An investigation by the board, released Wednesday, said the pilot lost control of the chopper while trying to find a spot to land in the Birch Mountain area near Fort McMurray. The aircraft, operated by Wood Buffalo Helicopters, collided with a tall stand of poplar trees before dropping to the ground.
The board found that the helicopter had slowed and wind created the flying phenomenon known as "loss of tail rotor effectiveness."
"It is the result of the tail rotor not providing adequate thrust to maintain directional control," the board said in its report. "If not corrected, (it) can result in the loss of the helicopter."
Two wildlife biologists with Alberta Sustainable Resource Development were on board the May 29 flight to collect discarded radio collars from vanishing woodland caribou herds in the area. Equipment was tracking the lost collars and, when the helicopter landed close enough, the workers were to set off on foot and collect them.
Kristina Norstrom, 39, of Athabasca, Alta., was killed along with the pilot, Bryce Campbell, 35, of Golden, B.C. Both were sitting on the right side of the chopper, which hit the ground.
The second scientist, Simon Slater, was sitting in the front left passenger seat. Although he was injured, he was able to crawl out of the wreckage through a broken front window, said the report.
At the time of the crash, a colleague described Slater's wounds as serious: internal injuries, cracked ribs and damaged vertebrae. A government spokeswoman said she couldn't comment on how he has recovered.
Board investigator Fred Burow said aerial survey flights are usually slow and low to the ground. The pilot, who showed no signs of fatigue, had received proper training that included what to do in the case of loss of tail rotor effectiveness.
Pilots would typically reduce an aircraft's power, he said. "The problem with that is if you're close to the ground or close to obstacles, you will start descending and possibly contact those obstacles before you can arrest the rotation."
Burow said such episodes are uncommon and occur with little warning.
"One day it might not happen. You change the winds a little bit and you could be in a different situation."
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