476
14 CFR Ch. I (1–1–14 Edition)
§ 25.967
(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.
(d) For pressurized fuel tanks, it
must be shown by analysis or tests
that the fuel tanks can withstand the
maximum pressure likely to occur on
the ground or in flight.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–11, 32 FR 6913, May 5,
1967; Amdt. 25–40, 42 FR 15043, Mar. 17, 1977]
§ 25.967
Fuel tank installations.
(a) Each fuel tank must be supported
so that tank loads (resulting from the
weight of the fuel in the tanks) are not
concentrated on unsupported tank sur-
faces. In addition—
(1) There must be pads, if necessary,
to prevent chafing between the tank
and its supports;
(2) Padding must be nonabsorbent or
treated to prevent the absorption of
fluids;
(3) If a flexible tank liner is used, it
must be supported so that it is not re-
quired to withstand fluid loads; and
(4) Each interior surface of the tank
compartment must be smooth and free
of projections that could cause wear of
the liner unless—
(i) Provisions are made for protection
of the liner at these points; or
(ii) The construction of the liner
itself provides that protection.
(b) Spaces adjacent to tank surfaces
must be ventilated to avoid fume accu-
mulation due to minor leakage. If the
tank is in a sealed compartment, ven-
tilation may be limited to drain holes
large enough to prevent excessive pres-
sure resulting from altitude changes.
(c) The location of each tank must
meet the requirements of § 25.1185(a).
(d) No engine nacelle skin imme-
diately behind a major air outlet from
the engine compartment may act as
the wall of an integral tank.
(e) Each fuel tank must be isolated
from personnel compartments by a
fumeproof and fuelproof enclosure.
§ 25.969
Fuel tank expansion space.
Each fuel tank must have an expan-
sion space of not less than 2 percent of
the tank capacity. It must be impos-
sible to fill the expansion space inad-
vertently with the airplane in the nor-
mal ground attitude. For pressure fuel-
ing systems, compliance with this sec-
tion may be shown with the means pro-
vided to comply with § 25.979(b).
[Amdt. 25–11, 32 FR 6913, May 5, 1967]
§ 25.971
Fuel tank sump.
(a) Each fuel tank must have a sump
with an effective capacity, in the nor-
mal ground attitude, of not less than
the greater of 0.10 percent of the tank
capacity or one-sixteenth of a gallon
unless operating limitations are estab-
lished to ensure that the accumulation
of water in service will not exceed the
sump capacity.
(b) Each fuel tank must allow drain-
age of any hazardous quantity of water
from any part of the tank to its sump
VerDate Mar<15>2010
10:12 Mar 18, 2014
Jkt 232046
PO 00000
Frm 00486
Fmt 8010
Sfmt 8010
Y:\SGML\232046.XXX
232046
pmangrum on DSK3VPTVN1PROD with CFR