An air traffic control glitch has led to disruption at both Belfast International and Belfast City airports on Saturday.
Passengers faced cancellations as well as delays due to problems with the internal telephone system as the National Air Traffic Control Service (NATS) at Swanwick in Hampshire.
The technical difficulties were not expected to be resolved before 6pm.
Thousands of passengers were affected right across the UK with some flights from the Republic of Ireland also disrupted.
Anyone flying in or out of the UK on Saturday evening is being advised to check with their airline for the latest advice.