That runway with a crest can hide a big obstruction

[pelmet]

During night operations at Toronto/Lester B. Pearson Intl, ON (CYYZ), Ground Control (ATC) cleared Tractor 245, which was towing a WestJet Boeing 737 aircraft, across Runway 33R at Taxiway Sierra. Shortly after, Toronto Tower (ATC) cleared C-FSRY, a Bombardier DHC-8-400 aircraft operated by Jazz Aviation Lp as flight JZA875, for take-off on Runway 33R. JZA875 started the takeoff roll when the tractor with the towed aircraft were in the middle of the runway. Runway 33R has a slight crest with the threshold areas being lower than the center. The flight crew of JZA875 did not see the obstruction until the aircraft was almost airborne, with the tractor and the towed aircraft clearing off the other side.

The Runway Incursion Monitoring and Collision Avoidance System (RIMCAS) had been deselected for Runway 33R shortly before the event due to a persistent false target causing frequent alarms.