What happened
On the morning of April 26, 1996, an AS-350BA helicopter, registered as C-GRGK, departed from a base in Revelstoke, British Columbia, for a scheduled snow-sampling mission. After refueling at Golden, the pilot and two passengers began a visual flight rules (VFR) flight across the mountainous region to various sampling sites. Following several successful landings, the aircraft arrived at the Goldstream site at approximately 1325 MDT.
During the mission, the helicopter encountered difficult weather conditions. A witness in the valley reported heavy, falling snow and low visibility in the area. While the exact timing of the engine failure is unknown, the helicopter eventually crashed in rugged terrain at an elevation of approximately 6,200 feet. The impact was severe, involving a high rate of descent and a collision with trees, resulting in 3 fatalities and the total destruction of the aircraft.
The investigation
Investigators examined the wreckage and the engine components to determine the cause of the power loss. The Turbomechanica Arriel 1B engine was tested and found to be mechanically sound, with no evidence of fuel contamination or mechanical deficiency. However, the wreckage patterns indicated the engine was not delivering significant power at the moment of impact.
Technical analysis of the engine intake and the surrounding weather conditions suggested that snow ingestion was the most probable cause of the engine flame-out. The investigation also looked into the aircraft's emergency equipment and found that the emergency locator transmitter (ELT) was in the OFF position, meaning it did not activate during the crash. Additionally, investigators reviewed the applicability of an existing Airworthiness Directive (AD) regarding flight in falling snow, noting that different operators held conflicting interpretations of the time limits imposed by the directive.
Findings
- The engine experienced a flame-out, likely due to the ingestion of snow.
- The pilot was forced into an autorotative descent over inhospitable, mountainous terrain.
- The aircraft struck trees during the final stage of the descent, making the crash unsurvivable.
- Adverse weather conditions and difficult terrain contributed to the accident.
- The ELT was not armed prior to the flight.
- The existing Airworthiness Directive regarding flight in snow was ambiguous, leading to inconsistent industry interpretations.