All UK airspace is expected to be open from 1300 GMT, the UK's air traffic control authority NATS has confirmed, lifting a no-fly zone in Northern Ireland and Western Scotland.
Airports in Dublin, Shannon, Cork, Knock, Donegal, Waterford, Kerry, Galway and Sligo have now been cleared by the Irish Aviation Authority to resume normal operations, although clearing the backlog may take some time.
"We expect operations to be normal at all Irish Airports for the rest of today," said the Irish Aviation Authority, before adding further warning.
"Winds are forecast to continue coming from a Northerly direction for the next few days and this could lead to further problems."
The Eyjafjallajokull volcano is still erupting, according to the Met Office's Volcanic Ash Advisory Centre, with ash plumes up to 18,000 feet (5480 m). It expects that the current cloud is likely to extend slightly further east over the UK by 6 AM on May 5.
Irish Aviation Authority http://www.iaa.ie
National Air Traffic Services http://www.nats.co.uk/
Met Office Volcanic Ash Advisory Centres http://www.metoffice.gov.uk/aviation/vaac/Reuse content