(3) A placard prohibiting smoking may be used if ashtrays are not provided. If ashtrays are provided, an adequate number shall be provided, and the installation must have an inner fire resistant liner to close off the ashtray cavity or receptacle when the ashtray is removed.
(4) All illuminated "no smoking" sign or signs must be used when prescribed.
Flightcrew must be able to control illumination of the signs.
(5) If a hand-held fire extinguisher is installed to comply with an operating rule, Advisory Circular 20-42C, Hand Fire Extinguishers for Use in Aircraft, contains acceptable information about hand-held fire extinguishers.
359. § 27.855 CARGO AND BAGGAGE COMPARTMENTS.
a. Explanation.
(1) Cargo and baggage compartments must be constructed of or lined with--
(i) Fire resistant material; or
(ii) Flame resistant material for compartments readily accessible to the crew while in flight.
(2) A liner or a separately constructed compartment shall protect the aircraft structure from significant loss of strength in the event of a compartment fire.
(3) Whenever essential or critical controls, wiring, lines, etc., are located in a compartment, they must be protected as prescribed.
(4) For historical reference, this design standard was adopted in 1953 by Amendment 6-4 to CAR Part 6 for normal category rotorcraft and adopted into FAR Part 27. The expressed interest, paraphrased from the preamble for the amendment, is to provide protection from a compartment fire to a degree which will ensure that a controlled autorotational landing can be made during a period of at least 5 minutes after start and detection of a fire. No distinction was made for twin-engine rotorcraft. A distinction was made between accessible and inaccessible compartments.
(5) It is recommended that tiedown straps or nets, if installed, should be made of material that is at least flame resistant.
(6) Reference is made to § 27.853 and Paragraph 358 of this AC for flammability standards of certain materials.
b. Procedures.
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(1) For a compartment accessible in flight, a flame resistant liner, box, or closure of the compartment is required. For an inaccessible compartment, a fire resistant liner, an aluminum inner skin, box, or closure of the compartment is required.
Advisory Circular 23-2, Flammability Tests, provides information about material flammability tests.
(2) Only fire resistant material may be used in inaccessible compartments.
Carpets and wall coverings may not be used.
(3) Flame resistant materials may be used on floors, walls, and ceilings of accessible compartments.
(4) Although not specified in the standards, it is recommended that tiedown nets or straps comply with the self-extinguishing flammability standards of § 29.853(a)(3). Cargo compartment blankets or covers should comply with the flammability standards of § 29.853(a) (2). However, it is acceptable to use tiedown equipment that meets the flame resistant material standard.
(5) It is recommended that compartments use design features that seal the compartment and prevent airflow into (or out of) the compartment. The objective is to limit the air supply to a potential fire.
(6) Controls, wiring, equipment, and accessories should not be routed through, mounted in, or exposed to the compartment. If these items, as described in § 27.855(b), are in the compartment, they should be protected by a cage or rigid housing adequate to protect the items. To maintain the compartment integrity for fire containment, it may be necessary to separate these items from the compartment by an appropriate fire resistant or flame resistant housing or enclosure.
360. § 27.859 (Amendment 27-23) HEATING SYSTEMS.
a. Explanation. This regulation ensures that onboard heating systems (of all type designs) are safe during normal and survivable emergency operations. Thus, as a minimum, each heating system type design must meet the applicable requirements of § 27.859.
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 (i.e., either a reverse or different path than the intended path) as a result of a change in internal 456 Par 359
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 worse case flow reversal (backfire) and the local heater system geometry.
(4) Heater zone (or region). A geometric zone defined by the heater type, heater size, 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 § 27.859. The method-of-compliance relative to each subsection of § 27.859 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 § 27.859(a), mechanical devices such as shrouds or barriers should be used to create a double walled (fail-safe) condition, i.e., two equal barrier failures must occur to allow carbon monoxide to mix with cabin air. Phased inspections to ensure continued airworthiness should be considered, as well. The purpose of these 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 Par 360 457
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.
(2) For compliance with § 27.859(b), heat exchangers should meet the requirements of Paragraph 549 of this AC, and be readily inspectable either by complete disassembly or by use of other equivalent design maintenance provisions (such as removable inspection covers). Inspectability should be demonstrated during certification by a design review, an inspection demonstration or a combination.
(3) For compliance with § 27.859(c), 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 must be provided and evaluated during certification that meet these same requirements. Several combustion heaters are approved under 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 §§ 27.1183, 27.1185, 27.1189, and 27.1191 (reference Paragraphs 585, 586, 588, and 589 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. If not previously TSO approved the detectors should be evaluated during the overall system certification effort. 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). 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.
(4) For compliance with § 27.859(d), 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.
(5) For compliance with § 27.859(e), 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 sate distance should be determined analytically, by test, or a combination, if the analytical 458 Par 360
results are not conclusive. The design should be reviewed to ensure that combustion air ducts are not connected to the ventilating air stream, except when an equivalent safety finding can be made that shows backfires or reverse burning cannot induce flames or fumes into the ventilating air stream 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.
(6) For compliance with § 27.859(f), the design and installation of all standard 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 failure conditions. If the part (or parts) either has not lost its ability to function: has lost only 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.).
(7) For compliance with § 27.859(g), 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 § 27.859(g)). These separate safety controls must comply with § 27.859(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.
(8) For compliance with § 27.859(h), 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.
(9) For compliance with § 27.859(i), each heater exhaust system design should be reviewed, tested, or a combination to ensure proper compliance with § 27.1121 and § 27.1123 (reference AC Paragraphs 548 and 549, respectively). Each exhaust shroud Par 360 459
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 under pressure while undergoing critical service loads and motions to ensure no leakage occurs. 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.
(10) For compliance with § 27.859(j), each heater's fuel system design must be reviewed to ensure that compliance with the powerplant fuel system requirements of Part 27 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 27. The finding should ensure that the safety intent of § 27.859() 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.
(11) For compliance with § 27.859(k), 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 9, 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. § 27,861 FIRE PROTECTION OF STRUCTURE, CONTROLS, AND OTHER PARTS.
a. Explanation.
(1) As stated in the rule, parts essential to a controlled landing that would be affected by a powerplant fire are to be protected so they can perform their essential functions for at least 5 minutes under any foreseeable powerplant fire condition.
(2) To achieve the objective of the rule, essential parts of the rotorcraft as defined by the rule are to be isolated from a powerplant fire by a firewall (§ 27.1191) or must be protected so they can perform their essential functions for at least 5 minutes under any foreseeable powerplant fire condition.
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(3) Insufficient protection to provide enough time for a controlled landing would represent an unsafe feature or characteristic for the rotorcraft design.
(4) Section 27.1193(d) requires each cowling and engine compartment covering to be at least fire resistant. Also, § 27.1193(e) requires that each part of the cowling or engine compartment covering, subject to high temperature due to its nearness (proximity) to exhaust system parts or exhaust gas impingement, must be fireproof.
(5) In addition, § 27.1194 requires that all surfaces aft of and near powerplant compartments, other than tail surfaces not subject to heat, flames, or sparks emanating trom a powerplant compartment, be at least fire resistant.
b. Procedures.
(1) If each part described in the rule is isolated completely by firewalls, compliance is obtainable.
(2) If each part described by the rule is made of fireproof material, such as steel, compliance is obtained.
(3) If any part described by the rule does not comply with 361b(1) or (2), it shall be proven that it will perform its function under the prescribed conditions. Compliance may be demonstrated by the following criteria:
(i) The parts shall 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.
(il) 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, but stiffness may also be a factor) of the parts are the temperature of the part, time interval at the elevated temperature, size, and heat absorption or rejection.
(iv) The factors affecting the temperature of the part are location and distance from the fire and flames and temperature of the flames (2,000° F +50° F should be used unless proven to be inapplicable).
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(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 rotorcraft with the engine mounted on top at the fuselage centerline. 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 autorotational flight loads and the landing load. A flame from an appropriate-sized burner, measuring 2,000° F t50° 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 should not penetrate the panel skin.
(vii) Other rotorcraft designs may have engines located on top of the fuselage 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 361b(3)(ii, (3) iii), and (3)(iv) are important to an analysis.
361A. § 27.861 (Amendment 27-26) FIRE PROTECTION OF STRUCTURE, CONTROLS, AND OTHER PARTS.
a. Explanation.
(1) Amendment 27-26 revised the regulation to allow use of parts made from standard fireproof materials of known acceptable dimensions in areas affected by powerplant fires without further proof or qualification. Previously, the standard imposed a performance criteria regardless of the materials and part dimensions used.
(2) "Fireproof" and "fire resistant" are defined in FAR Part 1, § 1.1.
b. Procedures.
(1) A part of acceptable geometry made of steel, or another fireproof material, may be used to comply with the standard.
(2) A material system, panel, or assembly would be equivalent to steel provided it successfully completes the flammability tests described in Paragraph 361b(3) (vi) of this AC, for Category B rotorcraft adjusted for the time period appropriate to the rotorcraft application.
462 Par 361
(3) It is appropriate to further define "fire resistant." A material system, panel, or assembly would be equivalent to aluminum (fire resistant) if it successfully completes the following flammability test. Locate a specimen (approximately 8 inches square) of the material system panel, assembly, or part at approximately a 45° angle to a horizontal line. Apply the limit or normal operating load. Impinge a 2000 +150° F (1093 + 83°C) flame on the article for at least 5 minutes duration. Flame penetration of the test article is not allowed. In addition, the part or component should be able to perform its intended function, as installed, during and after the test.
362. § 27,863 (Amendment 27-16) FLAMMABLE FLUID FIRE PROTECTION
a. Background.
(1) The development of § 27.863 can be traced through CARs 6.485 and
6.486, and subsequent Amendment 27-16.
(2) Investigation of several accidents disclosed evidence of in-flight fires caused by leakage of flammable fluids to ignition sources. The revisions to § 27.863 adopted by Amendment 27-16 require significantly more attention to overall fire protection and prevention.
b. Explanation.
(1) Prior to Amendment 27-16, this rule only required either a means to prevent ignition of flammable fluids or vapors or a means to control any resulting fire. Isolation of flammable fluids and vapors from ignition sources by shrouding or sealing was the normal method of compliance. With Amendment 27-16, the rule further requires the assumption that these means fail or are ineffective and a fire does occur. Means to minimize the consequence of these fires must be provided. Specifically identified considerations must include the flammability of any combustible or absorbing materials, electrical faults, malfunction of protective devices, and so forth.
(2) The rule does not require the entire rotorcraft to be a "designated fire zone."
c. Methods of Compliance.
(1) To minimize the probability of ignition of fluids and vapors after single failure of a component or systems, the following methods may be used:
(i) Shroud and drain flammable fluid systems (including steel fluid lines, fittings, etc.) and provide the systems with fuel and vapor seals with respect to potential ignition sources (electrical wiring and equipment, hot bleed air lines, etc.).
(ii) Provide other effective separation, ventilation, or overheat shutdown devices, etc., to preclude ignition.
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(iii) Ensure that electrical equipment in the areas subject to flammable fluids and vapors is either hermetically sealed or has been tested and shown to be free of ignition capability. Paragraph 621 of this advisory circular describes acceptable guidance for such laboratory testing.
(iv) Place a restricting orifice in fluid pressure lines routed to instruments and transducers.
(v) Ensure fluid lines are not located so as to be subject to abrasion during normal operations. Cargo compartments should be evaluated for potential line damage due to cargo movement.
(2) To minimize hazards if ignition occurs:
(i) Provide fireproof designs, firewall isolation, or equivalent means for critical structure, equipment, and personnel areas.
(її) Consider fire detection, extinguishment, shutoff valves, fire suppression systems, etc.
(3) In considering compliance, the actual protective measures may be related to the situation, considering the quantity and flammability characteristic of the fluid, the fire damage tolerance of the area, and the means available to the crew to minimize hazards from the fire. If action by the crew is necessary, a quick acting means (not necessarily fire detectors) must be provided to alert the crew in the event of a fire.
Details of any action required by the crew should be included in the Rotorcraft Flight Manual.
(4) Compliance with § 27.863(d) requires, a minimum, type design data defining each area where flammable fluids or vapors might escape.
363.-372. RESERVED.
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SECTION 22. EXTERNAL LOAD ATTACHING MEANS.
373. § 27.865 (Amendment 27-11) EXTERNAL LOAD ATTACHING MEANS.
a. Explanation.
(1) If certification for external load operations is requested, the rule requires that the external load attaching means be substantiated by test or analysis for a limit static load equal to or greater than 2.5 times the maximum external load for which certification is requested. The factor of 2.5 times the maximum external load was established as a minimum strength requirement by Part 133 operations to account for loading effects of sling-load angles up to 30° from the vertical. Allowance for reducing the 30° angle is provided if substantiated.
(2) The rule requires that a quick-release device be installed on one of the pilot's primary controls so the pilot can quickly release the external load during an emergency situation. In addition, a backup manual mechanical control for the quick-release device is required to be readily accessible to either the pilot or another crewmember.
(3) The rule requires appropriate placards or markings stating the maximum authorized external load.
b. Procedures.
(1) The maximum external load for which authorization is requested should not exceed the rated capacity of the quick-release device. The quick-release device should be strength tested (with FAA/AUTHORITY witness) if it is not produced to a recognized industry or military standard.
(2) Substantiation of external loading requirements must include any direction making an angle of 30° (with the exception of directions having a forward component).
(reference § 27.865(a).)
The sling-load angle (i.e., the angle between the vertical direction and the sling-load cable supporting the external load) should not exceed an angle of 30° to minimize the cable tension load.
(ii) The 30° angle may be reduced if an operating limitation is established limiting external load operations to such angles for which compliance has been shown or if the reduced angle cannot be exceeded in service. The lesser angle should be substantiated by flight testing.
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(3) The external load releasing system is specified to include a quick release device installed on one of the pilot's primary controls. It is usually installed on the cyclic stick to allow the pilot to release the load with minimum distraction after maneuvering the load into the release position.
(4) A manual mechanical control for the quick-release device is specified to be installed and be readily accessible to the pilot or to another crewmember. A sufficient amount of slack should be provided in the control cable to permit complete cargo movement without tripping the cargo release.
373A. § 27.865 (Amendment 27-26) EXTERNAL LOAD ATTACHING MEANS.
a. Explanation. Amendment 27-26 added two requirements to § 27.865:
(1) Section 27.865(a) is clarified to allow use of a design factor less than
2.5g's, for rotorcraft load combinations A, B, and C non-human external cargo applications provided the lower load factor is not likely to be exceeded by virtue of the rotorcraft characteristics and capability. That is, the rotorcraft design factors may be used for the cargo device system.
(2) Section 27.865(d) was added to clarify and specify the fatigue requirements for the external cargo attaching means.
b. Procedures. All of the policy material pertaining to this section remains in effect with the following additions:
(1) For § 27.865(a), if a design limit load factor less than 2.5g's is requested, the applicant should provide a rational analysis and/or a flight operations data base that clearly shows that the load factor requested is unlikely to be exceeded in service.
NOTE: § 27.337(b) requires use of 2.0 g's as a minimum.
(2) § 27.865(d), all failures of the cargo attaching means (and the associated critical components) that are likely to be hazardous to the rotorcraft should be identified by an acceptable means, such as a Failure Mode Effect Analysis (FMEA). The critical components associated with these failures modes should receive a fatigue analysis and/or test to ensure that the likelihood of a failure occurring is minimized. In the majority of cases, an analysis using the methods of AC 20-95, "Fatigue Evaluation of Rotorcraft Structure", will be sufficient. If any component has a service life and/or mandatory inspection these components and each mandatory life should be identified, approved, and placed in the airworthiness limitations section of the maintenance manual or Instructions for Continued Airworthiness. See Paragraph 729 (§27.1529) of the AC for information on these manuals.
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