CS 25.965 Fuel tank tests

(a)It must be shown by tests that the fuel tanks, as mounted in the aeroplane can withstand, without failure or leakage, the more critical of the pressures resulting from the conditions specified in sub-paragraphs (a)(1) and (2) of this paragraph. In addition it must be shown by either analysis or tests, (see AMC 25.965(a)) that tank surfaces subjected to more critical pressures resulting from the conditions of sub-paragraphs (a)(3) and (4) of this paragraph, are able to withstand the following pressures:

(1)An internal pressure of 24 kPa (3·5 psi).

(2)125% of the maximum air pressure developed in the tank from ram effect.

(3)Fluid pressures developed during maximum limit accelerations, and deflections, of the aeroplane with a full tank.

(4)Fluid pressures developed during the most adverse combination of aeroplane roll and fuel load.

(b)Each metallic tank with large unsupported or unstiffened flat surfaces, whose failure or deformation could cause fuel leakage, must be able to withstand the following test, or its equivalent, without leakage or excessive deformation of the tank walls:

(1)Each complete tank assembly and its supports must be vibration tested while mounted to simulate the actual installation.

(2)Except as specified in sub-paragraph (b)(4) of this paragraph, the tank assembly must be vibrated for 25 hours at an amplitude of not less than 0.8 mm (1/32 of an inch) (unless another amplitude is substantiated) while two-thirds filled with water or other suitable test fluid.

(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 speeds is critical, the test frequency of vibration must be 2 000 cycles per minute.

(ii)If only one frequency of vibration resulting from any rpm within the normal operating range of engine 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 speeds is critical, the most critical of these frequencies must be the test frequency.

(4)Under sub-paragraph (b)(3)(ii) and (iii) of this paragraph, the time of test must be adjusted to accomplish the same number of vibration cycles that would be accomplished in 25 hours at the frequency specified in sub-paragraph (b)(3)(i) of this paragraph.

(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 12·5 hours.

(c)Except where satisfactory operating experience with a similar tank in a similar installation is shown, non-metallic tanks must withstand the test specified in sub-paragraph (b)(5) of this paragraph, with fuel at a temperature of 43.3°C (110°F). During this test, a representative specimen of the tank must be installed in a supporting structure simulating the installation in the aeroplane.

(d)For pressurised fuel tanks, it must be shown by analysis or tests that the fuel tanks can withstand the maximum pressure likely to occur on the ground or in flight.