San Francisco: In what one aviation expert called a near-miss of what could have been the largest aviation disaster ever, an Air Canada pilot on Friday narrowly avoided a tragic mistake: landing on the San Francisco International Airport taxiway instead of the appropriate runway.

Sitting on Taxiway C shortly before midnight were four fully-loaded airplanes full of passengers and gas awaiting permission to take off, according to the Federal Aviation Administration, which is investigating the "rare" incident.

Investigators are trying to determine how close the Air Canada pilot came to disaster. Credit:AP

An air traffic controller sent the Air Canada Airbus 320 on a "go-around" - an unusual event where pilots must pull-up and circle around to try again - before landing safely, according to the federal agency.

FAA investigators are still trying to determine how close the Air Canada aircraft came to landing and potentially crashing into the four aircraft below, but the apparent pilot error already has the aviation industry buzzing.