The Piper PA-31 Navajo is a family of twin-engined utility aircraft designed and built by Piper Aircraft for small cargo and feeder airlines, and as a corporate aircraft. Production ran from 1967 to 1984. It was license-built in a number of Latin American countries. Development In 1962, Piper began developing a six- to eight-seat twin-engined corporate and commuter transport aircraft under the project name Inca, at the request of company founder William T. Piper. Looking like a scaled-up PA-30 Twin Comanche, the PA-31 made its first flight on 30 September 1964, and was announced later that year. It is a low-wing monoplane with a conventional tail, powered by two Lycoming TIO-540-A turbocharged engines in "tiger shark" cowlings, a feature shared with the Twin Comanche and the PA-23 Aztec. As testing proceeded, two cabin windows were added to each fuselage side and the engines were moved further forward. The PA-31, named "Navajo" after the native American tribe, was certified by the FAA on 24 February 1966, again in mid-1966 with an increase in maximum takeoff weight (MTOW) from , and deliveries began in 1967. The PA-31-300 was certified by the FAA in June 1967, the only variant without turbocharged engines: Lycoming IO-540-M1A5 engines driving two-bladed propellers. Unofficially, the initial model was referred to as the PA-31-310. Only 14 PA-31-300 were built in 1968 and 1969: the smallest variant production. In January 1966, development of the PA-31P Pressurized Navajo had begun : Piper's first pressurized aircraft. The PA-31P (or PA-31P-425 unofficially) was certified in late 1969. It was powered by Lycoming TIGO-541-E engines, had a longer nose, fewer and smaller windows, fuel tanks in the engine nacelles and a one-piece airstair cabin entry door instead of the split pair of doors. MTOW was increased to . The PA-31P was produced from 1970 to 1977. The 1971 Navajo B featured air conditioning, new storage lockers in the rear of the engine nacelles, increased baggage space, a third door next to the cabin doors for easier baggage loading, and an optional separate door for the pilot to enter the cockpit. In September 1972, Piper unveiled the PA-31-350 Navajo Chieftain, a Navajo B stretched by for up to ten seats, with more powerful engines and counter-rotating propellers to prevent critical engine handling problems. The Chieftain was powered by Lycoming TIO-540 variants, with an opposite-rotation LTIO-540 on the right-hand wing, and MTOW was increased to .