Flat light contributed to the 2020 collision of a helicopter with the frozen surface of Lac Saint-Jean, Quebec
Dorval, Quebec, 1 December 2021 — Today, the Transportation Safety Board of Canada (TSB) released its investigation report (A20Q0015) into a helicopter collision with the frozen surface of Lac Saint-Jean, Quebec, drawing attention to how optical illusions can affect spatial awareness and increase the risk of controlled flight into terrain (CFIT).
On the morning of 22 January 2020, two helicopters operated by Quebec’s Service aérien gouvernemental (SAG) took off from the Montréal/St-Hubert Airport, Quebec, bound for Saint-Henri-de-Taillon, Quebec, to provide air support to a search for snowmobilers who had been reported missing the day before. Early in the afternoon, one of the two helicopters was released from this assignment and took off from Saint-Henri-de-Taillon, bound for the La Tuque Aerodrome, Quebec, with one pilot alone on board. Approximately seven minutes after takeoff, the helicopter struck the frozen, snow-covered surface of Lac Saint-Jean. The aircraft was destroyed but there was no post-impact fire. Despite serious injuries, the pilot was able to egress from the helicopter and call the SAG dispatcher to report the accident.
The investigation found that even though the shoreline was visible in the distance, once the pilot moved laterally away from the shoreline and passed some islands, there was a significant decrease in reliable visual cues on the ground and this decrease went unnoticed by the pilot. These cues enable pilots to establish and maintain their height visually over the snow-covered surface of a lake. Despite good visibility, flat light was also obscuring the shadows and contrast at the snow-covered surface of the lake, reducing the visual cues needed for depth perception and three-dimensional vision. Even when visibility is good and the horizon is visible, a loss of depth perception may go undetected by a pilot. Given that flat light is an optical illusion, neither flight experience nor an instrument rating can help to better identify the loss of 3D vision. This illusion adversely affects spatial awareness and increases the risk of CFIT if it is not recognized.
The investigation also found that pilot’s knowledge and training did not provide him with the skills to recognize the risks associated with low contrast resulting from flat light while he was in cruise flight, and good visibility made it possible to see the shoreline in the distance. The reference documents provided by Transport Canada do not make a clear distinction between the phenomenon of flat light, and that of whiteout, creating a risk that pilots will not differentiate between the specific threats associated with each hazard.
In this occurrence, wearing a flight helmet and using the 4-point harness helped to reduce the severity of the injuries to the pilot, who was able to egress from the aircraft and contact the dispatcher to get help quickly. The pilot was wearing a flight helmet even though the SAG does not require pilots to wear one when conducting flights on a Bell 206 aircraft. The TSB has previously highlighted the importance of wearing a helmet to prevent fatal injuries or to reduce the effects of non-fatal head injuries received in an accident, notably in an air transportation safety issue investigation (SII) report A15H0001 into reducing the risks associated with air-taxi operations in Canada.
See the investigation page for more information.
The TSB is an independent agency that investigates air, marine, pipeline, and rail transportation occurrences. Its sole aim is the advancement of transportation safety. It is not the function of the Board to assign fault or determine civil or criminal liability.
For more information, contact:
Transportation Safety Board of Canada