Transportation authorities are investigating after an Air Canada pilot nearly landed a jet full of passengers on a taxiway where four other planes were waiting, coming within metres of what would have been a disastrous collision.

The incident took place late Friday night at San Francisco International Airport. According to a preliminary summary released Tuesday by Canada’s Transportation Safety Board, the Air Canada jet was already over the taxiway on a landing approach when a crew member from another airline alerted air traffic control that it appeared to be on a collision course.

The Air Canada pilot pulled up, and overflew the first two planes by just 30 metres.

“If it is true, what happened probably came close to the greatest aviation disaster in history,” said retired United Airlines Capt. Ross Aimer, CEO of Aero Consulting Experts.

“If you could imagine an Airbus colliding with four passenger aircraft wide bodies, full of fuel and passengers, then you can imagine how horrific this could have been,” he said.

Pilots and aviation experts who spoke to the Star described the incident as rare, and said that consequences would have been severe if the pilot hadn’t changed course.

“Certainly the potential was there for something catastrophic to have happened,” said Greg McConnell, chairman of the Canadian Federal Pilots Association.

Flight AC759 took off from Toronto at around 9:25 p.m. and according to Air Canada had 135 passengers and five crew members on board.

Just before midnight, the plane was cleared to land on a runway at the San Francisco airport. But according to a statement from the U.S. Federal Aviation Administration the pilot “inadvertently” lined up for a taxiway that runs parallel to the runway instead — where there were four aircraft waiting to take off.

An air traffic controller sent the Airbus A320 around, and the plane “landed without incident” on the second approach, said the FAA.

John Dejak, president of Aviotec International, an airport and aviation consultancy firm, questioned how any pilot could have mistaken the taxiway for the landing strip.

“I’m frankly baffled,” he said “It would be very difficult to confuse the lights of the taxiway to the lights of the runway.”

Runways are “lit up like a Christmas tree,” particularly at night, and look very different from taxiways, said Greg Feith, a former senior air safety investigator with the U.S. National Transportation Safety Board (NTSB).

Runway lights are brighter, clearly defined, and a different colour than the taxiway lights, he said. Experts said technology in the cockpit should have also told the pilots they were off course.

Feith said he expects investigators to look at whether all the lighting and guidance instruments were working at the time, determine the procedures the pilots used, talk to the crew about what they saw inside and outside the plan, and determine to what extent human error played a role.

Audio posted on the website LiveATC.net, which catalogues air traffic control calls, offers a window into the incident.

The Air Canada pilot asks if he’s clear to land, saying he sees some lights on the runway.

Air traffic control says he’s clear — there’s nobody else on the runway.

The pilot confirms, and then another voice cuts in:

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‘Where’s this guy going? He’s on the taxiway.”

The pilot is quickly told to go around, and the pilot complies.

“Air Canada flew directly over us,” a United Airlines pilot later says.

“Yeah I saw that, guys,” says another voice.

According to the Transportation Safety Board summary, after missing the first two planes by 30 metres, the Air Canada flight overflew the third and fourth aircraft by 60 metres and 90 metres respectively. The report says the “closest lateral proximity” of the Air Canada jet to one the planes on the taxiway was roughly nine metres.

Local weather forecasts indicate that that the sky was clear at the time of the incident. According to the National Weather Service, “no significant weather was observed” at San Francisco International Airport on Friday.

In an email, Air Canada spokesperson Peter Fitzpatrick declined to identify the pilot or say how much flight experience he had. He declined to answer questions about whether the pilot has been removed from duty or if he was believed to have been at fault.

“We are still investigating the circumstances and therefore have no additional information to offer,” Fitzpatrick said.

Keith Holloway, a spokesperson for the U.S. NTSB, said the agency was notified about the incident roughly a day after it happened, and is taking the lead on the investigation, with help from the FAA.

“We are collecting flight information and we are going to also talk to air traffic control communicators . . . to see what information they can provide for us,” said Holloway, who added that the NTSB would also likely interview the Air Canada crew.

Holloway said that NTSB probes can take between 12 and 18 months, but because the San Francisco incident didn’t result in any injuries or damage to aircraft, it would likely be completed sooner.

A spokesperson for the Canadian government’s Transportation Safety Board said the agency would act as an “accredited representative’ in the U.S.-led investigation. The agency’s role would be to facilitate information sharing between Air Canada and the U.S. investigators, he said.

With files from Star wire services

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