Aer Lingus traffic statistics for September show that the airline's load factor, or amount of seats filled, on long-haul flights fell to 67.9 percentage points, compared to 72.8 percentage points in the same month last year.
The airline has put this down to more available seats after the acquisition of two new planes.
Load factor on short-haul flights was up - it rose 0.5% to 80.5%.
Overall the load factor for last month came in at 74.6 percentage points, which compared to 76.9 percentage points last year.
However, passenger numbers were up 9% in the month to 847,000 compared to September last year.
Notes from both Davy & Goodbody stockbrokers this morning said the Aer Lingus passenger figures were 'encouraging'.
Goodbody analyst Joe Gill said: 'It appears that, overall, travel demand in Ireland has remained strong through September.'
The airline launched its first of three new transatlantic routes to Washington DC in August 2007, and will begin services to San Francisco and Orlando at the end of this month.
Meanwhile, British budget airline easyJet said passenger numbers had risen 14.2% year-on-year in September to 3.4 million.
