For two tense minutes on Sunday night, an Air Canada flight bound for San Francisco mysteriously went silent.

Fearing there was another plane on the runway, an air traffic controller frantically instructed the plane to abort landing. The order was issued six times. Each time, Air Canada did not respond.

A supervisor was then dispatched to flash a red light gun towards the jet to try to get the pilot’s attention in a desperate bid to alert the crew not to land.

The plane landed anyway — at 9:26 p.m. local time. The pilot explained they were having a problem with their radio.

“That’s pretty evident,” the controller at San Francisco International Airport responded.

Radio conversation between SFO air traffic control and Air Canada flight 781

Details of the incident involving Air Canada Flight 781 from Montreal were heard in a recording posted on the website LiveATC.net , and recounted by the Federal Aviation Administration.

It’s the second time in three months Air Canada has come under fire for an improper landing at the same airport. Sunday’s flight involving an Airbus A320 is being investigated by Canadian and U.S. aviation officials for a serious communication failure.

“I don’t understand it,” said Greg McConnell, chairman of the Canadian Federal Pilots Association. “If air traffic control tells you to pull up and go around that’s a directive and you simply do it.”

After this incident, McConnell believes Canada should conduct an audit of the aviation industry, “before something catastrophic happens.”

FAA spokesman Ian Gregor told the Star in an email the inbound Flight AC781 was initially cleared for landing — this instruction was acknowledged by the crew when they were approximately 10 kilometres away from the airport.

Peter Fitzpatrick, an Air Canada spokesperson, also said the flight proceeded to land normally, after receiving proper clearance to do so.

“Upon landing, the crew was informed the tower had attempted unsuccessfully to contact the aircraft,” he said in an email to the Star. “However the message was not received by the crew.”

Gregor said a radar replay showed the previous arrival was clear of the runway when the Air Canada flight landed.

“I find it very strange that an aircraft that’s been cleared to land on the runway suddenly has some kind of radio failure,” said McConnell.

McConnell, and Ross Aimer, CEO of Aero Consulting Experts, explained that modern aircrafts have two or three radios working at all time in a plane: a primary, a secondary, and a back up.

“[Pilots] try to maintain a very strict radio discipline,” said Aimer. “When I don’t hear a transmission within 30 seconds in a very busy airport like San Francisco, like Toronto, I know something’s wrong.”

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McConnell agreed. “Generally you switch to the other radio,” he said. “If you notice there are no radio transmissions being made, you simply call for radio check.” McConnell said this was part of a pilot’s standard protocol.

Aimer hypothesizes that this may have been “a man-made failure.”

“Perhaps, they may have inadvertently switched their frequency to the ground control, for example,” he said. “Radios these days don’t fail that easy unless we mess with it.”

In an emailed statement to the Star, Chris Praught, spokesperson for the Air Canada Pilots Association, said the flight crew is working with the FAA to determine what happened.

Transport Canada has also been made aware of the incident. In an emailed statement, they told the Star they are “in contact with Air Canada to establish facts and verify compliance with safety regulations.”

In July, at the same airport, an Air Canada jet with 140 people on board nearly landed on a taxiway where four other planes were waiting to depart, avoiding a near catastrophic collision.

In that instance, the flight mistook the taxiway for a runway and pulled up and missed two planes by just 30 metres.

“Perhaps this is systemic in nature,” said McConnell. “With the frequency with which these things are happening, perhaps it’s time for a full-scale assessment and audit.”

In June, the federal government’s Standing Committee on Transport, Infrastructure and Communities released a report on aviation safety in Canada and made 14 recommendations asking Transport Canada to make a thorough review of flight training, safety inspections, and pilot certifications.

One recommendation asks Transport Canada to “invite the International Civil Aviation Organization to conduct a comprehensive audit of Canada’s civil aviation oversight system.”

Transport Canada agrees with this recommendation and has planned the audit for 2020.

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