An Air Canada plane narrowly averted disaster after it almost landed on a taxiway with four other planes on it in San Francisco Friday night.
Air Canada flight AC759 from Toronto was cleared to land on runway 28R just before midnight, a statement from the Federal Aviation Administration said.
"However, the pilot inadvertently lined up for Taxiway C, which runs parallel to the runway," the statement said. "An air traffic controller sent the Air Canada jet around."
In an audio recording of the conversations between air traffic control and pilots available from Live ATC, the Air Canada pilot tells air traffic control he sees other lights on the runway before being told there are no other planes on 28R.
"You can begin to see there is uncertainty in the Air Canada crew's mind about what's going on," said former commercial pilot and aviation investigator John Cox, referencing the recording of communications.
Cox added that proven technologies have long been in place to prevent runway collisions.
"There are electronic devices that send radio signals up to the airplane for vertical and lateral alignment. And why those were not being followed is going to be a central question the investigators will look at," he said.
In the recording, a United Airlines pilot is heard saying "United One, Air Canada just flew directly over us."
Another voice is heard saying, "Where's this guy going? He's on the taxiway."
When air traffic control realizes the plane is headed for the taxiway, it is directed to go around and approach again. It landed without incident on the second attempt.
In an interview with the San Jose Mercury News, a former pilot said the plane avoided what could have been a "horrific" collision.
"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.
SF airport requires 'precision flying'
The FAA is investigating how close the Air Canada plane came to the four planes on the taxiway, adding that this type of incident is "very rare."
Cox echoed that near-hits during takeoffs and landings are rare, but was quick to identify certain design elements of the San Francisco airport that may have exacerbated the troubled approach.
He flew into the same airport "many, many times" as a pilot and said it requires "precision flying."
For example, the two adjacent runways are the closest of any pair used by commercial aircraft in the world, only about 229 metres between them.
Similarly, fewer than 150 metres separates the runway 28R from the taxiway.
But Cox still questions how the Air Canada crew may have confused the two strips of tarmac. At the San Francisco airport, runways are illuminated by clear or amber-hued lights while the taxiway is lined with blue lights.
"Everybody here did a good job" in averting a potential catastrophe, Cox said. "Now we just need to know why the Air Canada crew thought the taxiway was the runway to land on.
In a statement, an Air Canada spokesperson said the airline is also investigating.
"Air Canada flight AC759 from Toronto was preparing to land at San Francisco airport Friday night when the aircraft initiated a go-around," Peter Fitzpatrick said in the emailed statement.
"The aircraft landed normally without incident. We are still investigating the circumstances and therefore have no additional information to offer."