NTSB Identification: CHI06LA165.
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Accident occurred Saturday, June 24, 2006 in Bowling Green, MO
Probable Cause Approval Date: 07/25/2007
Aircraft: Luscombe 8A, registration: N2890K
Injuries: 1 Serious.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The airplane was substantially damaged during a forced landing to a cornfield following a loss of engine power after takeoff. The pilot sustained serious injuries. Postaccident examination revealed that the number two cylinder exhaust valve had fractured at the transition radius between the valve stem and the valve head. The fracture surface exhibited arrest lines, and ratchet marks consistent with fatigue fracture initiating from multiple origins. The fatigue features had progressed across approximately 95 percent of the stem diameter. Measurements of the valve stem diameter, and the valve guide inside diameter indicated that the running clearance was 0.015 to 0.017 inch at the inboard end, and 0.007 to 0.013 at the outboard end. The maximum serviceable limit for valve stem to valve guide clearance was 0.007 inch.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The loss of engine power due to fatigue fracture of the number two cylinder exhaust valve during initial climb after takeoff. A contributing factor was the unsuitable terrain (cornfield) encountered during the forced landing. Full narrative available
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