Missteps by tug drivers and miscommunication with controllers contributed to a 2023 close call involving a Jazz Aviation turboprop overflying two tugs on an Calgary runway.
That is according to the Transportation Safety Board of Canada (TSB), which says the De Havilland Dash 8-400 passed 107m (350ft) above the tugs.
“The driver misinterpreted the instructions of the ground controller and entered Runway 17R while the departing aircraft was beginning its take-off roll,” the TSB says in a final report released on 22 July.
The incident involved a Jazz flight 7124 from Calgary International airport on 6 October 2023.
That morning, Calgary’s “advanced surface movement guidance and control system” was inactive due planned software updates, leaving the airport’s three controllers relying “solely on visually scanning the areas for which they were responsible”, the report says.
At roughly 11:00 local time, two tugs were driving south along taxiway C, which runs parallel to runway 17R/35L. To avoid another Dash 8 taxing north on taxiway C, the tugs, instructed by a ground controller, turned right onto taxiway C2, which leads to Runway 17R/35L.
Ground controllers told the lead driver to hold short of the runway, which the tugs did at 11:03 local time. Meanwhile, flight 7124 was preparing to take-off from runway 17R.
After the taxiing Dash 8 had passed, the controller instructed the tugs “to proceed onto Taxiway C”, apparently intending them to do so by turning around on taxiway C2 – not by continuing onto runway 17R/35L.
But, contrary to airport procedures, the tugs had stopped so close the runway that the lead driver believed he lacked enough space to turn around. He also wrongly believed drivers were not supposed to turn around on taxiways.
“The route that did appear to make sense to the lead tug driver was to enter runway 17R and immediately navigate back to taxiway C,” the report says.
The tugs entered that runway just as flight 7124 started its take-off roll.
Noticing the danger, controllers, using what investigators call “non-standard” terminology, told the Dash 8 pilots to abort take-off. (The correct terminology should have been, “ABORT, ABORT. (aircraft ID). ABORT, ABORT”.)
The pilots did not hear the command and continued taking off, then saw the tugs ahead on the runway.
By that time the Dash 8 had reached its take-off decision speed. So the pilots proceeded, believing getting airborne was the safest option.
The Dash 8 overflew the tugs.
The TSB attributes the incident to factors including the lead tug driver misinterpreting the controller’s commands and incorrect phraseology used by the controller.
