The so-called US Big Three (USB3) carriers American, Delta, and United will have 55 to 56 daily flights to London this summer (double for both ways). American is Londons third-largest long-haul operator, United is fourth, and Delta is sixth. The trio has almost one in five of the UK capital’s long-haul flights (19%), rising to more than one in two (58%) when only the US is considered.