The Transportation Safety Board of Canada on Thursday released its report into a plane crash on the Dehcho's Little Doctor Lake that killed three people in August 2018.
A Simpson Air Cessna 206 floatplane lost control while landing at the lake when its right wing made contact with the lake's surface. The plane came to rest upside-down and partially submerged.
The pilot and one passenger were able to escape through a front door, but three other passengers could not find their way out and drowned.
Those who passed away were tourists Geoffrey Dean, 33, of Castor, AB; Stewart Edelman, 72, of Saskatoon; and Jean Edelman, 72, also of Saskatoon.
On Thursday, the Transportation Safety Board (TSB) said its report "re-emphasized the need for aircraft emergency exits to meet the basis of certification" in order to let people escape to safety in similar situations.
Back in February, in a safety advisory issued while the investigation remained ongoing, the TSB had called attention to issues with the Cessna 206's emergency exits.
The TSB said the position of the Little Doctor Lake aircraft's flaps – devices mounted on the wings to increase lift during flight – obstructed the rear cargo doors, which serve as an emergency exit, and represented a "significant safety issue."
Similar problems had been documented in a number of other air accidents involving the Cessna 206 over past decades.
"Over the years, the rear double cargo doors have been identified as a risk to passengers in emergency situations. As a result, the TSB and other investigative agencies have been advocating for changes to the door design," read a TSB statement on Thursday.
The TSB said Transport Canada – the federal agency responsible for transportation, which is entirely separate – would ask the US Federal Aviation Administration to require that the manufacturer, Cessna, "develop, deploy and mandate improvements to the cargo door design to ensure successful egress in the event of an accident on water."
Company introduces underwater training
Though many of the investigation's findings had formed part of February's interim safety advisory, there was some new information contained in the final report.
The TSB announced that, for the final 300 feet of its descent, the Simpson Air plane had not been able to maintain a stable approach, "which led to a hard landing and subsequent bounce." The pilot did not recover from this, which led the right wing to hit the lake surface and flip the aircraft.
Little Doctor Lake is susceptible to unpredictable winds, the TSB said, due to a gap in the mountain range on the west side of the lake. That can result in "significant wave action" on the lake.
"The approach was uneventful until approximately 300 feet above the surface of the water, when the rate of descent began to increase. The pilot increased power to compensate, resulting in the aircraft landing beyond the desired touchdown point," the report reads.
"At approximately 1830, the aircraft touched down along the north shore of the main body of the lake in a nose-high attitude, with the rear of the floats contacting the water first. The stall warning horn was sounding at the time. The aircraft then bounced and became airborne momentarily. The stall warning horn silenced briefly and then began sounding again. The aircraft bounced once more, this time on the rear of the left float, and then pitched forward and banked to the right. During the bouncing sequence, directional control was attempted with the use of left rudder. The right wing contacted the surface of the lake and the aircraft nosed over, coming to rest inverted and partially submerged.
"The pilot and one passenger were able to exit through the window in the pilot’s door and climbed up onto the floats. The pilot dove down to attempt to rescue the other passengers but was unable to open any doors. The pilot and surviving passenger were rescued by a nearby boater within 15 minutes. The three remaining occupants were unable to exit the aircraft and drowned; they were found inside the cabin with their seat belts undone."
An image published by the TSB shows the flaps blocking the emergency exit on the retrieved Cessna 206.
The investigation also noted that the pre-flight safety briefing had contained no instructions regarding what to do if the emergency exit rear cargo doors were blocked due to flap deployment, as turned out to be the case.
Floor matting installed by the airline did not comply with Cessna's parts manual, the TSB said. "Because the matting was fixed only at one end, once the aircraft overturned and was floating upside down, the strips hung down, blocking the spaces between the seats," read the report. "This could have made navigating those spaces difficult and could have added to the confusion as passengers tried to make their way to emergency exits."
Since the incident, Simpson Air has stopped operating the Cessna 206 on floats, the TSB reported. The safety board said the company had "started providing underwater egress training for all floatplane flight crews, and increased training and experience requirements for new crew members."
Around 250 aircraft of a similar design and type to the one used at Little Doctor Lake remain operational in Canada.
The lake – some 100 km west of Fort Simpson – has spectacular views and is becoming a popular destination with visitors to the Dehcho.