Expert: Heiko Hanusch - 2/26/2010

Question
I HAVE ALREADY RECEIVED MY PRIVATE PILOTīS LICENSE. RIGHT NOW I AM WORKING ON MY TIME BUILDING. NOT LONG AGO I HAD AN INCIDENT WITH MY AIRCRAFT. I WAS FOLLOWING THE SECURING PROCEDURES LISTED ON THE CHECKLIST FOR A CESSNA 152 AND AFTER TURNING ALL AVIONICS OFF AND PULLING THE MIXTURE TO FULL LEAN, I NOTICED THAT THE PROPELLER KEPT GOING EVEN AFTER I HAD TURNED THE MAGS OFF AND MASTER SWITCH OFF. EVERYTHING THAT COULD POWER THE PROPELLER WAS OFF,BUT STILL THE PROPELLER KEPT SPINNING AND I COULD SMELL SOMETHING WAS BURNING OUT, ALTHOUGH THERE WAS NO SMOKE. WAS THIS DONE BY AN OVERCHARGE MADE BY THE ALTERNATOR?
THANK YOU FOR TAKING MY QUESTION INTO CONSIDERATION

Answer
Victor,

Well there could be many reasons this happens.

First of, a electrical problem (a short of some sorts).

However the next issue is also very likely, if not the most likely, especially on hot days or badly tuned engines, hot cylinder heads... when that happens a spot somewhere in the cylinder head area (most likely the spark plug or some foreign object that protrudes from the head area) is glowing red hence providing a source for ignition. In this case the engine will run for a little while longer until this area cools sufficient to no longer cause ignition (if this is the cause the engine will sound "rough" as it continues to run).

On the other hand if you engine keeps running long after you turned everything off, you definitively have a electrical problem and that should be checked out by a mechanic. This problem can be here one day and gone the next (very typical of electrical issues)

Good Luck and be careful out there,

H2