What happened
On a morning involving significant weather-related changes to runway operations, an Avitec Tractor 197 was moving an Airbus A310 from Terminal 3 toward a de-icing facility. The tractor driver had received authorization to proceed via taxiway Sierra, which involves crossing Runway 15L. Simultaneously, Air Canada Flight 757, a Boeing 767-200, was cleared to position on the same runway and subsequently cleared for take-off.
As the tractor entered the runway, the driver did not realize the aircraft was in motion. The flight crew of Flight 7SB7 observed the tractor and tow entering their path during the take-off roll. The pilots reacted by rejecting the take-off, reaching a speed of over 90 knots at approximately 2500 feet down the runway before the aircraft slowed to under 40 knots.
The investigation
The investigation examined the coordination between ground and tower controllers during a period of high workload. Recent runway changes due to wind conditions had necessitated several amended clearances. The investigation found that the north ground controller issued a clearance to the tractor that implicitly allowed it to cross the active runway but failed to coordinate this movement with the north tower controller.
Furthermore, the investigation looked into the technical capabilities of the airport's surface detection equipment. While the airport utilized an airport surface detection system (ASDE), the runway incursion monitor/collision avoidance system (RIMCAS) was not yet commissioned for operational use at the time of the event. The investigation also reviewed the regulatory environment regarding airside vehicle operations and the lack of a national standard for vehicle movement on maneuvering areas.
Findings
- The north ground controller failed to coordinate the tractor's movement with the tower controller and did not provide an explicit instruction to cross the runway.
- Task saturation of the north ground controller, driven by a heavy workload from weather delays and runway changes, contributed to a lapse in attention.
- The tractor driver, while properly qualified, did not perceive the aircraft was in motion until the vehicle was already on the runway.
- Airside vehicle operators are not required to hold short of runways unless they have an explicit clearance to cross, meaning they do not provide the same level of independent defense against errors as pilots do.
- The lack of a requirement for ground traffic to monitor the tower frequency prevents vehicle operators from hearing critical take-off or landing clearances.