What happened
At approximately 12:09 mountain daylight time, a Bell 206B Jet Ranger helicopter, registered as C-GCHE, departed from the Bighorn Helicopters Inc. heliport near Cranbrook, British Columbia. The flight was part of a pre-planned mission for BC Hydro technicians to visually inspect high-voltage power lines. The mission required the aircraft to fly at low altitudes, roughly 20 to 30 feet above the power lines, at a steady ground speed.
While flying southbound at an altitude of approximately 120 feet, the aircraft experienced a sudden loss of engine power. This event triggered a rapid decay in rotor RPM, leaving the pilot with minimal control. The helicopter descended heavily into a paved street within a residential area. Upon impact, the aircraft struck a pedestrian on a sidewalk and collided with a moving motor vehicle. The resulting impact and subsequent intense fuel-fed fire destroyed the aircraft. The three occupants of the helicopter and the pedestrian were killed, while the occupant of the vehicle escaped without injury.
The investigation
The investigation focused on the sequence of events leading to the loss of power and the environmental factors that prevented a successful emergency landing. Investigators examined the engine, the fuel control unit (FCU), and the power turbine governor (PTG). While the cause of the engine power loss could not be definitively determined due to thermal damage to the FCU, investigators looked into potential fuel starvation or mechanical anomalies in the PTG.
Analysis of the flight profile revealed that the helicopter was operating within the manufacturer's "avoid" zones, as defined by the Height-Velocity Diagram (HVD). These zones represent flight conditions—specifically the combination of low altitude and low airspeed—where a successful autorotative landing is nearly impossible following an engine failure. The investigation also reviewed the regulatory framework regarding low-altitude flights over built-up areas under the Canadian Aviation Regulations (CARs).
Findings
- The engine lost power at an altitude and airspeed that prevented the development of a stable autorotative flight, leading to a rapid loss of rotor RPM and a high rate of descent.
- The aircraft was operating in a flight regime that the manufacturer identified as high-risk, where an engine failure would likely preclude a safe landing.
- The sudden loss of engine power left the pilot with insufficient time and altitude to maneuver around obstacles, such as houses, which ultimately forced the aircraft into a collision with the street.
- The pilot's attempts to avoid structures during the descent actually increased the rate of descent and worsened the aircraft's stability.
Safety action
Following the accident, several organizations implemented changes:
- Transport Canada developed a logic chart to assist pilots in making safer decisions regarding minimum altitudes and distances over built-up areas.
- Bighorn Helicopters Inc. updated its operational procedures for low-altitude flight and implemented a new safety management system.
- BC Hydro suspended helicopter operations to develop new safety policies, which eventually included requiring twin-engine helicopters for high-risk profiles and implementing a formal helicopter management system.