US investigators have determined that the fortuitous sight of a snow-removal vehicle's headlamps prevented a runway collision after an Air Canada Embraer 190 had been cleared for take-off at Denver.
The vehicle had been the lead for a snow-clearance team at Denver on 31 January and had been instructed by tower controllers to proceed south on taxiway F, which runs parallel to the 12,000ft (3,660m) Runway 34R.
However, the vehicle's operator "misidentified" taxiway F, the US National Transportation Safety Board said, driving instead on to the runway from taxiway WC. The intersection lies about a third of the way along 34R.
In a statement to investigators the departure controller - a trainee under supervision - said flight AC1072 had lined-up for departure, ahead of a flight to Montreal.
"I scanned the runway and the ASDE-X [runway conflict system] and everything appeared clear," the controller said, adding that the Embraer 190 received take-off clearance a short time later.
The crew of the jet had released the parking brake but before advancing the throttles to begin the take-off run, the pilot saw the oncoming headlights of a vehicle on the centreline and informed the tower.
Weather data shows there was light snow and reduced visibility on the airport at the time. The vehicle entered the runway about 60s before the pilot saw its headlights.
While the ASDE-X system is designed to alert controllers to possible runway incursions, the NTSB said the algorithms were set to ignore vehicles travelling below 40kt (74km/h) to prevent nuisance alarms. The conflict alert did not trigger.
The aviation operations manager at Denver tower, who was overseeing the snow clearance, said he contacted the lead snow vehicle, coded Ops 6, to advise that something was on the runway.
"Ops 6 did not initially realise that he was the vehicle on the runway," said the NTSB. "While co-ordinating with the tower, Ops 6 attempted to visually identify the vehicle on Runway 34R before realising that his vehicle was the vehicle in question."
Source: Flight International
