Luscombe 8A N1444K accident near Cowiche, Washington

Probable cause

A partial loss of engine power during maneuvering flight due to an exhaust valve failure.

NTSB analysis

During a training flight, the airplane's occupants heard a hammering sound accompanied by an airframe vibration and reduction in engine power. The certified flight instructor took control of the airplane from the student and began to initiate a return to the airport. He decided that it was unlikely that they would be able to safely return, and he elected to perform a forced landing into a field. The airplane landed hard.

Examination of the engine revealed that the exhaust valve head most likely separated from its stem during flight, resulting in catastrophic failure to its associated cylinder components. Discoloration within the rocker area, exhaust valve guide, and cooling fins was consistent with heat damage, most likely caused by a stuck or sticking exhaust valve. The engine was manufactured in 1948, and its serial number did not match any records on file with the manufacturer. The maintenance records did not reveal a complete history of the engine's total flight time.

Text from the NTSB. Open the NTSB docket for WPR11LA391 for the full record.