The head of U.K. air traffic control services has said he does not believe a cyber attack caused the software issue that disrupted hundreds of thousands of passengers with flight cancelations on Tuesday.
"Obviously we will be doing a very thorough and full investigation. We have at this point ruled out cyber, we don't believe it was a cyber attack," Martin Rolfe told BBC Radio 4's Today program on Wednesday.
"I don't believe we've ever seen an incident happen more than once, so this will be something different that we've never seen in 50 years of operation," he added.
Flight tracking website Flightradar24 said 1,300 flights were canceled to and from U.K. airports on Tuesday, and that 177 flights had been canceled as of early Wednesday morning.
Nearly all the cancelations were at London's Heathrow, one of Europe's busiest airports. London's Stansted and Gatwick airports, Birmingham and Manchester were also severely impacted.