There will be no restrictions on travel in Irish airspace for at least the next 24 hours, the Irish Aviation Authority has said.
The authority said that all Irish airports remain open but that a small number of flights may be affected by the ash cloud caused by an Icelandic volcano because of restrictions in other European countries.
Aer Lingus today cancelled 20 flights to and from Glasgow, Edinburgh and Aberdeen.
"We have activated change for free and refund request facilities on aerlingus.com for customers impacted by this disruption," the airline said.
The cancellations were announced in spite of earlier assurances by the IAA that no flight disruptions were likely for at least 48 hours following the volcanic eruption at Grimsvötn in southeastern Iceland.
It expects to operate a full schedule tomorrow.
Ryanair cancelled some 30 flights to and from Glasgow Prestwick, Edinburgh and Aberdeen today but said it did not believe this was necessary.
Ryanair chief executive Michael O'Leary said the airline had completed a one-hour "verification flight" at up to 41,000ft in Scottish airspace this morning. It said the aircraft took off from Glasgow Prestwick, flew to Inverness, on to Aberdeen and down to Edinburgh.
In a statement, Ryanair said: "There was no visible volcanic ash cloud or any other presence of volcanic ash and the post-flight inspection revealed no evidence of volcanic ash on the airframe, wings or engines.
"The absence of any volcanic ash in the atmosphere supports Ryanair's stated view that there is no safety threat to aircraft in this mythical 'red zone', which is another misguided invention by the UK Met Office and the [Civil Aviation Authority]."
British transport secretary Phillip Hammond disputed this and said radar track information suggested the Ryanair flight had not in fact entered the “red zone”.
Met Éireann said it did not expect there to be problems tomorrow as a result of the ash cloud because of westerly winds but said that a low pressure band approaching from the Atlantic could lead to northerly winds later in the week which would be more likely to push ash particles into Irish airspace.
Aer Arann has cancelled a flight scheduled to travel from Dublin to Derry this eveing. Flights from Belfast International airport to Newcastle and Glasgow have also been cancelled.
The British government said today the ash would not lead to the total shutdown of airspace despite the cancellation of dozens of flights to and from Scotland.
Ash from the Icelandic volcano is likely to affect flights in parts of Denmark and southern Scandinavia today, European air traffic agency Eurocontrol said.
Scientists have described the eruption as the largest at the volcano for 100 years but said disruption on the same scale as that which followed the eruption at Eyjafjallajökull last year was unlikely.
Before Aer Lingus announced the cancellations, the aviation authority had warned that there was a risk some ash cloud could reach parts of northern Europe by today. While it did not expect any flight cancellations today or tomorrow, it stressed that the situation was “fluid” and said that things could change later in the week.
“We don’t believe there will be any kind of disruption in the next 48 hours,” said Martin Towey, the authority’s senior aviation executive.
European air traffic agency Eurocontrol said 250 flights had been cancelled in British airspace as the ash cloud has drifted lower from Iceland. It said that if the volcanic emissions continued at the same rate, the cloud could reach western French and northern Spanish airspace on Thursday and could affect flights in parts of Denmark and southern Scandinavia later today.
The Volcanic Ash Advisory Centre in London said the ash would reach Ireland by 6am today and warned airlines across Europe to prepare for possible disruption to flight schedules by the end of the week.
“This is a very different situation to last April,” a spokesman for the centre said. “The weather is much more changeable and there’s a lot more uncertainty. There’s no risk of the ash moving across the UK in the next day or so. But there is a possibility that we’ll see some volcanic ash towards the end of the week.”
The EU Commission said the eruption of the Grimsvötn volcano could affect Irish and British airspace but said it was too early to tell whether the airspace over other European countries might be affected.
The unexpected threat to air travel was reflected in the decision of the White House to bring forward US president Barack Obama’s departure from Ireland to Britain last night to avoid the ash plume.