Tens of thousands of passengers were caught up at several airports.
The UK’s main air traffic control provider said widespread disruption to flights was not caused by a cyber attack.
Flight monitoring website Flightradar24 said 1,300 flights had been cancelled to and from UK airports on Tuesday after a system issue hit Nats, the National Air Traffic Service, which provides air traffic control services to 15 UK airports.
Tens of thousands of passengers were caught up in the chaos, which continued on Wednesday with cancellations and delays expected as airlines deal with the knock-on impacts at airports including Heathrow, Gatwick, Manchester and Stansted.
According to FlightRadar, 246 flights had been cancelled at Heathrow Airport by 6am on Wednesday, while Gatwick passengers faced 33 cancellations.
Nats’ chief executive officer Martin Rolfe told BBC Radio 4’s Today Programme: “We will be doing a very, very thorough and full investigation.
“We have at this point ruled out cyber. We don’t believe it was a cyber attack.”
