An in-flight engine compartment
fire is usually caused by a failure that allows
a flammable substance, such as fuel, oil,
or hydraulic fluid, to come in contact with
a hot surface. This may be caused by a mechanical
failure of the engine itself, an engine-driven
accessory, a defective induction or exhaust
system, or a broken line. Engine compartment
fires may also result from maintenance errors,
such as improperly installed/fastened lines
and/or fittings resulting in leaks.
Engine compartment fires can be indicated
by smoke and/or flames coming from the engine
cowling area. They can also be indicated by
discoloration, bubbling, and/or melting of
the engine cowling skin in cases where flames
and/or smoke are not visible to the pilot.
By the time a pilot becomes aware of an in-flight
engine compartment fire, it usually is well
developed. Unless the airplane manufacturer
directs otherwise in the AFM/POH, the first
step on discovering a fire should be to shut
off the fuel supply to the engine by placing
the mixture control in the idle cut off position
and the fuel selector shutoff valve to the
OFF position. The ignition switch should be
left ON in order to use up the fuel that remains
in the fuel lines and components between the
fuel selector/shutoff valve and the engine.
This procedure may starve the engine compartment
of fuel and cause the fire to die naturally.
If the flames are snuffed out, no attempt
should be made to restart the engine.
If the engine compartment fire is oil-fed,
as evidenced by thick black smoke, as opposed
to a fuel-fed fire, which produces bright
orange flames, the pilot should consider stopping
the propeller rotation by feathering or other
means, such as (with constant-speed propellers)
placing the pitch control lever to the minimum
rpm position and raising the nose to reduce
airspeed until the propeller stops rotating.
This procedure stops an engine-driven oil
(or hydraulic) pump from continuing to pump
the flammable fluid that is feeding the fire.
Some light airplane emergency checklists direct
the pilot to shut off the electrical master
switch. However, the pilot should consider
that unless the fire is electrical in nature,
or a crash landing is imminent, deactivating
the electrical system prevents the use of
panel radios for transmitting distress messages
and also causes air traffic control (ATC)
to lose transponder returns.
Pilots of powerless single-engine airplanes
are left with no choice but to make a forced
landing. Pilots of twin-engine airplanes may
elect to continue the flight to the nearest
airport. However, consideration must be given
to the possibility that a wing could be seriously
impaired and lead to structural failure. Even
a brief but intense fire could cause dangerous
structural damage. In some cases, the fire
could continue to burn under the wing (or
engine cowling in the case of a single-engine
airplane) out of view of the pilot. Engine
compartment fires that appear to have been
extinguished have been known to rekindle with
changes in airflow pattern and airspeed.
The pilot must be familiar with the airplane’s
emergency descent procedures. The pilot must
bear in mind the following:
• The airplane may be severely structurally
damaged to the point that its ability to remain
under control could be lost at any moment.
• The airplane may still be on fire and
susceptible to explosion.
• The airplane is expendable and the
only thing that matters is the safety of those
on board.
