A March 29 runway incursion at Calgary International airport occurred when an aircraft maintenance technician became confused about a taxi route to a remote portion of the airport to conduct a nighttime engine runup, according to a report by the Transportation Safety Board of Canada. The mechanic started from the company ramp in the opposite direction from the instructions he was given. Contributing to the incursion was relatively poor visibility, as well as the tower controller’s failure to accurately monitor the Beech 1900’s progress on the airport surface detection radar system (ASDE).
The tower controller, who was alone at the time of the incident, did not assign a discrete transponder code to the mechanic taxiing the aircraft. It was later discovered the mechanic was unaware of the requirement for the transponder to be turned on during ground movement, which would have made it easier for the single tower controller to track the aircraft. The controller later reported observing a primary target on the ASDE approaching the active runway but incorrectly assumed it was an airport vehicle. The turboprop entered Calgary’s Runway 35L just as a Boeing 737 passed overhead, missing the Beech 1900 by 500 feet.