What happened
At approximately 10:35 PST, a Bell 407 helicopter, registration C-GNVI, was conducting a flight near Blue River, British Columbia, to drop off a group of skiers. The aircraft, operated by VIH Helicopters Ltd., was climbing at 65 knots and roughly 200 feet above the ground when a loud bang and vibration occurred. This event was immediately followed by low rotor RPM and engine-out warnings.
Within six seconds of the initial disturbance, the helicopter struck the snow-covered terrain. While the aircraft remained upright, the impact was heavy. The pilot and the ski guide, seated in the front of the cabin, sustained back injuries, though the five passengers in the middle and rear seats were uninjured. The aircraft sustained substantial structural damage.
The investigation
Investigators examined the Rolls Royce M250-C4 .47B engine and found that a portion of the inlet barrier filter had been deformed by airflow reversal, a characteristic of a compressor stall. Data from the engine's electronic control unit confirmed a temperature exceedance occurred alongside an engine surge and a rapid drop in torque and RPM.
Maintenance records showed the aircraft and engine were well-maintained, with the last routine inspection completed only eight hours prior to the accident. While a previous power turbine replacement had occurred 437 hours earlier due to a different bearing issue, the manufacturer determined that the previous failure was unrelated to this event.
Findings
- The investigation identified the failure of the No. 2 bearing, which supports the rear of the compressor, as the primary cause of the engine failure.
- This failure caused the compressor rotor to shift forward and contact the shroud, triggering the compressor stall and subsequent loss of power.
- The failure was driven by a tolerance stack-up in the No. 2 bearing that made it susceptible to large ball excursions during maneuvers.
- These excursions led to fatigue in the bearing separator and rapid component failure.
- The timing of the power loss—occurring at low altitude and low airspeed during final approach—directly contributed to the hard landing.