Air Traffic controllers say problems they were experiencing over the North of England and Scotland have been resolved.
Operations are back to normal, National Air Traffic Services (Nats) said.
Flights had been disrupted for much of the day, with average delays of up two hours.
Equipment used by the air traffic control centre in Prestwick, Ayrshire, is thought to have failed.
Prestwick controls flights over Scotland, the north of England and Northern Ireland.
Manchester, Liverpool, Leeds Bradford, Glasgow and Newcastle were among airports affected.
The new control centre at Prestwick became fully operational a year ago.