Enstrom F 28F N213BL accident near Tomah, Wisconsin

Probable cause

A loss of engine power due to the malfunction of the No. 4 cylinder intake valve.

NTSB analysis

The pilot felt a vibration in the cyclic control and he stated that the engine was running irregularly as he neared the intended application field on the agricultural application flight. He immediately elected to execute a precautionary landing to a cornfield; the corn crop was about 10 feet tall at the time. During the landing, the landing skids collapsed, and the tailboom was severed by a main rotor blade. A postaccident examination of the engine revealed that the No. 4 cylinder did not exhibit compression during crankshaft rotation. Further examination of the No. 4 cylinder revealed that the intake valve did not seat properly; a gap of about 0.015 inch existed when the valve should have been fully seated. Linear scoring was observed on the valve stem, and debris consistent with valve guide material was also recovered upon removal of the valve. No other anomalies with respect to the engine were observed. The engine had accumulated about 831 hours since overhaul. The helicopter maintenance records did not contain a record of any unresolved maintenance issues.

Text from the NTSB. Open the NTSB docket for CEN14LA412 for the full record.