The 767 is produced in three fuselage lengths. The original 767-200 entered service in 1982, followed by the 767-300 in 1986 and the 767-400ER, an extended-range (ER) variant, in 2000. The extended-range 767-200ER and 767-300ER models entered service in 1984 and 1988, respectively, while a production freighter version, the 767-300F, debuted in 1995. Conversion programs have modified passenger 767-200 and 767-300 series aircraft for cargo use, while military derivatives include the E-767 surveillance aircraft, the KC-767 and KC-46 aerial tankers, and VIP transports. Engines featured on the 767 include the General Electric CF6, Pratt & Whitney JT9D and PW4000, and Rolls-Royce RB211 turbofans.
United Airlines first placed the 767 in commercial service in 1982. The aircraft was initially flown on domestic and transcontinental routes, during which it demonstrated the reliability of its twinjet design. In 1985, the 767 became the first twin-engined airliner to receive regulatory approval for extended overseas flights. The aircraft was then used to expand non-stop service on medium- to long-haul intercontinental routes. In 1986, Boeing initiated studies for a higher-capacity 767, ultimately leading to the development of the 777, a