OTTAWA - An old radar, a driverless van, a 7-watt lightbulb and garbled communications all contributed to a near-collision at Pearson International Airport when a landing Air Canada jet passed just 10 metres over a vehicle that had rolled onto a runway, a safety watchdog says.
“That’s the amazing thing with this one. You get a series of very improbable events and they all line up,” said Ewan Tasker, a regional senior investigator with the Transportation Safety Board of Canada.
“It’s just incredible,” he said in an interview Wednesday.
He said the March 11, 2013 incident is a reminder why in aviation “every tiny, little detail matters.
“These crazy, unlikely things can happen. Luckily in this case we can all learn a lesson from it without anyone getting hurt,” Tasker said.
The safety board’s final report released Wednesday lays out the series of events that conspired to cause a near-disaster at Canada’s busiest airport.
It began near midnight when a technician servicing a jet parked at the airport’s east end got out of his van but left the motor running — in contravention of airport rules — and accidentally left it in gear.
Unnoticed in the darkness, the van began a slow roll across the apron, clipping the engine cowling of the parked jet and then continued in the direction of Runway 24 Right — and a potential collision with an Air Canada Embraer jet that was arriving from Edmonton.
In the control tower, the radar used to track vehicles and aircraft on the ground showed a slow-moving target and as it travelled onto the runway, air traffic controllers urgently tried to figure out what it was. One controller used binoculars to scan the area but was unable to spot anything.
Recognizing that the Air Canada jet, with five crew and 67 passengers onboard, was about to land on that very runway, a controller radioed instructions for the pilots to “pull up and go around.”
However, the crew missed that instruction because it coincided with a louder, automated altitude call-out in the cockpit.
Not getting a response, the controller again ordered the Air Canada crew to abandon their landing. But in this second call, the controller’s clipped instructions caused the jet’s call-sign to be truncated and the pilots — at this point just 37 metres off the ground — thought the instruction was for someone else and continued to a safe landing.
The jet had passed just 11 metres directly over the van, which the pilots never saw in the darkness.
Tasker’s investigation revealed that the ground radar system, an older version which has since been replaced, did not provide a timely alert to the looming conflict as intended.
The probe also found that the orange beacon atop the van — required of all vehicles at the airport — had only a 7-watt bulb, far dimmer than rules mandate. That weak bulb hindered efforts by controllers to spot the van from the control tower.
Finally, the controller’s instructions to “go around,” although clipped, failed to register with the pilots who, in the final stages of their approach, were expecting a “typical, non-eventful landing.”
“Without other supporting cues such as visually sighting an obstacle, the crew did not interpret the instruction to apply to them,” the report said. “Consequently, the communication was insufficient to challenge the flight crew’s mental model of the situation.”
The van was later discovered in the grass where it had clipped a taxiway sign. Its engine was running, headlights were on and the transmission was in drive.
In the wake of the incident, the safety board says that Greater Toronto Airports Authority, which operates Pearson airport, has reinforced its rules that require drivers to turn off vehicles and apply the parking brake before leaving them unattended.