Robinson R22 N393LE accident near Logan, Utah

Probable cause

The flight instructor’s delayed remedial action and inadequate supervision during a practice autorotation, which resulted in a failure to maintain adequate main rotor rpm. Contributing to the accident was the wet landing surface.

NTSB analysis

During the 180-degree autorotation, the student pilot maintained an airspeed of 65 knots, with rotor rpm in the green. As the student rolled out of the turn about 300 feet above ground level and at 70 knots, the rotor rpm continued to remain in the green. However, before the flare, the rotor rpm began to decay and failed to build as the flare was entered. The flight instructor then took control of the helicopter and immediately rolled on throttle to recover engine power and to maintain rotor rpm, but there was insufficient engine power to recover, and the low rotor rpm light and horn activated. Because power was not available for a full-power-on landing, the flight instructor initiated a full-down autorotation to a taxiway. During the landing, the helicopter skidded across and off the wet taxiway into loose gravel and mud before the left skid dug into the ground, resulting in the helicopter rolling over and coming to rest on its left side. The helicopter sustained substantial damage to its welded frames, firewall, and tail cone. The flight instructor reported no preaccident mechanical or malfunctions or failures with the helicopter or flight controls that would have precluded normal operation.

Text from the NTSB. Open the NTSB docket for WPR13CA068 for the full record.