British Airways said "significant technical issues" had resulted in a number of flight cancellations and disruption across its operation on Friday.
The airline said the problem, which was affecting its website, app, and airport operations, had not been caused by a cyber attack.
"We are experiencing significant technical issues this evening which are affecting the running of our operation and regrettably has led to the cancellation of a number of flights," it said in a statement.
It was working to get as many flights away as possible, it said, and customers on flights that had not been cancelled could still check in at the airport.
The airline, owned by IAG ICAG.L, was hit by a major computer system failure in 2017 that stranded 75,000 passengers over a holiday weekend, sparking a public relations disaster and pledges from the carrier that it would do better in future.
Users on Twitter posted messages on Friday asking BA when the problem would be fixed, with one customer showing a video of lengthy queues at check-in for what he said was a Miami to London flight, while another user posted pictures of blank screens.
Not seen this before at Heathrow. Staff doing their best, amid a lot of cancellations caused by the @british_airways IT issue. pic.twitter.com/OadreQMfF8
— George Eykyn (@geykyn) February 26, 2022
All stranded at 5am at the airport. All flights cancelled #BritishAirways pic.twitter.com/m6FseDCv2M
— ana.o (@ana_ouriques) February 26, 2022
BA and Virgin Atlantic began routing flights around Russian airspace on Friday after London and Moscow banned each other's airlines in tit-for-tat retaliation over the Ukraine invasion.
Britain's National Cyber Security Centre (NCSC), a part of the GCHQ eavesdropping intelligence agency, had warned companies and organisations to bolster their online defences against cyber attacks after Russia invaded Ukraine.
The airline said it would make decisions about its schedule on Saturday as soon as it could.
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