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If you think you have an electrical
fire, it's no good just using the
extinguisher, because you may be
treating the symptom and not the
cause, although there is a school of
thought that advocates not using an
extinguisher at all if you can possibly
help it, due to the fumes and stuff
you have to breathe in until you
land. Whatever you do, transmit a
Mayday before it’s too late—you can
always downgrade it afterwards. Bear
in mind also that your first strike
with your extinguisher is the best,
because the contents and pressure
decrease from then on.
Next, put an oxygen or smoke mask
on, if you have one, then bring on
essential electrics one at a time until
the smoke appears again.
On the ground, engine fire drills may
vary considerably between different
types, and these will have to be
memorized, but there are some
general points that can be made.
One is, before evacuating the
aircraft, make sure the parking brake
is off, so it can be moved
somewhere safer if things get out of
hand, always being aware that it
could run off by itself, as well! If the
fire has been caused by spilt fuel, has
Airframes, Engines & Systems 229
spread to the ground under the wing
and the other engine has been
started, taxi clear of the area (or
more specifically, the fuel on the
ground) before evacuation, keeping
the fire on the downwind side. If the
other engine has not been started,
evacuate first, carrying out what
drills you can.
If you can, use the radio to summon
help, and take the extinguisher.
Remember that human beings en
masse need very different handling
than when encountered singly.
In the air, initial shut down actions
are similar everywhere—after
performing vital actions from
memory (e.g. identifying the source
and all that), refer to the checklist to
see if you haven't forgotten anything.
If the engine has been secured
promptly, the fire should go out
quickly after the fuel supply has been
cut off. You will find, however, that
structural failure of the wing will be
imminent after about two minutes if
the fire is uncontrolled, which is a
sobering enough thought to make
you commence emergency descent
IMMEDIATELY, no matter how
good it looks.
If you've got fire extinguishers in the
engine bays, delay actuating them
until the engine has been secured
and you've no reason to suspect a
false alarm; that is, unless you can
actually see signs of a fire. In the
cabin, whether in the air or on the
ground, the priority is to get out, and
as soon as possible, because if the
flames don't get you, the fumes will.
The only difference between the two
situations is how quickly this can be
done, and what you can do about it.
Heat sensors can be found in many
engine compartments, with smoke
detectors in cabins, toilets, or
anywhere convenient. Infra red
systems detect the light from flames
or glowing metal (also used by
railways to detect hot wheels). Some
systems in small helicopters use a
very thin wire, with another even
thinner one inside, separated by a
conductor that will vapourise with
heat. When the two wires connect, a
circuit is completed and a warning
will go off. Sometimes, however,
theses can short out, particularly on
misty or otherwise humid days, and
create false alarms.
If there isn't actually an extinguisher
in the engine, at the very least there
should be a firewall shutoff, operated
from the cockpit, that will stop the
flow in fuel and hydraulic lines (PA
31, etc). If there isn't one of those,
try for a fuel valve that stops the flow
to the engine (Bell 206).
An engine-based system will have
CO2 or Halon in cylinders.
The recommended extinguisher for
wheel assemblies is dry powder.
Autopilots, etc
Those in large aeroplanes control
attitudes in pitch, roll and yaw and
are known as 3-axis (a 2-axis controls
pitch and roll, and a single-axis roll
only). You will be able to maintain
an altitude or heading, intercept and
follow a radial or localiser and keep
to a descent pattern. However, when
following a radial, the results can
often be unsettling to passengers, as
the system chases the needle too
much. A better solution is to use the
heading bug and chase the needles
yourself so you don't spill the coffee.
230 Canadian Professional Pilot Studies
A flight management system takes
　
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