"The aircraft deviated from altitude and then, from its heading, rolled to the right and spiralled down. In a spiral, generally speed builds up pretty fast," said Wray Tsuji of the Transportation Safety Board of Canada as he led reporters around the wreckage of the Piper PA-46 Malibu.

"The pilot reported some problems with his instruments and if you're flying in cloud or whatever and you don't have visual reference, the instruments are the only thing you can rely on," he said.

"If you're going down and you pull on the control to bring the nose back up again, at high speeds, you end up overloading the wings or the tail," Tsuji said.