NTSB Identification: WPR11LA391
14 CFR Part 91: General Aviation
Accident occurred Wednesday, August 17, 2011 in Cowiche, WA
Probable Cause Approval Date: 05/15/2012
Aircraft: LUSCOMBE 8A, registration: N1444K
Injuries: 2 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

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.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

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

Full narrative available

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