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14 CFR Ch. I (1–1–18 Edition) 

§ 121.223 

endangering the safety of the airplane 
or the occupants. Each Class D com-
partment must comply with the fol-
lowing: 

(1) It must have a means to exclude 

hazardous quantities of smoke, flames, 
or noxious gases from entering any 
compartment occupied by the crew or 
passengers. 

(2) Ventilation and drafts must be 

controlled within each compartment so 
that any fire likely to occur in the 
compartment will not progress beyond 
safe limits. 

(3) It must be completely lined with 

fire-resistant material. 

(4) Consideration must be given to 

the effect of heat within the compart-
ment on adjacent critical parts of the 
airplane. 

(f)  Class E. On airplanes used for the 

carriage of cargo only, the cabin area 
may be classified as a Class ‘‘E’’ com-
partment. Each Class E compartment 
must comply with the following: 

(1) It must be completely lined with 

fire-resistant material. 

(2) It must have a separate system of 

an approved type smoke or fire detec-
tor to give warning at the pilot or 
flight engineer station. 

(3) It must have a means to shut off 

the ventilating air flow to or within 
the compartment and the controls for 
that means must be accessible to the 
flight crew in the crew compartment. 

(4) It must have a means to exclude 

hazardous quantities of smoke, flames, 
or noxious gases from entering the 
flight crew compartment. 

(5) Required crew emergency exits 

must be accessible under all cargo 
loading conditions. 

§ 121.223

Proof of compliance with 

§ 121.221. 

Compliance with those provisions of 

§ 121.221 that refer to compartment ac-
cessibility, the entry of hazardous 
quantities of smoke or extinguishing 
agent into compartments occupied by 
the crew or passengers, and the dissipa-
tion of the extinguishing agent in Class 
‘‘C’’ compartments must be shown by 
tests in flight. During these tests it 
must be shown that no inadvertent op-
eration of smoke or fire detectors in 
other compartments within the air-
plane would occur as a result of fire 

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. 

§ 121.225

Propeller deicing fluid. 

If combustible fluid is used for pro-

peller deicing, the certificate holder 
must comply with § 121.255. 

§ 121.227

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— 

(1) There is a means to allow crew-

members to shut off the supply of fuel 
to these lines; or 

(2) 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 incorporate no fit-
tings on or within the personnel or 
cargo areas and are suitably routed or 
protected to prevent accidental dam-
age. 

(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. 

§ 121.229

Location of fuel tanks. 

(a) Fuel tanks must be located in ac-

cordance with § 121.255. 

(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. 

§ 121.231

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 airplanes between which there may 
be relative motion must incorporate 
provisions for flexibility. 

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