Air passengers have faced more disruption this week
Airports across the UK have reopened after the latest closures due to volcanic ash from Iceland, air traffic controllers have said.
Flights were grounded on Wednesday night in Northern Ireland, western Scotland and England's far south-west.
But the ash cloud moved west overnight and has cleared UK airspace, air traffic control body Nats said.
Last month, thousands of Britons were stranded overseas after ash shut down airspace across Europe.
The latest disruption started on Monday, and has confused many air travellers as authorities repeatedly closed, then reopened, airports.
All airfields in Northern Ireland, including Belfast, plus Islay, Campbeltown, Ronaldsway, Lands End and the Isles of Scilly were declared free of the no-fly zone at 0700 BST on Thursday.
Glasgow had reopened at 0100 BST and planes had taken to the skies again in Edinburgh on Wednesday evening.
However, the Irish Aviation Authority (IAA) has re-imposed flight restrictions at six airports in the Irish Republic between midnight and 1300 BST on Friday.
The airports affected are Shannon, Donegal, Knock, Galway, Kerry and Sligo. Dublin, Cork and Waterford airports will remain open.
The UK's National Air Traffic Services (Nats) said in a statement: "We continue to maintain close dialogue with the Met Office and with the CAA, which is responsible for imposing no-fly zones."
Consumer magazine Which? Holiday said it was important people made sure they were covered by the CAA-run Air Travel Organisers' Licensing (Atol) scheme.
Rochelle Turner, head of research for Which? Holiday, said: "The last few weeks have shown how vital it is to make sure you're protected in case something goes wrong with your holiday.
"Most insurers now exclude disruption caused by the Icelandic volcanic ash from new policies, so the only way to be absolutely certain your whole holiday is protected is to book a package holiday through an Atol-protected agent."
British Airways said the previous six-day closure of UK airspace due to volcanic ash led to passenger numbers being down by a quarter last month, compared with a year earlier.