A Delta Air Lines plane takes off at Reagan National Airport in Arlington, Virginia, on Dec. 24, 2021.Eric Lee | Bloomberg | Getty ImagesFor United Airlines CEO Scott Kirby, there's his airline, his carrier's main rival, Delta Air Lines, and then everyone else.Delta and United accounted for more than 86% of the profits posted by the seven largest airlines last year. Airline margins are notoriously thin, less than 4% last year, compared with close to 20% for big U.S. companies, according to the Airlines for ...