background image

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 

VerDate Sep<11>2014 

09:06 Jun 28, 2024

Jkt 262046

PO 00000

Frm 00544

Fmt 8010

Sfmt 8010

Y:\SGML\262046.XXX

262046

jspears on DSK121TN23PROD with CFR