The student pilot reported that he was flying north of the departure airport when the Cessna 150’s engine began running roughly.
He attempted to return to the airport, but was unable, so he landed in a cornfield near Madison, S.D.
The airplane nosed over in the 7-foot-tall corn and sustained substantial damage to both wings.
Examination of the airplane revealed that the engine’s No. 3 cylinder exhaust valve was stuck in its valve guide, and the No. 3 exhaust valve rocker arm was fractured.
A maintenance record entry indicated that the Nos. 1, 3, and 4 cylinders had experienced valves sticking and had been sent back to the overhaul vendor for service. The cylinders were reinstalled three days before the accident.
Based on the available evidence, the partial loss of engine power was likely due to the No. 3 cylinder exhaust valve becoming stuck, which resulted in a secondary overload failure of the associated rocker arm and a substantial reduction in engine power output.
Probable cause: A stuck No. 3 cylinder exhaust valve, which resulted in failure of the associated rocker arm, a partial loss of engine power, and the subsequent forced landing into tall vegetation.
NTSB Identification: CEN18LA329
This August 2018 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.
I would be willing to make a friendly wager that they were running 100LL.
Rich,
I can guarantee that they use 100LL, the only leaded fuel available, which is the cause of the buildup of deposits on the valve stem.
Mike Busch just ran a seminar on this.
I fault the engine shop where they probably did not ream the exhaust guide for the proper clearance….twice.
The O-200, O-300 was designed to run on 87 octane avgas. So, we all know to lean aggressively right after engine start to reduce the deposits by heating the cylinders quickly.