Piper PA28 N9139J accident near Lancaster, Tennessee

Probable cause

The fatigue failure of an exhaust valve, resulting in a partial loss of engine power.

NTSB analysis

About 20 to 25 minutes into the flight the engine lost power and began to run rough. The pilot described the power loss as if the engine was firing on two cylinders. He reported that the airframe began shaking and the airplane began losing altitude. Attempts to restore power were unsuccessful. Unable to make it to the nearest airport, the pilot chose a field in which to land. He notified air traffic control of the loss of engine power and performed a forced landing in a field. At touchdown, the nose landing gear collapsed and the engine mount was substantially damaged.

Postaccident examination of the engine revealed the No. 2 cylinder exhaust valve stem fractured due to fatigue that initiated on the outer surface. The resulting separation of the valve head resulted in the reported partial loss of engine power and rough running engine.

Review of the engine maintenance records revealed it had been 39 years since the No. 2 exhaust valve was replaced, and 34 years since the valve guides were replaced. Although engine manufacturer service instructions are not mandatory for Part 91 operators, the engine manufacturer recommended engine overhaul within 12 years of either being put in service or last overhaul. The most recent engine overhaul had been 45 years earlier.

Text from the NTSB. Open the NTSB docket for ERA23LA264 for the full record.