Chickaloon, AK, USA
N357CH
EUROCOPTER AS-350 BA
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.
On June 23, 2008, about 1045 Alaska daylight time, a Eurocopter AS-350BA helicopter, N357CH, sustained substantial damage when it collided with snow-covered terrain on the Matanuska Glacier, about 40 miles east of Chickaloon, Alaska. The helicopter was conducting an external load operation at 8,950 feet msl under Title 14, CFR Part 133, when the accident occurred. The helicopter was operated by Last Frontier Air Ventures Ltd., Sutton, Alaska. The commercial certificated pilot, and the sole passenger, were not injured. Visual meteorological conditions prevailed in the area of the accident. VFR company flight following procedures were in effect. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on June 23, the director of operations for the operator reported that the pilot was inserting an external load containing about 400 pounds of equipment at a remote camp for the National Outdoor Leadership School (NOLS). The director of operations indicated that the pilot contacted him via satellite phone to report the accident, stating that during the insertion, he descended into the helicopter's own main rotor vortex, and then collided with the snow. The pilot prepared a written statement on June 25, in which he reported that he planned to transport a total of 14 passengers, and their gear, from the toe of the Matanuska Glacier to the top, to set up a camp. His first flight was with three passengers and some internal cargo. During his first landing approach, the pilot said he aborted his landing pattern and pulled maximum power. The main rotor rpm drooped to about 365 rpm, with a power setting of between 81 to 83 percent torque, and the low rotor speed warning horn sounded for a few seconds. The pilot landed on his second landing approach without problem. He then departed and returned to the toe of the glacier. The pilot prepared an external load of gear in a net, to be attached to the bottom of the helicopter by a 50 foot long line. He selected a NOLS student to assist him with connecting the long line to the helicopter, and to disconnect it if necessary at the top of the glacier. The student had previous experience in the U.S. Air Force, but was not a trained employee of the operator. Upon his return to the toe of the glacier, the pilot landed, and remained at the helicopter flight controls while the NOLS student attached the long line and boarded the helicopter. The pilot 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, and upon arrival at the upper camp, established a 75 foot hover while pulling maximum power. He then reduced power to lower the cargo net to the snow. The pilot said he reduced power too much, and the helicopter began to descend rapidly. He said 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 the snow and rolled onto its right side. The pilot and the NOLS student were not injured. Using global positioning system (GPS) data provided by the operator, and the NOLS students, the accident location was about 8,950 feet mean sea level (msl). Using the weight of the helicopter, its fuel, and the occupant and cargo weights provided by the pilot, the helicopter's gross weight was about 4,286 pounds. The helicopter's maximum gross weight was 4,630 pounds. According to the HOGE performance charts contained in the helicopter's flight manual, at 4,286 pounds, the helicopter should have been capable of an HOGE altitude of about 9,500 feet msl. The operator did not submit a Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1.
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.
Source: NTSB Aviation Accident Database
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