Ireland says its airports will reopen after the latest aerial shutdown caused by ash from an Icelandic volcano which sparked air travel chaos in Europe last month.
Britain's flight ban on Northern Irish and some Scottish airspace remained in place until the end of Wednesday, but authorties were optimistic conditions would improve the following day.
The Irish Aviation Authority (IAA) said Wednesday restrictions would be lifted progressively from 4:00 am (0300 GMT) on Thursday, with Dublin airport among the first to start up flights again.
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"The current ash cloud is moving south westwards and airport restrictions will be lifted according to its progress," said the aviation regulator in a statement.
Aer Lingus said it planned to operate all transatlantic services on Thursday, and the majority of its short-haul flights.
Its low-fares rival Ryanair said all services to Dublin would operate throughout the day, while flights would begin to use other airports from midday onwards.
Britain's Civil Aviation Authority (CAA) said its flight ban affecting airports at Glasgow in Scotland and Belfast in Northern Ireland would remain until 1:00 am (0000 GMT) Thursday.
Mabel McGeachie, 62, was caught up in the chaos when her easyJet flight from Glasgow to Malaga in Spain was cancelled.
"We are feeling disappointed as we were looking forward to it, and I don't think we'll be able to rearrange it," she said.
But restrictions on Edinburgh airport were lifted at 7:00 pm (1800 GMT) and air traffic controllers said conditions may improve the following day.
"Advice suggests that the cloud will continue to move southwesterly overnight and we therefore hope that fewer restrictions will be necessary Thursday," said the National Air Traffic Services, which manage British airspace.
CAA chief executive Andrew Haines meanwhile warned ash would likely play havoc with British air travel for "the foreseeable future."
"Our advice to passengers is to listen to updates and contact their airline before leaving home if they are concerned their travel plans may be affected," he said.
Wednesday's airspace shutdowns followed a closure of Irish, Northern Irish and some Scottish airspace for several hours the previous day, which caused the cancellation of hundreds of flights.
Airspace across Europe was closed for up to a week last month after the eruption of Iceland's Eyjafjoell volcano, but was re-opened after emergency talks between European governments, airlines and regulators.
The aerial shutdown was the biggest in Europe since World War II.
In Iceland itself Tuesday, the Eyjafjoell volcano spewed more ash than in recent days, although the level remained much lower than when the eruption began three weeks ago, an Icelandic geophysicist told AFP.
"The plume has increased. It is black... There is more ash in the plume and it is (rising) higher," Sigrun Hreinsdottir of the University of Iceland in Reykjavik said Wednesday.
Aer Lingus said the flight ban last month had cost it about 20 million euros (26 million dollars), while warning that "the final cost will depend on the actual level of customer claims."
The Association of British Insurers estimated Tuesday that the travel chaos caused by the ash had cost insurers around 62 million pounds (94 million dollars, 72 million euros).
Eurocontrol, the continent's air traffic control co-ordinator, said more than 100,000 flights to, from and within Europe had been cancelled between April 15 and 21, preventing an estimated 10 million passengers from travelling.
