NTSB Identification: SEA98LA106.
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Accident occurred Saturday, June 27, 1998 in OAKDALE, WA
Probable Cause Approval Date: 01/10/2000
Aircraft: Schweizer G-164B, registration: N7502C
Injuries: 1 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.
According to the pilot, during takeoff, approximately 10 feet above the ground, the aircraft started backfiring and losing power. He aborted the takeoff, but was unable to get the aircraft stopped before impacting a ditch just off the departure end of the airstrip. A post-accident inspection of the engine by an FAA Airworthiness Inspector found that a portion of the number three cylinder head casting through which the exhaust valve rocker pin passes had fractured. This allowed the number three cylinder exhaust valve to remain in the closed position during the time that it should have been open, resulting in a loss of power. The rocker box casting was sent to the NTSB metallurgical laboratory for further analysis. That examination revealed that the fracture in the casting was the result of a fatigue crack that originated in the wall of the hole in the casting through which the rocker arm pivot bolt passed. It could not be determined what caused the fatigue crack to initiate.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: A fatigue failure of the number three cylinder exhaust rocker box assembly, compromising the ability of the exhaust valve to operate. Factors include a ditch at the end of the runway. Full narrative available
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