The pilot reported that, after takeoff, the Zenith CH-750’s engine lost partial power about 100 feet above ground level and that he then attempted to return to the airport in Allentown, Pennsylvania.
He added that “the engine would not keep me flying and the airplane just fell into the forest.”
The pilot was seriously injured in the accident.
During the on-scene examination, the No. 1 spark plug was found missing from the cylinder head, but still attached to the ignition lead. The threads were stripped out of the cylinder head. It is likely that the No. 1 spark plug was liberated from the cylinder head due to the stripped threads, which led to the partial loss of engine power.
Probable cause: A partial loss of engine power due to the No. 1 spark plug being liberated from the cylinder head due to the stripped threads in the cylinder head. Contributing to the accident was the pilot’s decision to attempt to return to the airport while at a low altitude.
NTSB Identification: ERA15LA311
This August 2015 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.
The report in itself isn’t very useful since the engine is what failed and it doesn’t specify the type of engine. O-200, Jabiru, Rotex? Nope. Go to the NTSB report to get the N number, then look up the plane in the FAA registry and you find it’s another Corvair failure. Wow. One would think a 6 cyl Corvair would keep a CH-750 in the air running on 5 cyl??? Corvairs aren’t known for throwing plugs, but it was also undoubtedly a used head, so this was an inspection/maintenance issue.
Just for the sake of clarity tests have been run on Corvair flight motors that showed they still made significant power with only five cylinders running. Why this engine did not at least allow the aircraft to maintain altitude is a question mark. Maybe there was more going on then just the potentially stripped thread spark plug. I say potentially because it is a crashed aircraft so maybe that is damage after the fact. We do not know how well the inspection was done this being a GA aircraft and an EAB with a non certified engine at that so not of much interest to the FAA or NTSB.
That’s the essence of “experimental…” Will the engine still develop power when a cross threaded spark plug departs its socket?
The spark plug could have just been loose or more likely way over-torqued which displaced the threads and lead to the failure.
Without any compression in the cylinder, at least one other cylinder would be down due to induction disruption..