What happened
At approximately 1815 mountain daylight time, a Bell 206B Jet Ranger, registration C-GPGX, was departing from a landing area near the Nose Mountain fire observation tower in Alberta. The aircraft, operated by Precision Helicopters Inc., was carrying a pilot and three initial attack firefighters on a mission for the Alberta Ministry of Sustainable Resource Development Forest Protection Branch.
After performing a hover-taxi to avoid a brush pile, the pilot departed toward the west. As the helicopter crossed the rim of a nearby escarpment, it began to yaw to the right. The pilot attempted to correct the rotation with full left pedal, but was unable to maintain control. To stop the yaw, the pilot lowered the collective, which caused the aircraft to descend into the terrain. The helicopter struck the ground and rolled onto its left side, causing one fatality and one serious injury. The pilot and the remaining firefighter sustained minor injuries.
The investigation
The investigation focused on the aircraft's performance capabilities, weight and balance accuracy, and environmental conditions. Investigators examined the engine, which was a modified Rolls-Royce 250 C20, and found no mechanical failures in the flight controls or tail rotor drive system.
Analysis of the weight and balance revealed that the takeoff weight was approximately 3245 pounds, exceeding the maximum takeoff weight of 3200 pounds and the hover out-of-ground effect (HOGE) limit of 2925 pounds for the prevailing conditions. The investigation also looked into the weight estimation practices used by the crew and the lack of a formal system for providing accurate passenger and gear weights.
Findings
- The helicopter was operating over its maximum allowable weight due to inaccurate passenger and equipment weight estimates.
- The pilot had estimated passenger weights without accounting for the additional 14 to 17 pounds of personal firefighting gear worn by each crew member.
- High density altitude, shifting tailwinds, and the loss of ground effect as the aircraft crossed the escarpment rim created a synergistic effect that exceeded engine and rotor performance limits.
- The aircraft entered a state of unanticipated right yaw (loss of tail rotor effectiveness) because the tail rotor could not provide sufficient thrust to counter the main rotor torque.
- The severity of the injuries was increased by the main rotor penetrating the cabin and the fact that one passenger was likely not wearing a shoulder harness.
- There was no formal system in place for the Forest Protection Branch to provide pilots with precise weights for firefighters and their equipment.