UK flight schedules resume amid warning of further delays
UK flights returning to normal after software glitch
(about 9 hours later)
Airline passengers have been warned there could be further disruption today due to Saturday's technical fault at the National Air Traffic Service.
Normal service is being resumed at the UK's major airports after cancellations and delays during the weekend.
Hundreds of flights were delayed or cancelled and Nats said there might be a knock-on effect for services.
Thousands of passengers had travel plans disrupted when a software failure struck the air traffic control centre at Swanwick early on Saturday morning.
But airports across the UK say they are hoping to return to normal operations after the telephone glitch.
The glitch was fixed by 19:30 GMT.
The software failure at Nats Swanwick centre in Hampshire was fixed after about 12 hours.
On Sunday, Heathrow - the worst affected airport - reported 18 cancellations, while Gatwick and Stanstead said they had been operating flights smoothly all day.
Thousands of passengers faced cancellations and long waits after the Nats internal phone system broke down, resulting in it being able to handle about 20% fewer flights than on a normal Saturday.
The breakdown occurred when the National Air Traffic Service (Nats) computer system was making the switchover from the quieter night time mode to the busier daytime setup.
Nats announced at 19:30 GMT on Saturday that the problem had been resolved.
It was unable to handle the normal volume of flights for a Saturday and said it dealt with 20% fewer than it would have expected.
Juliet Kennedy from Nats said controllers were now able to manage normal levels of traffic, but added passengers could potentially continue to experience some delays because of the earlier problems.
Nats stressed that safety was never at risk.
"The system from an air traffic perspective is already back to normal," she told the BBC.
'No compensation'
"I recognise of course that airlines have their schedules disrupted because they end up with aeroplanes in the wrong place so it may take them some time to restore their operation to normal."
A spokeswoman for Heathrow Airport, which had cancelled 228 flights by 18:55 GMT on Saturday, said the few cancellations on Sunday were "mostly due to crew displacement".
Lisa Smith, who is trying to travel to Lapland with her son Thomas, was among those still facing delays at Norwich Airport.
"Apart from that we are pretty much running as normal," she added.
"We came here two years ago to go and the plane was delayed then and then it was cancelled because there was too much ice on the runway, so it's a little bit like deja-vu," she said.
A Stansted Airport spokesman said there had been no problems on Sunday, while a Gatwick Airport spokeswoman said: "We've been back to business as usual from this morning."
The worst-affected airport, Heathrow, which had cancelled 228 flights by 18:55 GMT on Saturday, said there were no planned changes to its schedule.
Airports affected on Saturday also included Manchester, Birmingham, Leeds Bradford, Doncaster Robin Hood, Belfast International, Dublin and Newcastle.
But along with many other airports it was advising passengers to check their flight's status before travelling.
Overnight, airports were advising passengers to check their flight's status before travelling.
Airports affected on Saturday also included Gatwick, Stansted, Cardiff, Belfast and Glasgow.
By 16:00 GMT on Saturday, Nats said it had handled 2,576 flights compared with 2,905 at the same time last week.
By 16:00 GMT on Saturday, Nats said it had handled 2,576 flights compared with 2,905 at the same time last week.
Ryanair said 300 of its flights had been delayed on Saturday with 12 cancelled, and called on the Civil Aviation Authority (CAA) to act.
Ryanair said 300 of its flights had been delayed on Saturday, with 12 cancelled.
"While we acknowledge problems can occur, where is the contingency?" it said in a statement.
It criticised Nats in a statement, saying: "While we acknowledge problems can occur, where is the contingency?"
By Saturday evening Gatwick airport said it was "returning to normal operations". A spokeswoman said it was "not expecting serious disruption" on Sunday.
Delays at Stansted on Saturday averaged two to four hours, a spokeswoman for the airport said.
Delays at Stansted averaged two to four hours, a spokeswoman for the airport said, adding that schedules were expected to return to normal on Sunday but warning there could be "minor delays".
Eurocontrol - which manages European air safety - said around 1,300 flights, or 8% of all air traffic on the continent, had been "severely delayed".
Eurocontrol - which manages European air safety - said around 1,300 flights, or 8% of all air traffic on the continent, had been "severely delayed".
Belfast International Airport and Dublin Airport both reported a number of cancellations.
The Association of British Travel Agents said that frustrated passengers would not be entitled to compensation.
Manchester Airport had been "only minimally affected" by the problem while Leeds Bradford, Birmingham, Doncaster Robin Hood and Newcastle airports all reported minor delays, with flights to London worst affected.
"In a situation like this it's not actually deemed to be the airlines' fault," head of communications Victoria Bacon told BBC News.
Nats said the problem at Swanwick arose in the early hours of Saturday morning when the night-time operation failed to properly switch over to the daytime system.
Nats said in a statement on Saturday evening: "The reduction in capacity has had a disproportionate effect on southern England because it is extremely complex and busy airspace and we sincerely regret inconvenience to our airline customers and their passengers."
The software failure happened when the 23 controllers working overnight were due to hand over to the 125 on the day shift at around 06:00 GMT.
The communications failure was a totally different issue to a software problem that saw flights in southern England delayed due to "technical problems" in July, according to the BBC's transport correspondent Richard Westcott.
The problems prevented staff opening new control positions to deal with busier daytime traffic.
A Nats spokesman said controllers used the system to speak to other air traffic agencies both in the UK and Europe and it was "very complex and sophisticated... not simply internal telephones".
The BBC's transport correspondent Richard Westcott said it was a totally different issue to a software problem that saw flights in southern England delayed due to "technical problems" in July.
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