United Airlines and American Airlines are vying for dominance at Chicago's O'Hare International Airport. On Tuesday, United Airlines announced that it plans to have its biggest summer at O'Hare, with a record 750 flights a day. This is about 200 more flights than its next largest competitor and the largest schedule ever flown by any airline operating at the airport, according to United. Just days before United announced its expanded schedule, American Airlines announced a slate of new routes from its hub in Chicago. The airline said that the city "has remained an important part of the airline’s story" since the late 1920s.