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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 

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337 

Federal Aviation Administration, DOT 

§ 125.173 

the shutoff means after it has been 
closed. 

§ 125.157 Lines and fittings. 

(a) Each line, and its fittings, that is 

located in a designated fire zone, if it 
carries flammable fluids or gases under 
pressure, or is attached directly to the 
engine, or is subject to relative motion 
between components (except lines and 
fittings forming an integral part of the 
engine), must be flexible and fire-re-
sistant with fire-resistant, factory- 
fixed, detachable, or other approved 
fire-resistant ends. 

(b) Lines and fittings that are not 

subject to pressure or to relative mo-
tion between components must be of 
fire-resistant materials. 

§ 125.159 Vent and drain lines. 

All vent and drain lines, and their 

fittings, that are located in a des-
ignated fire zone must, if they carry 
flammable fluids or gases, comply with 
§ 125.157, if the Administrator finds that 
the rupture or breakage of any vent or 
drain line may result in a fire hazard. 

§ 125.161 Fire-extinguishing systems. 

(a) Unless the certificate holder 

shows that equivalent protection 
against destruction of the airplane in 
case of fire is provided by the use of 
fireproof materials in the nacelle and 
other components that would be sub-
jected to flame, fire-extinguishing sys-
tems must be provided to serve all des-
ignated fire zones. 

(b) Materials in the fire-extin-

guishing system must not react chemi-
cally with the extinguishing agent so 
as to be a hazard. 

§ 125.163 Fire-extinguishing agents. 

Only methyl bromide, carbon dioxide, 

or another agent that has been shown 
to provide equivalent extinguishing ac-
tion may be used as a fire-extin-
guishing agent. If methyl bromide or 
any other toxic extinguishing agent is 
used, provisions must be made to pre-
vent harmful concentrations of fluid or 
fluid vapors from entering any per-
sonnel compartment either because of 
leakage during normal operation of the 
airplane or because of discharging the 
fire extinguisher on the ground or in 
flight when there is a defect in the ex-

tinguishing system. If a methyl bro-
mide system is used, the containers 
must be charged with dry agent and 
sealed by the fire-extinguisher manu-
facturer or some other person using 
satisfactory recharging equipment. If 
carbon dioxide is used, it must not be 
possible to discharge enough gas into 
the personnel compartments to create 
a danger of suffocating the occupants. 

§ 125.165 Extinguishing agent con-

tainer pressure relief. 

Extinguishing agent containers must 

be provided with a pressure relief to 
prevent bursting of the container be-
cause of excessive internal pressures. 
The discharge line from the relief con-
nection must terminate outside the 
airplane in a place convenient for in-
spection on the ground. An indicator 
must be provided at the discharge end 
of the line to provide a visual indica-
tion when the container has dis-
charged. 

§ 125.167 Extinguishing agent con-

tainer compartment temperature. 

Precautions must be taken to ensure 

that the extinguishing agent con-
tainers are installed in places where 
reasonable temperatures can be main-
tained for effective use of the extin-
guishing system. 

§ 125.169 Fire-extinguishing system 

materials. 

(a) Except as provided in paragraph 

(b) of this section, each component of a 
fire-extinguishing system that is in a 
designated fire zone must be made of 
fireproof materials. 

(b) Connections that are subject to 

relative motion between components of 
the airplane must be made of flexible 
materials that are at least fire-resist-
ant and be located so as to minimize 
the probability of failure. 

§ 125.171 Fire-detector systems. 

Enough quick-acting fire detectors 

must be provided in each designated 
fire zone to assure the detection of any 
fire that may occur in that zone. 

§ 125.173 Fire detectors. 

Fire detectors must be made and in-

stalled in a manner that assures their