Canadian investigators have detailed an incursion incident at Toronto Pearson during which a Bombardier Q400 commenced its take-off roll while an aircraft was being towed across the runway.

The Jazz turboprop (C-FSRY) had been cleared for take-off on runway 33R during the night of 2 July, states Transportation Safety Board of Canada.

But ground control had already cleared a tractor crew, towing a WestJet Boeing 737, to cross the same runway.

Investigators point out that the runway has a "slight crest", with the centre being higher than the threshold areas. The Q400 began its take-off run while the tractor and the 737 were "in the middle of the runway," the TSB says.

"The flight crew of [the Q400] did not see the obstruction until the aircraft was almost airborne, with the tractor and towed aircraft clearing off the other side," it adds.

Although Toronto Pearson has a runway incursion and monitoring system, the initial incident filing states that this equipment had been disengaged shortly before the event owing to a "persistent false target" which was causing frequent alarms.

Source: Cirium Dashboard