In September 1972, Piper unveiled the PA-31-350 Navajo Chieftain, a stretched version of the Navajo B with more powerful engines and counter-rotating propellers to prevent critical engine handling problems. The fuselage was lengthened by 2 ft 0 in (0.61 m), allowing for up to ten seats in total. Variants of the Lycoming TIO-540 developing 350 hp (261 kW) were fitted to the Chieftain, with an opposite-rotation LTIO-540 installed on the right-hand wing; MTOW was increased to 7,000 lb (3,175 kg). The Chieftain's introduction was delayed by a flood at Piper's factory at Lock Haven, Pennsylvania caused by Hurricane Agnes, and deliveries did not commence until 1973. In 1974, Piper used a Navajo B as the basis for developing a new model, the PA-31-325 Navajo C/R. The Navajo C/R had lower-power versions of the counter-rotating engines of the Chieftain, rated at 325 hp (242 kW). After certification of the PA-31-325 in May 1974, production commenced in the 1975 model year. The Navajo B was also superseded in the 1975 model year, by the Navajo C version of the PA-31 model. -- Wikipedia