The entire airline's check-in and operational systems were affected by the issue, including its customer service phone lines and rebooking function. The airline planned to fly all of its long-haul flights from Heathrow, with some delays, and some cancellations and delays on short-haul flights.
"The terminals at Heathrow and Gatwick have become extremely congested and we have canceled all flights from Heathrow and Gatwick before 6 pm United Kingdom time today, so please do not come to the airports".
Thousands of angry British Airways passengers on Sunday confronted long lines, confusion and canceled flights at London's Heathrow and Gatwick airports as the airline worked to fix computer systems crippled by a massive global IT failure.
BA advised customers to continue checking the status of their flight on its website www.ba.com before travelling to the airport.
BA is hoping to operate a near-normal service on Bank Holiday Monday, but is telling passengers who do not wish to risk disruption: "Even if your flight is still operating, you can get a full refund or rebook to travel up to the end of November".
BA Chief Executive Alex Cruz had said it was believed "the root cause [of the computer problems] was a power supply issue".
British Airways (BA) had earlier said it plans to resume most of its flights out of Heathrow and Gatwick airports on May 28, following major IT system disruption that had grounded planes since May 27. Thousands gather in Terminal 5 departure lounge, at London's Heathrow Airport after flights were canceled due to the airport suffering an IT systems failure.
In September a year ago BA apologized to passengers for check-in delays caused by operational glitches that delayed flights at Gatwick and Heathrow, in a repeat of a similar incident that affected London-area flights for the airline last July.
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Airport staff had handed out the yoga mats, as well as thin blankets, for people who were stuck there overnight, she added.
The Financial Times, however, is reporting that almost a third of British Airways flights have been canceled today as well.
"We rebooked for Venice for tonight, which they also have canceled now", she told Sky News.
Passengers were asked to contact the airline in order to locate their luggage, after many were forced to leave Heathrow without claiming their bags.
She said there were "just queues everywhere" and her plane was cancelled at the last minute.
The Guardian reported that the IT failure had caused severe disruptions to British Airways global operations.
The airline said its terminals at Heathrow and Gatwick became "extremely congested" due to the computer problems.
"This is a very serious problem, they should have been able to switch to an alternative system - surely British Airways should be able to do this", he said.