534
14 CFR Ch. I (1–1–24 Edition)
§ 27.954
valve required by § 27.995 if the line be-
tween the valve and the engine com-
partment does not contain a hazardous
amount of fuel that can drain into the
engine compartment.
(2) At least two vents arranged to
minimize the probability of both vents
becoming obstructed simultaneously.
(3) Filler caps designed to minimize
the probability of incorrect installa-
tion or inflight loss.
(4) A fuel system in which those parts
of the system from each tank outlet to
any engine are independent of each
part of each system supplying fuel to
other engines.
§ 27.954
Fuel system lightning protec-
tion.
The fuel system must be designed
and arranged to prevent the ignition of
fuel vapor within the system by—
(a) Direct lightning strikes to areas
having a high probability of stroke at-
tachment;
(b) Swept lightning strokes to areas
where swept strokes are highly prob-
able; or
(c) Corona and streamering at fuel
vent outlets.
[Amdt. 27–23, 53 FR 34212, Sept. 2, 1988]
§ 27.955
Fuel flow.
(a)
General. The fuel system for each
engine must be shown to provide the
engine with at least 100 percent of the
fuel required under each operating and
maneuvering condition to be approved
for the rotorcraft including, as applica-
ble, the fuel required to operate the en-
gine(s) under the test conditions re-
quired by § 27.927. Unless equivalent
methods are used, compliance must be
shown by test during which the fol-
lowing provisions are met except that
combinations of conditions which are
shown to be improbable need not be
considered.
(1) The fuel pressure, corrected for
critical accelerations, must be within
the limits specified by the engine type
certificate data sheet.
(2) The fuel level in the tank may not
exceed that established as the unusable
fuel supply for that tank under § 27.959,
plus the minimum additional fuel nec-
essary to conduct the test.
(3) The fuel head between the tank
outlet and the engine inlet must be
critical with respect to rotorcraft
flight attitudes.
(4) The critical fuel pump (for pump-
fed systems) is installed to produce (by
actual or simulated failure) the critical
restriction to fuel flow to be expected
from pump failure.
(5) Critical values of engine rotation
speed, electrical power, or other
sources of fuel pump motive power
must be applied.
(6) Critical values of fuel properties
which adversely affect fuel flow must
be applied.
(7) The fuel filter required by § 27.997
must be blocked to the degree nec-
essary to simulate the accumulation of
fuel contamination required to acti-
vate the indicator required by
§ 27.1305(q).
(b)
Fuel transfer systems. If normal op-
eration of the fuel system requires fuel
to be transferred to an engine feed
tank, the transfer must occur auto-
matically via a system which has been
shown to maintain the fuel level in the
engine feed tank within acceptable
limits during flight or surface oper-
ation of the rotorcraft.
(c)
Multiple fuel tanks. If an engine
can be supplied with fuel from more
than one tank, the fuel systems must,
in addition to having appropriate man-
ual switching capability, be designed to
prevent interruption of fuel flow to
that engine, without attention by the
flightcrew, when any tank supplying
fuel to that engine is depleted of usable
fuel during normal operation, and any
other tank that normally supplies fuel
to the engine alone contains usable
fuel.
[Amdt. 27–23, 53 FR 34212, Sept. 2, 1988]
§ 27.959
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.
§ 27.961
Fuel system hot weather oper-
ation.
Each suction lift fuel system and
other fuel systems with features condu-
cive to vapor formation must be shown
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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.
(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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