Passengers numbers at Aer Lingus increased by 2.4 per cent in January compared to the same month in 2006.
But the airline's load factor - the number of seats it fills - decreased by 3.7 per cent to 69.9 per cent as a consequence of new flights and increased frequencies on existing routes.
The airline said it carried 591,000 passengers as an increase in short-haul flights offset a decline in long-haul passengers.
Short-haul routes accounted for 518,000 of the passengers, with the remaining 73,000 thousand travelling to long-haul destinations such as New York, Boston and Dubai
The load factor on short-haul flights fell 4.2 per cent to 67.4 per cent while the load factor on long-haul flights fell 2.4 per cent at 7.3 per cent.
Revenue at the airline rose 1.2 per cent in January overall, compared to the same month in 2006, rising 7.8 per cent on short haul flights but falling 6.5 per cent on long-haul flights.