534 

14 CFR Ch. I (1–1–19 Edition) 

§ 27.963 

by test to operate satisfactorily (with-
in certification limits) when using fuel 
at a temperature of 110 

°

F under crit-

ical operating conditions including, if 
applicable, the engine operating condi-
tions defined by § 27.927 (b)(1) and (b)(2). 

[Amdt. 27–23, 53 FR 34212, Sept. 2, 1988] 

§ 27.963

Fuel tanks: general. 

(a) Each fuel tank must be able to 

withstand, without failure, the vibra-
tion, inertia, fluid, and structural loads 
to which it may be subjected in oper-
ation. 

(b) Each fuel tank of 10 gallons or 

greater capacity must have internal 
baffles, or must have external support 
to resist surging. 

(c) Each fuel tank must be separated 

from the engine compartment by a 
firewall. At least one-half inch of clear 
airspace must be provided between the 
tank and the firewall. 

(d) Spaces adjacent to the surfaces of 

fuel tanks must be ventilated so that 
fumes cannot accumulate in the tank 
compartment in case of leakage. If two 
or more tanks have interconnected 
outlets, they must be considered as one 
tank, and the airspaces in those tanks 
must be interconnected to prevent the 
flow of fuel from one tank to another 
as a result of a difference in pressure 
between those airspaces. 

(e) The maximum exposed surface 

temperature of any component in the 
fuel tank must be less, by a safe mar-
gin as determined by the Adminis-
trator, than the lowest expected 
autoignition temperature of the fuel or 
fuel vapor in the tank. Compliance 
with this requirement must be shown 
under all operating conditions and 
under all failure or malfunction condi-
tions of all components inside the 
tank. 

(f) Each fuel tank installed in per-

sonnel compartments must be isolated 
by fume-proof and fuel-proof enclosures 
that are drained and vented to the ex-
terior 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 
§ 27.952, and must be adequate to with-
stand loads and abrasions to be ex-
pected in personnel compartments. 

(g) Each flexible fuel tank bladder or 

liner must be approved or shown to be 
suitable for the particular application 
and must be puncture resistant. Punc-
ture resistance must be shown by 
meeting the TSO-C80, paragraph 16.0, 
requirements using a minimum punc-
ture force of 370 pounds. 

(h) Each integral fuel tank must have 

provisions for inspection and repair of 
its interior. 

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as 
amended by Amdt. 27–23, 53 FR 34213, Sept. 2, 
1988; Amdt. 27–30, 59 FR 50387, Oct. 3, 1994] 

§ 27.965

Fuel tank tests. 

(a) Each fuel tank must be able to 

withstand the applicable pressure tests 
in this section without failure or leak-
age. If practicable, test pressures may 
be applied in a manner simulating the 
pressure distribution in service. 

(b) Each conventional metal tank, 

nonmetallic tank with walls that are 
not supported by the rotorcraft struc-
ture, and integral tank must be sub-
jected to a pressure of 3.5 p.s.i. unless 
the pressure developed during max-
imum limit acceleration or emergency 
deceleration with a full tank exceeds 
this value, in which case a hydrostatic 
head, or equivalent test, must be ap-
plied to duplicate the acceleration 
loads as far as possible. However, the 
pressure need not exceed 3.5 p.s.i. on 
surfaces not exposed to the accelera-
tion loading. 

(c) Each nonmetallic tank with walls 

supported by the rotorcraft structure 
must be subjected to the following 
tests: 

(1) A pressure test of at least 2.0 p.s.i. 

This test may be conducted on the 
tank alone in conjunction with the test 
specified in paragraph (c)(2) of this sec-
tion. 

(2) A pressure test, with the tank 

mounted in the rotorcraft structure, 
equal to the load developed by the re-
action of the contents, with the tank 
full, during maximum limit accelera-
tion or emergency deceleration. How-
ever, the pressure need not exceed 2.0 
p.s.i. on surfaces not exposed to the ac-
celeration loading. 

(d) Each tank with large unsupported 

or unstiffened flat areas, or with other 
features whose failure or deformation 

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