Ryanair revealed a 22% fall in profits after it was impacted by rising fuel costs and "unnecessary" disruption caused by Iceland's volcano.
The low-cost airline booked exceptional costs of €50m (£42.4m) after the closure of European airspace forced the cancellation of 9,400 Ryanair flights in April and May and the loss of 1.5 million passengers.
After initially refusing to compensate customers beyond a refund for their ticket, Ryanair, which has hubs at George Best Belfast City and City of Derry airports, subsequently agreed to cover the costs of refreshments and accommodation for passengers who could not get home.
Yesterday it said it was still processing claims under the "unfair and disproportionate" EU regulations, adding that it will be some time before the exact cost of the cancellations is known.
The estimate of €50m meant pre-tax profits for the company's first quarter to June 30 fell to €104.6m (£88.7m) from €134.6m a year earlier.
Fuel costs rose by 34% to €287m (£243.3m) due to higher oil prices and the introduction of new routes.
The airline is due to open its 42nd and 43rd new bases in Barcelona and Valencia in September and November respectively and said it continued to see "enormous opportunities" to grow the business across Europe.
However, it recently announced that it will cut winter capacity in the UK by 16%, including a 17% reduction in its services at Stansted airport in Essex, where the carrier will handle 1.5 million fewer passengers than last winter.
Ryanair chief executive Michael O'Leary cited the "damaging" Air Passenger Duty airport departure tax as a reason for the capacity reduction.
And while sticking by forecasts for full-year profits, he said the airline remained cautious about prospects for the rest of the year.
Hitting out at the so-called 'tourist tax' in the Republic, Mr O'Leary said: "The Irish government's disastrous €10 tourist tax has caused a continuing collapse in Irish tourism. Traffic at Dublin airport in May fell 15% and is on track to fall to just 17 million passengers in 2010, down almost 30% from the 23.5m passengers handled in 2008.
"The Government's failed policy of gouging tourists with a €10 tax must be scrapped," he said.