What happened
On 13 December 2017, an ATR 42-320, registration C-GTWEA, was performing a series of scheduled instrument flight rules operations for West Wind Aviation L.P. throughout northern Saskatchewan. During the initial pre-flight briefing, both the dispatcher and the flight crew identified forecasts for icing along the intended route. Despite this knowledge, the decision was made to proceed with the flight plan, which included stops at several remote locations lacking adequate de-icing capabilities.
After an initial leg from Saskatoon to Prince Albert, the aircraft departed for Fond-du-Lac Airport. During the approach to Fond-du-Lac, the crew encountered in-flight icing and engaged the aircraft's de-icing and anti-icing systems. While these systems were active, they were unable to prevent all ice from accumulating on unprotected surfaces or shed all ice from the boots. The crew noted the presence of ice but did not observe any changes in aircraft handling, leading them to proceed with the landing.
Post-accident analysis of flight data revealed that the aircraft's lift was reduced by 10% and drag increased by 28% just prior to touchdown, confirming significant residual ice was present. Following a 48-minute stop on the ground, the aircraft prepared for a flight to Stony Rapids with 22 passengers and 3 crew members. During this time, despite the absence of active precipitation, environmental conditions allowed for further frost or ice formation on the existing ice crystals. An external inspection by the first officer was conducted, but due to poor lighting and a lack of proper equipment, the inspection was limited to a visual check from the aircraft stairs.
The investigation
Investigators examined the flight data recorder, which provided critical evidence of the aerodynamic changes occurring during the final approach. The investigation also focused on the effectiveness of the aircraft's ice protection systems and the limitations of the de-icing boots in the encountered conditions. Furthermore, the investigation looked into the ground inspection procedures and the environmental conditions at Fond-du-Lac Airport during the aircraft's turnaround.