SAN FRANCISCO — New details about a near catastrophic collision at SFO Friday night — and the revelation about just how close the fully-loaded planes came — sent shudders through the aviation community Tuesday.

Related Articles Exclusive: SFO near miss might have triggered ‘greatest aviation disaster in history’ The wayward Air Canada pilot who was about to land his plane on a crowded San Francisco International Airport taxiway Friday night dropped as low as 175 feet before throttling the engines and pulling up and over four fully-loaded passenger jets waiting to take off, according to multiple online flight tracking systems.

How could that happen? Adding to the confusion: One of the airport’s two runways was closed and darkened at the time of the incident, and there are indications that only a single air traffic controller may have been working in the tower.

Courtesy of flightaware.com

Air traffic control audio illustrates that it was only after a pilot on the ground warned that the Air Canada plane was off target and heading towards him that a “go-around” was ordered by the tower and the pilot quickly pulled up.

“Where’s this guy going? He’s on the taxiway,” the unidentified pilot blasts over air traffic frequency.

The incident drew enough international attention to prompt a National Transportation Safety Board probe Tuesday, supplementing the ongoing Federal Aviation Administration investigation into the near catastrophic miss.

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One aviation expert pointed to a series of mistakes as possible contributing factors that could have led to one of the deadliest aviation disasters ever — with about 1,000 people on board the five airplanes.

The FlightAware and WebTrak online tracking systems showed the Air Canada Airbus 320 on its approach, dropping to as low as 175 feet and 200 feet, respectively, before increasing altitude above Taxiway C, flying over three United Airlines and one Philippine Airlines plane. The taxiway runs parallel and just to the right of Runway 28R where the pilot had clearance to land.

“That’s very close. Extremely close,” said retired United Airlines Capt. Ross Aimer, CEO of Aero Consulting Experts. Airplanes can be as tall as 60 feet, and Aimer said he has heard from sources in the industry that the Air Canada plane got within 100 to 200 feet of the four planes on the ground.

“That pilot was what broke that chain of events,” Aimer said. “He saw an airplane coming in toward his airplane, and he questioned it and got the attention of the air traffic controller.”

At 11:55 p.m., the time of the incident, Runway 28L was closed with its lights dark, according to the FAA. Aimer said it was possible that scenario shifted the Air Canada pilot’s orientation to the right where he would think Taxiway C was actually his runway. At one point in the audio the pilot asks about navigation lights on his intended runway and is reassured no aircraft is there.

“It’s a pretty major screw-up,” said Ryan Jorgenson, senior aviation data analyst with FlightAware, of a pilot mistaking a busy taxiway for a runway.

Listening to the audio and speaking to aviation sources, Aimer said it appeared only one air traffic controller was handling both ground and tower frequencies that night, which left him concerned.

“It still was a pretty busy time, there was a lot of traffic taking off and landing,” Aimer said. “That was something that I felt uncomfortable with.”

SFO spokesman Doug Yakel referred questions about the incident to the FAA which staffs the control towers.

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SFO is known to have runways close together, Aimer said, but the airport has a good reputation for landings among pilots. Yakel said Runways 28L and 28R are separated by 750 feet, which qualifies the airport for the FAA’s Closed-Space Parallel Runway procedures.

Jorgenson said that, depending on the airline, some pilots are required to operate their Instrument Landing System even when making a visual landing in good weather. That equipment would show the appropriate runway in crosshairs, and if a pilot was veering off course it would become obvious, Jorgenson said.

Jorgenson said each airline is different, but he suspected the pilot would be required to take some re-training.

Union City resident Anne Guzman was with her parents and two sisters on the last leg of a return flight from Barcelona, among a plane full of tired Air Canada passengers.

“As far as I could remember, just before landing, the plane suddenly jerked up and was going up and circling again,” Guzman said. “The pilot only said that we would be making a turn around because we had to re-align once more … (I) don’t remember any explanation or people asking for more details afterwards. I don’t remember any concern from that announcement and maybe around 10 minutes after, we landed smoothly.”

She read about the close call Monday on the Mercury News website.

“I thought the whole flight was very calm and normal, until learning about this news!” she wrote in an email. “(I’m) very grateful for those responsible for being alert and seeing that the flight path was corrected. Hopefully, more serious counter-measures will be implemented because of this near-miss and that this can be completely avoided in the future.”

Another passenger from Oakland, who did not want to use his name and was also returning from Europe, described the landing as he looked out the window from his aisle seat.

“I could see the peninsula lights getting closer, then the water, then the runway lights that are planted in the Bay,” he said. “Finally, I could see the actual airport runway and lights, which if you’re familiar flying into SFO, means that you are seconds from touchdown.

“Then the plane pointed up at full throttle, and at what felt like a much steeper angle than a typical takeoff. I grabbed the arm rests, you heard some passenger commotion and confusion, and we were back up above the runway,” he said.

A flight attendant charged uphill in the steeply climbing aircraft reassuring passengers, he said, when the captain announced they were performing a “go-around” and would line up again. The second landing was uneventful until the Oakland resident got to baggage claim.

“Air Canada lost my luggage for the next 48 hours,” he said.