Hughes 269A N37754 accident near Mc Cool Junction, Nebraska

Probable cause

The flight instructor’s inadequate supervision of the student pilot’s entry into the autorotation, which resulted in a hard landing. Contributing to the accident was the loss of engine power as a result of the student pilot rapidly lowering the helicopter’s collective and the partly obstructed air filter.

NTSB analysis

After takeoff, about 400 feet above ground level and about 50 knots airspeed, the flight instructor reduced the throttle to idle so the student pilot could demonstrate an autorotation. The student dropped the collective to enter the autorotation, and the engine stopped producing power; the helicopter descended rapidly and landed hard. A postaccident examination of the helicopter revealed an obstructed air filter. It is likely that the student lowered the collective too quickly, which, combined with the obstructed air filter, created a rich fuel mixture and loss of engine power. The student pilot mismanaged the autorotation and the instructor did not intervene in a timely manner to prevent the hard landing.

Text from the NTSB. Open the NTSB docket for CEN12LA648 for the full record.