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Aero-Tips 10.30.06

Engine fires during start can happen any time for any number of reasons, but by far they most frequently occur in cold weather from over-priming. What should we do in the event of an engine fire on the ground?

Checklist

Most aircraft manuals have a checklist that outlines steps to follow in the vent of an engine fire on the ground. Not that you'd have time to pull out the Pilots Operating Handbook (POH) if it happens to you. You need to look in the POH for the airplane you're flying and memorize the procedure for the unlikely event you'll need to use it.

There are several variations on the procedure, but all contain these basic steps:

• Mixture.................IDLE CUTOFF
• Fuel selector...........OFF
• CONTINUE CRANKING TO PULL FIRE INTO INDUCTION SYSTEM
• EVACUATE THE AIRCRAFT

Again, review the POH for the airplane you're currently flying for the best technique to use.

Engine Types

There are two basic types of reciprocating aircraft engines:

• Carbureted engines. Fuel is combined with air and then pulled into the induction system through the carburetor venture. If a fire starts as a result of overpriming (or in some types, aggressively pumping the throttle during start) but the engine itself starts, suction may draw the fire inside the engine. Hence the advice to keep cranking the starter, although I know of no POH that provides any guidance on how long to keep cranking.
• Fuel-injected engines. Fuel is delivered directly to each cylinder, combining with air in the induction manifold just before the intake valve. Overpriming a fuel-injected engine may cause fuel to collect in the intake manifold, and cranking after a fire starts may pull the flames into the cylinders. But often overpriming a fuel-injected engine puts a lot of fuel in the exhaust manifold, and starter operation will do nothing to draw in the fire. So although continuing cranking may help in some cases, it's not as likely to put out the external fire as it might be with a carburetor.

Get out, check it out

It's fairly rare, but sometimes an engine fire after start eventually consumes and destroys the entire airplane. Crank a few seconds to try to draw in the fire, but then evacuate the aircraft and get well away. If a large-capacity fire extinguisher is available you might be able to put the fire out, but a small in-cabin type may not be adequate. Get your passengers and yourself out of danger.

If the fire does go out, whether through cranking or on its own after you evacuate, get a mechanic to remove the cowling and take a very good look at the aircraft for possible damage. If everything checks out okay, consider a local test flight before venturing out of the traffic pattern.

Avoidance

Carefully prime the engine before a cold-weather start. Preheat the engine if the temperature is below about 40 degrees F to make for an easier start. Better yet, hangar the airplane the night before if at all possible. Even an unheated hangar often keeps the engine warm enough to avoid the need for aggressive priming.

Aero-tip of the day: Know how to avoid engine fires during start, and what to do if one happens to you.

FMI: Aero-Tips