation and be able to carry loads and resist any failure that could cause hazardous loss of control when subjected to the temperature resulting from any foreseeable powerplant fire. Insufficient protection to provide enough time for a controlled landing would represent an unsafe feature or characteristic for the rotorcraft design.
(3) In addition, Paragraph 590 of § 29.1193(c) pertains to allowable opening in engine cowls and to fireproof skins in specified cases.
b. Procedures.
(1) If each part described in the rule is isolated completely by firewalls, compliance is obtained for Category A or B.
(2) If each part described by the rule is made of fireproof material such as steel, compliance is obtained for Category A or B.
(3) For some Category A rotorcraft, § 29.903(b) also imposes additional considerations where structure, controls, and other parts are common to the engine installation. For example, an interconnected engine mount must be fireproof and also perform its function and not affect the remaining engine in case of a powerplant fire. An evaluation should involve propulsion and airframe disciplines.
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(4) For Category B certification, if each part described by the rule does not comply as stated in (1) or (2), it must be proven that it will perform its function under the prescribed conditions. Compliance for Category B may be demonstrated by the following criteria:
(i) The parts must have a positive margin of safety for the appropriate flight and landing condition, including appropriate engine power conditions, under any foreseeable powerplant fire condition. The time interval under consideration here is the time necessary to complete an emergency descent (as described in the flight manual) and landing from the maximum operating altitude for which certification is requested. In no case is the total time interval to be less than 5 minutes.
(ii) The factors affecting the time interval should include the maximum height above the terrain, the maximum operating altitude, the flight manual recommendations for rate of descent, and a reasonable time for recognizing a powerplant fire.
(iii) The factors affecting the change in physical characteristics (strength primarily) of the parts are the temperature of the part, time interval at the elevated temperature, size, heat absorption or rejection.
(iv) The factors affecting the temperature of the part are location and distance from fire and flames, and temperature of the flames (2,000° F +50° F should be used unless proven otherwise).
(V) The rule requires substantiations for any foreseeable powerplant fire condition. Each rotorcraft design is unique and an evaluation of each design is necessary to establish the fire and flight conditions under consideration.
(vi) A very brief and simple example of compliance noted here may be helpful. This example pertains to a single engine Category B rotorcraft with the engine mounted on top at the fuselage center line. The engine is supported by all steel tubular mounts. The fuselage panel serves as a work deck as well as a firewall. A 15-minute duration is appropriate for this design. A representative panel of the firewall (deck) skin may be subjected to the autorotation flight loads and the landing load. A flame from an appropriate size burner, measuring 2,000° 150° F at the skin surface, should impinge on the loaded panel for 15 minutes. The panel may deform but must remain intact and sustain the appropriate load. The flame must not penetrate the panel skin.
(vii) Other rotorcraft designs may have engines located on top of the fuselage and under the main rotor. If cowls or firewalls do not isolate the rotors and essential controls, it must be determined by a rational analysis or by temperature measurement that the rotor and essential controls will perform their functions. Air flow through the rotor and factors noted in Paragraphs b(4)(ii), (ili), and (iv) are important to Par 361 537