What happened
The pilot was performing slope landing maneuvers in preparation for an upcoming check ride. While positioning the helicopter close to a hill to initiate the maneuver, the aircraft suddenly rolled to its left. The aircraft ended up upside down on top of the hill that the pilot had been attempting to land beside.
The investigation
Following the accident, the pilot expressed a suspicion that the tail rotor drive shaft had become disengaged, potentially causing the loss of control. To investigate this possibility, the NTSB Materials Laboratory examined the forward tail rotor shaft assembly and a portion of the adjoining rear tail rotor drive shaft. The inspection revealed no evidence of an in-flight disengagement of the tail rotor drive shaft assembly occurring prior to the impact.