323 

Federal Aviation Administration, DOT 

§ 125.145 

§ 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. 

(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. 

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