Cessna 150 N6341K accident near Madison, South Dakota

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 analysis

The student pilot reported that he was flying north of the departure airport when the airplane's engine began running roughly. He attempted to return to the airport but was unable to reach the airport and landed in a cornfield. The airplane nosed over in the 7-ft-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 3 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.

Text from the NTSB. Open the NTSB docket for CEN18LA329 for the full record.