Cessna 150L N150ET accident near Plymouth, Massachusetts

Probable cause

A partial loss of engine power during initial climb due to a stuck cylinder valve, which resulted from excessive corrosion and carbon deposits on the valve springs due to inadequate maintenance.

NTSB analysis

During initial climb, the engine began to run rough and experienced a partial loss of power. The pilot elected to land straight ahead into a cranberry bog. The pilot believed the loss of engine power was due to a stuck cylinder valve. Postaccident examination of the engine revealed that the No. 2 cylinder intake and exhaust valve springs exhibited excessive corrosion and carbon deposits, consistent with lack of use, which made them more susceptible to sticking. The extent of the corrosion was such that it presented over a long period of time and should have been addressed during routine maintenance. No other defects were noted with the engine that would have resulted in a partial loss of power.

The airplane had been operated for 17 hours since its most recent annual inspection, which was completed 11 months prior to the accident. The engine had been operated for 256 hours since its most recent overhaul, which was completed more than 10 years prior to the accident. The same airplane was involved in a forced landing to a cranberry bog 8 years earlier due to a stuck cylinder valve.

Text from the NTSB. Open the NTSB docket for ERA11LA383 for the full record.