632
14 CFR Ch. I (1–1–24 Edition)
§ 29.939
§ 29.939
Turbine engine operating
characteristics.
(a) Turbine engine operating charac-
teristics must be investigated in flight
to determine that no adverse charac-
teristics (such as stall, surge, of flame-
out) are present, to a hazardous degree,
during normal and emergency oper-
ation within the range of operating
limitations of the rotorcraft and of the
engine.
(b) The turbine engine air inlet sys-
tem may not, as a result of airflow dis-
tortion during normal operation, cause
vibration harmful to the engine.
(c) For governor-controlled engines,
it must be shown that there exists no
hazardous torsional instability of the
drive system associated with critical
combinations of power, rotational
speed, and control displacement.
[Amdt. 29–2, 32 FR 6914, May 5, 1967, as
amended by Amdt. 29–12, 41 FR 55473, Dec. 20,
1976]
F
UEL
S
YSTEM
§ 29.951
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 and auxiliary
power unit functioning under any like-
ly operating conditions, including the
maneuvers for which certification is
requested 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 engine or 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.
(c) Each fuel system for a turbine en-
gine must be capable of sustained oper-
ation throughout its flow and pressure
range with fuel initially saturated with
water at 80 degrees 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. 5084, 29 FR 16150, Dec. 3, 1964, as
amended by Amdt. 29–10, 39 FR 35462, Oct. 1,
1974; Amdt. 29–12, 41 FR 55473, Dec. 20, 1976]
§ 29.952
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 the 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 tanks 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
upture of the tank.
(5) The tank must drop freely and im-
pact 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, 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.
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Federal Aviation Administration, DOT
§ 29.952
(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
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 in-
advertent fuel shutoff in flight is im-
probable in accordance with § 29.955(a)
and must comply with the fatigue eval-
uation 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 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 § 29.571 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 component 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 § 29.571.
(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
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14 CFR Ch. I (1–1–24 Edition)
§ 29.953
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 50387, Oct. 3, 1994]
§ 29.953
Fuel system independence.
(a) For category A rotorcraft—
(1) The fuel system must meet the re-
quirements of § 29.903(b); and
(2) Unless other provisions are made
to meet paragraph (a)(1) of this section,
the fuel system must allow fuel to be
supplied to each engine through a sys-
tem independent of those parts of each
system supplying fuel to other engines.
(b) Each fuel system for a multien-
gine category B rotorcraft must meet
the requirements of paragraph (a)(2) of
this section. However, separate fuel
tanks need not be provided for each en-
gine.
§ 29.954
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 to areas
where swept strokes are highly prob-
able; and
(c) Corona and streamering at fuel
vent outlets.
[Amdt. 29–26, 53 FR 34217, Sept. 2, 1988]
§ 29.955
Fuel flow.
(a)
General. The fuel system for each
engine must provide the engine with at
least 100 percent of the fuel required
under all operating and maneuvering
conditions to be approved for the rotor-
craft, including, as applicable, the fuel
required to operate the engines under
the test conditions required by § 29.927.
Unless equivalent methods are used,
compliance must be shown by test dur-
ing which the following provisions are
met, except that combinations of con-
ditions which are shown to be improb-
able need not be considered.
(1) The fuel pressure, corrected for
accelerations (load factors), must be
within the limits specified by the en-
gine type certificate data sheet.
(2) The fuel level in the tank may not
exceed that established as the unusable
fuel supply for that tank under § 29.959,
plus that necessary to conduct the
test.
(3) The fuel head between the tank
and the engine must be critical with
respect to rotorcraft flight attitudes.
(4) The fuel flow transmitter, if in-
stalled, and the critical fuel pump (for
pump-fed systems) must be installed to
produce (by actual or simulated fail-
ure) the critical restriction to fuel flow
to be expected from component failure.
(5) Critical values of engine rota-
tional speed, electrical power, or other
sources of fuel pump motive power
must be applied.
(6) Critical values of fuel properties
which adversely affect fuel flow are ap-
plied during demonstrations of fuel
flow capability.
(7) The fuel filter required by § 29.997
is blocked to the degree necessary to
simulate the accumulation of fuel con-
tamination required to activate the in-
dicator required by § 29.1305(a)(18).
(b)
Fuel transfer system. If normal op-
eration of the fuel system requires fuel
to be transferred to another tank, the
transfer must occur automatically via
a system which has been shown to
maintain the fuel level in the receiving
tank within acceptable limits during
flight or surface operation of the rotor-
craft.
(c)
Multiple fuel tanks. If an engine
can be supplied with fuel from more
than one tank, the fuel system, in addi-
tion to having appropriate manual
switching capability, must be designed
to prevent interruption of fuel flow to
that engine, without attention by the
flightcrew, when any tank supplying
fuel to that engine is depleted of usable
fuel during normal operation and any
other tank that normally supplies fuel
to that engine alone contains usable
fuel.
[Amdt. 29–26, 53 FR 34217, Sept. 2, 1988, as
amended by Amdt. 29–59, 88 FR 8739, Feb. 10,
2023]
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