Federal Aviation Administration, DOT
Section 125.161

Section 125.175

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 subjected to flame, fire-extinguishing systems must be provided to serve all designated fire zones.
(b) Materials in the fire-extinguishing system must not react chemically with the extinguishing agent so
as to be a hazard.
Section 125.163

Fire-extinguishing agents.

Only methyl bromide, carbon dioxide,
or another agent that has been shown
to provide equivalent extinguishing action may be used as a fire-extinguishing agent. If methyl bromide or
any other toxic extinguishing agent is
used, provisions must be made to prevent harmful concentrations of fluid or
fluid vapors from entering any personnel 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 extinguishing system. If a methyl bromide system is used, the containers
must be charged with dry agent and
sealed by the fire-extinguisher manufacturer 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.
Section 125.165 Extinguishing
agent
tainer pressure relief.

con-

Extinguishing agent containers must
be provided with a pressure relief to
prevent bursting of the container because of excessive internal pressures.
The discharge line from the relief connection must terminate outside the
airplane in a place convenient for inspection on the ground. An indicator
must be provided at the discharge end
of the line to provide a visual indication when the container has discharged.

Section 125.167 Extinguishing
agent
container compartment temperature.
Precautions must be taken to ensure
that the extinguishing agent containers are installed in places where
reasonable temperatures can be maintained for effective use of the extinguishing system.
Section 125.169 Fire-extinguishing
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-resistant and be located so as to minimize
the probability of failure.
Section 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.
Section 125.173

Fire detectors.

Fire detectors must be made and installed in a manner that assures their
ability to resist, without failure, all vibration, inertia, and other loads to
which they may be normally subjected.
Fire detectors must be unaffected by
exposure to fumes, oil, water, or other
fluids that may be present.
Section 125.175 Protection of other airplane
components against fire.
(a) Except as provided in paragraph
(b) of this section, all airplane surfaces
aft of the nacelles in the area of one
nacelle diameter on both sides of the
nacelle centerline must be made of material that is at least fire resistant.
(b) Paragraph (a) of this section does
not apply to tail surfaces lying behind
nacelles unless the dimensional configuration of the airplane is such that
the tail surfaces could be affected readily by heat, flames, or sparks emanating from a designated fire zone or
from the engine from a designated fire
zone or from the engine compartment
of any nacelle.

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