Air Tractor Inc AT 502B N61267 accident near Monroe, Nebraska

Probable cause

Loss of propeller thrust for reasons that could not be determined, since examination of the airplane's engine, propeller, and associated accessories revealed no anomalies.

NTSB analysis

The commercial pilot was performing an aerial application flight when the airplane experienced a partial loss of engine power. The engine instruments showed that the engine was operating, but was producing less than idle power. The pilot applied full throttle with no effect. He subsequently turned the airplane into the wind, lowered the flaps, and when he heard corn hitting the bottom of the airplane, pulled the control stick full aft to stall the airplane. The left wing dropped and the airplane turned 90° as it impacted the ground. The engine continued to run until the pilot shut it down and exited the airplane.

An examination of the airplane's engine, propeller governor, fuel control unit, and fuel pump revealed no anomalies. An engine data recorder showed an exceedance of the N1 upper limit, followed by a decrease in internal turbine temperature, N1, and propeller rpm, consistent with a lower output by the engine.

The data were reviewed by the engine manufacturer, who concluded that the data were consistent with a feathered propeller; however, the reason for the propeller feathering could not be determined based on the available information.

Text from the NTSB. Open the NTSB docket for CEN15LA389 for the full record.