Investigation Summary
The investigation by the Transportation Safety Board of Canada (TSB) revealed a systemic failure in winter operations at remote airports. The aircraft arrived at Fond-du-Lac with residual ice after encountering icing conditions on approach. During the 48-minute ground stop, additional ice accreted due to conditions conducive to frost formation. The First Officer performed an external inspection in the dark without a flashlight and from a distance, failing to appreciate the severity of the contamination. The TSB found that departing with surface contamination had become a 'normalized' unsafe practice at remote airports like Fond-du-Lac, which lacked adequate de-icing equipment. On the accident flight, the ice increased drag by 58% and decreased lift by 25%. Upon liftoff, the aircraft experienced an uncommanded roll to the left. The captain, expecting normal handling, was unable to stabilize the resulting oscillations due to diminished roll damping caused by the ice. The TSB also noted that the ATR 42's fuselage design lacked specific crashworthiness parameters for impact energy absorption, which contributed to the severity of injuries when the wing structure collapsed into the cabin.
Final Conclusions
The TSB final report (A17C0146), published on 28 October 2021, concluded that the primary cause was the crew's decision to depart with ice-contaminated critical surfaces. Contributing factors included the inadequacy of de-icing equipment at Fond-du-Lac, the normalization of unsafe practices regarding ice, and the crew's continuation bias. The report also highlighted that the ATR 42's fuselage was not designed for crashworthiness in terms of impact energy absorption, which led to the wing structure collapsing into the cabin and causing serious injuries.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Captain
In command of the flight.
First Officer
A captain acting as First Officer for this flight.
Systems & Failure Modes
De-icing Boots
Pneumatic boots on the leading edges designed to crack and shed ice; however, they are not designed to remove all types of ice or prevent accumulation on unprotected surfaces.
Fuselage Structure
The ATR 42 design did not include specific crashworthiness parameters for impact energy absorption, leading to a collapse of the wing structure into the passenger cabin during the vertical deceleration.
Interesting Facts
- 01Upon arrival at Fond-du-Lac, the aircraft's drag was already increased by 28% and lift decreased by 10% due to residual ice from the inbound leg.
- 02At the time of the accident takeoff, ice contamination had increased drag by 58% and decreased lift by 25%.
- 03Fond-du-Lac Airport lacked adequate de-icing equipment, providing only a hand-held spray bottle, two ladders, and a small container of fluid.
- 04A TSB survey found that 74% of pilots had seen aircraft take off with contaminated surfaces in the previous five years, indicating a systemic issue.
- 05The aircraft was destroyed by the impact, with the most severe damage occurring where the wing support structure failed and collapsed into the cabin.
- 06The flight attendant seat failed during the impact due to previous unapproved repairs, impeding her ability to assist in the evacuation.
- 07While initial reports cited 7 serious injuries, the final TSB assessment confirmed 10 occupants received serious injuries and 15 received minor injuries; one seriously injured passenger died 12 days later.
- 08The aircraft collided with terrain 17 seconds after takeoff following an uncommanded roll and subsequent pilot-induced oscillation.
- 09An unrestrained infant passenger received flailing and crushing injuries during the accident sequence because the aircraft was not equipped with regulated child restraint systems.
Safety Actions & Advisories
TSB Recommendation A18-02
Urged Transport Canada to collaborate with operators to identify and equip remote airports with adequate de-icing and anti-icing equipment.
TSB Recommendation A18-03
Called for increased compliance with regulations to ensure no aircraft takes off with contaminated critical surfaces.