Federal Aviation Administration, DOT

Section 25.965

temperatures that would constitute a
fire hazard under the conditions specified in Section 25.721(b).
(5) Fuel tank installations must be
such that the tanks will not rupture as
a result of the landing gear or an engine pylon or engine mount tearing
away as specified in Section 25.721(a) and (c).
(e) Fuel tank access covers must
comply with the following criteria in
order to avoid loss of hazardous quantities of fuel:
(1) All covers located in an area
where experience or analysis indicates
a strike is likely must be shown by
analysis or tests to minimize penetration and deformation by tire fragments, low energy engine debris, or
other likely debris.
(2) All covers must be fire resistant
as defined in part 1 of this chapter.
(f) For pressurized fuel tanks, a
means with fail-safe features must be
provided to prevent the buildup of an
excessive pressure difference between
the inside and the outside of the tank.

spaschal on DSK3GDR082PROD with CFR

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25-40, 42 FR 15043, Mar. 17,
1977; Amdt. 25-69, 54 FR 40354, Sept. 29, 1989;
Amdt. 25-139, 79 FR 59430, Oct. 2, 2014]

Section 25.965 Fuel tank tests.
(a) It must be shown by tests that the
fuel tanks, as mounted in the airplane,
can withstand, without failure or leakage, the more critical of the pressures
resulting from the conditions specified
in paragraphs (a)(1) and (2) of this section. In addition, it must be shown by
either analysis or tests, that tank surfaces subjected to more critical pressures resulting from the condition of
paragraphs (a)(3) and (4) of this section,
are able to withstand the following
pressures:
(1) An internal pressure of 3.5 psi.
(2) 125 percent of the maximum air
pressure developed in the tank from
ram effect.
(3) Fluid pressures developed during
maximum limit accelerations, and deflections, of the airplane with a full
tank.
(4) Fluid pressures developed during
the most adverse combination of airplane 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 paragraph
(b)(4) of this section, the tank assembly
must be vibrated for 25 hours at an amplitude of not less than 1-32 of an inch
(unless another amplitude is substantiated) while 2-3 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 r.p.m. 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 r.p.m. 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 r.p.m. within the normal operating range of engine speeds is critical, the most critical of these frequencies must be the
test frequency.
(4) Under paragraphs (b)(3)(ii) and
(iii) of this section, 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 paragraph
(b)(3)(i) of this section.
(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 15Section on both sides of the horizontal (30Section 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 121-2 hours.
(c) Except where satisfactory operating experience with a similar tank in
a similar installation is shown, nonmetallic tanks must withstand the test
specified in paragraph (b)(5) of this section, with fuel at a temperature of 110
SectionF. During this test, a representative
specimen of the tank must be installed
in a supporting structure simulating
the installation in the airplane.

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