Eurocopter AS 350 B3 N105LN accident near Marana, Arizona

Probable cause

The improper use of the throttle by the pilot receiving instruction, and the check pilot's inadequate supervision and delayed remedial action, which resulted in the collision with terrain.

NTSB analysis

During a practice hovering autorotation the helicopter impacted terrain, which resulted in substantial damage to the tailboom. The left seat check pilot who was giving instruction to the right seat pilot reported that a clear, flat area had been identified for hovering autorotation practice. After being briefed by the check pilot, the right seat pilot brought the helicopter up to a 3- to 5-foot hover. The check pilot stated, "I reminded the pilot that he would retard the throttle. [The] aircraft drifted up to less than 10 feet, [and] before I could correct the altitude deviation the [right seat] pilot aggressively retarded the throttle. The aircraft was allowed to settle to approximately 4 feet before the collective pull was initiated, but I was unable to sufficiently arrest the descent." An examination of the helicopter by a Federal Aviation Administration airworthiness inspector revealed that the tailboom had been wrinkled as a result of the impact with terrain.

Text from the NTSB. Open the NTSB docket for WPR10CA028 for the full record.