684 

14 CFR Ch. I (1–1–14 Edition) 

§ 27.967 

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 
could cause leakage, must be subjected 
to the following test or its equivalent: 

(1) Each complete tank assembly and 

its support must be vibration tested 
while mounted to simulate the actual 
installation. 

(2) The tank assembly must be vi-

brated for 25 hours while two-thirds 
full of any suitable fluid. The ampli-
tude of vibration may not be less than 
one thirty-second of an inch, unless 
otherwise substantiated. 

(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 or rotor sys-
tem speeds is critical, the test fre-
quency of vibration, in number of cy-
cles per minute must, unless a fre-
quency based on a more rational cal-
culation is used, be the number ob-
tained by averaging the maximum and 
minimum power-on engine speeds 
(r.p.m.) for reciprocating engine pow-
ered rotorcraft or 2,000 c.p.m. for tur-
bine engine powered rotorcraft. 

(ii) If only one frequency of vibration 

resulting from any r.p.m. within the 
normal operating range of engine or 
rotor system speeds is critical, that 
frequency of vibration 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 or rotor system speeds is critical, 
the most critical of these frequencies 
must be the test frequency. 

(4) Under paragraphs (d)(3)(ii) and 

(iii) of this section, the time of test 
must be adjusted to accomplish the 
same number of vibration cycles as 
would be accomplished in 25 hours at 
the frequency specified in paragraph 
(d)(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 degrees on both sides of 
the horizontal (30 degrees 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

1

⁄

2

 

hours. 

(Secs. 313(a), 601, and 603, 72 Stat. 752, 775, 49 
U.S.C. 1354(a), 1421, and 1423; sec. 6(c), 49 
U.S.C. 1655(c)) 

[Amdt. 27–12, 42 FR 15045, Mar. 17, 1977] 

§ 27.967

Fuel tank installation. 

(a) Each fuel tank must be supported 

so that tank loads are not con-
centrated on unsupported tank sur-
faces. In addition— 

(1) There must be pads, if necessary, 

to prevent chafing between each tank 
and its supports; 

(2) The padding must be non-

absorbent or treated to prevent the ab-
sorption of fuel; 

(3) If flexible tank liners are used, 

they must be supported so that it is 
not necessary for them to withstand 
fluid loads; and 

(4) Each interior surface of tank com-

partments must be smooth and free of 
projections that could cause wear of 
the liner unless— 

(i) There are means for protection of 

the liner at those points; or 

(ii) The construction of the liner 

itself provides such protection. 

(b) Any spaces adjacent to tank sur-

faces must be adequately ventilated to 
avoid accumulation of fuel or fumes in 
those spaces due to minor leakage. If 
the tank is in a sealed compartment, 
ventilation may be limited to drain 
holes that prevent clogging and exces-
sive pressure resulting from altitude 
changes. If flexible tank liners are in-
stalled, the venting arrangement for 
the spaces between the liner and its 
container must maintain the proper re-
lationship to tank vent pressures for 
any expected flight condition. 

(c) The location of each tank must 

meet the requirements of § 27.1185 (a) 
and (c). 

(d) No rotorcraft skin immediately 

adjacent to a major air outlet from the 
engine compartment may act as the 
wall of the integral tank. 

[Doc. No. 26352, 59 FR 50387, Oct. 3, 1994] 

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