Incident Overview
An aircraft engaged in agricultural operations experienced an engine power loss during a swath run, resulting in the aircraft settling into trees. The flight had been in progress for approximately 15 minutes when the pilot began the fourth swath run and the aircraft started to settle. The pilot jettisoned the load but did not adjust the throttle or mixture controls; he stated that he had set these controls for the operation and tightened the friction adjustment. The mixture had been leaned to peak temperature and then enriched so that the cylinder head temperature was peak temperature minus 125 degrees Fahrenheit. The manifold pressure was set at 32 inches, and the propeller RPM was 2400.
Pilot Actions and Observations
The pilot reported that he did not move or adjust the throttle or mixture from the time he set them after the initial level-off until ground impact. He noted that after the accident, these controls were in a normal flight position. The pilot was wearing a helmet and commented that it would be possible for the engine to stop without him hearing it.
Post-Accident Findings
Inspection of the propeller condition indicated that the engine was not producing power at the time of impact. However, during subsequent examination of the powerplant, nothing was found to be wrong. No mechanical or system failures were identified. The investigation confirmed that the engine stopped producing power, but the reason for the power loss remains undetermined based on available evidence.
Conclusion
The aircraft struck trees following an unexplained loss of engine power during an agricultural swath run. The pilot did not alter power or mixture settings after initial setup. Despite the power loss, the engine showed no defects upon inspection.