On August 9, 2001, an Air Tractor AT-401 (registration N10140) was involved in an aviation accident near Grand Coteau, LA. Investigators recorded the probable cause as: the loss of engine power while maneuvering, which resulted from a fractured #4 cylinder head at the exhaust valve rocker arm boss. A contributing factor was the lack of suitable terrain for the forced landing. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
An agricultural airplane lost engine power during a turn, forcing a landing in a sweet potato field. The main landing gear collapsed upon touchdown. Post-accident examination found a fractured cylinder head.
Accident Sequence
The agricultural airplane had completed a spray pass from south to north. During a turn-around maneuver, the engine lost power. The pilot emptied the aircraft's load and initiated a forced landing toward a dirt road, but the airplane was unable to reach the road. The airplane touched down in a sweet potato field, perpendicular to the rows, with its right wing first. Upon touchdown, the main landing gear collapsed. The airplane came to rest upright.
Post-Accident Examination
An examination of the engine revealed that the #4 cylinder head had fractured at the exhaust valve rocker arm boss. A review of maintenance records showed that on August 4, 2001 (4.4 hours prior to the accident), the Pratt & Whitney R-1340-AN-1 engine's cylinder heads had been inspected for cracking in accordance with Airworthiness Directive 99-11-02. No cylinder head cracking was noted during that inspection.