On April 17th 1967 Piper started to deliver the first Navajos, its new 6-9 seat, twin-engined aircraft which was the largest so far manufactured by them. Piper was obviously targeting the emerging market of private planes for businessmen; initial tests were performed by the prototype which flew on September 30th 1964. It was powered by two Avco Lycoming IO-540-M 300hp engines, and was named Piper PA-31-300 Navajo.
In 1977 the PA-31T with two 325hp engines became the PA-31T Cheyenne II, after the production of the ill powered PA-31T1 Cheyenne I (2xPTA-11 of 500hp). Then, in 1981, Piper produced the PA-31T2 Cheyenne IIXL with a lengthened fuselage and two 750hp PTA-132 engines. By 1986 only the PA-31-350, PA-31T1 and PA-31T2 were still on the production line, and Piper decided to roll out the PA-31P-350 Mojave, a Cheyenne with 350 hp engines.
The Navajo six/eight seat cabin class twin has been adapted to a number of commuter, charter, air taxi, light freight and executive transport roles, and has spawned a series of developments.