The McDonnell Douglas DC-10 is an American trijet wide-body aircraft manufactured by McDonnell Douglas. The DC-10 was intended to succeed the DC-8 for long-range flights. It first flew on August 29, 1970; it was introduced on August 5, 1971, by American Airlines. The trijet has two turbofans on underwing pylons and a third one at the base of the vertical stabilizer. The twin-aisle layout has a typical seating for 270 in two classes. The initial DC-10-10 had a 3,500 nmi (6,500 km) range for transcontinental flights. The DC-10-15 had more powerful engines for hot and high airports. The DC-10-30 and -40 models (with a third main landing gear leg to support higher weights) each had intercontinental ranges of up to 5,200 nmi (9,600 km). The KC-10 Extender (based on the DC-10-30) is a tanker aircraft operated primarily by the United States Air Force.