spaschal on DSK3GDR082PROD with CFR

Section 27.953

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

incorporate the following design features:
(i) The load necessary to separate a
breakaway coupling must be between
25 to 50 percent of the minimum ultimate failure load (ultimate strength)
of the weakest component in the fluidcarrying 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 separate whenever its ultimate load (as defined in paragraph (c)(1)(i) of this section) is applied in the failure modes
most likely to occur.
(iii) All breakaway couplings must
incorporate design provisions to visually ascertain that the coupling is
locked together (leak-free) and is open
during normal installation and service.
(iv) All breakaway couplings must incorporate 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 couplings, 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
Section 27.955(a) and must comply with the fatigue
evaluation
requirements
of
Section 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 installed greater than 25 to 50 percent of
the ultimate load (strength) of the
weakest component in the line and
must comply with the fatigue requirements of Section 27.571 without leaking.
(d) Frangible or deformable structural
attachments. Unless hazardous relative
motion of fuel tanks and fuel system
components to local rotorcraft structure is demonstrated to be extremely
improbable in an otherwise survivable
impact, frangible or locally deformable
attachments of fuel tanks and fuel system components to local rotorcraft
structure must be used. The attachment of fuel tanks and fuel system
components to local rotorcraft struc-

ture, whether frangible or locally deformable, must be designed such that
its separation or relative local deformation 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 frangible or deformable attachments must
be as follows:
(1) The load required to separate a
frangible attachment from its support
structure, or deform a locally deformable 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 ultimate 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 fatigue requirements of Section 27.571.
(e) Separation of fuel and ignition
sources. To provide maximum crash resistance, fuel must be located as far as
practicable from all occupiable areas
and from all potential ignition sources.
(f) Other basic mechanical design criteria. Fuel tanks, fuel lines, electrical
wires, and electrical devices must be
designed, constructed, and installed, as
far as practicable, to be crash resistant.
(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]

Section 27.953 Fuel system independence.
(a) Each fuel system for multiengine
rotorcraft must allow fuel to be supplied to each engine through a system
independent of those parts of each system 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

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