Hughes OH-6A N4191T accident near Santa Teresa, New Mexico

Probable cause

The flight instructor's failure to maintain helicopter control during a practice autorotation, which resulted in a hard landing and structural damage to the tail boom and subsequent failure of the tail rotor drive system.

NTSB analysis

After the pilot undergoing instruction completed a series of practice maneuvers, the flight instructor assumed the controls and initiated a hover taxi to return the helicopter to the ramp. During the hover taxi, the helicopter shuddered and yawed abruptly to the right. Despite the instructor's reduction of throttle and collective, the yaw developed into an uncontrolled spin, and the helicopter impacted terrain.

The pilot undergoing instruction reported that the final maneuver the pilot had performed before the hover taxi was a full-down autorotation. She reported that, during the maneuver’s landing flare, the helicopter struck the ground hard enough that she believed the tail stinger contacted the ground. The pilots paused to assess the helicopter, and it appeared undamaged. She reported that because the instructor remained concerned, they elected to end the training flight and return for further inspection of the helicopter.

Although the instructor did not characterize the landing as hard, examination of the helicopter revealed upward bending and buckling of the lower vertical stabilizer and stinger, upward deformation of the tail boom, and rotational scoring on the tail rotor drive shaft consistent with contact with the tail rotor pitch control rod during a hard landing. These findings are consistent with a preaccident tail strike that compromised the structural integrity of the tail boom and damaged the tail rotor drive system. The structure ultimately failed as the helicopter was being taxied.

Text from the NTSB. Open the NTSB docket for WPR25LA101 for the full record.