More than a third of British Airways flights from Heathrow have been cancelled as disruption to passengers enters a second day.
The airline was hit by a worldwide computer system power failure on Saturday, causing cancellations and delays for thousands of passengers.
Sunday departures from Gatwick are delayed, but none have been cancelled.
The airline urged people to check the status of flights before before travelling to the airport.
Heathrow Airport is providing an updated schedule on its website, as is Gatwick.
BA apologised to customers for the issue, which is thought to have been caused by a problem with the IT system’s power supply.
Between 06:00 and 11:00 BST on Sunday, 143 British Airways flights were scheduled to depart from London Heathrow and Gatwick Airport.
So far 90 flights have left Heathrow and 36 have been cancelled.
At Gatwick, one BA flight has been cancelled. Other flights are returning to schedule.
The airline is liable to reimburse thousands of passengers for refreshments and hotel costs.
Customers displaced by flight cancellations can claim up to £200 a day for a room (based on two people sharing), £50 for transport between the hotel and airport, and £25 a day per adult for meals and refreshments.