Aer Lingus is just a brand-name within IAG, similar to British Airways, Iberia and Vueling. Ownership isn't the key driver here. Aer Lingus aircraft are better-suited to the MAN Transatlantic routes than those in the British Airways fleet. New A321LR's are available for JFK and BOS, and the A333's have a cabin layout which is well-suited to a leisure-heavy route ... expected to be used on MAN-MCO.