The McDonnell Douglas DC-9 (initially known as the Douglas DC-9) is a twin-engine, single-aisle jet airliner. It was first manufactured in 1965 with its maiden flight later that year. The DC-9 was designed for frequent, short flights. The final DC-9 was delivered in October 1982.
The DC-9 was followed in subsequent modified forms by the MD-80, MD-90 and Boeing 717. With the final two deliveries of the 717 in 2006, production of the DC-9 aircraft family ceased after 41 years and nearly 2,500 units built.
Design and development
During the 1950s, Douglas Aircraft began studying a short-medium range airliner to complement its higher capacity, long range DC-8. A medium range, four-engine design was studied, but it did not receive enough interest from airlines and was abandoned. Then in 1960, Douglas signed a two-year contract with Sud Aviation for technical cooperation. As part of the agreement Douglas would help market and support the Sud Aviation Caravelle along with license-production of an American version if orders were high enough. However, no orders were received and Douglas returned to its design studies after the two years.
In 1962, early design studies were underway. The first version seated 63 passengers and had a gross weight of 69,000 lb (31,300 kg). This design was changed into what would be initial DC-9 variant. Douglas officially gave approval to produce the DC-9 on April 8, 1963. Unlike the competing but slightly larger Boeing 727 trijet, which used as many 707 components as possible, the DC-9 was an all-new design. The DC-9 features two rear fuselage-mounted Pratt & Whitney JT8D turbofan engines, relatively small, efficient wings, and a T-tail. The DC-9's maximum takeoff weight was limited to 80,000 lb (36,300 kg) for a two-person flight crew by Federal Aviation Agency regulations at the time. DC-9 aircraft have 5 seats across for economy seating. The airplane seats 80 to 135 passengers depending on version and seating arrangement. (Note: DC stands for Douglas Commercial.)
The DC-9 was designed for short to medium routes, often to smaller airports with shorter runways and less ground infrastrucure than the major airports being served by larger designs like the 707 and DC-8. Consequently, accessibility and short field characteristics were called for. The tail mounted engine design facilitated a clean wing designs without engine pods, which had numerous advantages. First, flaps and slats could run the entire span of the wing, unimpeded by pods on the leading edge and engine blast concerns on the trailing edge. This simplified the design, improved airflow at low speeds and enabled lower takeoff and approach speeds, thus lowering field length requirements and keeping wing structures light. The second advantage of the tail-mounted engines was the reduction in foreign object damage from ingested debris from runways and aprons. Third, the absence of engines in underslung pods provided a reduction in ground clearance, making the aircraft more accessible to baggage handlers and passengers. Turnarounds were simplified by built-in airstairs, including one in the tail, which shortened boarding and deplaning times.
The first DC-9, a production ship, flew in February 1965. The second DC-9 flew a few weeks later and entered service with Delta Air Lines in late 1965. The initial Series 10 would be followed by subsequent growth variants. The final DC-9 series was the -50, which first flew in 1974. The DC-9 was a commercial success with 976 built when the production ended in 1982.
The DC-9 is one of the longest lasting aircraft in operation. Its reputation for reliability and efficiency drove strong sales of its successors well into the 2000s. The DC-9 family is one of the most successful jet airliners with a total of over 2,400 units produced; it ranks third behind the second place Airbus A320 family with over 3,000 produced, and the first place Boeing 737 with over 6,000 produced.
Studies aimed at further improving DC-9 fuel efficiency, by means of retrofitted wingtips of various types, were undertaken by McDonnell Douglas. However these did not succeed in demonstrating significant benefits, especially with existing fleets shrinking. The wing design makes retrofitting difficult.
The DC-9 was followed by the introduction of the MD-80 series in 1980. The MD-80 series was originally called DC-9-80 series. It was a lengthened DC-9-50 with a higher maximum takeoff weight (MTOW), a larger wing, new main landing gear, and higher fuel capacity. The MD-80 series features a number of variants of the Pratt & Whitney JT8D turbofan engine having higher thrust ratings than those available on the DC-9.
The MD-80 series was further developed into the McDonnell Douglas MD-90 in the early 1990s. It has yet another fuselage stretch, a glass cockpit (first introduced on the MD-88) and completely new International Aero V2500 high-bypass turbofan engines. In comparison to the very successful MD-80, relatively few MD-90 examples were built.
The final variant of the DC-9 family was the MD-95, which was renamed the Boeing 717-200 after McDonnell Douglas's merger with Boeing in 1997 and before aircraft deliveries began. The fuselage length and wing are highly similar to those found on DC-9-30 aircraft, but much use was made of lighter, modern materials. Power is supplied by two BMW/Rolls-Royce BR715 high bypass turbofan engines.
The -10 series was earliest and smallest DC-9 series was 104.4 ft (31.8 m) long and had a maximum weight of 82,000 lb (37,000 kg). Power was a pair of 12,500 lbf (56 kN) Pratt & Whitney JT8D-5 or 14,000 lbf (62 kN) JT8D-7 engines. A total of 137 were built. Models -11, -12, -13, -14, -15, -15F and -15RC were produced. Delta Air Lines was the initial operator.
This was designed to satisfy a Scandinavian Airlines request for improved short field performance by using the more powerful engines and improved wings of the -30 combined with the shorter fuselage used in the -10. Ten Series 20 aircraft were produced, all of them Model -21.
The -30 was the definitive series with 662 produced, accounting for about 60% of production. The -30 entered service with Eastern Airlines in February 1967 with a 14 ft 9 in (4.5 m) fuselage stretch, wingspan increased by just over 3 ft (0.9 m) and full-span leading edge slats, improving takeoff and landing performance. Gross take-off weight was typically 110,000 lb (50,000 kg). Engine options for Models -31, -32, -33 and -34 included the P&W JT8D-7 and JT8D-9 rated at 14,500 lbf (64 kN) of thrust, or JT8D-11 rated at 15,000 lbf (67 kN) of thrust.
This further lengthened version entered service with SAS in March 1968. With a 6 ft 6 in (2 m) longer fuselage, accommodation was up to 125 passengers. The -40 was fitted with Pratt & Whitney engines of between 14,500 and 16,000 lbf (64 and 71 kN). A total of 71 were produced.
The -50 was the largest DC-9 to fly. It features an 8 ft 2 in (2.5 m) fuselage stretch and seats up to 139 passengers. It started revenue service in August 1975 with Eastern Airlines and included a number of detail improvements, a new cabin interior, and more powerful JT8D-15 or -17 engines in the 16,000 and 16,500 lbf (71 and 73 kN) class. McDonnell Douglas delivered 96, all as Model -51. Some visual cues to distinguish this version from other DC-9 variants include side strakes (fins) below the side cockpit windows and thrust reversers rotated about 22 degrees.
Military and government
C-9: Several -30 series with side cargo door were purchased by the US armed forces. The C-9A Nightingale medevac configuration was for the U.S Air Force. The C-9B Skytrain II was for the U.S Navy and Marines, used for fleet logistics support moving both personnel and light cargo. The VC-9C is a VIP transport version for the US Air Force, used to transport Cabinet members and other high-ranking officials.
A total of 232 DC-9 aircraft (all variants) were in service as of April 2009, including commercial operators Northwest Airlines (63), ABX Air (49), Aserca Airlines (18), USA Jet Airlines (8), 1Time (4), Laser YV (4), Aeropostal-LAV (4), and other operators with fewer aircraft.
Northwest Airlines operates a fleet of DC-9 aircraft, most of which are over 30 years old. With severe increases in fuel prices in the summer of 2008, Northwest Airlines finally began retiring its DC-9s, switching to Airbus A319s that are 27% more fuel efficient.
Because of the usage of the aging JT8D engines, as of late 2000s DC-9s are considered gas guzzlers when compared to other more recent airliner designs. Studies aimed at improving DC-9 fuel efficiency, by means of retrofitted wingtip extensions of various types, have not succeeded in demonstrating significant benefits.
With the existing DC-9 fleet shrinking, modifications do not appear to be likely to occur, especially since the wing design makes retrofitting difficult. Thus, DC-9s are likely to be further replaced in service by new Boeing 737, Airbus A320, Embraer E-Jets aircraft, or the new, emerging Bombardier CSeries airliner. However, it is probable that a modest number of DC-9s will continue to productively fly for many years to come. As the Northwest/Delta merger progresses, Delta has pulled several stored DC-9s back into service.
One ex SAS DC-9-21 is operated as a skydiving jump platform at Perris Valley Airport in Perris, California. With the steps on the ventral stairs removed, it is the only airline transport class jet certified to date by the FAA for skydiving operations as of 2008.
Accidents and incidents
As of March 2009, the DC-9 has been involved in 117 incidents, including 101 hull-loss accidents, with 2,135 fatalities.
Sources: McDonnell Douglas DC-9 data.
Published - July 2009
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