The Transport Secretary has told MPs she did not believe the air traffic control problems that have caused chaos for hundreds of thousands of passengers were “unavoidable”.
Travellers were caught up in the disruption after hundreds of flights were cancelled following the Nats technical issue on Tuesday.
Cancellations and delays continued on Wednesday as airlines dealt with knock-on impacts at airports including Heathrow, Gatwick, Manchester and Stansted.
Addressing the Commons on Wednesday afternoon, Heidi Alexander said: “A four-hour air traffic outage yesterday left hundreds of thousands of passengers facing cancellations, diversions, and delays.
“I would like to apologise wholeheartedly to passengers for this disruption.
“We often take for granted the way in which our aviation system just works, but yesterday that was not the case.
“Safety must remain air traffic controllers’ overriding priority, and this morning I have spoken to Nats chief executive Martin Rolfe, who informed me this outage was due to a technical issue at their Swanwick site.
“So, while my understanding from Nats is that we can rule out a cyber attack on this occasion, I do not believe this issue was unavoidable.
“We also spoke this morning about how Nats responded to resolve and minimise the disruption as quickly as possible, and I am grateful to the airports and airlines who responded straight away.”
Ms Alexander said she had asked the Civil Aviation Authority to conduct an independent review into the incident, which is due to report to her within six months.
Aviation analytics company Cirium said as of Wednesday at 3pm, more than 300 flights had been cancelled or not taken off that day and more than 2,000 flights over the last two days had been affected.
British Airways said the fault had forced it to cancel almost 550 of its flights, which had impacted more than 85,000 passengers.
The airline said it was “incredibly sorry” to its customers and that the issue had been “entirely out of our control”.
Nats has apologised for disruption to passengers and airlines, for which Mr Rolfe said he took “full responsibility”.
The chief executive has come under fire from Wizz Air following the fault, while Ryanair called on Mr Rolfe to resign.
Earlier on Wednesday, Downing Street said the Government still had confidence in Mr Rolfe.
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