The pilot of an Air Canada plane carrying 140 passengers made a last-minute manoeuvre to avoid landing on a taxiway at San Francisco International Airport where four passenger jets were lined up to take off.
Federal officials said they are investigating why the pilot mistakenly made his approach toward the taxiway instead of the runway just to the left.
An air traffic controller ordered the Airbus 320 to abort and circle for another landing, which it did without incident on Friday night.
Aviation-safety consultant Todd Curtis said it was "definitely a serious event since a landing on an active taxiway could lead to a catastrophic accident".
In audio posted on liveatc.net, which records flight communications, the pilot on the plane from Toronto and the air traffic controller sounded calm as the close call unfolded.
At first, the pilot said he sees "some lights on the runway", apparently alluding to planes on the taxiway, the aviation equivalent of feeder roads that planes use to roll between runways and terminals.
The controller assures the pilot there is no one on the runway. Seconds later, another voice - apparently one of the pilots on the taxiway - interjects, "Where's this guy going? He's on the taxiway."
The controller orders the Air Canada jet to "go around", and the pilot acknowledges the command.
Roughly 30 seconds later, a United Airlines pilot on the taxiway says the jet "flew directly over us".
Federal Aviation Administration spokesman Ian Gregor would not comment on how close Air Canada Flight 759 came to disaster, citing his agency's ongoing investigation.
The National Transportation Safety Board also will review what happened.
"Any time you have an incident where there's a potential for a catastrophic event, we take an interest," spokesman Keith Holloway said.
It is rare for pilots to mistake a taxiway for a runway, and when it happens, it usually involves small planes at smaller airports. Taxiways do not have the same distinctive markings and lighting as runways.
Investigators will focus on "how did this series of errors occur, and why didn't safeguards kick in earlier than they did?" said John Cox, a safety consultant and retired airline pilot.
Mr Cox said it was likely that even if the air traffic controllers did not order the Air Canada plane to pull up and make another approach, the crew would have seen planes on the taxiway in time to avoid landing on them.
He said pilots practice low-altitude go-arounds and can perform them even 20ft or 30ft above the ground.
Investigators will be able to determine the Air Canada plane's altitude and exact location using the flight-data recorder.