Section 25.952

14 CFR Ch. I (1-1-19 Edition)

or auxiliary power unit is permitted to
be in operation.
(b) Each fuel system must be arranged so that any air which is introduced 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 engine must be capable of sustained operation throughout its flow and pressure
range with fuel initially saturated with
water at 80 SectionF 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 engine 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]

Section 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 Administrator. 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 exchanger using fuel as one of its fluids
may not result in a hazardous condition.
[Amdt. 25-40, 42 FR 15043, Mar. 17, 1977]

spaschal on DSK3GDR082PROD with CFR

Section 25.953 Fuel system independence.
Each fuel system must meet the requirements of Section 25.903(b) by - 
(a) Allowing the supply of fuel to
each engine through a system independent of each part of the system supplying fuel to any other engine; or
(b) Any other acceptable method.
Section 25.954 Fuel system lightning protection.
(a) For purposes of this section - 
(1) A critical lightning strike is a
lightning strike that attaches to the
airplane in a location that, when combined with the failure of any design

feature or structure, could create an
ignition source.
(2) A fuel system includes any component within either the fuel tank structure or the fuel tank systems, and any
airplane structure or system components that penetrate, connect to, or are
located within a fuel tank.
(b) The design and installation of a
fuel system must prevent catastrophic
fuel vapor ignition due to lightning and
its effects, including:
(1) Direct lightning strikes to areas
having a high probability of stroke attachment;
(2) Swept lightning strokes to areas
where swept strokes are highly probable; and
(3) Lightning-induced or conducted
electrical transients.
(c) To comply with paragraph (b) of
this section, catastrophic fuel vapor ignition must be extremely improbable,
taking into account flammability, critical lightning strikes, and failures
within the fuel system.
(d) To protect design features that
prevent catastrophic fuel vapor ignition caused by lightning, the type design must include critical design configuration
control
limitations
(CDCCLs) identifying those features
and providing information to protect
them. To ensure the continued effectiveness of those design features, the
type design must also include inspection and test procedures, intervals between repetitive inspections and tests,
and mandatory replacement times for
those design features used in demonstrating compliance to paragraph (b)
of this section. The applicant must include the information required by this
paragraph in the Airworthiness Limitations section of the Instructions for
Continued Airworthiness required by
Section 25.1529.
[Doc. No. FAA-2014-1027, Amdt. 25-146, 83 FR
47556, Sept. 20, 2018]

Section 25.955 Fuel flow.
(a) Each fuel system must provide at
least 100 percent of the fuel flow required under each intended operating
condition and maneuver. Compliance
must be shown as follows:
(1) Fuel must be delivered to each engine at a pressure within the limits
specified in the engine type certificate.

314

VerDate Sep<11>2014

12:50 Apr 30, 2019

Jkt 247046

PO 00000

Frm 00324

Fmt 8010

Sfmt 8010

Y:\SGML\247046.XXX

247046