All flights in and out of Northern Ireland and the Irish Republic are to be grounded from 0700 BST because of fresh risks from volcanic ash.
Airspace over the Outer Hebrides in Scotland is already closed, affecting operations from Stornoway, Tiree, Barra and Benbecula.
Flights in the rest of the UK are operating as normal.
An ash plume is drifting south from the same Icelandic volcano that wreaked havoc to European air travel in April.
Imtiaz Tyab reports.
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