Robinson Helicopter Company R22 N231TM accident near Alexander City, Alabama

Probable cause

The pilot’s delayed decision to initiate an autorotation and her subsequent improper conduct of the autorotation, which resulted in a hard landing, after the helicopter started vibrating for reasons that could not be determined because postaccident examinations revealed no anomalies that would have precluded normal operation.

NTSB analysis

After departure, the helicopter began to vibrate at an altitude of about 300 feet above ground level (agl). The pilot chose to return to the airport to perform a precautionary landing. The pilot initiated an autorotation about 100 feet agl at an airspeed of between 45 to 50 knots but could not control the helicopter. The pilot applied aft cyclic to flare the helicopter; however, it did not lose airspeed. The low rotor rpm aural warning activated during the maneuver, and the helicopter subsequently landed hard and rolled over on its right side. Postaccident examinations of the engine and airframe did not reveal any anomalies that would have caused the vibration the helicopter experienced after takeoff. If the pilot had initiated the autorotation sooner, she may have had adequate airspeed to establish the glide and a sufficient amount of rotor rpm to cushion the landing and retain positive control of the helicopter.

Text from the NTSB. Open the NTSB docket for ERA13LA045 for the full record.