CS 26.440 Fuel system crash resistance

Compliance with point 26.440 of Part26 is demonstrated by complying with: CS 27.952 of CS27 or the equivalent, CS 29.952 of CS29 or the equivalent; and CS 27.963 of CS27 or the equivalent, CS 29.963 of CS29 or the equivalent; and CS 27.973 of CS27 or the equivalent, CS 29.973 of CS29 or the equivalent; and CS 27.975(b) of CS27 or the equivalent, CS 29.975(a) of CS29, or with the following:

(a)For helicopters under point 26.440(a)(1) or 26.440(b)(1):

(1)Each fuel tank, or the most critical fuel tank, must be subjected to a drop test that results in no subsequent leakage of the fluid that is contained within it, using the following parameters:

(i)the tank must be dropped from a height of at least 15.2 m (50 ft);

(ii)the surface that the tank will impact after it has been dropped must not be capable of absorbing the energy of the impact (i.e. the surface must not deform as a result of the impact);

(iii)the tank must be filled with water to a level that is 80 % of the normal, full capacity of the tank; and

(iv)the tank must drop freely and impact in a horizontal position of ±10 °.

(2)Self-sealing breakaway fuel line 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.

(i)The design and construction of self-sealing breakaway fuel line couplings must incorporate the following design features:

(A)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 lb), regardless of the size of the fluid line.

(B)A breakaway coupling must separate whenever its ultimate load (as defined in subparagraph (b)(1)(i)) is applied in the failure modes that are most likely to occur.

(C)All breakaway couplings must incorporate design provisions to visually ascertain that the coupling is locked together (leakage-free) and is open during normal installation and service.

(D)All breakaway couplings must incorporate design provisions to prevent uncoupling or unintended closing due to operational shocks, vibrations or accelerations.

(E)No breakaway coupling design may allow the release of fuel once the coupling has performed its intended function.

(ii)All individual breakaway couplings, coupling fuel feed systems or equivalent means must be designed, tested, installed and maintained so that inadvertent fuel shut-off in flight is improbable in accordance with CS 27.955(a) or CS 29.955 or the equivalent, and must comply with the fatigue evaluation requirements of CS 27.571 or CS 29.571, as appropriate, or the equivalent, without leakage.

(iii)Alternate means equivalent to the use of breakaway couplings must not create a survivable impact-induced load on the fuel line to which they are installed, which is greater than 25 % to 50 % of the ultimate load (strength) of the weakest component of the line, and must comply with the fatigue evaluation requirements of CS 27.571 or CS 29.571, as appropriate, or the equivalent, without leakage.

(3)Fuel tanks, fuel lines, electrical wires and electrical devices must be designed, constructed and installed, as far as practicable, to be crash-resistant.

(4)Rigid or semi-rigid fuel tank or bladder walls must be impact- and tear-resistant.

(5)Each flexible fuel tank bladder or liner must be approved or shown to be suitable for the specific application and must be puncture-resistant. Puncture resistance must be shown by using the methodology that is contained in paragraph 16.0 of European Technical Standard Order (ETSO)C80, when resisting a minimum puncture force of:

(i)1646 N (370 lbs)

(ii)1112 N (250 lbs) if the drop test that is required in paragraph (a) is successfully conducted with the tank enclosed in a surrounding structure that is representative of the tank installation that includes any projections or other design features that are likely to contribute to the rupture of the tank.

(6)The venting system must be designed to minimise spillage of fuel through the vents to an ignition source in the event of either a rollover during landing, ground operation or a survivable impact.

(b)For helicopters under points 26.440(a)(2) or 26.440(b)(2):

(1)Each fuel tank, or the most critical fuel tank, must be subjected to a drop test that results in no subsequent leakage of the fluid that is contained within it, using the following parameters:

(i)the tank must be dropped from a height of at least 15.2 m (50 ft);

(ii)the surface that the tank will impact after it has been dropped must not be capable of absorbing the energy of the impact (i.e. the surface must not deform as a result of the impact);

(iii)the tank must be filled with water to a level that is 80 % of the normal, full capacity of the tank; and

(iv)the tank must drop freely and impact in a horizontal position of ±10 °.

(2)Fuel tanks, fuel lines, electrical wires, and electrical devices must be designed, constructed and installed, as far as practicable, to be crash-resistant.

(3)Each flexible fuel tank bladder or liner must be approved or shown to be suitable for the specific application and must be puncture-resistant. Puncture resistance must be shown by using the methodology that is contained in paragraph 16.0 of European Technical Standard Order (ETSO)C80, when resisting a minimum puncture force of 1112 N (250 lbs).

[Issue: 26/5]