History of the Flight
The helicopter, a Robinson R44 Raven II (registration C-GNYT, serial number 10883) operated by Wild Water Heli-Fishing Ltd., departed Nahanni Butte, Northwest Territories, with a pilot and two passengers on board for a day visual flight rules flight. The helicopter was contracted to transport two passengers to a hunting area about 25 nautical miles west of Nahanni Butte. While en route, the pilot overflew a ridge where guides and hunters were located and decided to land to speak with them.
At 1655 Mountain Daylight Time, during an attempted landing on a narrow ridge in steep mountainous terrain, the helicopter turned 180 degrees and descended down a slope. The tail boom struck the ground, and the helicopter tumbled down the mountainside, breaking up and coming to rest about 900 feet below the ridge. The helicopter was destroyed by a post-impact fire. The emergency locator transmitter on board did not transmit.
Survivability
All occupants were wearing three-point harnesses, but the retention system failed due to structural disintegration during the crash. The pilot was ejected from the helicopter as it tumbled down the slope and came to rest about 150 feet uphill from the main wreckage, sustaining non–life-threatening serious injuries. The pilot was not wearing a helmet at the time of the accident. Both passengers sustained fatal blunt force trauma injuries. One passenger was found with the main wreckage, and the other was found 10 feet uphill.
The ground party notified the outfitter by satellite telephone, and a rescue party dispatched from Fort Simpson, Northwest Territories, evacuated the pilot five hours after the accident. The helicopter was equipped with a GPS-based tracking device, which helped locate the site. No signal was received from the 406 MHz emergency locator transmitter, likely due to destruction by fire.
Company Operation and Aircraft Information
Wild Water Heli-Fishing Ltd. held a valid Air Operator Certificate for air taxi operations under subpart 703 of the Canadian Aviation Regulations. The accident helicopter was the company's only aircraft. The pilot served as chief pilot and operations manager. Maintenance was contracted to approved maintenance organizations. The helicopter had been owned by the company since 2006 and was certified, equipped, and maintained in accordance with regulations.
In March 2009, Robinson Helicopter Company issued Service Bulletin SB-68, calling for replacement of a rigid engine fuel supply line with a flexible one to reduce post-accident fuel leaks. This was completed on C-GNYT in May 2009.
Weather and Weight and Balance
At the site, winds were light from the west, temperature estimated at 20 °C, and sky clear. A search and rescue Bell 206B helicopter encountered moderate turbulence and downdrafts near the ridge. The helicopter was fueled to about half capacity, with a weight of 2385 pounds, 115 pounds below maximum. Weight and center of gravity were within prescribed limits.
Aircraft Performance and Landing Site
The engine was developing full available power, and no mechanical flight control difficulties occurred. Performance charts indicated that at 2385 pounds, 20 °C, zero wind, and 100% rotor rpm, the maximum pressure altitude for hover out of ground effect was 5200 feet; hover in ground effect was 8760 feet. The pressure altitude at the attempted landing site was 5100 feet, leaving a 100-foot hover out of ground effect margin under ideal conditions.
The landing site was on a 4600-foot ridge oriented about 025/205 degrees true, above the tree line, mostly razor-backed with uneven elevation. The proposed landing area was about 20 by 25 feet. The eastern shale slope was approximately 45 degrees, forming a gully where the main wreckage came to rest.
Pilot Experience and Training
The pilot was certified and qualified. He had 3000 hours total flight time exclusively on the R44 and 100 hours on fixed-wing aircraft. Mountain flight training was completed in 2006 with 21 hours of flight time, and he had accumulated about 2700 hours of mountain flying experience in similar terrain, including many landings on the same ridge. The pilot's duty day began at 0900 after nine hours of rest.
Findings as to Causes and Contributing Factors
The shallow approach downwind of the ridge placed the helicopter in an area of subsiding air, which increased the sink rate. To overcome the sink rate, the pilot had to demand more engine power than was available, resulting in a loss of rotor speed. To avoid injury to persons in the landing area, the pilot aborted the landing by turning 60 degrees. During the aborted landing, the helicopter's tail struck the top of the ridge, precipitating a fall down the steep shale slope, culminating in complete destruction of the helicopter and a post-crash fire.