Eurocopter AS 350 BA N230CH accident near Juneau, Alaska

Probable cause

Upslope wind conditions while the helicopter was operating at ground idle, which resulted in the helicopter rollover. Contributing to the accident was the lack of manufacturer data regarding the effect of upslope wind conditions on helicopter ground idle operations.

NTSB analysis

The helicopter pilot was landing at a remote off-airport site, located on an outcrop on the side of a steep slope. The pilot reported that after landing, he initiated the shutdown checklist, including a 2-minute cool down. About 1.5 minutes later, the pilot noticed a strong upslope wind, and the helicopter turned to the right. The pilot attempted to offset the turn with left pedal, but at low rpm, the pedal had no effect. The helicopter lifted off the ground about 3 to 5 feet in a slightly nose-high attitude and simultaneously rolled to the left. The pilot attempted to offset the roll with right cyclic input with no effect. The helicopter continued to lift and roll to the left until the main rotor blades impacted the ground. The helicopter came to rest on its left side.

The National Weather Service forecast included surface wind of 35 to 45 knots. Upslope wind conditions developed due to the terrain features and created a situation that the pilot was unable to overcome when the helicopter was at ground idle. Although the pilot checked current and forecast weather before departure, he was unaware that the forecast wind would have such an effect because of a lack of manufacturer data regarding the effect of upslope wind on an idle helicopter.

Text from the NTSB. Open the NTSB docket for ANC11LA108 for the full record.