The chaos that hit UK airports was clearing last night - but 38 flights have been cancelled at Heathrow this morning.
While air traffic control company Nats declared its systems are back to full operational capacity, the flight mayhem at some of the nation's busiest thoroughfares could still be a reality for some passengers.
Dozens of flights were cancelled and many others delayed after a computer failure at Nats' company headquarters at Swanwick, Hampshire, yesterday afternoon.
A spokesman for Heathrow said 38 flights are cancelled before 9.30am today "as a knock on from yesterday".
Nats said at about 8pm last night: "Following a technical fault with the flight data system used by air traffic controllers at Swanwick, Nats can confirm that the system has been restored to full operational capability and a thorough investigation is continuing to identify the root cause.
"Although operational restrictions applied during the failure have been lifted, it will take time for flight operations across the UK to fully recover so passengers should contact their airline for the status of their flight. We apologise for the impact that this issue has had, and the delays and inconvenience caused."
The company has ruled out a power outage as the source of the glitch at Nats' state-of-the-art £700 million centre.
Airports as far north as Aberdeen and Edinburgh were affected by the computer problem. Other airports that reported delays yesterday afternoon included Manchester, Stansted and Luton.
Budget flier easyJet said last night: "EasyJet has had to cancel 10 flights to and from London Gatwick, however all aircraft which were earlier diverted have all now continued to their original destinations. In addition, it is likely that other flights to and from the south of the UK will suffer delays this evening."
The airline said it had cancelled two Gatwick-bound flights scheduled for today.
Gatwick Airport said yesterday evening: "Some cancellations should be expected and passengers are advised to contact their airline for the latest flight information.
"All departing flights were affected for a period but the situation is improving and we (are) hoping to restore a near normal service later this evening."
At Heathrow, a spokesman said yesterday there had been 70 cancellations out of about 1,300 scheduled flights. "They're coming back to normal now," he said.
The airport put extra staff on duty and were due to be open later than usual to try to get stranded passengers in the air.
In a statement on its website yesterday evening British Airways said: "While the system is slowly recovering, we anticipate the knock-on effects to take some time to resolve. Additional staff have been brought in to assist our customers and we have booked a large number of hotel rooms to accommodate those who have been disrupted."
Birmingham Airport had experienced delays but reported its air traffic was back to normal by 8pm.
Transport Secretary Patrick McLoughlin described the disruption as unacceptable.
He said: "Any disruption to our aviation system is a matter of the utmost concern, especially at this time of year in the run up to the holiday season.
"Disruption on this scale is simply unacceptable and I have asked Nats for a full explanation of this evening's incident. I also want to know what steps will be taken to prevent this happening again."
Press Association sports reporter Simon Peach, who landed at Heathrow yesterday afternoon from Istanbul, said passengers on his plane had been told they could not have their hold luggage back yet.
"There are large queues at baggage reclaim, and there was an announcement that everyone on my British Airways flight could not have their luggage now. The airline will be sending it by courier to people's homes," he said.
"This is affecting people flying in as well as flying out and will cost the airlines money - it is not a cheap mistake."
Among those still queuing at Heathrow last night was Kevin Read, 38, an HGV driver from Bristol.
He was there to pick up his wife Phennapha and baby son Brandon.
"They are flying back from Thailand and were supposed to arrive at 5pm," he said. "The board says the flight was cancelled but I heard someone say that it's been diverted to Copenhagen. It's a nightmare situation for my wife - she's travelling alone with a nine-month-old baby and all the luggage.
"There's a lot of Heathrow staff around and they are being helpful, but there's not many BA staff here and they are the ones with information to do with flights.
"I queued for an hour at the customer service desk but they couldn't tell me anything."Suggest a correction