NTSB Identification: SEA02LA123.
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Accident occurred Saturday, July 06, 2002 in Weiser, ID
Probable Cause Approval Date: 05/13/2003
Aircraft: Grumman-Schweizer G-164B, registration: N8440K
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.
The pilot of the "Agcat" cropduster had just taken off and was making his first spray run over a field when the Pratt & Whitney R-1340 engine began to run rough. He pulled up and executed a right turn away from obstacles crossing the Snake River during which the engine abruptly stopped. The pilot rolled out and executed a forced landing in a beet field during which the aircraft crossed an elevated dirt/gravel roadway bounded on its north and south edges by a shallow ditch, and the aircraft's landing gear separated from the airframe. The aircraft then nosed over and came to a stop. The engine, which had been overhauled and inspected 81 and 31 hours respectively, was examined. The examination revealed that the number 3 cylinder exhaust valve steel pushrod was broken near the rocker arm end of the rod and the rod displayed very slight bending deformation. The separation surfaces of the broken rod end were observed to be mechanically battered. Removal or separation of the exhaust pushrod results in the exhaust valve's inability to open during the exhaust phase cycle for the associated cylinder, and can result in hot exhaust from the cylinder back-flowing out the intake valve when it opens during the intake cycle.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The fracture of the number 3 cylinder exhaust pushrod resulting in the exhaust valve's inability to open during the exhaust cycle and the subsequent engine stoppage. Contributing factors were the ditch and elevated roadway which the aircraft crossed during the gear collapse. Full narrative available
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