Flights between Ireland and the London area were suspended for a time this morning after a suspected computer glitch shut down the British air-traffic control system.
The problem was identified and fixed and flights resumed later. However, a backlog is expected to cause major flight disruption.
Airport departures across Britain were suspended after the problem emerged after 6 a.m. A manual system was put into operation to allow aircraft already in the air to land safely.
Aer Rianta said 21 departures were affected in Dublin and eight inbound flights were disrupted. "There will be knock on effects right through the day," a spokesman said.
In Shannon five inbound and outbound flights were affected, while four flights were disrupted in Cork Airport.
The spokesman said some flights from Ireland to Paris could also be affected because they pass through British airspace. Passengers travelling from Ireland are advised to check in as normal and contact their airline.
A spokesman for Britain's National Air Traffic Services (NATS) said: "We are fully operational now. We are now dealing with the backlog of delays. It affected all airports in England and Wales."
"It was a problem with the flight data processing system. We are looking into that now. It was not sabotage," he added.
A spokesman for British Airways said flights were resuming at London's Heathrow, the world's busiest international airport, but there was a huge backlog of traffic.
