The DC-9-40 is a narrow-body jet aircraft built by McDonnell Douglas in response to a Scandinavian Airlines System (SAS) requirement. The aircraft is powered by more powerful Pratt and Whitney engines and can accommodate up to 125 passengers in a single-class configuration.
On November 28, 1967, the first flight of the McDonnell Douglas D-9-40 occurred. The DC-9-40 is a further lengthened version of the McDonnell Douglas DC-9 single-aisle airliner. In response to a request from the Scandinavian Airlines System (SAS) who needed a larger capacity development of the DC-9, McDonnell Douglas came up with the DC-9-40. In comparison with the previous series DC-9-30, the fuselage of the latter aircraft is 2-meter longer, increasing seating capacity in a single-class configuration up to 125 passengers. Other versions include the DC-9-10 and DC-9-20.
The Series 40 was powered by Pratt and Whitney JT8D engines. The JT8D is a low-bypass turbofan engine with a rated thrust range of 14,500 lbf to 16,000 lbf. It is an axial-flow front turbofan incorporating the dual-spool design. There are two coaxially-mounted independent rotating assemblies in the engine such as the first rotating assembly for the low-pressure compressor (LPC) which composed of the first six stages driven by the second downstream turbine, and the second rotating assembly which is in-charged for the high-pressure compressor (HPC) section that has seven stages and is driven by the first upstream single-stage turbine.
The DC-9-40 has an exterior length of 38.28 meters, an exterior height of 4.7 meters, a tail height of 8.7 meters, and a fuselage diameter of 3.35 meters. It has a wingspan of 28.44 meters, a wing area of 93 square meters, and a wheelbase of 17.1 meters. The cabin height is 2.05 meters, the cabin width is 3.12 meters, and the cabin length is 24.6 meters.
The aircraft has a maximum cruising speed of 485 knots and a long-range cruising speed of 443 knots. It can fly up to 35,000 feet, can climb at a rate of 3,000 feet per minute, and has a travel range of 1,200 nautical miles. It has a maximum takeoff distance of 2,000 meters and a maximum landing distance of 1,500 meters.
On March 12, 1968, the DC-9-40 first entered service with Scandinavian Airlines System. There were 71 DC-9-40s produced in total.