Aer Lingus, which transformed into a no-frills airline in order to compete with bigger Irish rival Ryanair, said the partnership would allow Irish and U.S. travellers to book seats between Ireland and the 51 destinations in one go. Aer Lingus Chief Executive Dermot Mannion, who has been fighting a takeover bid by Ryanair since his airline's privatisation and stock market debut last October, said the tie-up was a significant development for both carriers.