title-14-part-27-sec27-965

535

Federal Aviation Administration, DOT

§ 27.965

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.

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.

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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536

14 CFR Ch. I (1–1–24 Edition)

§ 27.967

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

⁄

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.

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]

§ 27.969

Fuel tank expansion space.

Each fuel tank or each group of fuel

tanks with interconnected vent sys-
tems must have an expansion space of