NTSB Identification: CHI04CA162.
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Accident occurred Wednesday, June 23, 2004 in Britton, SD
Probable Cause Approval Date: 09/01/2004
Aircraft: Air Tractor AT-401, registration: N1013N
Injuries: 1 Uninjured.

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.

The aerial-application airplane impacted soft terrain and nosed over during a forced landing following a loss of engine power. The pilot reported the engine began running rough after he completed his spraying and was returning to the departure airport. The pilot stated he eventually had to perform a forced landing into a soft field, during which the airplane nosed over. The engine was inspected and the shaft mount for the number eight cylinder rocker-arm was cracked and separated, consistent with damage caused by a stuck exhaust valve.

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

The loss of engine power due to a stuck exhaust valve and the unsuitable terrain encountered during the forced landing. A factor to the accident was the soft terrain condition.

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