Eurocopter AS-350 BA N357CH accident near Chickaloon, Alaska

Probable cause

The pilot's incorrect actions during an out-of ground-effect hover, which resulted in the helicopter entering a main rotor ring vortex state, and a settling with power condition, producing an excessive descent rate and collision with terrain.

NTSB analysis

Prior to the accident flight, the pilot transported several students from the National Outdoor Leadership School and their equipment to a remote glacier camp at about 8,950 feet mean sea level (msl). During that flight, the main rotor rpm dropped enough to sound the low rotor speed warning horn for a few seconds. At a staging area, in preparation for the accident flight, the pilot prepared an external load of about 400 pounds of equipment in a net to be attached to the bottom of the helicopter by a 50-foot-long line. The pilot then lifted off into an out-of-ground-effect hover (HOGE) to assess the required power, and noted that he needed about 70 percent power to maintain a hover. He then flew to the top of the glacier with the external cargo net; upon arrival at the upper camp, he established a 75-foot hover while pulling maximum power. He then reduced power to lower the cargo net to the snow. The pilot said that he reduced power too much and that the helicopter began to descend rapidly. He said that he felt a small vibration, reminiscent of entering the vortex ring produced by the main rotors. The vibration then smoothed out, but the helicopter was descending quickly. The pilot applied power but did not release the external load. The helicopter collided with snow and rolled onto its right side. The helicopter's gross weight at the time of the accident, including the external load, fuel, and the weight of the pilot and passenger, was about 4,286 pounds. At that weight, the helicopter should have been capable of an HOGE of about 9,500 feet msl.

Text from the NTSB. Open the NTSB docket for ANC08LA076 for the full record.