The McDonnell Douglas C-9 was a military variant of the DC-9 single-aisle airliner of McDonnell Douglas. It was introduced in 1968 and retired with the United States Air Force in September 2005, the United States Navy in July 2014, and the United States Marine Corps in April 2017. A total of forty-eight C-9s were built.
In 1966, the United States Air Force had a requirement for an aeromedical transport aircraft that led to the order of C-9A Nightingale in the next year. In 1968, aircraft deliveries started. In the course of 1968 to 1969, the USAF obtained twenty-one C-9A Nightingales. From 1968 to 2005, the aircraft were in service as a medical evacuation transport, passenger aircraft, and were used in other special operations.
In April 1972, the United States Navy placed its initial order for five C-9Bs; however, this order did not push through. In 1976, six aircraft were delivered to the United States Navy and the United States Marine Corps. The C-9B served as a convertible cargo and passenger aircraft for the US Navy and Marine Corps. It was delivered from 1973 to 1976. On June 28, 2014, the final C-9B was retired in service with the United States Navy. The variant was also used by the National Aeronautics and Space Administration to replace the KC-135.
The aircraft has an external length of 36.35 meters, an external height of 4.7 meters, a tail height of 8.5 meters, and a fuselage width of 3.3 meters. The wheelbase is 16.22 meters. It has a wingspan of 28.47 meters and a wing area of 93 square meters. The C-9B also features an avionics weather radar system.
The C-9B is powered by two Pratt and Whitney JT8D-9 engines rated at 14,500 lbf thrust each. It is a dual-spool low-bypass turbofan engine with an axial-flow, one-stage fan, six-stage low-pressure, seven-stage high-pressure compressor, nine can-annular combustors, and one-stage high-pressure, three-stage low-pressure turbine.
The aircraft has a high takeoff weight of 49,9895 kg. The landing weight is 44,906 kg and the empty weight is 27,079 kg. It was also fitted with auxiliary fuel tanks located beneath the cargo hold to build up the travel range to almost 2,520 nautical miles. It has a maximum speed of 500 knots and a cruise speed of 485 knots.