What happened
On a winter morning in La Ronge, Saskatchewan, a Transwest Air Limited De Havillable DHC-6 Series 100, registration C-FCCE, attempted a short take-off and landing (STOL) technique from a snow-covered ski strip. As the aircraft accelerated, the nose ski and the left main ski lifted from the surface. However, the aircraft immediately began to veer to the right and roll.
The pilot, believing the aircraft was already airborne, chose to continue the take-off rather than aborting. During this maneuver, the right ski remained in contact with the snow, creating a significant drag differential. The aircraft briefly cleared a nearby gully but remained in a steep right bank. As the crew attempted to adjust flaps to gain altitude, the right wing tip struck the ground and a perimeter fence, eventually leading the aircraft to crash into a nearby treeline. The seven people on board—two crewmembers and five passengers—evacuated the wreckage with minor injuries.
The investigation
Investigators examined the aircraft's condition and the crew's pre-flight procedures. While the first officer had performed an external inspection and brushed snow from the wings, no tactile test was performed to ensure all frozen contaminants were removed. Evidence suggested that previous temperature fluctuations had caused snow to melt and refreeze on the wing surfaces, creating a layer of contamination that was not entirely cleared.
The investigation also looked into the aircraft's maintenance and operational history. While the engine mounts showed pre-existing fatigue cracks, investigators determined that the engine separation seen in the wreckage was a result of impact forces rather than a pre-impact failure. Furthermore, the investigation found that the crew was utilizing a STOL take-off procedure that the operator was not authorized to perform on this specific aircraft.
Findings
- Asymmetric wing contamination likely created a lift differential, causing the aircraft to roll and yaw to the right.
- The crew performed an unauthorized STOL take-off, which significantly reduced the aircraft's safety margins regarding stall and control speeds.
- The loss of lateral control, combined with the low speed of the STOL maneuver and subsequent flap adjustments, caused the aircraft to strike obstacles.
- Maintenance inspection requirements for engine vibration isolator assemblies were less thorough than the manufacturer's recommendations, allowing fatigue cracks to go undetected.
- The operator's safety management system failed to identify deviations from standard operating procedures.