HUNDREDS of flights were grounded today as a volcanic ash cloud loomed over Ireland and parts of Scotland.
Thousands of travellers faced further misery as a six hour no-fly zone was imposed across the Republic and Northern Ireland.
Airspace over the Outer Hebrides was also closed to operations last night.
Airlines warned passengers not to travel to airports without checking on-line that their flight is departing.
Flights from continental Europe will not be impacted by the plume of ash from Iceland’s volcano Eyjafjallajokull, which caused travel chaos when it forced the closure of much of Europe’s airspace for almost a week last month.
The Irish Aviation Authority (IAA) and UK’s Civil Aviation Authority (CAA) are monitoring the latest situation after it was predicted ash concentrations would exceed acceptable engine manufacturer tolerance levels.
Eamon Brennan, IAA chief executive, said that, based on the new regime imposed in Europe last week, officials had no choice but to impose a no-fly zone from 7am to 1pm.
"The decision is based on the safety risks to crews and passengers as a result of the drift south of the volcanic ash cloud caused by the north easterly winds," he added.
The situation will be reviewed again at 9am.
Almost 440 flights had been due to depart and fly in to Dublin Airport throughout today, with more scheduled from Shannon, Galway, Sligo, Knock, Donegal, Cork and Kerry.
Ryanair cancelled all its flights to and from the Republic of Ireland, Belfast and Derry City from 6am to 2pm, with Aer Lingus suspending all Irish services to the UK and Europe until 1pm.
However all but one of its transatlantic services to the US will operate, subject to delays.
Aer Arann was forced to cancel services to and from Derry and Donegal airports last night while easyJet warned of possible disruptions on services to Northern Ireland and Scotland.
Irish Ferries said it had space on its services between Ireland and the UK and Ireland and France.
Elsewhere the CAA said airspace over the Outer Hebrides was closed to all operations from 6pm last night, with the closure affecting operations from Stornoway, Tyree, Barra and Benbecula.
It later revealed there would be a no-fly zone over Northern Ireland from 7am, meaning Belfast International, Belfast City and City of Derry airports would be closed.
"The CAA is closely monitoring the situation and will update the advice to operators and passengers as latest updates are produced by the Met Office," it added.
Highlands and Islands Airports Ltd said flights to and from Tiree, Barra and Benbecula in the Outer Hebrides and Campbeltown in Argyll were suspended.