What happened
At 2020 Pacific daylight time, a Eurocopter AS350 B2 helicopter, registration C-GSHH, was performing a mission for the British Columbia Forestry Service near the extinct Flourmill Volcano. The aircraft was tasked with relocating 11 firefighters and equipment from a recently prepared mountainside helipad to a staging area.
After passengers boarded, the pilot attempted an initial takeoff but aborted due to engine parameters approaching limits. A second attempt successfully lifted the aircraft into a five-foot hover. As the pilot began a climbing turn to the left to transition into forward flight, the low rotor RPM warning horn sounded. The pilot attempted to return to the pad, but the aircraft drifted 20 feet downhill and descended. The main rotor blades struck a large tree stump adjacent to the pad, causing the helicopter to roll onto its left side. While the three passengers escaped quickly, the pilot delayed his exit to ensure the engine and fuel systems were shut down. The four occupants sustained minor injuries, and the aircraft suffered substantial damage.
The investigation
The TSB examined the engine, fuel control unit, and aircraft maintenance records. The Turbomeca Arriel 1D1 engine was found to be performing within manufacturer specifications, with no mechanical deficiencies identified. Investigations into the fuel supply confirmed no contamination was present.
Engineers also analyzed the throttle cable, which had become kinked due to the impact, preventing the pilot from immediately retarding the throttle after the rollover. The investigation also reviewed the aircraft's weight and balance, noting the helicopter was operating at approximately 4825 pounds, near its maximum capacity for the given conditions.
Findings
- The helicopter was operating at near-maximum gross weight in a high-power state.
- The pilot encountered down-flowing air at the accident site, which reduced the aircraft's vertical performance.
- The decision to execute a left turn increased the power demand on the tail rotor when the pilot attempted to correct the turn, leading to a rapid decay in rotor RPM.
- The steep slope and physical constraints of the temporary helipad prevented a successful recovery or landing once the descent began.