Aer Lingus is an oddball airline. Geographically Ireland is well-placed for connections between the U.S. and Europe, in addition to serving a major tourist destination. They’re owned by the same company as British Airways and Iberia. However,

• They are not a member of the oneworld alliance
  
• They are, however, a codeshare partner of American Airlines and part of an anti-trust immunized, revenue-sharing joint venture across the Atlantic
  
• Yet they still also codeshare with United Airlines and partner with United’s MileagePlus

A British Airways Executive Club member can fly United Airlines, credit the miles to Aer Lingus, and then transfer them to BA. They can earn miles on United or American if they wish.

And United’s MileagePlus members have been able to redeem miles for travel on Aer Lingus, while American AAdvantage members cannot – even though American and Aer Lingus share revenue across the Atlantic. Bizarre!

But this arbitrage play may be able to come to and end, and perhaps American Airlines frequent flyers will get a new option? Aer Lingus and United Airlines are terminating their codeshare agreement.

.@United and @AerLingus are terminating their codeshare agreement as of next Friday (27 OCT 2023). It has been in place since July 2008.#AvGeek #PaxEx

— Seth Miller (@WandrMe) October 20, 2023

Assuming that the United MileagePlus-Aer Lingus Aer Club partnership ends as well, which seems to be coming, it will no longer be possible for BA (as well as Iberia and Qatar Airways) members to earn their own points by flying United. However an end to that codeshare could presage moving closer to American, which would be fantastic for AAdvantage members.

Aer Lingus just moved to terminal 7 at New York JFK, and not the American Airlines terminal 8 which would make far more sense for them. Perhaps they’ll reconsider, and even as American gets slots returned to them by JetBlue with the end of that partnership they should be able to make room.