In this Tuesday, Jan. 10, 2017 file photo, British Airways planes are parked at Heathrow Airport during a 48hr cabin crew strike in London. Air travelers faced delays Saturday, May 27, 2017 because of a worldwide computer systems failure at British Airways, the airline said. BA apologized in a statement for what it called an "IT systems outage" and said it was working to resolve the problem. It said in a tweet that Saturday's problem is global.(AP Photo/Frank Augstein, file) British Airways said Sunday it was still working to restore its computer systems but hoped to resume flights from London airports, a day after a global IT failure crippled its services.
The airline said that it hopes to operate a "near normal schedule" at Gatwick and the "majority of services" from Heathrow on Sunday.
"Work continues to restore all of our IT systems but we expect some further disruption today," BA said in a statement.
BA canceled all flights from both airports Saturday, upending the travel plans of tens of thousands of people on a busy U.K. holiday weekend. It blamed a power supply issue for the outage and said there was no sign it was under cyberattack.
BA operates hundreds of flights from Heathrow and Gatwick on a typical day—and both are major hubs for worldwide travel.
On Saturday, passengers at Heathrow and Gatwick faced long lines at check-in counters and the failure of both the airline's website and its mobile app. BA said the crash also affected its call centers.
Many passengers complained about a lack of information from the airline.
"Some 80-year-old lady was standing around waiting for announcements, et cetera, and she fell over," said Londoner Terry Page, who managed to get on one of the last flights from Heathrow to Dallas-Fort Worth Saturday. He and other passengers arrived, but their luggage did not.
Passengers stand with their luggage outside Terminal 5 at London's Heathrow airport after flights were canceled due to the airport suffering an IT systems failure, Saturday, May 27, 2017. British Airways canceled all flights from London's Heathrow and Gatwick airports on Saturday as a global IT failure upended the travel plans of tens of thousands of people on a busy U.K. holiday weekend. (AP Photo /Jo Kearney) "We helped her up and she said 'I'm just so tired,'" Page said. "It's been a terrible, terrible day."
The airline said it would refund or rebook customers affected by the IT failure.
While not that frequent, when airline outages do happen, the effects are widespread, high-profile and can hit travelers across the globe.
BA passengers were hit with severe delays in July and September 2016 because of problems with the airline's online check-in systems.
In August 2016, Delta planes around the world were grounded when an electrical component failed and led to a shutdown of the transformer that provides power to the airline's data center. Delta said it lost $100 million in revenue as a result of the outage.
In this image taken from the twitter feed of Emily Puddifer, a view of Terminal 5 departure lounge, at London's Heathrow airport after flights were canceled due to the airport suffering an IT systems failure, Saturday, May 27, 2017. British Airways canceled all flights from London's Heathrow and Gatwick airports on Saturday as a global IT failure upended the travel plans of tens of thousands of people on a busy U.K. holiday weekend. (Emily Puddifer via AP) 
In this image taken from the twitter feed of Emily Puddifer, people gather in the Terminal 5 departure lounge, at London's Heathrow airport after flights were canceled due to the airport suffering an IT systems failure, Saturday, May 27, 2017. British Airways canceled all flights from London's Heathrow and Gatwick airports on Saturday as a global IT failure upended the travel plans of tens of thousands of people on a busy U.K. holiday weekend. (Emily Puddifer via AP)
Explore further: BA outage creates London travel chaos; power issue blamed