317 

Federal Aviation Administration, DOT 

§ 25.965 

temperatures that would constitute a 
fire hazard under the conditions speci-
fied in § 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 en-
gine pylon or engine mount tearing 
away as specified in § 25.721(a) and (c). 

(e) Fuel tank access covers must 

comply with the following criteria in 
order to avoid loss of hazardous quan-
tities 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 penetra-
tion and deformation by tire frag-
ments, 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. 

[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] 

§ 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 leak-
age, the more critical of the pressures 
resulting from the conditions specified 
in paragraphs (a)(1) and (2) of this sec-
tion. In addition, it must be shown by 
either analysis or tests, that tank sur-
faces subjected to more critical pres-
sures 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 de-
flections, of the airplane with a full 
tank. 

(4) Fluid pressures developed during 

the most adverse combination of air-
plane roll and fuel load. 

(b) Each metallic tank with large un-

supported 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 exces-
sive 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 am-
plitude of not less than 

1

⁄

32

of an inch 

(unless another amplitude is substan-
tiated) 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 result-

ing 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 vi-
bration must be the test frequency. 

(iii) If more than one frequency of vi-

bration resulting from any r.p.m. with-
in the normal operating range of en-
gine speeds is critical, the most crit-
ical 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 assem-

bly must be rocked at the rate of 16 to 
20 complete cycles per minute, through 
an angle of 15

° 

on both sides of the hor-

izontal (30

° 

total), about the most crit-

ical axis, for 25 hours. If motion about 
more than one axis is likely to be crit-
ical, the tank must be rocked about 
each critical axis for 12

1

⁄

2

hours. 

(c) Except where satisfactory oper-

ating experience with a similar tank in 
a similar installation is shown, non-
metallic tanks must withstand the test 
specified in paragraph (b)(5) of this sec-
tion, with fuel at a temperature of 110 

°

F. 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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