On March 7, 2003, a Stinson 108-1 (registration N8344K) was involved in an aviation accident near Eloy, AZ. Investigators recorded the probable cause as: Total loss of engine power due to fatigue fracture of the number 4 cylinder exhaust valve. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During cruise flight, the engine lost power after the number 4 cylinder exhaust valve fractured and separated. The airplane performed a forced landing to a plowed field, nosed over, and came to rest inverted.
Accident Summary
During cruise flight, the engine lost total power. The pilot initiated a forced landing to a plowed field. The airplane nosed over during the landing and came to rest inverted.
Examination Findings
At the accident site, investigators noted a large amount of oil covering the exterior of the fuselage. Additionally, the number 3 and number 4 cylinder assemblies had become detached from the engine.
Engine Examination
The engine was disassembled for further examination. The number 4 cylinder exhaust valve was found to have fractured, with the separation occurring between the valve head and the stem. The fracture face was examined and displayed features consistent with fatigue.
Probable cause
Total loss of engine power due to fatigue fracture of the number 4 cylinder exhaust valve.