A number of flights to and from Ireland were delayed today due to technical issues at Britain's Air Traffic Control in Swanwick, Southern England.
Intending passengers were advised to check with their airline for updates in advance of travelling.
A National Air Traffic Control Services spokesman said: "The problem that arose this morning with the ground communications system in the area control operations room at NATS Swanwick has now been resolved and operations are returning to normal."
The problem occurred when the 23 controllers on a night shift at Swanwick handed over to the 125 controllers on the day shift at about 6am.
It was not until 7.30pm that NATS announced that the problem had been fixed.
NATS said that by 4pm they had handled 2,576 flights compared with the 2,905 flights that were dealt with at the same time last week.
This means that they were operating at about 88% of normal capacity.
Both Aer Lingus and Ryanair have said passengers experienced delays this evening but airlines hope that flights will be back on schedule by tomorrow morning.
Aer Lingus has said those affected by flight cancellations can change their booking to the next available flight free of charge.