The Airbus A321 is the stretched variant of the A320 family, designed to carry more passengers on the same basic airframe. It entered service with Lufthansa in 1994 and quickly became the preferred aircraft for high-density narrowbody routes in Europe and later North America. The A321 seats 180 to 220 passengers and competes directly with the Boeing 737-900 and 737 MAX 9. The aircraft has always outsold its Boeing competitors in this size category, and the difference has grown since the introduction of the A321neo. The ceo variant remains in service with many airlines but has been out of production since the neo took over the line. American Airlines, JetBlue, and several European carriers still operate large A321 fleets.