One of my colleagues believes that Aer Lingus has a system whereby you clear US immigration in Dublin prior to departing for the US. This would obviously save a lot of time at the end of the journey but is it correct?
The U.S. and Ireland entered into a preclearance arrangement in 1986. Only immigration checks are performed, with customs and agriculture inspections still done on arrival in the U.S. Ñ therefore passengers from Ireland must still land at international terminals.
Dublin Airport's Terminal 2, currently in the planning stages, will have full US Customs and Border Protection facilities. This will allow passengers from T2 to leave US airports (including domestic airports, if any airline decides to serve them) upon landing without further inspection. Shannon will have similar facilities by the end of 2008.