NTSB Identification: DFW05CA186.
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Accident occurred Thursday, July 21, 2005 in Tallulah, LA
Probable Cause Approval Date: 10/27/2005
Aircraft: Grumman-Schweizer G-164A, registration: N8891H
Injuries: 1 Minor.

NTSB investigators used data provided by various entities, including, but not limited to, the Federal Aviation Administration and/or the operator and did not travel in support of this investigation to prepare this aircraft accident report.

At the completion of an east to west spray pass over a field, the bi-wing agricultural airplane's engine experienced a loss of power and exhibited an unusual vibration. The 2,697-hour private pilot turned the airplane in a southerly direction in an attempt to fly back to the originating airport. Realizing that the engine was not developing sufficient power to return to the airport, the pilot turned the airplane approximately 180-degrees towards a road that he thought would make a suitable landing area. Before the pilot could reach the road, the engine started making "popping" noises, trailing smoke, and experienced a further reduction of power. The pilot then elected to land in a cotton field. During the landing roll the left main landing gear collapsed and the airplane nosed over coming to rest in an inverted position. An examination of the engine revealed the number five-cylinder exhaust valve rocker arm mounting boss was fractured approximately 180 degrees around its circumference. This fracture allowed the exhaust valve to remain closed.

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

The partial loss of engine power as result of the fracture of the number five-cylinder exhaust valve rocker arm mounting boss. A contributing factor was the lack of suitable terrain for the forced landing.

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