Federal Aviation Administration, DOT

Section 27.961

valve required by Section 27.995 if the line between the valve and the engine compartment 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 installation 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.
Section 27.954 Fuel system lightning protection.
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 attachment;
(b) Swept lightning strokes to areas
where swept strokes are highly probable; or
(c) Corona and streamering at fuel
vent outlets.

spaschal on DSK3GDR082PROD with CFR

[Amdt. 27-23, 53 FR 34212, Sept. 2, 1988]

Section 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 applicable, the fuel required to operate the engine(s) under the test conditions required by Section 27.927. Unless equivalent
methods are used, compliance must be
shown by test during which the following 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 Section 27.959,
plus the minimum additional fuel necessary 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 pumpfed 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 Section 27.997
must be blocked to the degree necessary to simulate the accumulation of
fuel contamination required to activate
the
indicator
required
by
Section 27.1305(q).
(b) Fuel transfer systems. If normal operation of the fuel system requires fuel
to be transferred to an engine feed
tank, the transfer must occur automatically via a system which has been
shown to maintain the fuel level in the
engine feed tank within acceptable
limits during flight or surface operation 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 manual 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]

Section 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 operations and flight maneuvers involving
that tank.
Section 27.961 Fuel system hot weather operation.
Each suction lift fuel system and
other fuel systems with features conducive to vapor formation must be shown

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