A report released Thursday by the Transportation Safety Board detailed events before the plane went down near Ivanhoe Lake on Aug. 22, 2013.
The board said the Transwest Air pilot hadn't slept well the night before and woke up with stomach cramps. He didn't report the illness, even though airline policy requires pilots who feel unwell to contact officials and remove themselves from duty.
The 25-year-old pilot made several flights throughout the North as scheduled that day, but ran into several problems: wind often made it difficult to dock the plane, it got stuck on several sandbars and a water rudder broke.
While waiting for repairs to the rudder in Stony Rapids, Sask., the pilot turned down offers of lunch and ate a few crackers. People said the usually happy and relaxed man "appeared increasingly agitated, withdrawn and short-tempered."
Then, during a landing at Scott Lake, N.W.T., a wing of DHC-3 Otter struck a strand of trees.
"There was a loud bang and the aircraft swung to the right," said the report. It said the pilot next had trouble manoeuvring to a dock and brusquely ordered a passenger out of a seat.
"Damage to the right-wing leading edge and fibreglass wing tip was evident and was pointed out to the pilot, but the comment was dismissed," the report said.
"A detailed inspection by a qualified person, as required by company policy, would have been required to determine the full extent of the damage to the wing, wing tip and wing attachment points."
Staff at a lodge in Scott Lake suggested to Transwest Air operations staff that the pilot spend the night, but he turned down the offer. Even though he had already been working for 12 hours and wasn't feeling well, he went ahead with his 13th flight of the day to Ivanhoe Lake.
It was an "unsafe decision," said the board.
The plane was reported overdue the next day. Wreckage was later found in an unnamed lake in the area and RCMP divers recovered the pilot's remains. He has not been publicly identified.
The aircraft was not equipped with a flight data recorder or a cockpit voice recorder. But the board said it's likely the pilot lost control "due to interference between parts of the falling wing tip, acting under air loads."
Transwest Air, based in Prince Albert, Sask., sent a memo to all of its pilots after the crash reminding them not to work if they don't feel fit to fly.
"Looking at it analytically, we were already doing everything that should have prevented this from happening in the first place," said Garrett Lawless, chief operating officer with the airline.
The company is now working to develop and implement a new training program for staff that deals more with human factors and decision-making, Lawless said.
Note to readers: This is a corrected story. A previous version said staff at Stony Rapids suggested the pilot spend the night.