Canadian investigators have disclosed that an Air Canada Airbus A319 touched down at San Francisco despite its crew's not hearing the landing clearance.
The aircraft (C-FZUJ) had been operating from Toronto on 3 October, says Transportation Safety Board of Canada.
It states that San Francisco controllers cleared the aircraft to land.
"However, it was not heard by the flight crew because the approach frequency had not been switched to the tower frequency," it adds.
The aircraft landed without further incident.
None of the 110 occupants was injured, says the safety board. Air Canada is conducting an investigation into the event.