Bell 206 N3211N accident near Bountiful, Utah

Probable cause

The pilots' inaccurate assessment of the snow depth on the landing zone, which resulted in a landing on snow deeper than that for which the helicopter was equipped and led to dynamic rollover.

NTSB analysis

The helicopter-rated private pilot was receiving instruction to obtain his commercial helicopter certificate. He and the flight instructor were practicing landings and takeoffs at a snow-covered remote landing zone (LZ) in mountainous terrain. They completed one successful landing and takeoff, and, after a second uneventful landing, the helicopter sat on the snow for a few minutes before the instructor initiated the next takeoff. Just after engine power application, the right forward skid sank into the snow, and the instructor was unable to prevent the ensuing dynamic rollover. The helicopter came to rest on its right side on top of the snow.

The area located just forward and to the right of the helicopter was covered with snow less than 6 inches thick, and grass protruded through the snow, which likely led the pilots to assume that this was a representative depth for the snow on the entire LZ. However, although the snow surface was essentially level, the terrain underlying the snow was not level, and the helicopter had landed on snow that was about 2 ft deep. The instructor was not qualified by the school to conduct operations on deep snow, and the helicopter was not equipped to land on snow deeper than about 6 inches. The pilots did not report any pre-existing mechanical deficiencies or failures, and examination of the helicopter did not reveal evidence of any pre-existing mechanical deficiencies.

Text from the NTSB. Open the NTSB docket for WPR14LA113 for the full record.