History of Flight
On the day of the accident, the Eurocopter AS350 B2 (Astar) helicopter, registration C-GSHH, was on contract to the British Columbia Forestry Service (BCFS) to transport firefighters and their equipment. The flight was intended to relocate 11 firefighters and light personal equipment from a mountainside helipad at 5200 feet elevation, five nautical miles west of the extinct Flourmill Volcano, to a staging area approximately one nautical mile away.
The pilot landed on the recently prepared pad. With the helicopter still running at flying rotor rpm and light on the skids, four passengers boarded with a small amount of personal equipment. The pilot increased collective pitch to lift into a hover, but the engine parameters approached their limits, prompting him to discontinue and lower the collective. The left rear passenger exited, and the pilot again raised the collective, attaining a stable five-foot hover. Satisfied with the engine readings, he increased collective and climbed to approximately 20 feet while allowing the nose to swing left to turn downhill for forward flight.
As the helicopter turned through 100 degrees of left turn, the low rotor rpm warning horn sounded. The pilot decided to return to the pad and allowed the left turn to continue. By the time the helicopter regained its original heading, it had drifted approximately 20 feet downhill and was still descending. The main rotor blades struck a large tree stump adjacent to the pad, causing the helicopter to roll over and come to rest on its left side, nearly inverted. Three passengers quickly escaped; the pilot delayed to shut down the engine, which was still running, then exited. All four occupants sustained minor injuries. The helicopter was substantially damaged. The emergency locator transmitter activated automatically at rollover. No fire occurred.
Pilot Information
The pilot held appropriate training and licensing for the AS350 B2 and firefighting support. He had over 3000 hours of flight time, including more than 1000 hours in the AS350, and had worked for the operator in forest fire management for several years. A review of flight and duty times for the period leading to the accident showed no deviation from Transport Canada regulations, and he had not recently engaged in arduous operational activities.
Weather Conditions
No formal weather observation existed for the accident site, but reports from adjacent areas and witnesses indicated visual flight rules (VFR) conditions. Surface wind was light from the northeast, with moderate wind at tree-top level and a significant down-flow over the site. Outside air temperature (OAT) readings varied: nearby areas reported 24°C to 28°C earlier, but after recent rain showers, the helicopter's OAT gauge read 22°C to 24°C. Performance calculations in the report used 20°C.
Aircraft Information
The helicopter, manufactured in 1999, had accumulated approximately 1880 flight hours. It was certified and maintained per regulations, with no deferred defects. The fuel system contained about 650 pounds of fuel at the time of the accident, confirmed by post-crash measurements. Fuel samples showed no contamination; supply and quality were not considered contributory.
Weight and balance calculations indicated a gross weight of approximately 4825 pounds, slightly below the maximum certificated weight of 4961 pounds. The center of gravity was 126.1 inches from the datum, slightly forward of the maximum forward limit of 125.9 inches at that weight.
Performance Analysis
Because the helicopter reached 15 to 20 feet and the terrain was steep, no ground effect benefit was likely. The hover out-of-ground-effect (HOGE) chart from the rotorcraft flight manual was appropriate. Using 20°C OAT, 5200 feet pressure altitude, and 4825 pounds gross weight, the helicopter was about 150 pounds below the maximum permissible weight for HOGE. As temperature increased to 25°C, this margin would diminish to zero. Factors such as wind, pilot handling, and engine/rotor efficiency would also affect performance. Calculated vertical climb speed was approximately 300 feet per minute at take-off power and 590 feet per minute at maximum power, each increased by 230 feet per minute due to left pedal input, yielding a maximum possible 820 feet per minute.
Engine and Fuel Control Unit Examination
The Turbomeca Arriel 1D1 engine was removed and tested in a certified test cell. No deficiency or degradation in performance that would have contributed to the loss of rotor rpm was found. The engine met specifications except for a minor power shortfall of about 5 kW (1% of target) below the repair limit, which was considered negligible. The fuel control unit (FCU) was inspected and bench-tested; no significant defect was found. A slight decrement in FCU acceleration characteristics was noted, but its effect would have been unnoticeable given the engine was already at high hover power. The throttle cable was found kinked and immovable due to impact distortion, consistent with a fully-opened throttle lever position during the hover. After the rollover, the pilot repeatedly attempted to retard the throttle but the cable jammed, causing the lever to break; he then shut down the engine using the fuel shut-off control lever.
Injuries and Damage
All four occupants sustained minor injuries. The helicopter was substantially damaged.
Probable Cause
The source does not state a probable cause.