SAN FRANCISCO INT’L AIRPORT (KPIX 5) – The Federal Aviation Administration is investigating another incident involving the landing of an Air Canada flight at San Francisco International Airport on Sunday night.

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According to the FAA, Flight 781 from Montreal was cleared to land on runway 28-R by air traffic control. The tower then then repeatedly instructed the crew to execute a “go-around,” since officials were unsure that another plane would be clear of the runway.

Within 30 seconds, the flight crew was told to go around five times.

Officials said the Air Canada crew did not acknowledge the instructions after being told multiple times to go around, prompting an airport supervisor to use a red light gun to alert the crew.

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The Air Canada jet was able to land safely at 9:26 p.m. A radar replay showed the other plane was clear of the runway when the Air Canada jet landed.

Afterwards, the crew told the tower they had a radio problem.

Retired Captain Ross Aimer says he flew into SFO hundreds of times during his career.

His explanation for this confusion?

“I’m afraid these fellows were almost clueless,” said Aimer.”I would look back at these guys scheduling practice, see if they’re dead tired or whatever it is. This is sloppy radio discipline.”

That was unsettling news for air Canada passengers like Paul Child who are already nervous about flying.

“I just don’t want anything to go wrong, to be honest with you,” said Child. “And I’ve got to fly back from Toronto next week with Air Canada. So yeah, it’s a bit of a worry.”

In a written statement, Air Canada told KPIX 5, “After receiving proper clearance to land it proceeded to do so and landed normally. 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 is investigating the circumstances.”

Sunday night’s incident took place three months after another Air Canada jet came within seconds of crashing into two other planes full of passengers, when the pilot almost landed on the taxiway. In that case, the plane made a go-around and landed safely.