b. Procedures.
(1) Compliance with § 29.1193(a) can be shown by analyzing the cowling and engine compartment covering and determining that no structural degradation will occur under the highest loads experienced on the ground or in flight.
(2) Compliance with § 29.1193(b) can be accomplished by ensuring that the drain will discharge positively with no traps and is a minimum of 0.25 inches in diameter. No drain may discharge where it might cause a fire hazard. This can be demonstrated by colored liquid flowing through the drain system while in flight. The dye should not impinge on any ignition source during any approved flight regime.
(3) Compliance with the fireproof requirements of § 29.1193(c), (d), and (e) can be accomplished by demonstrating that the material will withstand a 2,000° F + 50° F flame for 15 minutes while still fulfilling its design purpose. This testing should accurately simulate, as near as practicable, the likely fire environment to prove the materials and components will provide the necessary fire containment when exposed to a fire situation in service. In addition to the fireproof requirements, the requirements of § 29.1191 must also be met. The primary objectives are:
To contain and isolate a fire and prevent other sources of fuel and/or oxygen from feeding the existing fire; and
(ii) To ensure that components of the engine control system will function effectively to permit a safe landing and/or shutdown of the engine.
590A. § 29.1193 (Amendment 29-26) COWLING AND ENGINE COMPARTMENT COVERING.
a. Explanation. Amendment 29-26 adds a new § 29.1193(f) that requires redundant retention means for each panel, cowling, engine, or rotor drive system covering that can be opened or readily removed. Conventional fasteners for these devices are subject to frequent operation by maintenance personnel and have deteriorated, failed from wear or vibration, or been left unsecured after preflight inspections. Such a failure could be hazardous if a loose panel, cowling, or covering strikes, or is struck by, the rotors or by critical controls.
b. Procedures.
(1) Compliance with § 29.1193(f) can be accomplished by simulating, or actually failing, one or more of the retention devices or by structural analysis. If a failure of a single retention device can contribute to multiple failures, these multiple failures Par 590 905
should be considered. It should be shown that the cowling or cover will not open, strike, or be struck by the rotor or other critical component.
(2) Consideration should be given to minimize the possibility of latches being improperly closed that could result in a cowl coming open in flight.
(3) The failure of one latching device should not cause the failure of another latching device.
(4) The consequences of "forgetting" to latch a cowl should be considered.
(5) The use of safety straps should be considered to minimize the impact of a latching device failure.
591. § 29.1194 (Amendment 29-3) OTHER SURFACES.
a. Explanation. This section states the fire resistance requirements for material surfaces near engine compartments and designated fire zones (other than tail surfaces not subject to heat, flames, or sparks emanating from a designated fire zone or engine compartment).
b. Definition.
(1) Other Surface. Any airtrame, system, or powerplant component aft of and near an engine compartment, a designated fire zone, or another heat source which would receive a heat flux as a result of a fire in the engine compartment or fire zone that would require the component to be fire resistant.
(2) Fire Resistant. In accordance with § 1.1, is defined as follows:
(i) Sheet metal or structural members with the capacity to withstand the heat associated with the fire at least as well as aluminum alloy in dimensions appropriate for the purpose for which they are used.
(ii) Fluid carrying lines, fluid system parts, wiring, air ducts, fittings and powerplant controls with the capacity to perform their intended functions under the heat and other conditions resulting from a fire.
(3) Eire. A fire in either an engine compartment or a designated fire zone is assumed to occur that produces a heat flux on a system, airframe or powerplant component aft of or near the fire. The effect of each such fire on other surfaces must be considered on a case-by-case basis to determine the critical case. Unless a more rationale definition is furnished and approved during certification, the fire in any engine compartment or designated fire zone should be assumed, for purposes of analysis, to be a severe fire (see definition in Paragraph 360).
906 Par 590A
c. Procedures.
(1) Other surfaces should be identified during certification by a design review and by a conservative, thorough hazard analysis based on an analytical estimate of the total heat flux (i.e., conduction, convection, and radiation in combination, as applicable) using the definition of a severe fire and of the resultant "other surface" temperature based on a single fire occurring in each engine compartment and designated fire zone, on a case-by-case basis. Once the other surfaces are identified and their severe fire induced maximum temperatures determined, their configuration and material selection should be reviewed on a case-by-case basis to determine either that they are fire resistant, that they can be made fire resistant (within the limits of practicability), or that it is impracticable to make them fire resistant. If the non-fire resistant other surfaces can be readily made fire resistant they should be. If it is impracticable to make them fire resistant, then they should be relocated, insulated, or a combination in order to reduce the total incident heat flux (and, thus, lower their surface temperature) so that they no longer need to be fire resistant. If insulation is used to shield a surface that is subjected to a significant temperature, it must be fire resistant.
(2) A partial validation of analytical heat flux models using the definition of a severe fire can sometimes be achieved during certification tests by using thermocouples or heat-sensitive stickers to measure in-flight temperature ranges and distributions on other surfaces from known thermal environments in engine compartments or other designated fire zones.
592. § 29.1195 (Amendment 29-17) FIRE EXTINGU SHING SYSTEMS.
a. Explanation. This section specifies the types of rotorcraft which must have fire extinguishing systems and the number of discharges. The types of tests and airflow conditions are also specified for demonstration of compliance.
b. Procedures.
(1) The requirements are applicable to each turbine engine powered rotorcraft, Category A reciprocating engine powered rotorcraft, and each Category B reciprocating engine powered rotorcraft with an engine of more than 1,500 cubic inches. There must be a fire extinguishing system for the designated fire zones defined in § 29.1181.
(2) A fire extinguishing system should dilute all of the atmosphere within and entering a compartment with sufficient inert agent that it will not support combustion, and continue the process long enough to extinguish the existing flame and either dissipate the vapors or eliminate the ignition sources. Conventional systems utilize perforated tubing or discharge nozzles to distribute a specific quantity of agent in approximately 2 seconds. HRD (high rate of discharge) systems utilize open end tubes to deliver a given quantity of agent within 1.35 seconds for CO2 and 1 second for all Par 591 907
other agents. The HRD systems are recommended for use in compartments having high airflow where the required discharge rates can be more effectively provided by a HRD rather than a perforated tubing system. Tests indicate that unrestricted release through such an open end tube distribution system can be relied on for adequate distribution, provided the outlets are located properly. Although the discharge times given above are considered satisfactory, any reduction in discharge time below that specified would improve system effectiveness. However, consideration should be given to the time requirements for draining accumulated combustibles, dissipating combustible vapors and cooling or eliminating ignition sources to assure that the minimum agent concentration is maintained for a duration sufficient to prevent reignition of the combustibles.
(3) The possible variety of tankage and plumbing configurations to accomplish the result should be examined for each specific aircraft in order to achieve the optimum.
Systems can vary from tankage in a central location, which is directed through complex distribution systems to various hazards, to agent which is tanked adjacent to each hazard. Terminology generally accepted to define various arrangements is as follows:
(i) Central System: A single supply of agent, centrally located, with valves to direct the agent to any protected zone or zones.
(її) Individual System: A separate supply of agent for each protected zone or zones.
(4) The selection of the distribution system should be made with full cognizance of the hazards to be covered. The distributor system (i.e., discharge nozzles fed individually by lines from a central manifold) is the most efficient. The complexity of such a system, however, may show it in a less favorable light than the loop or ring system (i.e., orifices drilled in a distribution line, the loop being fed from one end, and the ring being fed from a point on a continuous circle) as far as weight, complexity of manufacture and types of hazard to be covered are concerned. For HRD systems, open feed lines are recommended. In high air flow zones, outlets should be located as far upstream as possible with the discharge directed across the air stream and slightly downstream such that a helical spray pattern is produced. In zones of low or negligible air flow, the outlet location is not critical but a location at the top-center of the zone with the agent directed downward is suggested.
(5) In a conventional CO2 system, all lines upstream of direction valves should be 4,000 PSI (27,600 kPa) burst and lines which are open should be 2,000 PSI (13,800 kPa) burst. Care should be taken to insure that all valving and/or equipment in the distribution line has an appropriate flow rate. Expansion of fittings, tee, etc., should be checked to insure that not over 150 percent of the inflow area exists downstream.
130 percent is accepted as the safest target value. If overexpansion occurs, snow will form and plug the lines. Because of high storage pressure, the orifice areas of a conventional CO2 system seem to act as the flow control with system flow losses as a 908 Par 592
minor effect. Because of this, distribution systems of 50 ft. (15.24m) or less can be satisfactorily computed by the following factor:
Line Area = 10 sq. in./lb CO2/sec (142.2 mm?/kgCO2/sec).
(ii) Orifice Area = .072 sq. in./lb CO2/sec (102.4 mm?/kgCO/sec) (72 percent of equivalent line area).
(Ш) Min. Orifice Size = 1/16 in. (1.6 mm) diameter.
(6) In low pressure systems such as "CB" and CHBr, line and fitting losses become a greater effect in the discharge rates and distribution than was true with CO2.
Consideration should be given to the small I.D. of an AN line fitting with respect to the I.D. of the mating tube sizes. This may be done by extra pressure drop allowances, by enlarging these fittings, or by making special fittings. Within reasonable line lengths, however, area factors can be used with fair accuracy. (It is generally conceded that a system designed to these factors, especially a complex layout, should be carefully tested or analyzed for time of discharge and distribution.) These areas are as follows:
(i) Line Area = 07 sq. in./Ib agent/sec (99.6 mm /kg agent/sec).
(®) Orifice Area = 05 sq. in./lb agent/sec (71.1 mm?/kg agent/sec) (72 percent of equivalent line area).
(ili) Min. Orifice Area = 1/32 in. (.8 mm) diameter.
(7) For HRD systems of all types, feed line cross-sectional area is dependent upon the rate desired and upon system volume considerations. The minimum diameter of the feed line is established by the required rate; the maximum diameter of the feed line, and by the need for keeping the system volume at a minimum. Specifically, with the propelling gas in a system pressurized to 400 PSI (2760 kPa), the "volumetric efficiency" should be at least 0.50; that is, the original volume of the propelling gas in the system should be at least ½ the volume of the entire system, including that of the agent container. It is recommended that for HRD systems the feed lines be open. No nozzles or series of perforations are required. It is believed that the unrestricted release of the more volatile liquid agents, as well as carbon dioxide, can be relied upon for adequate distribution, provided the outlets are properly located. It is important that any such system be carefully tested for time of discharge, distribution, and minimum concentrations.
(8) From the basic definition, the system should be effective if the distribution of the agent floods the various portions of a compartment simultaneously and dilutes the incoming air. It is noted that the typical high flow compartment requires a greater proportion of its total agent discharged at the air inlet than does the conventional low air flow zone. All parts of the fire extinguisher system directed to any one powerplant Par 592 909
installation should be discharged simultaneously. The theory behind the HRD type system is that with rapid discharge of the agent, the concentration necessary for extinguishment is reached more rapidly with correspondingly less time for dissipation or dilution of the agent by incoming air. The duration of this critical concentration necessary for extinguishment is believed to remain the same as for conventional systems.
(9) Detailed system configuration recommendations are not available for conventional systems; however, the recommendations on the configuration of HRD systems would probably apply equally well to all types. For HRD systems, it is recommended that feed lines be as short as possible, requiring that agent containers be as close as practical to the zones to be protected. Feed lines should be direct; the fewer fittings and turns, the better. Expansions and restrictions have adverse effects on rate; and it is probable that in a feed line with long rises or many changes or direction, quantities of propelling gas can get past a liquid agent, thus reducing the discharge rate and making the discharge sporadic and ineffective. Where such fittings, changes of direction, and long vertical rises are unavoidable, compensation in the form of additional agent may be necessary.
(10) A fixed "one shot" fire extinguisher system should be provided for the heater extinguisher system in order to extinguish the fire in the combustion chamber.
The regions surrounding the heater and combustion chamber must also be protected if these regions contain components with potential combustible leakage. No fire extinguishment is needed in cabin air passages.
593. § 29,1197 (Amendment 29-13) FIRE EXTINGUISHING AGENTS.
a. Explanation.
(1) Fire extinguishing agents used in rotorcraft fire extinguishing systems must be capable of extinguishing any fire in the area where the system is installed.
(2) The extinguishing agent must maintain its effectiveness after prolonged storage under the environmental conditions of the compartment in which it is stored.
(3) If a toxic extinguishing agent is used, the harmful concentration level of the fluid vapors must be determined and it must be shown that it is not possible for this concentration level to enter into any personnel compartment.
b. Procedures.
(1) The fire extinguishing system should dilute all of the atmosphere within and entering a compartment with sufficient inert agent so that combustion cannot be supported. The extinguishing process should continue for a duration sufficient in length to extinguish any existing flame. When a compartment is to be flooded with agent and 910 Par 592
there is a source of fresh air entering the compartment, the incoming air should be either shut off prior to the release of the agent or rendered inert by directing extinguishing agent into the air blast (preferably the former) or the quantity of agent should be increased to offset the incoming airflow.
(2) There are a number of extinguishing agents which have been used on rotorcraft in the past. The following list identifies the agent and some advantages and disadvantages of each.
Agents Advantages Carbon Dioxide Safest agent to use from the COz standpoint of toxicity and corrosion hazards.
Methyl More effective for equal mass than Bromide COz. Approx. 80 percent of this CHzBr agent by weight as compared to CO2 is required.
Less variation in vapor pressure than CO2. Much lower container pressure required resulting in lighter containers. Treated magnesium alloys are satisfactory for use in CHBr systems outside of the potential fire zones.
Disadvantages Mental confusion and suffocation hazard to occupants if sufficient gas is discharged into personnel compartments. CO2 has an extremely large variation in vapor pressure with temperature which makes it necessary to use stronger (heavier) containers than are required for methyl bromide.
Much more toxic than CO2. Due to its toxic effects on humans, CHBr should not be used as a fire extinguisher agent in areas where harmful time concentrations can enter personnel compartment.
Aluminum alloy material should not be used in methyl bromide systems due to serious corrosion and possible spontaneous ignition.
Rapidly corrodes aluminum, magnesium, and zinc.
Tubing systems should be vented at all times and steps should be taken to free the tubing of residual methyl bromide after each discharge.
Containers must be recharged at the extinguisher manufacturer's plant or at a depot by specially trained personnel.
Par 593 911
Agents Advantages Disadvantages Bromo- Low vapor pressure compound - Toxic when burned.
chloro- 3 PSIA (20.7 Kpa) at 70° F (21.1°C).
methane ("CB") One of the more effective agents.
CH2BrCI Dibro- Low vapor pressure compound - Very toxic when burned.
modi- 14 PSIA (96.5 Kpa) at 70° F Tluoro- (21.1° C). One of the more effective methane agents.
CFzBr Non-corrosive to aluminum, steel and brass.
Bromotri One of the more effective agents.
fluoromethane Low toxicity in natural condition and when burned.
Non-corrosive to aluminum, steel and brass.
Nitrogen Nz If a fuel tank inerting system using N2 is provided, use as extinguishing agent may be considered. N2 offers cooling not available with CF3Br.
High vapor pressure compound - 220 PSIA (1517 Kpa) at 70° F
(21.1° C).
Least toxic of agents in burned condition except for CO2.
3 - 4 times quantity and rate of conventional agents required.
Note: The relative effectiveness of the various agents listed above is considerably influenced by the type of system employed, high rate discharge or conventional; by the method of distribution, open end outlet, nozzle, or spray ring; and by the air flow conditions.
(3) The extinguishing agent must not be affected by the temperature extremes experienced in the compartments in which they are stored. The agent containers should be either "winterized" for extreme temperature operation or so located in the rotorcraft that they will not be subjected to extreme temperatures. Safe limits for unwinterized carbon dioxide cylinders are approximately 0° F (-18° C) to 140° F (60° C).
The cartridge detonators have a variable age-with-temperature limit. Contact should be made with the manufacturer for the latest information available for both installation and storage temperatures.
(4) It must be shown by test that the harmful level of toxic fluid or vapors cannot enter into any personnel compartment due to leakage or activation of the system during normal operation of the rotorcraft in flight or on the ground. The entire 912 Par 593
fire extinguishing system should be mocked-up or installed in the aircraft down to and including distribution tubing and outlets. The tests should be conducted under actual or simulated cruise conditions. The system should be discharged, and compliance verified by use of an appropriate method for measuring agent concentration.
594. § 29.1199 (Amendment 29-13) EXTINGUISHING AGENT CONTAINERS.
a. Explanation.
(1) This section presents the requirements for fire extinguisher containers.
The containers are subjected to high internal pressures for the propulsion of the agent as well as a wide range of external environmental temperatures.
(2) The containers must be adequately protected to preclude any adverse effect on the operation of the system from these external influences.
b. Procedures.
(1) Each extinguishing agent container must have a pressure relief valve which will open at a pressure that is below the burst pressure of the agent container.
The pressure relief valve lines must be located and protected so that they cannot be clogged by dirt, ice, or other contaminates. Both the agent container burst pressure and the relief valve opening pressure limits should be verified by test. Agent containers which meet military specification, MIL-C-22284, requirements are acceptable.
(2) The containers should be located so that an indicator is readily visible to determine if the container has discharged or the charging pressure is below operating minimums. The number and size of agent containers should be adequate to obtain the established agent concentration and duration for the intended compartment. It is preferred that the agent supply containers and the flow control valves are not located in a fire zone.
(3) The brackets for mounting the containers and securing the discharge lines should be designed to withstand all loads to which they may be subjected due to recoil during discharge or any other applied load factor.
(4) The agent containers should be protected from extreme temperature excursions which could have an adverse effect upon the operation of the extinguishing system. Safe temperature limits for "unwinterized" carbon dioxide cylinders are approximately 0° F (-18° C) to 140° F (60° C). Safe limits for "CB" and CHBr spheres are approximately -65° F (-54° C) to 200° F (93° C). The cartridge detonators have a variable age-with-temperature limit and the manufacturer should be contacted for the latest information on installation and storage temperatures. Location of the container in the aircraft should take these temperature limits into consideration.
Par 593 913
595. § 29.1201 FIRE EXTINGUISHING SYSTEM MATERIALS.
a. Explanation.
(1) Many different fire extinguishing agents are available for use in fire extinguishing systems. The choice of extinguishing agent should take into account the chemical reaction (if any) between the extinguishing agent and the materials utilized in the extinguishing system. If there are any incompatibilities, they should not create a hazard by creating volatile or toxic vapors or fumes which could feed a fire or cause injury to passengers, crew, or other personnel.
(2) The fire extinguishing components in an engine compartment must be fireproof to ensure operation in the event of a compartment fire.
b. Procedures.
(1) Compliance with the requirements of § 29.1201(a) can be demonstrated by analysis, test, or a combination of both.
(2) Certification data submitted by the applicant should contain a listing of the chemical ingredients of the extinguishing agent and the other materials in the extinguishing system. These data should also show that the chemical reaction (if any) of these materials, when combined, does not create a hazard.
(3) Where chemical compounds exist and the chemical reaction is not predictable when two different compounds are combined, actual tests may be necessary to determine the hazard potential.
(4) Analysis, test, or a combination of both may be used to demonstrate compliance with the fireproof requirement for all fire extinguishing components located within the engine compartment.
596. § 29.1203 (Amendment 29-40) FIRE DETECTOR SYSTEMS.
a. Explanation.
(1) Fire detection systems are required in turbine engine powered rotorcraft, Category A reciprocating engine powered rotorcraft and each Category B reciprocating engine powered rotorcraft where the engine displacement is greater than 900 cubic inches.
(2) This section specifies material, installation, and some operational requirements for fire detectors to ensure prompt detection of fire in the fire zones and other designated areas.
914 Par 595
b. Procedures.
(1) The detector system should be designed for highest reliability to detect a fire and not to give a false alarm. It is desirable that it only responds to a fire and misinterpretation with a lesser hazard should not be possible. Engine overtemperature, harmless exhaust leakage, and bleed air leakage should not be indicated by a fire detector system. A fire detection system should be reserved for a condition requiring immediate measures such as engine shutdown or fire extinguishing. There are three general types of detector-procedure systems that are commonly used:
A manual system utilizes warning lights to alert the pilot who then follows prescribed cockpit procedure as a countermeasure. A manual system is adequate for hazards in which a few seconds are not important.
(ii) There is also a semi-automatic system. Occasionally a rotorcraft becomes so complex that the emergency procedure exceeds reasonable expectations of the pilot. In such cases, psychology should be weighted against complexity, and "panic switches," combining multiple procedure functions, should be provided to simplify the mental demands on the pilot. Speed is gained by such designs for hazards which may need it.
(iii) The detector of an automatic system automatically triggers the appropriate countermeasures and warns the pilot simultaneously. Such a system should be carefully evaluated to assure that the advantages outweigh the disadvantages and potential malfunctions.
(2) Fires, or dangerous fire conditions can be detected by means of various existing techniques. The following is a partial list of available detectors:
(1) Radiation-sensing detectors.
(il) Rate-of-temperature-rise detectors.
(III) Overheat detectors.
(iv) Smoke detectors.
(v) CO detectors.
(vi) Combustible mixture detectors.
(vii) Fibre-optic detectors.
Par 596 915
(vili) Ultraviolet.
(ix) Observation of crew or passengers.
(3) In many rotorcraft it is desirable to have a detection system which incorporates several of these different types of detectors. Radiation-sensing detectors are most useful where the materials present will burn brightly soon after ignition, such.
as in the powerplant accessory section. Rate of rise detectors are well-suited to compartments of normally low ambient temperatures and low rates of temperature rise where a fire would produce a high temperature differential and rapid temperature rise.
it should be noted that under certain circumstances, where a relatively slow temperature increase occurs over a considerable period of time, a fire can occur without detection by rate of rise detectors. Overheat detectors should be used wherever the hazard is evidenced by temperatures exceeding a predicted, set value. Smoke detectors may be suited to low air flow areas where materials may burn slowly, or smolder. Fibre-optic detectors can be used to visually observe the existence of flame or smoke. The three major detector types used for fast detection of fires are the rascal sensing, fate of rich senses ere within a visible satice ovine artectors are detectors can be obtained in either "continuous" or "unit" type.
(4) The detector system should:
Indicate fire within 15 seconds after ignition, and show which engine compartment in which the fire is located.
(її) Remain on for the duration of the fire.
Indicate when the fire is out.
(iv) Indicate re-ignition of the fire.
(v) Not by itself precipitate or add to the potential of any other hazards.
(vi) Not cause false warnings under any flight or ground operating condition.
A false fire detector indication could significantly increase crew workload, impair crew efficiency, or reduce safety margins and so is classified as a major failure condition. In consequence, such false fire detector indication should be shown to be improbable based on a probability assessment and service experience of the fire detector system.
If the probability of the fire detection system experiencing a false indication cannot be shown to be improbable, a secondary means of determining the validity of the fire indication should be provided.
916 Par 596