Belfast international is currently the 2nd busiest airport in Ireland but it's only a matter of time before it will be eclipsed by Cork with its growth rates over the last decade to be the nation's second busiest.
Even though as a Corkman I'd love to see that being true, it just isn't going to happen.
Look at the populations of Munster and Ulster. Munster has 1.1 million people. Ulster has 2 million (1.7 million of whom are in Northern Ireland). Munster has two medium-sized airports (Cork & Shannon) and two small (Kerry and Waterford). Ulster has two medium-sized (Belfast International and Belfast City) and one small (City of Derry) and a
tiny one in Carrickfinn. Considering the populations served, the only way BFS could be smaller than ORK is if it lost a load of passengers to BHD, but then BHD would end up taking the title of second biggest.