The pilot and his passenger prepared for a night flight from the airport in Raleigh/Durham, North Carolina, in the flying club’s Piper PA-28 to maintain the pilot’s currency.
He tried to start the engine three times, priming the engine a total of 11 times, and “pumping” the throttle during one attempt, but it did not start.
Concerned that he may have flooded the engine, he waited five minutes before attempting another start with full throttle and mixture at idle/cutoff.
After this attempt, the passenger noted smoke and he realized that the engine was on fire.
He told his passenger to get out of the airplane and attempted to extinguish the fire with the onboard fire extinguisher. However, the fire substantially damaged the airplane’s fuselage, engine mounts, and firewall.
The pilot reported no mechanical malfunctions or failures with the airplane that would have precluded normal operation.
The Pilot’s Operating Handbook for the airplane suggested priming one to three times before engine start.
Probable Cause: The pilot’s flooding the engine with fuel during a cold engine start, which resulted in an engine fire.
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This January 2023 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
On cold days at our flight school, students would catch our Cessna 150 aircraft on fire, due mainly to the rotten O-200 priming system. All the primer does is squirt fuel into the carburetor throat which then runs down into the airbox, and onto the wheel pant if you prime it enough. If I recall, the POH said to prime 6 times on very cold days.
While continuing cranking is protocol for flooding, it doesn’t correct gas on fire from over flooding dripping out of the drain hole onto the cowling and ground. This is lack of mechanical knowledge situations not particularly covered in checklists.
Funniest thing I ever heard in an airline simulator: Captain, when faced with an engine fire: “Don’t panic. Remember, it was on fire when we started it.”
But seriously folks, over-priming an engine is never a good idea. I know of one person whose hot start procedure for a fuel
Injected engine was to flood it first, then do a flooded start procedure (full throttle and mixture at idle cutoff. Crank until it starts then slowly ease in the mixture and retard the throttle). This usually worked, until one day he had an engine fire. Oops.
In its engine operating manual, Continental warns against over-priming.
Many an induction system fire has be sucked back into and extinguished in the engine by a knowledgeable pilot or mechanic knowing that the fire would go out when the engine eventually started.