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473 

Federal Aviation Administration, DOT 

§ 25.955 

the tank capacity. It must be impos-
sible to fill the expansion space inad-
vertently with the airplane in the nor-
mal ground attitude. 

(c) Augmentation system drains 

must be designed and located in ac-
cordance with § 25.1455 if— 

(1) The augmentation system fluid is 

subject to freezing; and 

(2) The fluid may be drained in flight 

or during ground operation. 

(d) The augmentation liquid tank ca-

pacity available for the use of each en-
gine must be large enough to allow op-
eration of the airplane under the ap-
proved procedures for the use of liquid- 
augmented power. The computation of 
liquid consumption must be based on 
the maximum approved rate appro-
priate for the desired engine output 
and must include the effect of tempera-
ture on engine performance as well as 
any other factors that might vary the 
amount of liquid required. 

(e) This section does not apply to fuel 

injection systems. 

[Amdt. 25–40, 42 FR 15043, Mar. 17, 1977, as 
amended by Amdt. 25–72, 55 FR 29785, July 20, 
1990; Amdt. 25–115, 69 FR 40527, July 2, 2004] 

F

UEL

S

YSTEM

 

§ 25.951

General. 

(a) Each fuel system must be con-

structed and arranged to ensure a flow 
of fuel at a rate and pressure estab-
lished for proper engine and auxiliary 
power unit functioning under each 
likely operating condition, including 
any maneuver for which certification is 
requested and during which the engine 
or auxiliary power unit is permitted to 
be in operation. 

(b) Each fuel system must be ar-

ranged so that any air which is intro-
duced into the system will not result 
in— 

(1) Power interruption for more than 

20 seconds for reciprocating engines; or 

(2) Flameout for turbine engines. 
(c) Each fuel system for a turbine en-

gine must be capable of sustained oper-
ation throughout its flow and pressure 
range with fuel initially saturated with 
water at 80 

°

F and having 0.75cc of free 

water per gallon added and cooled to 
the most critical condition for icing 
likely to be encountered in operation. 

(d) Each fuel system for a turbine en-

gine powered airplane must meet the 
applicable fuel venting requirements of 
part 34 of this chapter. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–23, 35 FR 5677, Apr. 8, 
1970; Amdt. 25–36, 39 FR 35460, Oct. 1, 1974; 
Amdt. 25–38, 41 FR 55467, Dec. 20, 1976; Amdt. 
25–73, 55 FR 32861, Aug. 10, 1990] 

§ 25.952

Fuel system analysis and test. 

(a) Proper fuel system functioning 

under all probable operating conditions 
must be shown by analysis and those 
tests found necessary by the Adminis-
trator. Tests, if required, must be made 
using the airplane fuel system or a test 
article that reproduces the operating 
characteristics of the portion of the 
fuel system to be tested. 

(b) The likely failure of any heat ex-

changer using fuel as one of its fluids 
may not result in a hazardous condi-
tion. 

[Amdt. 25–40, 42 FR 15043, Mar. 17, 1977] 

§ 25.953

Fuel system independence. 

Each fuel system must meet the re-

quirements of § 25.903(b) by— 

(a) Allowing the supply of fuel to 

each engine through a system inde-
pendent of each part of the system sup-
plying fuel to any other engine; or 

(b) Any other acceptable method. 

§ 25.954

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; and 

(c) Corona and streamering at fuel 

vent outlets. 

[Amdt. 25–14, 32 FR 11629, Aug. 11, 1967] 

§ 25.955

Fuel flow. 

(a) Each fuel system must provide at 

least 100 percent of the fuel flow re-
quired under each intended operating 
condition and maneuver. Compliance 
must be shown as follows: 

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