Thousands of passengers suffered from delays and cancellations over the weekend after a system failure at the National Air Traffic Service's (NATS) Swanwick control centre.
In a notice at 12:30pm on Saturday, NATS said that the problem was related to the internal telephone system used by its air traffic controllers and would take about six hours to resolve.
"At night, when it's quiet, sectors of airspace are combined. As it gets busier in the daytime the sectors are split out again and additional control positions are opened to meet the traffic demand. Because of the problem with the internal telephone system, it was not possible to open the additional control positions this morning, resulting in a significant reduction in capacity in some areas of UK en-route airspace," NATS said.
The company insisted that safety had not been compromised at any time.
It said that it handled about 1,700 flights on Saturday by midday - 300 less than the 2,000 flights it normally would have handled.
Later on Saturday, NATS said that the problems had been resolved and that operations were returning to normal.
"To be clear, this is a very complex and sophisticated system with more than a million lines of software. This is not simply internal telephones, it is the system that controllers use to speak to other air traffic control agencies both in the UK and Europe and is the biggest system of its kind in Europe," the organisation claimed.
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