Correct. An Aer Lingus flight can be used as an Excursionist Perk -- any MileagePlus redemption partner can. However, they don't appear to serve Reykjavik, and if they did, I'm not convinced you'd find seven award seats. The OP can certainly look to book an excursion somewhere else, though. It doesn't have to be between the US and Ireland -- there's no backtracking rule. Anywhere in Europe qualifies. (Heck, Dublin-Vladivostok would qualify, if you could find a way to fly it on *A without changing planes somewhere in Asia. )