title-14-part-27-sec27-952

532

14 CFR Ch. I (1–1–24 Edition)

§ 27.951

drive system associated with critical
combinations of power, rotational
speed, and control displacement.

[Amdt. 27–1, 32 FR 6914, May 5, 1967, as
amended by Amdt. 27–11, 41 FR 55469, Dec. 20,
1976]

UEL

YSTEM

§ 27.951

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 functioning
under any likely operating condition,
including the maneuvers for which cer-
tification is requested.

(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.

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as
amended by Amdt. 27–9, 39 FR 35461, Oct. 1,
1974]

§ 27.952

Fuel system crash resistance.

Unless other means acceptable to the

Administrator are employed to mini-
mize the hazard of fuel fires to occu-
pants following an otherwise surviv-
able impact (crash landing), the fuel
systems must incorporate the design
features of this section. These systems
must be shown to be capable of sus-
taining the static and dynamic decel-
eration loads of this section, consid-
ered as ultimate loads acting alone,
measured at the system component’s
center of gravity, without structural
damage to system components, fuel
tanks, or their attachments that would
leak fuel to an ignition source.

(a)

Drop test requirements. Each tank,

or the most critical tank, must be
drop-tested as follows:

(1) The drop height must be at least

50 feet.

(2) The drop impact surface must be

nondeforming.

(3) The tank must be filled with

water to 80 percent of the normal, full
capacity.

(4) The tank must be enclosed in a

surrounding structure representative
of the installation unless it can be es-
tablished that the surrounding struc-
ture is free of projections or other de-
sign features likely to contribute to
rupture of the tank.

(5) The tank must drop freely and im-

pact in a horizontal position

(6) After the drop test, there must be

no leakage.

(b)

Fuel tank load factors. Except for

fuel tanks located so that tank rupture
with fuel release to either significant
ignition sources, such as engines, heat-
ers, and auxiliary power units, or occu-
pants is extremely remote, each fuel
tank must be designed and installed to
retain its contents under the following
ultimate inertial load factors, acting
alone.

(1) For fuel tanks in the cabin:
(i) Upward—4g.
(ii) Forward—16g.
(iii) Sideward—8g.
(iv) Downward—20g.
(2) For fuel tanks located above or

behind the crew or passenger compart-
ment that, if loosened, could injure an
occupant in an emergency landing:

(i) Upward—1.5g.
(ii) Forward—8g.
(iii) Sideward—2g.
(iv) Downward—4g.
(3) For fuel tanks in other areas:
(i) Upward—1.5g.
(ii) Forward—4g.
(iii) Sideward—2g.
(iv) Downward—4g.
(c)

Fuel line self-sealing breakaway

couplings. Self-sealing breakaway cou-
plings must be installed unless haz-
ardous relative motion of fuel system
components to each other or to local
rotorcraft structure is demonstrated to
be extremely improbable or unless
other means are provided. The cou-
plings or equivalent devices must be
installed at all fuel tank-to-fuel line
connections, tank-to-tank intercon-
nects, and at other points in the fuel
system where local structural deforma-
tion could lead to the release of fuel.

(1) The design and construction of

self-sealing breakaway couplings must

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Federal Aviation Administration, DOT

§ 27.953

incorporate the following design fea-
tures:

(i) The load necessary to separate a

breakaway coupling must be between
25 to 50 percent of the minimum ulti-
mate failure load (ultimate strength)
of the weakest component in the fluid-
carrying line. The separation load
must in no case be less than 300 pounds,
regardless of the size of the fluid line.

(ii) A breakaway coupling must sepa-

rate whenever its ultimate load (as de-
fined in paragraph (c)(1)(i) of this sec-
tion) is applied in the failure modes
most likely to occur.

(iii) All breakaway couplings must

incorporate design provisions to vis-
ually ascertain that the coupling is
locked together (leak-free) and is open
during normal installation and service.

(iv) All breakaway couplings must in-

corporate design provisions to prevent
uncoupling or unintended closing due
to operational shocks, vibrations, or
accelerations.

(v) No breakaway coupling design

may allow the release of fuel once the
coupling has performed its intended
function.

(2) All individual breakaway cou-

plings, coupling fuel feed systems, or
equivalent means must be designed,
tested, installed, and maintained so
that inadvertent fuel shutoff in flight
is improbable in accordance with
§ 27.955(a) and must comply with the fa-
tigue evaluation requirements of
§ 27.571 without leaking.

(3) Alternate, equivalent means to

the use of breakaway couplings must
not create a survivable impact-induced
load on the fuel line to which it is in-
stalled greater than 25 to 50 percent of
the ultimate load (strength) of the
weakest component in the line and
must comply with the fatigue require-
ments of § 27.571 without leaking.

(d)

Frangible or deformable structural

attachments. Unless hazardous relative
motion of fuel tanks and fuel system
components to local rotorcraft struc-
ture is demonstrated to be extremely
improbable in an otherwise survivable
impact, frangible or locally deformable
attachments of fuel tanks and fuel sys-
tem components to local rotorcraft
structure must be used. The attach-
ment of fuel tanks and fuel system
components to local rotorcraft struc-

ture, whether frangible or locally de-
formable, must be designed such that
its separation or relative local defor-
mation will occur without rupture or
local tear-out of the fuel tank or fuel
system components that will cause fuel
leakage. The ultimate strength of fran-
gible or deformable attachments must
be as follows:

(1) The load required to separate a

frangible attachment from its support
structure, or deform a locally deform-
able attachment relative to its support
structure, must be between 25 and 50
percent of the minimum ultimate load
(ultimate strength) of the weakest
component in the attached system. In
no case may the load be less than 300
pounds.

(2) A frangible or locally deformable

attachment must separate or locally
deform as intended whenever its ulti-
mate load (as defined in paragraph
(d)(1) of this section) is applied in the
modes most likely to occur.

(3) All frangible or locally deformable

attachments must comply with the fa-
tigue requirements of § 27.571.

(e)

Separation of fuel and ignition

sources. To provide maximum crash re-
sistance, fuel must be located as far as
practicable from all occupiable areas
and from all potential ignition sources.

(f)

Other basic mechanical design cri-

teria. Fuel tanks, fuel lines, electrical
wires, and electrical devices must be
designed, constructed, and installed, as
far as practicable, to be crash resist-
ant.

(g)

Rigid or semirigid fuel tanks. Rigid

or semirigid fuel tank or bladder walls
must be impact and tear resistant.

[Doc. No. 26352, 59 FR 50386, Oct. 3, 1994]

§ 27.953

Fuel system independence.

(a) Each fuel system for multiengine

rotorcraft must allow fuel to be sup-
plied to each engine through a system
independent of those parts of each sys-
tem supplying fuel to other engines.
However, separate fuel tanks need not
be provided for each engine.

(b) If a single fuel tank is used on a

multiengine rotorcraft, the following
must be provided:

(1) Independent tank outlets for each

engine, each incorporating a shutoff
valve at the tank. This shutoff valve
may also serve as the firewall shutoff