ED Decision 2003/16/RM
(a) Each fuel system must be constructed and arranged to ensure a flow of fuel at a rate and pressure established for proper engine and auxiliary power unit functioning under any likely operating conditions, including the manoeuvres for which certification is requested and during which the engine or auxiliary power unit is permitted to be in operation.
(b) Each fuel system must be arranged so that:
(1) No engine or fuel pump can draw fuel from more than one tank at a time; or
(2) There are means to prevent introducing air into the system.
(c) Each fuel system for a turbine engine must be capable of sustained operation throughout its flow and pressure range with fuel initially saturated with water at 27°C (80°F) and having 0.20 cm3 of free water per litre (0.75 cc per US-gallon) added and cooled to the most critical condition for icing likely to be encountered in operation.
CS 29.952 Fuel system crash resistance
ED Decision 2003/16/RM
Unless other means acceptable to the Agency are employed to minimise the hazard of fuel fires to occupants following an otherwise survivable impact (crash landing), the fuel systems must incorporate the design features of this paragraph. These systems must be shown to be capable of sustaining the static and dynamic deceleration loads of this paragraph, considered as ultimate loads acting alone, measured at the system component’s centre of gravity without structural damage to the system components, fuel tanks, or their attachments that would leak fuel to an ignition source.
(a) Drop test requirements. Each tank, or the most critical tank, must be drop-tested as follows:
(1) The drop height must be at least 15.2m (50 ft).
(2) The drop impact surface must be non deforming.
(3) The tanks must be filled with water to 80% of the normal, full capacity.
(4) The tank must be enclosed in a surrounding structure representative of the installation unless it can be established that the surrounding structure is free of projections or other design features likely to contribute to rupture of the tank.
(5) The tank must drop freely and impact in a horizontal position ± 10°.
(6) After the drop test, there must be no leakage.
(b) Fuel tank load factors. Except for fuel tanks located so that tank rupture with fuel release to either significant ignition sources, such as engines, heaters, and auxiliary power units, or occupants is extremely remote, each fuel tank must be designed and installed to retain its contents under the following ultimate inertial load factors, acting alone.
(1) For fuel tanks in the cabin –
(i) Upward – 4 g.
(ii) Forward – 16 g.
(iii) Sideward – 8 g.
(iv) Downward – 20 g.
(2) For fuel tanks located above or behind the crew or passenger compartment that, if loosened, could injure an occupant in an emergency landing –
(i) Upward – 1.5 g.
(ii) Forward – 8 g.
(iii) Sideward – 2 g.
(iv) Downward – 4 g.
(3) For fuel tanks in other areas –
(i) Upward –1.5 g.
(ii) Forward – 4 g.
(iii) Sideward – 2 g.
(iv) Downward – 4 g.
(c) Fuel line self-sealing breakaway couplings. Self-sealing breakaway couplings must be installed unless hazardous relative motion of fuel system components to each other or to local rotorcraft structure is demonstrated to be extremely improbable or unless other means are provided. The couplings or equivalent devices must be installed at all fuel tank- to-fuel line connections, tank-to-tank interconnects, and at other points in the fuel system where local structural deformation could lead to release of fuel.
(1) The design and construction of self- sealing breakaway couplings must incorporate the following design features:
(i) The load necessary to separate a breakaway coupling must be between 25 and 50% of the minimum ultimate failure load (ultimate strength) of the weakest component in the fluid-carrying line. The separation load must in no case be less than 1334 N (300 pounds), regardless of the size of the fluid line.
(ii) A breakaway coupling must separate whenever its ultimate load (as defined in sub-paragraph (c)(1)(i)) is applied in the failure modes most likely to occur.
(iii) All breakaway coupling must incorporate design provisions to visually ascertain that the coupling is locked together (leak-free) and is open during normal installation and service.
(iv) All breakaway couplings must incorporate design provisions to prevent uncoupling or unintended closing due to operational shocks, vibrations, or accelerations.
(v) No breakaway coupling design may allow the release of fuel once the coupling has performed its intended function.
(2) All individual breakaway couplings, coupling fuel feed systems, or equivalent means must be designed, tested, installed, and maintained so inadvertent fuel shutoff in flight is improbable in accordance with CS 29.955(a) and must comply with the fatigue evaluation requirements of CS 29.571 without leaking.
(3) Alternate, equivalent means to the use of breakaway couplings must not create a survivable impact-induced load on the fuel line to which it is installed greater than 25 to 50% of the ultimate load (strength) of the weakest component in the line and must comply with the fatigue requirements of CS 29.571 without leaking.
(d) Frangible or deformable structural attachments. Unless hazardous relative motion of fuel tanks and fuel system components to local rotorcraft structure is demonstrated to be extremely improbable in an otherwise survivable impact, frangible or locally deformable attachments of fuel tanks and fuel system components to local rotorcraft structure must be used. The attachment of fuel tanks and fuel system components to local rotorcraft structure. whether frangible or locally deformable, must be designed such that its separation or relative local deformation will occur without rupture or local tearout of the fuel tank or fuel system component that will cause fuel leakage. The ultimate strength of frangible or deformable attachments must be as follows:
(1) The load required to separate a frangible attachment from its support structure, or deform a locally deformable attachment relative to its support structure, must be between 25 and 50% of the minimum ultimate load (ultimate strength) of the weakest component in the attached system. In no case may the load be less than 1334 N (300 pounds).
(2) A frangible or locally deformable attachment must separate or locally deform as intended whenever its ultimate load (as defined in sub-paragraph (d)(1)) is applied in the modes most likely to occur.
(3) All frangible or locally deformable attachments must comply with the fatigue requirements of CS 29.571.
(e) Separation of fuel and ignition sources. To provide maximum crash resistance, fuel must be located as far as practicable from all occupiable areas and from all potential ignition sources.
(f) Other basic mechanical design criteria. Fuel tanks, fuel lines, electrical wires and electrical devices must be designed, constructed, and installed, as far as practicable, to be crash resistant.
(g) Rigid or semi-rigid fuel tanks. Rigid or semi-rigid fuel tank or bladder walls must be impact and tear resistant.
CS 29.953 Fuel system independence
ED Decision 2003/16/RM
(a) For Category A rotorcraft:
(1) The fuel system must meet the requirements of CS 29.903(b); and
(2) Unless other provisions are made to meet sub-paragraph (a)(1) , the fuel system must allow fuel to be supplied to each engine through a system independent of those parts of each system supplying fuel to other engines.
(b) Each fuel system for a multi-engine Category B rotorcraft must meet the requirements of sub-paragraph (a)(2). However, separate fuel tanks need not be provided for each engine.
CS 29.954 Fuel system lightning protection
ED Decision 2003/16/RM
The fuel system must be designed and arranged to prevent the ignition of fuel vapour within the system by:
(a) Direct lightning strikes to areas having a high probability of stroke attachment;
(b) Swept lightning strokes to areas where swept strokes are highly probable; and
(c) Corona and streamering at fuel vent outlets.
ED Decision 2012/022/R
(a) General. The fuel system for each engine must provide the engine with at least 100% of the fuel required under all operating and manoeuvring conditions to be approved for the rotorcraft, including, as applicable, the fuel required to operate the engines under the test conditions required by CS 29.927. Unless equivalent methods are used, compliance must be shown by test during which the following provisions are met, except that combinations of conditions which are shown to be improbable need not be considered.
(1) The fuel pressure, corrected for accelerations (load factors), must be within the limits specified by the engine type certificate data sheet.
(2) The fuel level in the tank may not exceed that established as the unusable fuel supply for that tank under CS 29.959, plus that necessary to conduct the test.
(3) The fuel head between the tank and the engine must be critical with respect to rotorcraft flight attitudes.
(4) The fuel flow transmitter, if installed, and the critical fuel pump (for pump-fed systems) must be installed to produce (by actual or simulated failure) the critical restriction to fuel flow to be expected from component failure.
(5) Critical values of engine rotational speed, electrical power, or other sources of fuel pump motive power must be applied.
(6) Critical values of fuel properties which adversely affect fuel flow are applied during demonstrations of fuel flow capability.
(7) The fuel filter required by CS 29.997 is blocked to the degree necessary to simulate the accumulation of fuel contamination required to activate the indicator required by CS 29.1305(a)(18).
(b) Fuel transfer system. If normal operation of the fuel system requires fuel to be transferred to another tank, the transfer must occur automatically via a system which has been shown to maintain the fuel level in the receiving tank within acceptable limits during flight or surface operation of the rotorcraft.
(c) Multiple fuel tanks. If an engine can be supplied with fuel from more than one tank, the fuel system, in addition to having appropriate manual switching capability, must be designed to prevent interruption of fuel flow to the engine, without attention by the flight crew, when any tank supplying fuel to that engine is depleted of usable fuel during normal operation and any other tank that normally supplies fuel to that engine alone contains usable fuel.
[Amdt 29/3]
CS 29.957 Flow between inter-connected tanks
ED Decision 2003/16/RM
(a) Where tank outlets are interconnected and allow fuel to flow between them due to gravity or flight accelerations, it must be impossible for fuel to flow between tanks in quantities great enough to cause overflow from the tank vent in any sustained flight condition.
(b) If fuel can be pumped from one tank to another in flight:
(1) The design of the vents and the fuel transfer system must prevent structural damage to tanks from overfilling; and
(2) There must be means to warn the crew before overflow through the vents occurs.
CS 29.959 Unusable fuel supply
ED Decision 2003/16/RM
The unusable fuel supply for each tank must be established as not less than the quantity at which the first evidence of malfunction occurs under the most adverse fuel feed condition occurring under any intended operations and flight manoeuvres involving that tank.
CS 29.961 Fuel system hot weather operation
ED Decision 2003/16/RM
Each suction lift fuel system and other fuel systems conducive to vapour formation must be shown to operate satisfactorily (within certification limits) when using fuel at the most critical temperature for vapour formation under critical operating conditions including, if applicable, the engine operating conditions defined by CS 29.927(b)(1) and (b)(2).
ED Decision 2003/16/RM
(a) Each fuel tank must be able to withstand, without failure, the vibration, inertia, fluid, and structural loads to which it may be subjected in operation.
(b) Each flexible fuel tank bladder or liner must be approved or shown to be suitable for the particular application and must be puncture resistant. Puncture resistance must be shown by meeting the ETSO-C80, paragraph 16.0, requirements using a minimum puncture force of 1646 N (370 pounds).
(c) Each integral fuel tank must have facilities for inspection and repair of its interior.
(d) The maximum exposed surface temperature of all components in the fuel tank must be less by a safe margin than the lowest expected auto-ignition temperature of the fuel or fuel vapour in the tank. Compliance with this requirement must be shown under all operating conditions and under all normal or malfunction conditions of all components inside the tank.
(e) Each fuel tank installed in personnel compartments must be isolated by fume-proof and fuel-proof enclosures that are drained and vented to the exterior of the rotorcraft. The design and construction of the enclosures must provide necessary protection for the tank, must be crash resistant during a survivable impact in accordance with CS 29.952, and must be adequate to withstand loads and abrasions to be expected in personnel compartments.
ED Decision 2003/16/RM
(a) Each fuel tank must be able to withstand the applicable pressure tests in this paragraph without failure or leakage. If practicable, test pressures may be applied in a manner simulating the pressure distribution in service.
(b) Each conventional metal tank, each non- metallic tank with walls that are not supported by the rotorcraft structure, and each integral tank must be subjected to a pressure of 24 kPa (3.5 psi) unless the pressure developed during maximum limit acceleration or emergency deceleration with a full tank exceeds this value, in which case a hydrostatic head, or equivalent test, must be applied to duplicate the acceleration loads as far as possible. However, the pressure need not exceed 24 kPa (3.5 psi) on surfaces not exposed to the acceleration loading.
(c) Each non-metallic tank with walls supported by the rotorcraft structure must be subjected to the following tests:
(1) A pressure test of at least 14 kPa (2.0 psi). This test may be conducted on the tank alone in conjunction with the test specified in subparagraph (c)(2).
(2) A pressure test, with the tank mounted in the rotorcraft structure, equal to the load developed by the reaction of the contents, with the tank full, during maximum limit acceleration or emergency deceleration. However, the pressure need not exceed 14 kPa (2.0 psi) on surfaces not exposed to the acceleration loading.
(d) Each tank with large unsupported or unstiffened flat areas, or with other features whose failure or deformation could cause leakage, must be subjected to the following test or its equivalent:
(1) Each complete tank assembly and its supports must be vibration tested while mounted to simulate the actual installation.
(2) The tank assembly must be vibrated for 25 hours while two-thirds full of any suitable fluid. The amplitude of vibration may not be less than 0.8 mm (one thirty-second of an inch), unless otherwise substantiated.
(3) The test frequency of vibration must be as follows:
(i) If no frequency of vibration resulting from any rpm within the normal operating range of engine or rotor system speeds is critical, the test frequency of vibration, in number of cycles per minute, must, unless a frequency based on a more rational analysis is used, be the number obtained by averaging the maximum and minimum power-on engine speeds (rpm) for reciprocating engine powered rotorcraft or 2000 cpm for turbine engine powered rotorcraft.
(ii) If only one frequency of vibration resulting from any rpm within the normal operating range of engine or rotor system speeds is critical, that frequency of vibration must be the test frequency.
(iii) If more than one frequency of vibration resulting from any rpm within the normal operating range of engine or rotor system speeds is critical, the most critical of these frequencies must be the test frequency.
(4) Under sub-paragraph (d)(3)(ii) and (iii), the time of test must be adjusted to accomplish the same number of vibration cycles as would be accomplished in 25 hours at the frequency specified in sub-paragraph (d)(3)(i).
(5) During the test the tank assembly must be rocked at the rate of 16 to 20 complete cycles per minute through an angle of 15° on both sides of the horizontal (30° total), about the most critical axis, for 25 hours. If motion about more than one axis is likely to be critical, the tank must be rocked about each critical axis for 12½ hours.
CS 29.967 Fuel tank installation
ED Decision 2003/16/RM
(a) Each fuel tank must be supported so that tank loads are not concentrated on unsupported tank surfaces. In addition:
(1) There must be pads, if necessary, to prevent chafing between each tank and its supports;
(2) The padding must be non-absorbent or treated to prevent the absorption of fuel;
(3) If flexible tank liners are used, they must be supported so that they are not required to withstand fluid loads; and
(4) Each interior surface of tank compartments must be smooth and free of projections that could cause wear of the liner, unless:
(i) There are means for protection of the liner at those points; or
(ii) The construction of the liner itself provides such protection.
(b) Any spaces adjacent to tank surfaces must be adequately ventilated to avoid accumulation of fuel or fumes in those spaces due to minor leakage. If the tank is in a sealed compartment, ventilation may be limited to drain holes that prevent clogging and that prevent excessive pressure resulting from altitude changes. If flexible tank liners are installed, the venting arrangement for the spaces between the liner and its container must maintain the proper relationship to tank vent pressures for any expected flight condition.
(c) The location of each tank must meet the requirements of CS 29.1185(b) and (c).
(d) No rotorcraft skin immediately adjacent to a major air outlet from the engine compartment may act as the wall of an integral tank.
CS 29.969 Fuel tank expansion space
ED Decision 2003/16/RM
Each fuel tank or each group of fuel tanks with interconnected vent systems must have an expansion space of not less than 2% of the combined tank capacity. It must be impossible to fill the fuel tank expansion space inadvertently with the rotorcraft in the normal ground attitude.
ED Decision 2003/16/RM
(a) Each fuel tank must have a sump with a capacity of not less than the greater of:
(1) 0.10% of the tank capacity; or
(2) 0.24 litres (0.05 Imperial gallon/one sixteenth US gallon).
(b) The capacity prescribed in sub-paragraph (a) must be effective with the rotorcraft in any normal attitude, and must be located so that the sump contents cannot escape through the tank outlet opening.
(c) Each fuel tank must allow drainage of hazardous quantities of water from each part of the tank to the sump with the rotorcraft in any ground attitude to be expected in service.
(d) Each fuel tank sump must have a drain that allows complete drainage of the sump on the ground.
CS 29.973 Fuel tank filler connection
ED Decision 2003/16/RM
(a) Each fuel tank filler connection must prevent the entrance of fuel into any part of the rotorcraft other than the tank itself during normal operations and must be crash resistant during a survivable impact in accordance with CS 29.952(c). In addition:
(1) Each filler must be marked as prescribed in CS 29.1557(c)(1);
(2) Each recessed filler connection that can retain any appreciable quantity of fuel must have a drain that discharges clear of the entire rotorcraft; and
(3) Each filler cap must provide a fuel- tight seal under the fluid pressure expected in normal operation and in a survivable impact.
(b) Each filler cap or filler cap cover must warn when the cap is not fully locked or seated on the filler connection.
CS 29.975 Fuel tank vents and carburetor vapour vents
ED Decision 2003/16/RM
(a) Fuel tank vents. Each fuel tank must be vented from the top part of the expansion space so that venting is effective under normal flight conditions. In addition:
(1) The vents must be arranged to avoid stoppage by dirt or ice formation;
(2) The vent arrangement must prevent siphoning of fuel during normal operation;
(3) The venting capacity and vent pressure levels must maintain acceptable differences of pressure between the interior and exterior of the tank, during:
(i) Normal flight operation;
(ii) Maximum rate of ascent and descent; and
(iii) Refuelling and defuelling (where applicable);
(4) Airspaces of tanks with interconnected outlets must be interconnected;
(5) There may be no point in any vent line where moisture can accumulate with the rotorcraft in the ground attitude or the level flight attitude, unless drainage is provided;
(6) No vent or drainage provision may end at any point:
(i) Where the discharge of fuel from the vent outlet would constitute a fire hazard; or
(ii) From which fumes could enter personnel compartments; and
(7) The venting system must be designed to minimise spillage of fuel through the vents to an ignition source in the event of a rollover during landing, ground operations, or a survivable impact.
(b) Carburettor vapour vents. Each carburettor with vapour elimination connections must have a vent line to lead vapours back to one of the fuel tanks. In addition –
(1) Each vent system must have means to avoid stoppage by ice; and
(2) If there is more than one fuel tank, and it is necessary to use the tanks in a definite sequence, each vapour vent return line must lead back to the fuel tank used for take-off and landing.
ED Decision 2003/16/RM
(a) There must be a fuel strainer for the fuel tank outlet or for the booster pump. This strainer must:
(1) For reciprocating engine powered rotorcraft, have 3 to 6 meshes per cm (8 to 16 meshes per inch); and
(2) For turbine engine powered rotorcraft, 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.
CS 29.979 Pressure refuelling and fuelling provisions below fuel level
ED Decision 2003/16/RM
(a) Each fuelling connection below the fuel level in each tank must have means to prevent the escape of hazardous quantities of fuel from that tank in case of malfunction of the fuel entry valve.
(b) For systems intended for pressure refuelling, a means in addition to the normal means for limiting the tank content must be installed to prevent damage to the tank in case of failure of the normal means.
(c) The rotorcraft pressure fuelling system (not fuel tanks and fuel tank vents) must withstand an ultimate load that is 2.0 times the load arising from the maximum pressure, including surge, that is likely to occur during fuelling. The maximum surge pressure must be established with any combination of tank valves being either intentionally or inadvertently closed.
(d) The rotorcraft defuelling system (not including fuel tanks and fuel tank vents) must withstand an ultimate load that is 2.0 times the load arising from the maximum permissible defuelling pressure (positive or negative) at the rotorcraft fuelling connection.