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14 CFR Ch. I (1–1–19 Edition) 

§ 29.957 

§ 29.957

Flow between interconnected 


(a) Where tank outlets are inter-

connected and allow fuel to flow be-
tween them due to gravity or flight ac-
celerations, it must be impossible for 
fuel to flow between tanks in quan-
tities great enough to cause overflow 
from the tank vent in any sustained 
flight condition. 

(b) If fuel can be pumped from one 

tank to another in flight— 

(1) The design of the vents and the 

fuel transfer system must prevent 
structural damage to tanks from over-
filling; and 

(2) There must be means to warn the 

crew before overflow through the vents 

§ 29.959

Unusable fuel supply. 

The unusable fuel supply for each 

tank must be established as not less 
than the quantity at which the first 
evidence of malfunction occurs under 
the most adverse fuel feed condition 
occurring under any intended oper-
ations and flight maneuvers involving 
that tank. 

§ 29.961

Fuel system hot weather oper-


Each suction lift fuel system and 

other fuel systems conducive to vapor 
formation must be shown to operate 
satisfactorily (within certification lim-
its) when using fuel at the most crit-
ical temperature for vapor formation 
under critical operating conditions in-
cluding, if applicable, the engine oper-
ating conditions defined by § 29.927(b)(1) 
and (b)(2). 

[Amdt. 29–26, 53 FR 34217, Sept. 2, 1988] 

§ 29.963

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-

(b) 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. 

(c) Each integral fuel tank must have 

facilities for inspection and repair of 
its interior. 

(d) The maximum exposed surface 

temperature of all components in the 
fuel tank must be less by a safe margin 
than the lowest expected autoignition 
temperature of the fuel or fuel vapor in 
the tank. Compliance with this re-
quirement must be shown under all op-
erating conditions and under all nor-
mal or malfunction conditions of all 
components inside the tank. 

(e) 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 
§ 29.952, and must be adequate to with-
stand loads and abrasions to be ex-
pected in personnel compartments. 

[Doc. No. 5084, 29 FR 16150, Dec. 3, 1964, as 
amended by Amdt. 29–26, 53 FR 34217, Sept. 2, 
1988; Amdt. 29–35, 59 FR 50388, Oct. 3, 1994] 

§ 29.965

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, 

each nonmetallic tank with walls that 
are not supported by the rotorcraft 
structure, and each integral tank must 
be subjected to a pressure of 3.5 p.s.i. 
unless the pressure developed during 
maximum limit acceleration or emer-
gency deceleration with a full tank ex-
ceeds this value, in which case a hydro-
static head, or equivalent test, must be 
applied 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 

(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 

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