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Federal Aviation Administration, DOT
§ 125.141
contained in any one compartment, ei-
ther during the time it is being extin-
guished, or thereafter, unless the extin-
guishing system floods those compart-
ments simultaneously.
§ 125.123 Propeller deicing fluid.
If combustible fluid is used for pro-
peller deicing, the certificate holder
must comply with § 125.153.
§ 125.125 Pressure cross-feed arrange-
ments.
(a) Pressure cross-feed lines may not
pass through parts of the airplane used
for carrying persons or cargo unless
there is a means to allow crewmembers
to shut off the supply of fuel to these
lines or the lines are enclosed in a fuel
and fume-proof enclosure that is venti-
lated and drained to the exterior of the
airplane. However, such an enclosure
need not be used if those lines incor-
porate no fittings on or within the per-
sonnel or cargo areas and are suitably
routed or protected to prevent acci-
dental damage.
(b) Lines that can be isolated from
the rest of the fuel system by valves at
each end must incorporate provisions
for relieving excessive pressures that
may result from exposure of the iso-
lated line to high temperatures.
§ 125.127 Location of fuel tanks.
(a) Fuel tanks must be located in ac-
cordance with § 125.153.
(b) No part of the engine nacelle skin
that lies immediately behind a major
air outlet from the engine compart-
ment may be used as the wall of an in-
tegral tank.
(c) Fuel tanks must be isolated from
personnel compartments by means of
fume- and fuel-proof enclosures.
§ 125.129 Fuel system lines and fit-
tings.
(a) Fuel lines must be installed and
supported so as to prevent excessive vi-
bration and so as to be adequate to
withstand loads due to fuel pressure
and accelerated flight conditions.
(b) Lines connected to components of
the airplane between which there may
be relative motion must incorporate
provisions for flexibility.
(c) Flexible connections in lines that
may be under pressure and subject to
axial loading must use flexible hose as-
semblies rather than hose clamp con-
nections.
(d) Flexible hoses must be of an ac-
ceptable type or proven suitable for the
particular application.
§ 125.131 Fuel lines and fittings in des-
ignated fire zones.
Fuel lines and fittings in each des-
ignated fire zone must comply with
§ 125.157.
§ 125.133 Fuel valves.
Each fuel valve must—
(a) Comply with § 125.155;
(b) Have positive stops or suitable
index provisions in the ‘‘on’’ and ‘‘off’’
positions; and
(c) Be supported so that loads result-
ing from its operation or from acceler-
ated flight conditions are not trans-
mitted to the lines connected to the
valve.
§ 125.135 Oil lines and fittings in des-
ignated fire zones.
Oil lines and fittings in each des-
ignated fire zone must comply with
§ 125.157.
§ 125.137 Oil valves.
(a) Each oil valve must—
(1) Comply with § 125.155;
(2) Have positive stops or suitable
index provisions in the ‘‘on’’ and ‘‘off’’
positions; and
(3) Be supported so that loads result-
ing from its operation or from acceler-
ated flight conditions are not trans-
mitted to the lines attached to the
valve.
(b) The closing of an oil shutoff
means must not prevent feathering the
propeller, unless equivalent safety pro-
visions are incorporated.
§ 125.139 Oil system drains.
Accessible drains incorporating ei-
ther a manual or automatic means for
positive locking in the closed position
must be provided to allow safe drainage
of the entire oil system.
§ 125.141 Engine breather lines.
(a) Engine breather lines must be so
arranged that condensed water vapor
that may freeze and obstruct the line
cannot accumulate at any point.
336
14 CFR Ch. I (1–1–24 Edition)
§ 125.143
(b) Engine breathers must discharge
in a location that does not constitute a
fire hazard in case foaming occurs and
so that oil emitted from the line does
not impinge upon the pilots’ wind-
shield.
(c) Engine breathers may not dis-
charge into the engine air induction
system.
§ 125.143 Firewalls.
Each engine, auxiliary power unit,
fuel-burning heater, or other item of
combusting equipment that is intended
for operation in flight must be isolated
from the rest of the airplane by means
of firewalls or shrouds, or by other
equivalent means.
§ 125.145 Firewall construction.
Each firewall and shroud must—
(a) Be so made that no hazardous
quantity of air, fluids, or flame can
pass from the engine compartment to
other parts of the airplane;
(b) Have all openings in the firewall
or shroud sealed with close-fitting fire-
proof grommets, bushings, or firewall
fittings;
(c) Be made of fireproof material; and
(d) Be protected against corrosion.
§ 125.147 Cowling.
(a) Cowling must be made and sup-
ported so as to resist the vibration, in-
ertia, and air loads to which it may be
normally subjected.
(b) Provisions must be made to allow
rapid and complete drainage of the
cowling in normal ground and flight at-
titudes. Drains must not discharge in
locations constituting a fire hazard.
Parts of the cowling that are subjected
to high temperatures because they are
near exhaust system parts or because
of exhaust gas impingement must be
made of fireproof material. Unless oth-
erwise specified in these regulations,
all other parts of the cowling must be
made of material that is at least fire
resistant.
§ 125.149 Engine accessory section dia-
phragm.
Unless equivalent protection can be
shown by other means, a diaphragm
that complies with § 125.145 must be
provided on air-cooled engines to iso-
late the engine power section and all
parts of the exhaust system from the
engine accessory compartment.
§ 125.151 Powerplant fire protection.
(a) Designated fire zones must be pro-
tected from fire by compliance with
§§ 125.153 through 125.159.
(b) Designated fire zones are—
(1) Engine accessory sections;
(2) Installations where no isolation is
provided between the engine and acces-
sory compartment; and
(3) Areas that contain auxiliary
power units, fuel-burning heaters, and
other combustion equipment.
§ 125.153 Flammable fluids.
(a) No tanks or reservoirs that are a
part of a system containing flammable
fluids or gases may be located in des-
ignated fire zones, except where the
fluid contained, the design of the sys-
tem, the materials used in the tank,
the shutoff means, and the connec-
tions, lines, and controls provide equiv-
alent safety.
(b) At least one-half inch of clear air-
space must be provided between any
tank or reservior and a firewall or
shroud isolating a designated fire zone.
§ 125.155 Shutoff means.
(a) Each engine must have a means
for shutting off or otherwise pre-
venting hazardous amounts of fuel, oil,
deicer, and other flammable fluids
from flowing into, within, or through
any designated fire zone. However,
means need not be provided to shut off
flow in lines that are an integral part
of an engine.
(b) The shutoff means must allow an
emergency operating sequence that is
compatible with the emergency oper-
ation of other equipment, such as
feathering the propeller, to facilitate
rapid and effective control of fires.
(c) Shutoff means must be located
outside of designated fire zones, unless
equivalent safety is provided, and it
must be shown that no hazardous
amount of flammable fluid will drain
into any designated fire zone after a
shutoff.
(d) Adequate provisions must be
made to guard against inadvertent op-
eration of the shutoff means and to
make it possible for the crew to reopen