麻豆传媒

The investigation into the close call involving an Air Canada flight at San Francisco International Airport last week continues, as the Transportation Safety Board released their preliminary occurrence summary of the incident Tuesday.

The incident, which saw Air Canada Flight 759 from Toronto inadvertently line up with a taxiway occupied by four aircraft instead of the assigned runway, was averted after air traffic control sent the Air Canada flight around for another approach, where they landed without incident.

The exchange between the pilot and air traffic control, recorded and posted on liveatc.net, provides some details from the incident.

The pilot, seeing 鈥渟ome lights on the runway,鈥� called into air traffic control, to confirm the landing.

"Air Canada 759 confirmed cleared to land runway 28 right," the tower responded. "There is no one on 28-Right but you."

Seconds later, another voice 鈥� seemingly one of the pilots waiting on the taxiway 鈥� interjects "Where's this guy going? He's on the taxiway."

The tower, seeing the plane was improperly lined up with the taxiway, told the plane to 鈥済o around鈥� and make another attempt at landing.

Shortly afterwards, a United Airlines pilot on the taxiway says the jet "flew directly over us."

According to the preliminary TSB report, the Air Canada plane was estimated to have flown over the first two aircraft by 100 feet, the third one by 200 feet and the last one by 300 feet, while the closest lateral distance between the planes was 29 feet.

The U.S. Federal Aviation Administration and Air Canada are still investigating, trying to determine if human error or controller procedure was behind the incident.

麻豆传媒 spoke with aviation experts for their insight into what could have gone wrong.

鈥楿nusual set of circumstances鈥�

Aviation consultant Keith Mackey, a former commercial airline pilot, says the incident was likely a result of a number of unusual factors all converging at once.

He explained that high-speed winds from the northwest forced the airport to close their two northerly running runways, normally used for takeoffs, and divert all traffic to the east-west runways normally used for landings.

These runways are only 750 feet apart, due to the location of the airport on a pier, which requires pilots to use an approach system set up the right of the runways.

According to Mackey, the procedure calls for planes using the right hand runway to be offset about 1200 feet to the right of the runway鈥檚 centreline until they are four miles from the runway. They then visually acquire the centreline and move the plane into position for landing.

This offset lined the Air Canada flight up roughly with the taxiway that ran parallel to the runway, where the pilot saw the lights and called the tower for confirmation that the flight was cleared to land.

Despite the close call, Mackey said there was little chance that the plane was actually in danger. 鈥淚鈥檓 quite certain there was no danger ever that the Air Canada pilot was going to land on top of those four airplanes on the taxi way,鈥� he told 麻豆传媒 Channel. .

鈥楽eries of errors鈥�

Aviation expert John Cox, a veteran major airline pilot, attributes the incident to a 鈥渟eries of errors.鈥� He cites the closed runway as playing a part in the confusion, but says that the Air Canada crew will 鈥渉ave some significant questions to answer鈥� in the process of determining what was at fault for the close call.

鈥淚t鈥檚 unusual to have an airliner line up on a taxiway instead of a runway,鈥� Cox told 麻豆传媒 Channel.

鈥淭he lighting is different, the markings are different, the electronic radio information that the airplane displays to the crew to make sure they鈥檙e lined up properly 鈥� all of those things are different.鈥�

Cox says that had the flight landed on the taxiway, it would have been a tragedy of 鈥渁n almost unimaginable size.鈥�

He commends the quick decision making of the other pilots for speaking up, saying 鈥渢he aviation system depends on a lot of people being aware and willing to speak up, and in this case they did that.鈥�

'Unlikely a crash would have occurred'

Aviation expert Phyl Durdey, meanwhile, declined to speculate on what may have caused the incident, saying only that the incident was 鈥渟urprising.鈥�

鈥淎ir Canada pilots are some of the best trained pilots in the world, and for something like this to happen, it鈥檚 unfortunate,鈥� Durdey said.

At the time of the incident, the pilot was on a visual approach, which Durdey says should have made it quickly evident that he was improperly lined up with the taxiway.

鈥淎 taxiway is going to be about 75 feet wide and have green lights on either side, green or blue lights on either side,鈥� Durdey said.

鈥淭he runway is 200 feet wide and has centre line lights, side lights, approach lights, there's no way you can mistake the difference between a taxiway and a runway.鈥�

Despite the seemingly close call, Durdey agrees that it鈥檚 unlikely that a crash would have actually occurred.

鈥淚f they had determined something was wrong, they would've turned around,鈥� he said.

With a report from CTV's Tracy Tong