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Air Canada planes are pictured at Toronto Pearson International Airport on May 18, 2014.Matthew Sherwood/The Globe and Mail

Investigators looking into what caused an apparent close call involving an Air Canada flight at San Francisco International Airport are expected to examine whether human error or controller procedures played a role in the incident, an aviation expert said Tuesday

The state of the aircraft's and controller's equipment, and the design of the air space will also be under review as officials try to determine how a flight from Toronto came to line up with a taxiway rather than the runway as it prepared to land, said Barry Wiszniowski, president of Aviation Safety Management Experts.

An Air Canada Airbus A320 was cleared to land on one of the runways at the San Francisco airport just before midnight on Friday when the pilot "inadvertently" lined up with the taxiway, which runs parallel to the runway, the U.S. Federal Aviation Authority said.

There were four aircraft lined up on the taxiway waiting for departure when the incident occurred, the FAA said in a statement. The Air Canada plane eventually made another approach and landed without incident, it said.

The FAA and Air Canada are investigating what happened.

"One of the questions that they may ask is were the pilots fatigued? ... Were they in their normal window of wakefulness?" Wiszniowski said. "There are a lot of questions that need to be asked."

Wiszniowski said the safety systems in place managed to prevent what could have been a serious incident, noting that at least one previous case in which a plane landed on a taxiway where there were other planes resulted in multiple fatalities.

Thirty-four people died in February 1991 when a USAir Boeing 737 landed on a taxiway at Los Angeles airport and collided with a commuter plane, causing a massive explosion. Sixty-seven passengers survived.

Air traffic management and equipment, as well as aircraft exterior lighting and visibility, were among the safety issues raised by the FAA in its report on that crash.

Recommendations made in the wake of such incidents have helped improve safety procedures, Wiszniowski said.

"The lessons learned from LAX — now at night, whenever an aircraft is on the runway, we turn our strobe lights on," he said. "When we cross a runway, even in the daytime, we turn our strobe lights on."

A similar report on Friday's incident will highlight areas for improvement, he said.

An exchange recorded by the website provided some details on the incident involving the Air Canada flight.

In the clip, the Air Canada pilot is heard requesting permission to land and is given the go-ahead from the control tower before another pilot issues a warning.

"Where is this guy going? He's on the taxi lane," the second pilot says in the recording.

The controller then tells the Air Canada pilot to pull up and go around.

The aviation agency said it is now investigating the distance between the Air Canada aircraft and the jets lined up on the taxiway.

Air Canada said 135 passengers and five crew members were aboard its plane, but gave little other information, citing its own ongoing investigation.

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