NTSB Identification: SEA04LA065.
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Accident occurred Monday, April 05, 2004 in Nezperce, ID
Probable Cause Approval Date: 06/30/2004
Aircraft: Grumman G-164, registration: N48564
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.

While en route to apply dry fertilizer to a field, the aircraft's engine popped and then experienced a significant loss of power. Because there was not sufficient power to keep the aircraft airborne, the pilot elected to execute a forced landing in a nearby field. He therefore started dumping his load of fertilizer, and attempted to set the aircraft down on the soft terrain. Although the touchdown was successful, soon thereafter the main gear sank into the soft terrain, and the right main gear leg folded aft. As the gear leg collapsed, the nose and right wing of the aircraft impacted the terrain. A post-accident inspection of the engine revealed that the head of the number seven cylinder had fractured circumferentially just above the location where the head screws into the cylinder barrel. Although the head had not separated from the barrel, the fracture was far enough around the barrel that it created a misalignment of the cylinder geometry to an extent that the intake valve would not close. There was no indication of detonation or any other anomaly that would have been expected to apply greater than normal loads to the cylinder structure.

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

The circumferential fracture of the number seven cylinder head while en route to an aerial fertilizer application, leading to a forced landing on soft terrain, resulting in the collapse of the right main gear leg. Factors include soft terrain at the location where the pilot found it necessary to attempt the forced landing.

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