Unless other means acceptable to the Administrator are employed to
minimize the hazard of fuel fires to occupants following an otherwise
survivable impact (crash landing), the fuel systems must incorporate the
design features of this section. These systems must be shown to be capable
of sustaining the static and dynamic deceleration loads of this section,
considered as ultimate loads acting alone, measured at the system
component's center of gravity without structural damage to the system
components, fuel tanks, or their attachments that would leak fuel to an
(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 tanks must be filled with water to 80 percent of the normal,
(4) The tank must be enclosed in a surrounding structure representative
of the installation unless it can be established that the surrounding
structure is free of projections or other design features likely to
contribute to upture of the tank.
(5) The tank must drop freely and impact in a horizontal position ±10°.
(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, heaters, and auxiliary power units, or occupants
is extremely remote, each fuel tank must be designed and installed to
retain its contents under the following ultimate inertial load factors,
(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
compartment that, if loosened, could injure an occupant in an emergency
(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 couplings must be installed unless hazardous 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 couplings or equivalent devices must be installed at all
fuel tank-to-fuel line connections, tank-to-tank interconnects, and at
other points in the fuel system where local structural deformation could
lead to the release of fuel.
(1) The design and construction of self-sealing breakaway couplings
must 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 fluid-carrying line. The separation load
must in no case be less than 300 pounds, regardless of the size of the
(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
inadvertent fuel shutoff in flight is improbable in accordance with
§29.955(a) and must comply with the fatigue evaluation requirements of
§29.571 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 §29.571 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 structure, 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 component 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
(3) All frangible or locally deformable attachments must comply with
the fatigue requirements of §29.571.
(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.