Accident Overview
On a day in 2004 or early 2005, a Canadian Helicopters Limited AS-350D (registration C-GVHB, serial number 1297) was conducting an air taxi flight in support of a geological survey team. The helicopter, operating under Canadian Aviation Regulations (CAR) 703, was flying approximately 45 nautical miles northwest of Nain, Newfoundland and Labrador. At about 1600 Atlantic daylight time, the pilot picked up a team of geologists and proceeded to reposition them 1.5 kilometers along a ridge line. While on short final to the intended landing site, the helicopter's rate of descent increased rapidly, and the pilot could not arrest the descent. The helicopter struck the ground in a gully just left of the intended touchdown point, coming to rest on its right side facing the direction of approach. The pilot and two passengers sustained only minor injuries; the helicopter was substantially damaged but there was no post-crash fire.
Accident Sequence
The pilot had been conducting multiple flights supporting a geological survey team based at Kingurutik Lake. On the day of the occurrence, the survey crew was working at an elevation of 2000 feet above sea level (asl) along a ridge line 10 km northwest of the lake. The terrain featured dramatic elevation changes, with differences of up to 1800 feet within one kilometer. Approximately three minutes before the accident, the pilot successfully landed on a rocky outcrop 1.5 km east of the crash site to embark two crew members. That approach was flown on a westerly heading parallel to the ridge line, with light winds from the west.
After departing the outcrop, the pilot flew westward along the ridge at about 200 feet above ground level (agl). The intended landing site was about 300 feet higher in elevation, located on the west side of the ridge in a bowl formed by an L-shaped ridge. The prevailing west wind crossed the ridge at a 90-degree angle. The pilot flew directly into the center of the bowl without conducting a reconnaissance pass. The initial approach was normal in terms of airspeed, attitude, and descent angle, but on short final the rate of descent increased sharply despite collective application. No control difficulties or buffeting were reported. The pilot steered toward a gully to avoid hitting an outcrop. The helicopter struck the ground upright, pivoted onto its nose, rotated 180 degrees clockwise, and came to rest on its right side. The pilot shut down the engine and electrical power, and all occupants exited through the forward passenger door. A satellite phone was used to notify the company, and a company helicopter arrived within 30 minutes for evacuation.
Pilot and Aircraft Background
The pilot had 1840 hours of rotorcraft flying time, with 1300 hours on type. He had approximately 150 hours of experience in terrain similar to the accident site but had never received comprehensive mountain flying training. Canadian Helicopters Limited provided mountain training for pilots in the Rockies but not for those on the east coast due to the generally flat terrain. The company was considering mountain training for pilots in Labrador because of the mountainous areas in the northern part of the province.
A review of the helicopter's technical logs and maintenance records showed it was certificated and maintained in accordance with regulations. The helicopter was in standard configuration, and weight and balance were within limits. The engine and rotor assemblies were functioning normally with no indication of power loss or control problems; both main and tail rotors were turning with considerable power at impact. The tail rotor driveshaft showed torsional shearing at the impact point. A GPS unit was removed for examination, but no useful flight path data could be retrieved.
Weather and Terrain
Weather at Nain was reported as: wind 130° True at 11 knots; visibility 15 statute miles; clouds broken at 3500 feet asl and overcast at 8500 feet asl; temperature 15°C; dew point 7°C; altimeter 29.87. In the Kingurutik Lake area, conditions were partly cloudy with sunny breaks, temperature 15°C to 20°C, and light westerly to southwesterly winds. Scattered rain showers and high cloud were moving from the southwest. Shortly after the accident, winds were light but from the southeast (up slope from the left of the approach path). Mountainous valleys often have unpredictable winds that parallel the valley and can be strong due to funnelling.
Possible Factors
The investigation considered vortex ring state (VRS) as a possible explanation, which requires near-zero airspeed, powered flight, and a rate of descent between 300 and 600 feet per minute. However, the approach flown would not normally put the helicopter in a position conducive to VRS, and no buffeting or poor control response was noted. If VRS was present, it was likely in an incipient stage.
Another possible factor was down-flowing air. The intended landing site was on the lee side of the ridge in a bowl. Wind striking the ridge at 90 degrees would flow smoothly upslope, then become turbulent as it breaks over the top and descends on the downwind side. The pilot had not reconnoitered the site to assess wind conditions or power requirements, and the approach was flown without an escape route. It is possible the helicopter entered an area of descending air from which recovery was not possible at low altitude.
Findings
The Transportation Safety Board of Canada determined that the reason for the sudden descent could not be established. Findings as to risk included that some company pilots operated in mountainous Labrador without mountain flying training, and that the pilot did not conduct a reconnaissance of the intended landing site. An additional finding noted that the use of a satellite phone to promptly notify company operations greatly improved the survival scenario.
Safety action taken by the company included distributing a safety alert letter about the accident and VRS, and the chief pilot reviewed training requirements to ensure pilots are appropriately trained for their operational environment prior to assignment.