Comment by HeyLaughingBoy
2 years ago
True story: I had that happen to an airplane. I was a student on a long solo flight and on the last two legs of that flight, the engine wouldn't shut off using the usual method of pulling the throttle back to idle and turning off the magneto.
It's been long enough that I don't remember what I did to get it shut off (maybe I toggled a circuit breaker?), but when I got back to base, I made a note in the airplane log about the problem and also left a note for my instructor, who was out that day.
When I came in for my next lesson, instructor mentioned that the next person to use the airplane, also a student on a solo cross-country, got stranded 100 miles away because when the engine wouldn't shut off, he panicked and pulled the throttle hard enough to rip the cable through the firewall. Airplane had to be put on a flatbed to get it back home.
Guess he didn't see my note!
Sounds like it might have been dieseling - enough carbon buildup glowing hot that even with both magnetos off it can still ignite the next rotation.
Usually there was a fuel disconnect along with the throttle that would eventually starve the engine.
That's probably what I did. Thinking back, the first time it happened, it just took about 10-15 seconds to shut off. The next time, when I was back at my home airport, it wouldn't stop running at all and I think I turned the fuel cutoff to get it to stop.