What happened
On a flight from a staging area north of Golden, British Columbia, to a recreation lodge, the pilot of an Aerospatiale AS 350B experienced a partial loss of engine power. While flying through the Blaeberry River valley at approximately 300 feet above ground level, the pilot noticed the main rotor RPM beginning to decay.
In an effort to maintain rotor speed and execute an emergency landing, the pilot lowered the collective control and initiated a steep, descending left turn toward a small clearing. During this maneuver, the main rotor blades made contact with a tree at the edge of the clearing. The helicopter subsequently struck the snow-covered ground with significant force. The pilot and two of the four passengers sustained serious injuries, while the other two passengers escaped with minor injuries. The impact caused substantial damage to the aircraft, including the separation of the tail boom from the fuselage.
The investigation
Investigators examined the engine, fuel control unit, and various aircraft systems to determine the source of the power reduction. Post-accident testing of the Turbomeccca Arriel 1B engine showed it was operating within normal specifications, and no defects were found in the fuel control unit.
Technical analysis of the wreckage confirmed that the engine was likely delivering reduced power prior to the rotor strike. The absence of deformation in the engine-to-transmission drive shaft couplings indicated that there was no sudden surge in engine power when the blades struck the tree. Furthermore, investigators found no evidence of snow or ice accumulation on the airframe or within the engine intake, and ruled out snow ingestion as a cause for the power loss, noting that such an event typically results in a complete flame-out rather than a partial loss of power.
Findings
- The aircraft experienced a partial loss of engine power for reasons that were not established.
- The pilot's attempt to maintain rotor RPM through a steep descent led to the main rotor blades striking a tree.
- The aircraft was properly certified, maintained, and operated within weight and center of gravity limits.
- There was no evidence of pilot fatigue, physiological impairment, or mechanical failure prior to the power loss.