More than one-quarter of Air Canada flights experienced delays on Friday as the airline worked to return service to normal following a technical malfunction the previous day.

Air Canada had warned travellers early Friday morning they should be prepared for further flight disruptions. In its daily travel outlook, the carrier said that while its IT system was stable, flights may be affected at nine of Canada’s busiest airports, including Toronto’s Pearson, Montreal, Vancouver and Calgary.

Thursday’s outage led to more than 500 flights – over three-quarters of its trips – to be delayed or cancelled on the day, creating what the airline said were “rollover effects” just prior to the weekend.

A total of 144 Air Canada flights, or 27% of the airline’s scheduled load, had been delayed Friday as of around 4:30 p.m. EDT, along with 33 cancellations, according to tracking service FlightAware.com.

An additional 56 flights with Air Canada Rouge saw delays, one-third of its daily load, plus 23 cancellations.

“Air Canada has stabilized its communicator system and it is functioning normally. However, due to the effects of Thursday’s IT issues on our schedule, some flights may be delayed this morning as we reposition aircraft and crew,” it said in an emailed statement.

“Customers are advised to check the status of their flight before going to the airport. Our flexible travel policy remains in effect for customers to change their travel plans at no charge.”

The airline did not clarify when it expected its flight schedule to fully return to normal.

Thursday’s disruption, sourced to the system used by the airline to communicate with aircraft and monitor their performance, came one week after Air Canada grounded its planes for about an hour when the same system experienced a separate issue.

That day, 241 Air Canada flights – 46% of its trips – were delayed, according to FlightAware. Another 19 flights were also cancelled.

Air Canada said it has been in the process of upgrading the communicator system.