past to obtain the effects of fuselage deformation on exit clearances during minor crash landings.
AC 27.807A. § 27.807 (Amendment 27-26) EMERGENCY EXITS.
a. Explanation. Amendment 27-26 added § 27.807(d)(3) which requires proof that all rotorcraft ditching configuration exits will also be free of interference from emergency flotation devices, whether stowed or deployed (inflated).
b. Procedures. All of the policy material pertaining to this section remains in effect with the tollowing additions:
(1) Test, demonstration, compliance inspection, or analysis is required to show the "ditching" exits are free from interference from stowed/deployed emergency flotation devices. In the event an analysis is insufficient or a given design is questionable, a demonstrating may be required. The demonstration would consist, as a minimum, of an accurate, full-size replica (or representation) of the rotorcraft and of the flotation devices both before, during, an after their deployment.
(2) The type inspection authorization may be used to perform a detailed compliance evaluation utilizing a full-scale rotorcraft in calm water.
(3) Designs may be accepted "by compliance visual inspection" if location of exit and flotation devices relative to each other ensure that interference is impossible.
In this case, a demonstration is unnecessary.
AC 27.807B § 27.807 (Amendment 27-37) EMERGENCY EXITS.
a. Explanation.
(1) Amendment 27-37 increases the maximum gross weight of a normal category rotorcraft from 6000 pounds to 7000 pounds and adds a passenger seat limitation of nine. In conjunction with the weight and passenger limitation and to support a potential increase of passengers, § 27.807 was completely rewritten to include the previous requirements but was revised to require at least one emergency exit on each side of the cabin readily accessible for each passenger. This is required regardless of whether the rotorcraft has a closed cabin or is ditching certified. In addition, at least one of the required exits must be usable in any probable attitude that may result from a crash. Doors intended for use during normal operations may also serve as emergency exits provided these doors comply with requirements specified for emergency exits..
(2) Each emergency exit must provide an unobstructed minimum opening equivalent to a 19-inch × 26-inch ellipse. The methods of opening or operating the emergency exit must be simple and obvious from both inside and outside the rotorcraft.
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AC 27-1B, Chg 1 2/12/03
(3) If equipped with emergency flotation devices, the revised rule still requires that the water or flotation devices do not obstruct the emergency exits whether stowed or deployed and the emergency exits must be above the water line. This must be shown by test, demonstration, or analysis. In addition, if certification with ditching provisions is requested, § 27.807(d) requires the emergency exit markings must remain visible if the rotorcraft is capsized and the cabin is submerged.
b. Procedures. The advisory material pertaining to this section is still in effect with the following additions.
(1) Inere must be at least one emergency exit on each side of the rotorcraft.
As a minimum, one of these exits must be usable in any probable attitude that may result from a crash.
(2) Each emergency exit must provide an unobstructed opening that is equivalent to a 19-inch × 26- inch ellipse. Each emergency exit must have simple and obvious methods of opening from the inside and the outside of the rotorcraft.
(3) Emergency exits are arranged and marked so that they are readily located and opened, even in darkness, and that they are reasonably protected from jamming by fuselage deformation.
(4) Functional tests of each emergency exit must be performed.
(5) If emergency flotation devices are installed, then tests, demonstration, or analysis are required to show that each emergency exit used for a ditching exit is above the water line and will open without interference from flotation devices, whether stowed or deployed. In addition, the required emergency exit markings must remain visible if the rotorcraft is capsized and the cabin is submerged.
AC 27.831. $ 27.831 VENTILATION.
a. Explanation.
(1) This rule specifies minimum ventilation requirements for each passenger and crew compartment. The passenger and crew compartments are required to be free from harmful or hazardous concentration of gases or vapors, and specifically for carbon monoxide, its concentration may not exceed 1 part in 20,000 parts of air during forward flight or hovering in still air.
(2) Failure conditions must also be considered when evaluating the ventilation system, and § 27.1309 is used to cover these aspects. Malfunctions concerning the ventilation system are covered here to make the discussion complete in one paragraph.
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(3) This system becomes more significant when engine bleed air is used for conditioning of the passenger and crew compartment's air. Certain data are necessary in order to analyze properly the bleed air provided under normal and malfunction conditions. The airframe manufacturer can normally look to the engine manufacturer for a specification of the maximum amount of air that can be extracted and the temperature of the extracted air. The engine manufacturer also normally provides a failure analysis that identifies ways the bleed air can be contaminated and the associated oil flow rates under each failure condition. The oil manufacturers are in a position to provide information regarding breakdown of the oil under different temperature conditions and the impact of that breakdown on the quality of the air being provided to the passenger and crew compartments.
b. Procedures.
(1) The passenger and crew compartments should be monitored under normal operating conditions for the presence of carbon monoxide. A carbon monoxide test kit is normally used for this evaluation. Air is monitored around crew stations, and outlets and different combinations of windows closed/open, heat off/on, air-conditioner off/on, etc., are checked to ensure all conditions are evaluated.
(2) When engine bleed air is used to condition the passenger and crew compartment's air, it should be initially substantiated that under normal operation, the amount of air being extracted does not exceed the limit established by the engine manufacturer. To accomplish this, determine the flight condition that will give the maximum bleed air flow through the flow limiter (venturi). The flow calculations should use this maximum flow condition and should also be made using the maximum tolerance diameter of the venturi throat.
(3) The engine bleed air should also be evaluated under malfunction conditions to determine a worst-case air contamination condition. (A typical worst-case malfunction is for an oil seal to fail in the engine that allows the engine oil supply to be introduced into the airflow.) With information regarding the contaminant, flow rate calculations can be made to predict the contamination levels that will be reached in the passenger and crew compartments and also the associated time duration of passenger and crew exposure. The severity of the exposure to the contaminated air is related to the temperature of the oil when it is introduced into the airflow. For example, synthetic base oils manufactured to MIL-L-7808 or MIL-L-23699 begin to break down into toxic components when the temperature exceeds 300° C (572° F). The oil manufacturers have evaluated this problem and should be in a position to provide data regarding the amount and type of toxic components to be expected, and the effect of introducing ne oke ponent to be those components into the passenger and crew compartments. Therefore, from information supplied by the engine manufacturer, the worst-case air contamination condition can be calculated, and this can be compared with results of the oil manufacturers' tests to determine if the concentrations are harmful or hazardous.
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AC 27.833. § 27.833 (Amendment 27-23) HEATERS.
a. Explanation.
(1) Amendment 27-23 added § 27.833 for combustion heaters which is derived from the lead-in paragraph of § 27.859(c) which relates to the fire protection requirements for fuel heaters. Section 27.833 was needed to facilitate the extensive changes made to § 27.859 and to achieve parallel rule construction with Part 29. This will ensure that all combustion heaters will be approved whether as a part of the type design or as a TSO approved combustion heater.
(2) Section 27.833 requires that each combustion heater be approved. The standard contains no provisions regarding functioning of the system, environmental considerations, or malfunctions; therefore, the provisions of §§ 27.1301 and 27.1309 should be used to evaluate those aspects of an installation. The ventilation provisions of § 27.831 should be considered as well as the fire protection and installation provisions of § 27.859.
b. Procedures.
(1) Technical Standard Order, TSO-C20, was issued June 15, 1949, and amended on April 16, 1951, and concerns combustion heaters. If a heater chosen for installation is qualified to the provisions of TSO-C20, it may be approved. If a unit is not TSO qualified, a qualification program for the heater itself in conjunction with the installation should be established. This program under the type design change procedures should be equal or equivalent to provisions of the TSO-C20.
(2) The TSO refers to the SAE Aeronautical Standard, AS 143B, which specifies the use of certain additional devices, design features, air supply considerations, performance tests, safety controls, environmental considerations, and so forth. Compliance with all of the provisions of the Aeronautical Standard should result in an approved unit; however, it will not necessarily result in a satisfactory installation. For environmental considerations, an environmental spectrum more suitable to rotorcraft may be used by referring to the latest version of Document No. RTCA/DO-160, Environmental Conditions and Test Procedures for Airborne Equipment, rather than the older AS 143B. Similarly, other specifications may also be satisfactory for compliance with the standard.
(3) The heater system installation evaluation should also consider functioning of the system based upon the provisions of § 27.1301 (see paragraph AC 27.1301).
Section 27.1309(a) is the regulatory basis for also considering environmental conditions (see paragraph AC 27.1309). The expected environmental conditions resulting from the particular rotorcraft installation should be compared to those specified in the TSO. If the conditions derived for § 27.1309 are not met, additional environmental considerations are appropriate. The provisions of § 27.1309(b) should be used to evaluate the possible malfunctions of the installed system. Such an evaluation should be Page D - 96
documented in a fault analysis. The air quality provisions of § 27.831 apply since Page D - 97
SUBPART D - DESIGN AND CONSTRUCTION
FIRE PROTECTION AC 27.853 § 27.853 (Amendment 27-17) COMPARTMENT INTERIORS.
a. Explanation.
(1) Crew and passenger compartments must have materials that are at least flash resistant or flame resistant as prescribed for the application cited in the standard.
(2) Whenever smoking is allowed, self-contained, removable ashtrays must be provided as stated. A placard or placards, if needed, may be used to prohibit smoking at all times in the crew and passenger compartment. If smoking is allowed, illuminated "no smoking" signs are required. The signs shall meet prescribed standards for passenger compartments that are separate from the flightcrew. Integral crew and passenger compartments (of smaller rotorcraft) do not require illuminated signs since oral commands or instructions from the flightcrew are sufficient.
(3) Amendment 27-17 revised paragraph (c) of § 27.853 by adding the standards for the "no smoking" illuminated signs that must be controllable by the flightcrew. Amendment 29-18 added the same standards for FAR Part 29 transport rotorcraft. The standard requires at least one illuminated sign for use in daylight as well as night in passenger compartments that are separate from the crew compartment. The sign shall be legible to each seated passenger. If forward and aft facing seats are installed, signs for each seat orientation may be needed as prescribed.
Section 29.853(c) of Amendment 29-18 is the same standard as § 27.853(c) of Amendment 27-17.
(4) Advisory Circular 23-2, Flammability Tests, August 20, 1984, provides historical background of the regulatory standards for flash resistant, flame resistant, fire resistant, and fireproof materials. The procedures in AC 23-2 may be used for FAR Part 27 standards. Section 27.853 does not impose standards for mandatory use of self-extinguishing materials. Nevertheless, the FAA/AUTHORITY encourages and recommends use of self-extinguishing interior materials that comply with § 29.853 of Amendment 29-17.
(5) Flammability standards for certain electrical wires or cables are specified in § 27.1365. See paragraph AC 27.1365 for information about electrical wires.
b. Procedures.
(1) Aircraft interior materials including consoles, cabinets, etc., are subject to the standards.
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(2) Advisory Circular 23-2 may be referred to in preparation of test proposals for flammability tests of interior materials.
(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.
AC 27.853A § 27.853 (Amendment 27-37) COMPARTMENT INTERIORS.
a. Explanation. Amendment 27-37 requires all materials in the cabin area to be flame resistant. Section 27.853(b) is now reserved, as the flammability requirements are not dependent on interior material location or function.
b. Procedures. The procedures of paragraph AC 27.853 still apply to the flammability requirements of interior materials except all interior materials must be flame resistant.
AC 27.855 $ 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
(il) 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 Page D - 99
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 AC 27.853 for flammability standards of certain materials.
b. Procedures.
(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.
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AC 27.859 § 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 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.
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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 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 AC 27.1123, 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 AC 27.1183, AC 27.1185, AC 27.1189, and AC 27.1191) 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 Page D - 102
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 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 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.
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(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 AC 27.1121 and AC 27.1123, 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 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(i) 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 AC 27.859b(9), above and paragraph AC 27.1123). 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.
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