The Microsoft outage has caused 1,078 flight cancellations worldwide, according to aviation analytics firm Cirium, but it warned there could be more.

The outage has affected the online check-in and reservations systems of a number of airlines, including Ryanair, American Airlines, British Airways, Kenya Airways, Delta Air Lines and Qantas.

BA warned of disruption to some flights but did not give specific numbers.

“Due to the widely-reported global Microsoft IT outage, some of our flights may experience disruption today. Our teams are working hard to manage the impact of this issue as quickly as possible,” it said.

Virgin Atlantic said its services were operating as scheduled.

Singapore Airlines said its service centre in Singapore and reservation hotlines are currently experiencing technical issues but there is currently no impact on SIA flights, which are operating as scheduled.

The outage has happened on the busiest day for UK flight departures this year, with over 3,214 departures alone – the highest number of daily departures since October 2019.

Over the weekend – Friday 19 – Sunday 21 July – a total of 9,075 flights are scheduled to depart UK airports – equating to over 1.6 million seats, according to Cirium.

Ryanair said online booking and check-in are currently unavailable but told passengers to check in at the airport. 

EasyJet said customers ‘should expect longer than usual airport queues’.

Air traffic control provider National Air Traffic Services (NATS) said it was unaffected by the IT outage.

“We are working closely with airports and airlines to understand how best we can support them and their customers. We advise passengers to check the status of their flight with their airline,” it said.