Hughes 269C N7480F accident near Spanish Fork, Utah

Probable cause

The loss of engine power during a practice autorotation for an undetermined reason.

NTSB analysis

The pilot receiving instruction was preparing for his upcoming checkride for a rotorcraft certificate. About 50 minutes into the flight, the flight instructor announced a simulated engine failure, and the pilot receiving instruction reduced throttle, lowered collective, and entered an autorotation. When the helicopter approached 500 ft above ground level (agl) and the instructor advised the pilot to recover, they realized that the engine had stopped producing power. The instructor took control of the helicopter about 200 ft agl and started to flare about 30 ft agl. He raised collective to cushion the landing, but the helicopter still had forward airspeed when it touched down on the soft ground, which resulted in a noseover.

Postaccident examination of the helicopter did not reveal any preimpact mechanical anomalies with the airframe or the engine. An engine run showed that with the throttle at the idle detent, the engine cut out intermittently, and the engine idle speed was about 500 rpm lower than the minimum idle speed given in the Pilot’s Operating Manual (POH) for the helicopter. However, the engine power could be advanced from idle to higher speeds, and the engine never lost power as occurred during the accident flight.

The flight instructor reported that the pilot receiving instruction would rapidly reduce throttle for practice autorotations, and the POH warned against rapid throttle reduction as it could result in a sudden stoppage of the engine; however, given that the pilot receiving instruction had been following this practice throughout the flight and during previous flights without issue, it is unlikely his rapid throttle reduction led to the loss of power. The investigation was unable to determine the reason for the loss of engine power.

The pilot receiving instruction had started his recovery from about 500 ft agl, which required the instructor to re-establish the autorotation following the loss of power. Although the instructor was successful in re-establishing autorotation, he was unable to fully arrest the helicopter’s forward motion before touchdown.

Text from the NTSB. Open the NTSB docket for WPR21LA086 for the full record.