§25.1731 Powerplant and APU fire detector system; EWIS

(a) EWIS that are part of each fire or overheat detector system in a fire zone must be at least fire-resistant. (b) No EWIS component of any fire or overheat detector system for any fire zone may pass through another fire zone, unless: (1) It is protected against the possibility of false warnings resulting from fires in zones through which it passes; or (2) Each zone involved is simultaneously protected by the same detector and extinguishing system. CS 25J901 Installation (See AMC 25J901) (a) For the purpose of this subpart, the APU installation includes: (1) The APU; (2) Each component that affects the control of the APU; (3) Each component that affects the safety of the APU. (b) For the purpose of this subpart, (1) An essential APU is defined as an APU whose function is required for the dispatch of the aeroplane and/or continued safe flight. (2) A non-essential APU is defined as an APU whose function is a matter of convenience, either on the ground or in flight, and may be shut down without jeopardising safe aeroplane operation. (c) For each APU: (1) The installation must comply with: (i) The installation instructions provided under CS-APU, and (ii) The applicable provisions of this subpart for non-essential APUs, or (iii) The applicable provisions of this subpart for essential APUs. (2) The components of the installation must be constructed, arranged, and installed so as to ensure their continued safe operation between normal inspections or overhauls. (See AMC 25J901(c)(2).) (3) The installation must be accessible for necessary inspections and maintenance; and (4) The major components of the installation must be electrically bonded to the other parts of the aeroplane. (See AMC 25J901(c)(4).) (d) The APU installation must comply with CS 25.1309, except that the effects of the following need not comply with CS 25.1309(b) (see AMC 25.901(c)): (1) APU case burn through or rupture; and (2) Uncontained APU rotor failure. AMC 25J901(c)(2) Assembly of Components The objectives of CS 25.671(b) should be satisfied with respect to APU systems, where the safety of the aeroplane could otherwise be jeopardised. AMC 25J901(c)(4) Electrical Bonding Where the APU is not in direct electrical contact with its mounting the engine should be electrically connected to the main earth system by at least two removable primary conductors, one on each side of the APU. CS 25J903 Auxiliary power unit (a) Each APU must meet the appropriate requirements of CS-APU for its intended function: (1) Essential: Category 1 APU, (2) Non-essential: Category 1 or Category 2 APU. (b) Reserved (c) Control of APU rotation and shut-down capability. (1) It shall be possible to shut down the APU from the flight deck in normal and emergency conditions. (2) Where continued rotation of an APU could jeopardise the safety of the aeroplane, there must be a means for stopping rotation. Each component of the stopping system located in the APU compartment must be at least fire resistant. (d) For APU installation: (1) Design precautions must be taken to minimise the hazards to the aeroplane in the event of an APU rotor failure or of a fire originating within the APU which burns through the APU casing. (See AMC 20-128A.) (2) The systems associated with APU control devices, systems and instrumentation, must be designed to give reasonable assurance that those APU operating limitations that adversely affect turbine rotor structural integrity will not be exceeded in service. (e) In-flight start capability. (1) For non-essential APUs that can be started in-flight and all essential APUs: (i) Means must be provided to start the APU in-flight, and (ii) An altitude and airspeed envelope must be established and demonstrated for APU in-flight starting. (2) For essential APUs: Cold soak must be considered in establishing the envelope of CS 25J903(e)(1)(ii). CS 25J939 APU operating characteristics (a) APU operating characteristics must be investigated in all aeroplane operating conditions from APU start until shutdown to determine that no adverse characteristics (such as stall, surge, or flame-out) are present, to a hazardous degree, during normal and emergency operation within the range of operation limitations of the aeroplane and of the APU. (b) Reserved (c) The APU air inlet system may not, as a result of air-flow distortion during normal operation, cause vibration harmful to the APU. (d) It must be established over the range of operating conditions for which certification is required, that the APU installation vibratory conditions do not exceed the critical frequencies and amplitudes established under CS-APU 120. CS 25J943 Negative acceleration No hazardous malfunction of an APU or any component or system associated with the APU may occur when the aeroplane is operated at the negative accelerations within the flight envelopes prescribed in CS 25.333. This must be shown for the greatest duration expected for the acceleration. AMC 25J943 APU Operating Characteristics 1 Compliance with CS 25J943 should be shown by design analysis and flight tests. The flight tests should include manoeuvre in which less than zero 'g' occurs for one continuous period of at least 5 seconds and a further manoeuvre with two periods of less than zero 'g' with a total time for these two periods of at least 5 seconds. 2 In the case of non-essential APUs, inadvertent shut-down due to negative accelerations is acceptable. FUEL SYSTEM CS 25J951 General (a) Each fuel system must be constructed and arranged to ensure a flow of fuel at a rate and pressure established for proper APU functioning under each likely operating condition, including any manoeuvre for which certification is requested and during which the APU is permitted to be in operation. (b) For essential APUs: Each fuel system must be arranged so that any air which is introduced into the system will not result in flameout. (c) For essential APUs: Each fuel system for an essential APU must be capable of sustained operation throughout its flow and pressure range with fuel initially saturated with water at 26.7 °C and having 0.20 cm3 of free water per liter added and cooled to the most critical condition for icing likely to be encountered in operation. CS 25J952 Fuel system analysis and test (a) Proper fuel system functioning under all probable operating conditions must be shown by analysis and those tests found necessary by the Agency. Tests, if required, must be made using the aeroplane fuel system or a test article that reproduces the operating characteristics of the portion of the fuel system to be tested. (b) The likely failure of any heat exchanger using fuel as one of its fluids may not result in a hazardous condition. CS 25J953 Fuel system independence Each fuel system must allow the supply of fuel to the APU: (a) Through a system independent of each part of the system supplying fuel to the main engines; or (b) From the fuel supply to the main engine if provision is made for a shut-off means to isolate the APU fuel line. CS 25J955 Fuel Flow (See AMC 25J955) (a) Each fuel system must provide at least 100 percent of the fuel flow required by the APU under each intended operating condition and manoeuvre. Compliance must be shown as follows: (1) Fuel must be delivered at a pressure within the limits specified for the APU. (2) For essential APUs: (i) The quantity of fuel in the tank may not exceed the amount established as the unusable fuel supply for that tank under the requirements of CS 25.959 plus that necessary to show compliance with this paragraph. (ii) Each main pump must be used that is necessary for each operating condition and attitude for which compliance with this paragraph is shown, and the appropriate emergency pump must be substituted for each main pump so used. (iii) If there is a fuel flowmeter, it must be blocked and the fuel must flow through the meter or its bypass. (See AMC 25J955(a)(2)(iii).) (b) For essential APUs: If an APU can be supplied with fuel from more than one tank, the fuel system must, in addition to having appropriate manual switching capability, be designed to prevent interruption of fuel flow to that APU, without attention by the flight crew, when any tank supplying fuel to that APU is depleted of usable fuel during normal operation, and any other tank, that normally supplies fuel to that APU, contains usable fuel. AMC 25J955(a)(2)(iii) Fuel Flow The word "blocked" should be interpreted to mean "with the moving parts fixed in the position for maximum pressure drop". CS 25J961 Fuel system hot weather operation For essential APUs: (a) The fuel supply of an APU must perform satisfactorily in hot weather operation. It must be shown that the fuel system from the tank outlet to the APU is pressurised under all intended operations so as to prevent vapour formation. Alternatively, it must be shown that there is no evidence of vapour lock or other malfunctioning during a climb from the altitude of the airport selected by the applicant to the maximum altitude established as an operating limitation under CS 25J1527, with the APU operating at the most critical conditions for vapour formation but not exceeding the maximum essential load conditions. If the fuel supply is dependant on the same fuel pumps or fuel supply as the main engines, the main engines must be operated at maximum continuous power. The fuel temperature must be at least 43°C at the start of the climb. (b) The test prescribed in sub-paragraph (a) of this paragraph may be performed in flight or on the ground under closely simulated flight conditions. If a flight test is performed in weather cold enough to interfere with the proper conduct of the test, the fuel tank surfaces, fuel lines, and other fuel system parts subject to cold air must be insulated to simulate, insofar as practicable, flight in hot weather. CS 25J977 Fuel Tank Outlet For essential APUs: (a) There must be a fuel strainer for the fuel tank outlet or for the booster pump. This strainer must prevent the passage of any object that could restrict fuel flow or damage any fuel system component. (b) The clear area of each fuel tank outlet strainer must be at least five times the area of the outlet line. (c) The diameter of each strainer must be at least that of the fuel tank outlet. (d) Each finger strainer must be accessible for inspection and cleaning. FUEL SYSTEM COMPONENTS CS 25J991 Fuel Pumps (See AMC 25J991) For essential APUs: (a) Main pumps. Each fuel pump required for proper essential APU operation, or required to meet the fuel system requirements of this subpart (other than those in sub-paragraph (b) of this paragraph), is a main pump. For each main pump, provision must be made to allow the bypass of each positive displacement fuel injection pump other than a fuel pump approved as part of the APU. (b) Emergency pumps. There must be emergency pumps or another main pump to feed an essential APU immediately after failure of any main pump (other than a fuel pump approved as part of the APU). AMC 25J991 Fuel Pumps If the fuel supply to the APU is taken from the fuel supply to the main engine, no separate pumps need be provided for the APU. CS 25J993 Fuel system lines and fittings (a) Each fuel line must be installed and supported to prevent excessive vibration and to withstand loads due to fuel pressure and accelerated flight conditions. (b) Each fuel line connected to components of the aeroplane between which relative motion could exist must have provisions for flexibility. (c) Each flexible connection in fuel lines that may be under pressure and subjected to axial loading must use flexible hose assemblies. (d) Flexible hose must be approved or must be shown to be suitable for the particular application. (e) No flexible hose that might be adversely affected by exposure to high temperatures may be used where excessive temperatures will exist during operation or after an APU shut-down. (f) Each fuel line within the fuselage must be designed and installed to allow a reasonable degree of deformation and stretching without leakage. CS 25J994 Fuel system components Fuel system components in an APU compartment or in the fuselage must be protected from damage which could result in spillage of enough fuel to constitute a fire hazard as a result of a wheels-up landing on a paved runway under each of the conditions prescribed in CS 25.721(b). CS 25J995 Fuel valves In addition to the requirements of CS 25J1189 for shut-off means, each fuel valve must be supported so that no loads resulting from their operation or from accelerated flight conditions are transmitted to the lines attached to the valve, unless adequate strength margins under all loading conditions are provided in the lines and connections. CS 25J997 Fuel strainer or filter For essential APUs: There must be a fuel strainer or filter between the fuel tank outlet and the inlet of either the fuel metering device or an APU driven positive displacement pump, whichever is nearer the fuel tank outlet. This fuel strainer or filter must: (a) Be accessible for draining and cleaning and must incorporate a screen or element which is easily removable; (b) Have a sediment trap and drain except that it need not have a drain if the strainer or filter is easily removable for drain purposes; (c) Be mounted so that its weight is not supported by the connecting lines or by the inlet or outlet connections of the strainer or filter itself, unless adequate strength margins under all loading conditions are provided in the lines and connections; and (d) Have the capacity (with respect to operating limitations established for the APU) to ensure that APU fuel system functioning is not impaired, with the fuel contaminated to a degree (with respect to particle size and density) that is greater than that established for the APU in CS-APU 250. OIL SYSTEM CS 25J1011 Oil System General (a) Each APU must have an independent oil system that can supply it with an appropriate quantity of oil at a temperature not above that safe for continuous operation. (b) The usable oil capacity may not be less than the product of the endurance of the aeroplane and the maximum allowable oil consumption of the APU plus a suitable margin to ensure system circulation. CS 25A1017 Oil lines and fittings (a) Each oil line must meet the requirements of CS 25J993 and each oil line and fitting in any designated fire zone must meet the requirements of CS 25J1183. (b) Breather lines must be arranged so that: (1) Condensed water vapour that might freeze and obstruct the line cannot accumulate at any point; (2) The breather discharge does not constitute a fire hazard; (3) The breather does not discharge into the APU air intake system. CS 25J1019 Oil Filter Where there is a filter in the APU lubrication system through which all the oil flows, it must be constructed and installed so that oil may flow at an acceptable rate through the rest of the system with the filter element completely blocked. An impending filter by-pass indication is required. CS 25J1021 Oil system drains A drain (or drains) must be provided to allow safe drainage of the oil system. Each drain must: (a) Be accessible; and (b) Have manual or automatic means for positive locking in the closed position. CS 25J1023 Oil radiators Each oil radiator must be able to withstand, without failure, any vibration, inertia, and oil pressure load to which it would be subjected in operation. CS 25J1025 Oil valves (a) Each oil shut-off must meet the requirements of CS 25J1189. (b) Each oil valve must have positive stops or suitable index provisions in the "on'' and "off'' positions and must be supported so that no loads resulting from its operation or from accelerated flight conditions are transmitted to the lines attached to the valve, unless adequate strength margins under all loading conditions are provided in the lines and connections. COOLING CS 25J1041 General (See AMC 25J1041.) The APU cooling provisions must be able to maintain the temperatures of APU components and fluids within the temperature limits established for these components and fluids, under critical ground and flight operating conditions, and after normal APU shutdown. AMC 25J1041 General The need for additional tests, if any, in hot climatic conditions should take account of any tests made by the APU constructor to establish APU performance and functioning characteristics and of satisfactory operating experience of similar power units installed in other types of aeroplane. The maximum climatic conditions for which compliance will be established should be declared and this should not be less severe than the ICAO Intercontinental Maximum Standard Climate (37·8°C (100oF) at sea-level). If the tests are conducted under conditions which deviate from the maximum declared ambient temperature, the maximum temperature deviation should not normally exceed 13·9°C (25°F). CS 25J1043 Cooling tests (a) General. Compliance with CS 25J1041 must be shown by tests, under critical conditions. For these tests, the following apply: (1) If the tests are conducted under conditions deviating from the maximum ambient atmospheric temperature, the recorded APU temperatures must be corrected under sub-paragraph (c) of this paragraph. (2) No corrected temperatures determined under sub-paragraph (a)(1) of this paragraph may exceed established limits. (b) Maximum ambient atmospheric temperature. A maximum ambient atmospheric temperature corresponding to sea level conditions must be established. The temperature lapse rate is 2.0°C per 300 metres of altitude above sea level until a temperature of -56.5°C is reached, above which altitude, the temperature is considered constant at -56.5°C. (c) Correction factor. Unless a more rational correction applies, temperatures of APU fluids and components for which temperature limits are established, must be corrected by adding to them the difference between the maximum ambient atmospheric temperature and the temperature of the ambient air at the time of the first occurrence of the maximum component or fluid temperature recorded during the cooling test. CS 25J1045 Cooling test procedures (a) Compliance with CS 25J1041 must be shown for the critical conditions that correspond to the applicable performance requirements. The cooling tests must be conducted with the aeroplane in the configuration, and operating under the conditions that are critical relative to cooling. For the cooling tests, a temperature is 'stabilised' when its rate of change is less than 1°C per minute. (b) Temperatures must be stabilised prior to entry into each critical condition being investigated, unless the entry condition normally is not one during which component and APU fluid temperatures would stabilise (in which case, operation through the full entry condition must be conducted before entry into the critical condition being investigated in order to allow temperatures to reach their natural levels at the time of entry). (c) Cooling tests for each critical condition must be continued until: (1) The component and APU fluid temperatures stabilise; (2) The stage of flight is completed; or (3) An operating limitation is reached. AIR INTAKE AND BLEED AIR DUCT SYSTEMS CS 25J1091 Air intake The air intake system for the APU: (a) Must supply the air required by the APU under each operating condition for which certification is requested, (b) May not draw air from within the APU compartment or other compartments unless the inlet is isolated from the APU accessories and power section by a firewall, (c) Must have means to prevent hazardous quantities of fuel leakage or overflow from drains, vents, or other components of flammable fluid systems from entering, (d) Must be designed to prevent water or slush on the runway, taxiway, or other airport operating surface from being directed into the air intake system in hazardous quantities, (e) Must be located or protected so as to minimise the ingestion of foreign matter during takeoff, landing, and taxiing. CS 25J1093 Air intake system icing protection (See AMC 25J1093) (a) Each non-essential APU air intake system, including any screen if used, which does not comply with CS 25J1093(b) will be restricted to use in non-icing conditions, unless it can be shown that the APU complete with air intake system, if subjected to the icing conditions, defined in Appendices C, O and P will not affect the safe operation of the aeroplane. b) For essential APUs: Each essential APU, with all icing protection systems operating, and screen if used, must: (1) operate throughout its flight power range in the icing conditions defined in Appendices C, O and P, and in falling and blowing snow within the limitations established for the aeroplane for such operation, without the accumulation of ice on the APU, air intake system components or airframe components that would do any of the following: (i) Adversely affect installed APU operation or cause a sustained loss of power; or an unacceptable increase in gas path operating temperature; or an airframe/APU incompatibility; or (ii) Result in unacceptable temporary power loss or APU damage; or (iii) Cause a stall, surge, or flameout or loss of APU controllability (for example, rollback). (2) operate for a minimum of 30 minutes on the ground in the icing conditions shown in Table 1 of CS 25.1093(b)(2), unless replaced by similar test conditions that are more critical. These conditions must be demonstrated with the available icing protection (if applicable) at its critical condition, without adverse effect. The applicant must document the APU minimum ambient temperature demonstrated, if any, and establish the aeroplane operating limitations. (See AMC 25J1093(b)) AMC 25J1093(b) Essential APU air intake system de-icing and anti-icing provisions 1. General In establishing compliance with the requirements of CS 25J1093(b), reference should be made to AMC 25.1093(b). All the reference made to “engine” may be transposed to “essential APU”. Engine test (especially CS-E 780) may refer to essential APU icing test done for the APU certification, if any. When the air intake is assessed separately, it should be shown that the effects of air intake icing would not invalidate the icing tests of CS-APU. Factors to be considered in such evaluation are: a. Distortion of the airflow and partial blockage of the air intake. b. The shedding into the APU of air intake ice of a size greater than the APU has been shown to ingest. c. The icing of any APU sensing devices, other subsidiary air intakes or equipment contained within the air intake. d. The time required to bring the protective system into full operation 2. Operating limitations The conditions defined in CS 25J1093(b)(2), in terms of time and temperature, should be considered as limitations necessary for the safe operation in freezing fog, and made available to the crew in the Aeroplane Flight Manual (refer to CS 25.1581). Nevertheless, the applicant may use an analysis to substantiate safe operation of the APU at temperatures below the demonstrated minimum temperature. No limitation would then be required in the Aeroplane Flight Manual. Any additional substantiation provided by the applicant to demonstrate the capability of an extended exposure beyond the conditions defined in CS 25J1093(b)(2), based on further testing and/or analysis, will be considered by the Agency. CS 25J1103 Air intake system ducts (a) Each air intake system duct must be: (1) Drained to prevent accumulation of hazardous quantities of flammable fluid and moisture in the ground attitude. The drain(s) must not discharge in locations that might cause a fire hazard; and (2) Constructed of materials that will not absorb or trap sufficient quantities of flammable fluids such as to create a fire hazard. (b) Each duct must be: (1) Designed to prevent air intake system failures resulting from reverse flow, APU surging, or inlet door closure; and (2) Fireproof within the APU compartment and for a sufficient distance upstream of the APU compartment to prevent hot gases reverse flow from burning through the APU air intake system ducts and entering any other compartment or area of the aeroplane in which a hazard would be created resulting from the entry of hot gases. The materials used to form the remainder of the air intake system duct and plenum chamber of the APU must be capable of resisting the maximum heat conditions likely to occur. (c) Each duct connected to components between which relative motion could exist must have means for flexibility. CS 25J1106 Bleed air duct systems (a) For APU bleed air duct systems, no hazard may result if a duct failure occurs at any point between the air duct source and the aeroplane unit served by the bleed air. (b) Each duct connected to components between which relative motion could exist must have a means for flexibility. (c) Where the airflow delivery from the APU and main engine is delivered to a common manifold system, precautions must be taken to minimise the possibility of a hazardous condition due to reverse airflow through the APU resulting from malfunctions of any component in the system. CS 25J1121 General (a) Each exhaust system must ensure safe disposal of exhaust gases without fire hazard or carbon monoxide contamination in any personnel compartment. For test purposes, any acceptable carbon monoxide detection method may be used to show the absence of carbon monoxide. (b) Each exhaust system part with a surface hot enough to ignite flammable fluids or vapours must be located or shielded so that leakage from any system carrying flammable fluids or vapours will not result in a fire caused by impingement of the fluids or vapours on any part of the exhaust system including shields for the exhaust system. (c) Each component that hot exhaust gases could strike, or that could be subjected to high temperatures from exhaust system parts, must be fireproof. All exhaust system components must be separated by fireproof shields from adjacent parts of the aeroplane that are outside the APU compartment. (d) No exhaust gases may discharge so as to cause a fire hazard with respect to any flammable fluid vent or drain. (e) Reserved (f) Each exhaust system component must be ventilated to prevent points of excessively high temperature. (g) Each exhaust shroud must be ventilated or insulated to avoid, during normal operation, a temperature high enough to ignite any flammable fluids or vapours external to the shroud. CS 25J1123 Exhaust piping (a) Exhaust piping must be heat and corrosion resistant, and must have provisions to prevent failure due to expansion by operating temperatures. (b) Piping must be supported to withstand any vibration and inertia loads to which it would be subjected in operation; and (c) Piping connected to components between which relative motion could exist must have means for flexibility. APU CONTROLS AND ACCESSORIES CS 25J1141 APU controls (a) Means must be provided on the flight deck for starting, stopping, and emergency shutdown of each installed APU. Each control must: (1) Be located, arranged, and designed under CS 25.777(a)(b)(c)(d) and marked under CS 25.1555(a); and (2) Be located so that it cannot be inadvertently operated by persons entering, leaving, or moving normally on the flight deck; and (3) Be able to maintain any set position without constant attention by flight crew members and without creep due to control loads or vibration; and (4) Have sufficient strength and rigidity to withstand operating loads without failure and without excessive deflection; and (5) For flexible controls, be approved or must be shown to be suitable for the particular application. (b) APU valve controls located in the flight deck must have: (1) For manual valves, positive stops or, in the case of fuel valves, suitable index provisions in the open and closed positions, (2) In the case of valves controlled from the flight deck other than by mechanical means, where the correct functioning of the valve is essential for the safe operation of the aeroplane, a valve position indicator which senses directly that the valve has attained the position selected must be provided, unless other indications in the flight deck give the flight crew a clear indication that the valve has moved to the selected position. A continuous indicator need not be provided. (c) For unattended operation, the APU installation must: (1) Provide means to automatically shutdown the APU for the following conditions: (i) Exceedence of any APU parameter limit or existence of a detectable hazardous APU operating condition; and (ii) Bleed air duct failure between the APU and aeroplane unit served by the bleed air, unless it can be shown that no hazard exists to the aeroplane. (2) Provide means to automatically shut off flammable fluids per CS 25J1189 in case of fire in the APU compartment. (d) APU controls located elsewhere on the aeroplane, which are in addition to the flight deck controls, must meet the following requirements: (1) Each control must be located so that it cannot be inadvertently operated by persons entering, leaving, or moving normally in the area of the control; and (2) Each control must be able to maintain any set position without creep due to control loads, vibration, or other external forces resulting from the location. (e) The portion of each APU control located in a designated fire zone that is required to be operated in the event of a fire must be at least fire resistant. CS 25J1163 APU accessories (a) APU mounted accessories must be approved for installation on the APU concerned and use the provisions of the APU for mounting. (b) Electrical equipment subject to arcing or sparking must be installed to minimise the probability of contact with any flammable fluids or vapours that might be present in a free state. (c) For essential APUs: If continued rotation of a failed aeroplane accessory driven by the APU affects the safe operation of the aeroplane, there must be means to prevent rotation without interfering with the continued operation of the APU. CS 25J1165 APU ignition systems Each APU ignition system must be independent of any electrical circuit except those used for assisting, controlling, or analysing the operation of that system. APU FIRE PROTECTION CS 25J1181 Designated fire zones (a) Any APU compartment is a designated fire zone. (b) Each designated fire zone must meet the requirements of CS 25J1185 through CS 25J1203. CS 25J1183 Lines, fittings and components (a) Except as provided in sub-paragraph (b) of this paragraph, each line, fitting, and other component carrying flammable fluid in any area subject to APU fire conditions, and each component which conveys or contains flammable fluid in a designated fire zone must be fire resistant, except that flammable fluid tanks and supports in a designated fire zone must be fireproof or be enclosed by a fireproof shield unless damage by fire to any non-fireproof part will not cause leakage or spillage of flammable fluid. Components must be shielded or located to safeguard against the ignition of leaking flammable fluid. (b) Sub-paragraph (a) of this paragraph does not apply to: (1) Lines and fittings already approved as part of an APU, and (2) Vent and drain lines, and their fittings, whose failure will not result in, or add to, a fire hazard. (c) All components, including ducts, within a designated fire zone which, if damaged by fire could result in fire spreading to other regions of the aeroplane, must be fireproof. Those components within a designated fire zone, which could cause unintentional operation of, or inability to operate essential services or equipment, must be fireproof. CS 25J1185 Flammable fluids (a) No tank or reservoir that is a part of a system containing flammable fluids or gases may be in a designated fire zone unless the fluid contained, the design of the system, the materials used in the tank, the shut-off means, and all connections, lines, and controls provide a degree of safety equal to that which would exist if the tank or reservoir were outside such a zone. (b) There must be at least 12,7 mm of clear airspace between each tank or reservoir and each firewall or shroud isolating a designated fire zone. (c) Absorbent materials close to flammable fluid system components that might leak must be covered or treated to prevent the absorption of hazardous quantities of fluids. CS 25J1187 Drainage and ventilation of fire zones (a) There must be complete drainage of each part of each designated fire zone to minimise the hazards resulting from failure or malfunctioning of any component containing flammable fluids. The drainage means must be: (1) Effective under conditions expected to prevail when drainage is needed; and (2) Arranged so that no discharged fluid will cause an additional fire hazard. (b) Each designated fire zone must be ventilated to prevent the accumulation of flammable vapours. (c) No ventilation opening may be where it would allow the entry of flammable fluids, vapours, or flame from other zones. (d) Each ventilation means must be arranged so that no discharged vapours will cause an additional fire hazard. (e) Unless the extinguishing agent capacity and rate of discharge are based on maximum air flow through a zone, there must be means to allow the crew to shut off sources of forced ventilation to any fire zone. CS 25J1189 Shut-off means (See AMC 25.1189) (a) Each APU compartment specified in CS 25J1181(a) must have a means to shut-off or otherwise prevent hazardous quantities of flammable fluids, from flowing into, within, or through any designated fire zone, except that shut-off means are not required for: (1) Lines, fittings and components forming an integral part of an APU; and (2) Oil systems for APU installations in which all external components of the oil system, including the oil tanks, are fireproof. (b) The closing of any fuel shut-off valve for any APU may not make fuel unavailable to the main engines. (c) Operation of any shut-off may not interfere with the later emergency operation of other equipment. (d) Each flammable fluid shut-off means and control must be fireproof or must be located and protected so that any fire in a fire zone will not affect its operation. (e) No hazardous quantity of flammable fluid may drain into any designated fire zone after shut-off. (f) There must be means to guard against inadvertent operation of the shut-off means and to make it possible for the crew to reopen the shut-off means in flight after it has been closed. (g) Each tank to APU shut-off valve must be located so that the operation of the valve will not be affected by the APU mount structural failure. (h) Each shut-off valve must have a means to relieve excessive pressure accumulation unless a means for pressure relief is otherwise provided in the system. CS 25J1191 Firewalls (a) Each APU must be isolated from the rest of the aeroplane by firewalls, shrouds, or equivalent means. (b) Each firewall and shroud must be: (1) Fireproof; (2) Constructed so that no hazardous quantity of air, fluid, or flame can pass from the compartment to other parts of the aeroplane; (3) Constructed so that each opening is sealed with close fitting fireproof grommets, bushings, or firewall fittings; and (4) Protected against corrosion. CS 25J1193 APU compartment (a) Each compartment must be constructed and supported so that it can resist any vibration, inertia, and air load to which it may be subjected in operation. (b) Each compartment must meet the drainage and ventilation requirements of CS 25J1187. (c) Reserved (d) Each part of the compartment subject to high temperatures due to its nearness to exhaust system parts or exhaust gas impingement must be fireproof. (e) Each aeroplane must: (1) Be designed and constructed so that no fire originating in any APU fire zone can enter, either through openings or by burning through external skin, any other zone or region where it would create additional hazards, (2) Meet sub-paragraph (e)(1) of this paragraph with the landing gear retracted (if applicable), and (3) Have APU compartment external skins, in areas subject to flame if a fire starts in an APU fire zone, complying with the following: (i) For in-flight operations, APU compartment external skins must be fireproof in the complete concerned areas, and (ii) For ground operations, APU compartment external skins must be: (a) Fireproof in the portions of the concerned areas where a skin burn through would affect critical areas of the aeroplane, and (b) Fire-resistant or compliant with subparagraph (e)(1) of this paragraph in the remaining portions of the concerned areas. (See AMC 25.1193(e)) CS 25J1195 Fire extinguisher systems (See AMC 25J1195) (a) There must be a fire extinguisher system serving the APU compartment. (b) The fire extinguishing system, the quantity of the extinguishing agent, the rate of discharge, and the discharge distribution must be adequate to extinguish fires. An individual 'one shot' system is acceptable. (See AMC 25J1195(b).) (c) The fire-extinguishing system for an APU compartment must be able to simultaneously protect each zone of the APU compartment for which protection is provided. AMC 25J1195(b) Fire extinguisher systems Acceptable methods to establish the adequacy of the fire extinguisher system are laid down in FAA Advisory Circular 20 – 100, with reference to Halon concentration levels. This AC is not applicable to extinguishing agents alternative to Halon. CS 25J1197 Fire extinguishing agents (a) Fire extinguishing agents must: (1) Be capable of extinguishing flames emanating from any burning of fluids or other combustible materials in the area protected by the fire extinguishing system; and (2) Have thermal stability over the temperature range likely to be experienced in the compartment in which they are stored. (b) If any toxic extinguishing agent is used, provisions must be made to prevent harmful concentrations of fluid or fluid vapours (from leakage during normal operation of the aeroplane or as a result of discharging the fire extinguisher on the ground or in flight) from entering any personnel compartment, even though a defect may exist in the extinguishing system. CS 25J1199 Extinguishing agent containers (a) Each extinguishing agent container must have a pressure relief to prevent bursting of the container by excessive internal pressures. (b) The discharge end of each discharge line from a pressure relief connection must be located so that discharge of the fire extinguishant agent would not damage the aeroplane. The line must be located or protected to prevent clogging caused by ice or other foreign matter. (c) There must be a means for each fire extinguishing agent container to indicate that the container has discharged or that the charging pressure is below the established minimum necessary for proper functioning. (d) The temperature of each container must be maintained, under intended operating conditions, to prevent the pressure in the container from: (1) Falling below that necessary to provide an adequate rate of discharge; or (2) Rising high enough to cause premature discharge. (e) If a pyrotechnic capsule is used to discharge the extinguishing agent, each container must be installed so that temperature conditions will not cause hazardous deterioration of the pyrotechnic capsule. CS 25J1201 Fire extinguishing system materials (a) No material in any fire extinguishing system may react chemically with any extinguishing agent so as to create a hazard. (b) Each system component in an APU compartment must be fireproof. CS 25J1203 Fire-detector system (a) There must be approved, quick acting fire or overheat detectors in each APU compartment in numbers and locations ensuring prompt detection of fire. (b) Each fire detector system must be constructed and installed so that: (1) It will withstand the vibration, inertia, and other loads to which it may be subjected in operation; (2) There is a means to warn the crew in the event that the sensor or associated wiring within a designated fire zone is severed at one point, unless the system continues to function as a satisfactory detection system after the severing; and (3) There is a means to warn the crew in the event of a short circuit in the sensor or associated wiring within a designated fire zone, unless the system continues to function as a satisfactory detection system after the short circuit. (c) No fire or overheat detector may be affected by any oil, water, other fluids, or fumes that might be present. (d) There must be means to allow the crew to check, in flight, the functioning of each fire or overheat detector electric circuit. (e) Wiring and other components of each fire or overheat detector system in a fire zone must be at least fire-resistant. (f) No fire or overheat detector system component for any fire zone may pass through another fire zone, unless: (1) It is protected against the possibility of false warnings resulting from fires in zones through which it passes; or (2) Each zone involved is simultaneously protected by the same detector and extinguishing system. (g) Each fire detector system must be constructed so that when it is in the configuration for installation it will not exceed the alarm activation time approved for the detectors using the response time criteria specified in ETSO-2C11e or an acceptable equivalent, for the detector. CS 25J1207 Compliance Unless otherwise specified, compliance with the requirements of CS 25J1181 through CS 25J1203 must be shown by a full scale test or by one or more of the following methods: (a) Tests of similar APU installations. (b) Tests of components. (c) Service experience of aircraft with similar APU installations. (d) Analysis unless tests are specifically required. CS 25J1305 APU instruments (a) The following instruments are required for all installation: (1) A fire warning indicator. (2) An indication than an APU auto-shutdown has occurred. (3) Any other instrumentation necessary to assist the flight crew in: (i) Preventing the exceedence of established APU limits, and (ii) Maintaining continued safe operation of the APU. (4) Instrumentation per subparagraph (3) need not be provided if automatic features of the APU and its installation provide a degree of safety equal to having the parameter displayed directly. (b) For essential APUs: In addition to the items required by CS 25J1305(a), the following indicators are required for an essential APU installation : (1) An indicator to indicate the functioning of the ice protection system, if such a system is installed; and (2) An indicator to indicate the proper functioning of any heater used to prevent ice clogging of fuel system components. CS 25J1337 APU instruments (a) Reserved (b) Reserved (c) Reserved (d) There must be a stick gauge or equivalent means to indicate the quantity of oil in each tank. CS 25J1501 General (a) Reserved (b) The operating limitations and other information necessary for safe operation must be made available to the crew members as prescribed in CS 25J1549, 25J1551, and 25J1583. CS 25J1521 APU limitations The APU limitations must be established so that they do not exceed the corresponding approved limits for the APU and its systems. The APU limitations, including categories of operation, must be specified as operating limitations for the aeroplane. CS 25J1527 Ambient air temperature and operating altitude The extremes of the ambient air temperature and operating altitude for which operation is allowed, as limited by flight, structural, APU installation, functional, or equipment characteristics, must be established. CS 25J1549 APU instruments For each APU instrument either a placard or colour markings or an acceptable combination must be provided to convey information on the maximum and (where applicable) minimum operating limits. Colour coding must comply with the following: (a) Each maximum and, if applicable, minimum safe operating limit must be marked with a red radial or a red line; (b) Each normal operating range must be marked with a green arc or green line, not extending beyond the maximum and minimum safe limits; (c) Each precautionary operating range must be marked with a yellow arc or a yellow line; and (d) Each APU speed range that is restricted because of excessive vibration stresses must be marked with red arcs or red lines. CS 25J1551 Oil quantity indicator Each oil quantity indicator must be marked with enough increments to indicate readily and accurately the quantity of oil. CS 25J1557 Miscellaneous markings and placards (a) Reserved (b) APU fluid filler openings. The following applies: (1) Reserved (2) Oil filler openings must be marked at or near the filler cover with the word "oil". AEROPLANE FLIGHT MANUAL CS 25J1583 Operating limitations APU limitations established under CS 25J1521 and information to explain the instrument markings provided under CS 25J1549 and CS 25J1551 must be furnished.