Aer Lingus says it carried just over one million passengers in August, up 8.8% on the same month last year.
The load factor, or percentage of seats filled, was 80.5% in the month, down 1.2 points on the same month last year.
The figures showed that its short-haul routes performed better, with a load factor of 83%, up marginally on a year earlier despite a 15% increase in capacity. Short-haul passenger numbers grew by 10.6% over the year.
Longer routes showed a drop of almost three points to 77.5% as passenger numbers fell 2.3% from August last year.
For the first eight months of the year, passenger numbers are up almost 10% on the same period last year at just over seven million, while load factors are down four points to 75.3%. Long-haul load factors are down 8% so far this year.