Code of Federal Regulations - Title 14

274

14 CFR Ch. I (1–1–14 Edition)

§ 23.951

UEL

YSTEM

§ 23.951

General.

(a) Each fuel system must be con-

structed and arranged to ensure fuel
flow at a rate and pressure established
for proper engine and auxiliary power
unit functioning under each likely op-
erating condition, including any ma-
neuver for which certification is re-
quested 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—

(1) No fuel pump can draw fuel from

more than one tank at a time; or

(2) There are means to prevent intro-

ducing air into the system.

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.

[Amdt. 23–15, 39 FR 35459, Oct. 1, 1974, as
amended by Amdt. 23–40, 55 FR 32861, Aug. 10,
1990; Amdt. 23–43, 58 FR 18971, Apr. 9, 1993]

§ 23.953

Fuel system independence.

(a) Each fuel system for a multien-

gine airplane must be arranged so that,
in at least one system configuration,
the failure of any one component
(other than a fuel tank) will not result
in the loss of power of more than one
engine or require immediate action by
the pilot to prevent the loss of power of
more than one engine.

(b) If a single fuel tank (or series of

fuel tanks interconnected to function
as a single fuel tank) is used on a mul-
tiengine airplane, the following must
be provided:

(1) Independent tank outlets for each

engine, each incorporating a shut-off
valve at the tank. This shutoff valve
may also serve as the fire wall shutoff
valve required if the line between the
valve and the engine compartment does
not contain more than one quart of
fuel (or any greater amount shown to

be safe) that can escape 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 the system supplying fuel to
any other engine.

[Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as
amended by Amdt. 23–7, 34 FR 13093 Aug. 13,
1969; Amdt. 23–43, 58 FR 18971, Apr. 9, 1993]

§ 23.954

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 on areas

where swept strokes are highly prob-
able; and

vent outlets.

[Amdt. 23–7, 34 FR 13093, Aug. 13, 1969]

§ 23.955

Fuel flow.

(a)

General. The ability of the fuel

system to provide fuel at the rates
specified in this section and at a pres-
sure sufficient for proper engine oper-
ation must be shown in the attitude
that is most critical with respect to
fuel feed and quantity of unusable fuel.
These conditions may be simulated in a
suitable mockup. In addition—

(1) The quantity of fuel in the tank

may not exceed the amount established
as the unusable fuel supply for that
tank under § 23.959(a) plus that quan-
tity necessary to show compliance with
this section.

(2) If there is a fuel flowmeter, it

must be blocked during the flow test
and the fuel must flow through the
meter or its bypass.

(3) If there is a flowmeter without a

bypass, it must not have any probable
failure mode that would restrict fuel
flow below the level required for this
fuel demonstration.

(4) The fuel flow must include that

flow necessary for vapor return flow,

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