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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