McDonnell Douglas MD-11

The McDonnell Douglas MD-11 is an American three-engine medium to long-range widebody airliner, with two engines mounted on underwing pylons and a third engine at the base of the vertical stabilizer. It is based on the DC-10, but featuring a stretched fuselage, increased wingspan with winglets, refined airfoils on the wing and tailplane, new engines and increased use of composite materials. It also features an all-digital glass cockpit that decreases the flight deck crew from the three required on the DC-10 to two by eliminating the necessity for a flight engineer.

Origins

Although the MD-11 program was launched in 1986, McDonnell Douglas started to search for a DC-10 derivative as early as 1976. Two versions were considered then, a DC-10-10 with a fuselage stretch of 40 feet (12.19 m) and a DC-10-30 stretched by 30 ft (9.14 m). That later version would have been capable of transporting up to 340 passengers in a multi-class configuration, or 277 passengers and their luggage over 5,300 nautical miles (9,800 km). At the same time, the manufacturer was searching to reduce wing and engine drag on the trijet. Another version of the aircraft was also envisaged, the "DC-10 global", aimed to counter the risks of loss of orders for the DC-10-30 that the Boeing 747SP and its range were creating. The DC-10 global would have incorporated more fuel tanks.^[1]

While continuing its research for a new aircraft, McDonnell Douglas designated the whole program as the DC-10 Super 60, having previously been known for a short time as DC-10 Super 50. The Super 60 was to be an intercontinental aircraft incorporating many aerodynamic improvements on the wings, and a fuselage lengthened by 26 feet 8 in (8.13 m) to allow up to 350 passengers to seat in a mixed class layout, compared to the capacity of 275 in the same configuration of the DC-10.^[1]

Following more refinements, the DC-10 Super 60 project was proposed, as of 1979, in three distinct versions like the DC-8. The DC-10-61 aimed to be a US domestic aircraft, able to carry 390 passengers on an airframe lengthened by 40 ft (12 m). Like for the DC-8, the series 62 was proposed as an intercontinental aircraft stretched by 26 ft 7 in (8.10 m) and capable to carry up to 350 passengers. And finally, the series 63 would have incorporated the same fuselage as the DC-10-61 as well as all the aerodynamic refinements of the -62. After the three DC-10 accidents in 1979 (American Airlines Flight 191, Western Airlines Flight 2605 and Air New Zealand Flight 901) which received great media coverage, the trijet program was seriously damaged by doubts regarding its structural integrity. For these reasons, and due to another downturn in the airline industry, all work on the Super 60 was stopped.^[1]

In 1981, a Continental Airlines DC-10-10 was leased to conduct more research and particularly the effects the then newly-designed winglets could have on aircraft performance. Different types of winglets were tested during that time in conjunction with NASA. McDonnell Douglas was again planning new DC-10 versions that could incorporate winglets and more efficient engines developed at the time by Pratt & Whitney (PW2037) and Rolls-Royce (RB.211-535F4). The manufacturer finally rationalized all these studies under the MD-EEE designation, that was later modified to MD-100 following some more changes. The MD-100 was proposed in two versions: the Series 10, having an airframe shorter by 6 ft 6 in (1.98 m) compared to the DC-10 and seating up to 270 passengers in a mixed class configuration; and the Series 20, incorporating a fuselage stretch of 20 ft 6 in (6.24 m) over the DC-10 and able to seat up to 333 passengers in the same kind of configuration as the Series 10. Both versions could be powered by the same engine families as the actual MD-11 plus the RB.211-600. But the situation for the manufacturer, and the airline industry in general, did not look bright. No new DC-10 orders were received, and many among the observers and customers doubted that the manufacturer would be around for much longer. Thus, the Board of Directors decided in November 1983 to cease once more all work on the projected new trijet.

Good times were back the following year and airlines were placing repeat orders for the MD-80 series jets that had helped the manufacturer to travel through the past difficult years. No new orders for the DC-10 had been received, (which inspired McDonnell Douglas even more to create a replacement) but the production line was nonetheless kept active thanks to a previous order for 60 KC-10A tankers from the USAF. McDonnell Douglas was still convinced that a new derivative for the DC-10 was needed, as shown by the second-hand market of its Series 30 as well as for the heavier DC-10-30ER version. Thus, in 1984 and for the first time, a new derivative aircraft for the DC-10 was designated MD-11. From the very beginning, the MD-11X was conceived in two different versions. The MD-11X-10, based on a DC-10-30 airframe, offered a range of 6,500 nmi (12,038 km) with passengers. That first version would have had a Maximum Take-Off Weight (MTOW) of 580,000 pounds (263,157 kg) and would have used CF6-C2 or PW4000 engines. The MD-11X-20 was to have a longer fuselage, accommodating up to 331 passengers in a mixed class layout, and a range of 6,000 nmi (11,100 km).

As more orders for the DC-10 were received, McDonnell Douglas used the time gained before the end of DC-10 production to consult with potential customers and to refine the proposed new trijet. In July 1985, the Board of Directors finally authorized the Long Beach plant to offer the MD-11 to potential customers. At the time, the aircraft was still proposed in two versions, both with the same fuselage length, a stretch of 22 ft 3 in (6.93 m) over the DC-10 airframe, as well as the same engine choice as the MD-11X. One version would have a range of 4,780 nmi (8,840 km) with a gross weight of 500,000 lb (227,000 kg) and transport up to 337 passengers, while the second would carry 331 passengers over 6,900 nmi (12,800 km). A year later, as several airlines had committed for the MD-11, the situation was looking optimistic. The aircraft was now a 320 seater baseline and defined as an 18 ft 7 in (5.66 m) stretch over the DC-10-30 powered by the new advanced turbofans offered by the major engine manufacturers and giving it a range of 6,800 nmi (12,600 km). Other versions, such as a shortened ER with a range of 7,500 nm (13,900 km), an all cargo offering a maximum payload of 200,970 lb (91,080 kg) and a Combi with a provision for ten freight pallets on the main deck, were proposed. Further growth of the aircraft was also foreseen, such as the MD-11 Advanced

Design phase

Finally, the MD-11 was launched on December 30, 1986 with commitments for 52 firm orders and 40 options^[2] in three different versions (passenger, combi and freighter) from ten airlines (Alitalia; British Caledonian; Dragonair; FedEx Express; Finnair; Korean Air; Scandinavian Airlines System; Swissair; Thai Airways International and Varig)^[2] and two leasing companies (Guinness Peat Aviation and Mitsui).^[2] Orders from Dragonair, Scandinavian and UTA,^[2] an undisclosed customer, were canceled by 1988. Assembly of the first MD-11 began on March 9, 1988, and the mating of the fuselage with wings occurred in October that year. First flight was originally planned to occur in March 1989, but numerous problems with the manufacturing, delays with suppliers producing essential components and labor industrial actions delayed the ceremonial roll out of the prototype until September of that year The following months were used to prepare the prototype for its maiden flight, which finally happened on January 10, 1990. The first two aircraft manufactured were intended for FedEx and thus, were already fitted with the forward side cargo door. They remained with the manufacturer as test aircraft until 1991 before being completely converted to freighters and delivered to their customer. FAA certification was achieved on November 8, 1990 while the European Joint Aviation Authorities (JAA) certified the MD-11 on October 17, 1991 after approximately 200 separate issues were resolved.

The first MD-11 was delivered to Finnair on December 7, 1990 and accomplished the first revenue service by an MD-11 on December 20, 1990, carrying passengers from Helsinki to Tenerife in the Canary Islands. MD-11 service in the U.S. was inaugurated by Delta Air Lines, also in 1990. It was during this period that flaws in the MD-11's performance began to become apparent. It failed to meet its targets for range and fuel burn. American Airlines in particular was unimpressed, as was Singapore Airlines, which canceled its order for 20 aircraft. American Airlines cited problems with the performance of the airframe and the Pratt & Whitney PW4000 engines selected for its use as reasons of the cancellation while the Singapore Airlines stated that the MD-11 could not operate on the airline's long haul routes. The figures revealed exclusively to Flight International show that, based on pre-flight estimates, the P&W-powered MD-11 should have been capable of a 7,000 nautical miles (12,950 km) range with 61,000 pounds (27,680 kg) of payload. Even with the Phase 1 drag reduction in place then, the aircraft could only achieve its full range with 48,500 lb (22,000 kg) of payload, or a reduced range of 6,493 nm (12,025 km) with a full payload.

In 1990, McDonnell Douglas, along with Pratt & Whitney and General Electric began a modification program known as the Performance Improvement Program (PIP) to improve the aircraft's weight, fuel capacity, engine performance, and aerodynamics. McDonnell Douglas worked with NASA's Langley Research Center to study aerodynamic improvements. The PIP lasted until 1995 and recovered the range for the aircraft. However, by this point sales of the MD-11 had already been significantly impacted.

The MD-11 was one of the first commercial designs to employ a computer-assisted pitch stability augmentation system that featured a fuel ballast tank in the tailplane, and a partly computer-driven horizontal stabilizer. Updates to the software package have achieved a situation where the plane's handling characteristics in manual flight are comparable to the DC-10, despite a much greater fuel efficiency achieved by the lessened drag of the smaller tailplane.

After McDonnell Douglas merged with Boeing in 1997, the new company decided that MD-11 production would continue, though only for the freighter variant. However, in 1998 Boeing announced it would end MD-11 production after filling current orders. The last passenger MD-11 built was delivered to Sabena in April 1998.The last two MD-11s were manufactured during June and September 2000, and delivered to Lufthansa Cargo on February 22 and January 21, 2001 respectively. Production ended because of lack of sales, resulting from internal competition from comparable aircraft, such as the Boeing 777 and external competition from the Airbus A330/A340. The trijet design of the MD-11 made it inherently less fuel efficient than similar-sized twin-engine jets. Since there was a large demand for cargo aircraft and because there was no 777 cargo version available at the time, many airlines using the MD-11 were eager to switch to the 777 as they had no problems selling their used MD-11s to cargo operators.

McDonnell Douglas and later Boeing performed studies on the feasibility of removing the tail engine and making it a two engine plane, but nothing came of it. McDonnell Douglas originally projected that it would sell more than 300 MD-11 aircraft, but only a total of 200 planes were built. The MD-11 was assembled at McDonnell Douglas's Douglas Products Division in Long Beach, California (later Boeing's).

Ini cockpit McDonnell Douglas MD-11