Aer Lingus has said that the disruption to air travel caused by volcanic ash cloud last month has cost it about 20m euros ($26.3m; £17.2m).
But it said this was an initial estimate, and the final figure depended on the actual level of customer claims.
Its comments came on the day that fresh risks from the volcanic ash cloud led to a further grounding of flights.
Earlier, all flights in and out of Northern Ireland and the Irish Republic were grounded.
Aer Lingus was forced to suspend all services to the UK and Europe, but has since begun flying again with Irish airspace reopened from 1300 BST.
Airspace over Scotland's Outer Hebrides has also reopened after an earlier closure.
In a trading update, Aer Lingus said that total revenues for the three months to 31 March fell by 1.8%. The operating loss for the quarter was 37.8m euros, compared with a deficit of 74.8m for the same three months of 2009.
The company said: "While the trading environment remains challenging, early indications on second quarter revenues are positive."
But Aer Lingus added: "We have limited visibility over the booking profile for [the rest of the year] and our key markets remain subdued.
"It is also uncertain whether the recent Icelandic volcanic eruptions will have a longer term impact on passenger travel plans."
Meanwhile in the UK the Association of British Insurers (ABI) said it expected travel insurance companies to pay out a total of £62m to passengers affected by the delays caused by the ash.
The ABI warned that this represented about 10% of the travel insurance market's income.