Among the leading US budget carriers, Allegiant Air, Frontier Airlines, and Spirit Airlines are key ultra-low-cost players. Spirit leads in fleet size with 176 aircraft, while Frontier operates 114, and Allegiant has 112. Spirit is also the oldest of the three.
Spirit Airlines was founded in 1983 and is based in Dania, Florida. It operates as an ultra-low-cost carrier with hubs at several major airports including Hartsfield-Jackson Atlanta International Airport and Chicago O'Hare International Airport. The airline favors Airbus jets, specifically the A320 and A321 series.
Frontier Airlines was established in 1994 with its headquarters in Denver, Colorado. Initially using Boeing 737-200s, it transitioned to a standardized Airbus fleet around the turn of the century. The original Frontier began service in 1950 but ceased operations before being revived by former staff.