What happened
While transporting five geologists to mountain locations west of Grande Cache, Alberta, a Canadian Helicopters Aerospatiale AS 350BA attempted to land on a ridge shoulder after several previous sites were rejected due to uncertain winds. As the pilot initiated a low hover, the aircraft lost directional control and a low main-rotor RPM warning was triggered. The helicopter rotated to the left, struck the terrain, and rolled onto its right side. The incident resulted in one serious injury and substantial damage to the aircraft.
The investigation
Investigators examined the wreckage and the engine, finding no mechanical discrepancies or system malfunctions that contributed to the crash. The engine continued to run after the impact, though the fuel shut-off control became jammed due to impact damage.
Analysis of the aircraft's weight revealed that the pilot had underestimated the takeoff weight. The helicopter's weight at the time of the accident was approximately 4,600 pounds, which exceeded the maximum permitted weight for an out-of-ground-effect (OGE) hover under the prevailing high-density altitude conditions. Specifically, the aircraft was roughly 225 pounds over the limit for a successful OGE hover. Discrepancies in weight included passenger weights being 25 pounds heavier than estimated, additional operational equipment, and 15 pounds of extra survival equipment stored in the tail boom that the pilot was unaware of.
Findings
- The pilot underestimated the gross weight of the aircraft, leading to a takeoff that exceeded the maximum gross weight.
- The attempt to perform an OGE hover at a weight exceeding the permitted limits most likely caused a reduction in main-rotor RPM and a subsequent loss of tail-rotor effectiveness.
- The terrain's rapid drop-off to the right reduced the performance benefits of ground effect, forcing the aircraft into a flight condition more characteristic of an OGE hover.
- The pilot was unaware of the additional survival equipment stored in the tail boom.