NTSB Identification: LAX03FA108.
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Accident occurred Friday, March 07, 2003 in ELOY, AZ
Probable Cause Approval Date: 12/28/2004
Aircraft: Stinson 108-1, registration: N8344K
Injuries: 1 Minor.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

The engine lost total power when the number 4 cylinder exhaust valve fractured and separated during cruise flight. During the forced landing to a plowed field the airplane nosed over and came to rest inverted. Examination of the airplane at the accident site revealed a large amount of oil on the exterior of the fuselage. The number 3 and 4 cylinders assemblies dislodged from the engine. An engine examination revealed that the number 4 cylinder exhaust valve had fractured between the valve head and stem. Examination of the fracture face disclosed features consistent with fatigue.

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

a loss of engine power caused by the fatigue failure of the number 4 cylinder exhaust valve.

Full narrative available

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