Just three months after an Air Canada flight nearly landed on a crowded taxiway at San Francisco’s SFO, another Air Canada flight appears to have disregarded orders from air traffic control to abort their landing.

The U.S. Federal Aviation Administration (FAA) said Tuesday that it was investigating an Air Canada flight from Montreal that landed at SFO Sunday, despite being told to execute a go-around.

According to Reuters, the flight crew received clearance for landing, but reportedly did not receive a subsequent message that had instructed the plane not to land as it wasn’t certain that an earlier arrival was completely clear of the runway.

When air traffic control did not receive a response from the flight crew, it reportedly used a flashing red light gun, which is standard protocol when there is no radio response.

FAA Spokesman Ian Gregor told Reuters that, “The Air Canada crew did not acknowledge any of the controller’s instructions.” Audio from the control tower indicates that the flight had been told six times to abort its landing. A spokeswoman for Air Canada, however, contended that the message had never been received by the flight crew.

Following the landing, the Air Canada (AIDIF) crew said they had a radio problem, which is the FAA is now investigating.