U.S. officials are investigating after an Air Canada flight from Montreal landed at a San Francisco airport, despite being told to divert due to a potential close call.

The U.S. Federal Aviation Administration says Air Canada flight 781 failed to respond to air traffic control instructions to delay landing, after initially being told it was safe to do so. Controllers feared the flight would come too close to another aircraft on the runway, but it nevertheless landed safely at San Francisco International Airport Sunday night.

An FAA spokesperson said the air traffic controllers repeatedly tried to contact the flight crew, first by radio and then through a flashing light signal. In an audio recording of the incident, controllers can be heard telling the flight five times to “go around” – an order that notifies pilots not to land.

Air Canada says the flight landed because it had been given clearance to do so.

“Upon landing the crew was informed the tower had attempted unsuccessfully to contact the aircraft, however the message was not received by the crew,” Air Canada told ABC News.

In the , the Air Canada crew can be heard reporting communications trouble after landing.

“There’s a problem with the radio here,” one of the pilots says.

“That’s pretty evident,” the controller replies.

Aviation expert Phyl Durdey says it’s rare for an aircraft’s communications system to fail, but the pilots likely would have been able to spot a potential collision and avoid it without being told.

“If there was an aircraft on the runway they would have seen it and they would have gone around themselves,” he told 鶹ý Channel on Tuesday. “Air Canada pilots are very well trained and I think they would have avoided any incident.”

He added that it’s not uncommon for the flight crew and air traffic control to be out of touch during the actual landing process.

“If Air Canada didn’t hear anything it wouldn’t have been out of the normal,” he said. “Once they landed and didn't get any instructions, then they would have realized there was a radio failure and they would have switched to their secondary radio.”

Durdey says investigators will interview the pilots and review recordings from the cockpit as part of their review of the incident.

He adds that the flight crew will probably continue flying in the wake of the incident.

“There’s nothing that the air crew did wrong,” he said.

“The only concern that air traffic control would have had was that the aircraft that landed before them hadn't cleared the taxi way as fast as they should have, so they tried to initiate a go-around. But there was no danger – perceived danger, anyway,” Durdey told CTV Montreal.

It’s the second time in four months that an Air Canada plane has had issues at San Francisco International Airport. Another near-collision occurred at the same airport in July.

Durdey says the two incidents are merely a “coincidence,” because a communications failure could happen to any airline.

“It just happened to be an Air Canada aircraft,” he said.