What happened
The aircraft was engaged in an agricultural application flight that had been underway for approximately fifteen minutes when the incident occurred. During the initiation of the fourth swath run, the plane began to descend toward the ground. The pilot responded by dumping the cargo load but maintained the throttle and mixture settings exactly as they had been established after initial level-off.
Prior to the event, the pilot had configured the engine for operation by leaning the mixture to peak cylinder head temperature and then enriching it by 125 degrees below that peak. The manifold pressure was set to 32 inches with the propeller at 2400 RPM. The pilot tightened the friction adjustment on these controls and stated they were not moved or adjusted again until ground impact. Although the pilot was wearing a helmet, he noted it might have been possible for the engine to stop without him hearing the failure.
The investigation
Examination of the propeller indicated that the engine was not generating power at the moment of impact. A thorough inspection of the powerplant followed, but investigators found no mechanical defects or anomalies that would explain the loss of thrust.