Aer Lingus is main source of US-bound transfers
The vast majority of passengers transferring at Dublin Airport to US-bound flights currently originate from the Aer Lingus network, coming from the UK and continental Europe.
Some regional UK cities, while large, don't have direct flights to the US and so passengers can fly to Dublin and then reach a number of American destinations, such as New York, San Francisco, Los Angeles, Washington DC, Chicago, Boston and Newark with Aer Lingus.
When Aer Lingus launched its service between Dublin and Hartford, Connecticut, last year, the passengers on the first flight had transferred to it at the Irish capital from countries such as the UK, Germany and Croatia.
Surprisingly, Aer Lingus has also managed to lure passengers to its transatlantic network from places such as Paris and Amsterdam - cities already well-served by US-bound flights.
Cost plays a role. It can work out cheaper for a passenger in Milan, for instance, to fly to Dublin to connect to a US-bound flight rather than fly direct from their home city.