Long before engines propel aircraft in the sky, they drive designs on the ground, providing the thrust for larger and longer-range models, which offer improved runway performance, reduced fuel consumption, and lower noise emissions. They certainly served as the catalyst for the McDonnell-Douglas MD-90, a development of the earlier MD-80 series of twin-jets. But its initially conceived turbofans looked nothing like the ones that had powered this predecessor.
Advancing powerplant technology, coupled with higher thrust capabilities, had already given rise to the original DC-9, whose capacity had increased from 90 in the baseline DC-9-10 to 139 in the ultimate DC-9-50 stretch. Refanned, their Pratt and Whitney JT8D engines had spawned the succeeding MD-80.
Incorporating the high pressure compressor and turbine speed, along with the combustion section, of the existing JT8D-9, it introduced a new six-stage low pressure compressor, a low pressure turbine, and a bypass duct.
Although its resultant increase in length-from 120 to 150 inches-and diameter-from 42.5 to 56.34 inches–would have created installation restrictions on wing-pylon mounted twins, such as the competing Boeing 737-300 to -500 series and the Airbus A-320 family, the aft-fuselage mounting characteristic of the DC-9 and the MD-80 proved no hindrance.
Installed on a DC-9-32, the turbofan, designated the JT8D-109, was first flight-tested on January 9, 1975 and certified as the JT8D-209 four years later, offering thrust capabilities of between 18,000 and 21,000 pounds in its several versions, the latter as the JT8D-219.
An MD-80 successor, powered by still-higher thrust engines and possibly incorporating a fuselage stretch for increased passenger capacities, would logically have hinged upon a further engine derivative. But Pratt and Whitney had developed the basic JT8D core to its ultimate capability and McDonnell-Douglas, at least initially, elected to explore the use of a radically different, hitherto untried engine that would offer a technological step-change.
Designated MD-X, and initially conceived in 1985, the aircraft, using an MD-80 fuselage, wing, and tailplane, discarded the traditional, nacelle-encased engine with one featuring exposed, unducted, highly-contoured, counter-rotating, multi-bladed fans, known both as an ultra high bypass powerplant (UHB) and an unducted fan (UDF), and jointly developed by Aeritalia, Saab-Scania, and Science Applications International Corporation of San Diego.
Fuel consumption on short- to medium-range routes was predicted to be an unprecedented 50-percent lower than that of current MD-80s and between 25- and 35-percent lower than that of emerging, but ducted turbofan designs.
Taking the form of the General Electric GE36, the unducted fan was installed on the left side of the MD-80 prototype, registered N980DC, and first flew in this guise from Edwards Air Force Base on May 18, 1987, requiring an extended pylon between the engine and the fuselage to provide sufficient clearance for blade rotations.
Several configurations were tested: with two, 12-foot-diameter, eight-bladed fans; ten forward and eight aft blades; and two six-bladed, counter-rotating fans, the latter as the Pratt and Whitney-Allison 578-DX. It first flew on April 13, 1989.
The type’s military potential was also explored. Entering the Navy’s Long-range ASW Capable Aircraft (LRAACA) competition, McDonnell-Douglas proposed a propfan-powered MD-87, although the contract was ultimately awarded to a P-3 Orion development.
Two commercial versions, promoted during early-1988 marketing campaigns, included a 114-passenger MD-91X, which was essentially an MD-87 counterpart, and a 165-passenger MD-92X, which corresponded to the full-length MD-88. A still-higher capacity version, with seating for 180, incorporated significant technological advancements, including laminar and turbulent boundary layer control, fly-by-wire and fly-by-light actuation, and a high aspect ratio supercritical wing. It was designated MD-94X.
Concurrent with these studies was another, more conventional design proposal, which offered a smaller technological leap with more traditional high bypass ratio turbofans-in this case, International Aero Engines (IAE) V2500s. Paralleling the earlier versions, McDonnell-Douglas conceived of an advanced twin-jet family, encompassing the 114-passenger MD-91V, the 165-passenger MD-92V, and the 180-passenger MD-93V.
Originally comprised of five companies, inclusive of Motoren und Turbinen (MTU) Daimler Benz, Fiat Aviazione, the Japanese Aero Engines Corporation (JAEC), Rolls Royce, and Pratt and Whitney, the International Aero Engines consortium was located in Pratt and Whitney’s own-and autonomous-East Hartford, Connecticut, headquarters.
Their design, the V2500, featured wide chord, semi-hollow fan blades consisting of metal honeycomb sandwiched between two titanium sheets. It was strong, but at the same time flexible enough to minimize damage from foreign object strikes and ingestion.
Its components were supplied by the consortium’s manufacturers themselves. JAEC, for instance, provided the fan and low pressure compressor. MTU supplied the low pressure turbine, Fiat Aviazione the gearbox, Rolls Royce the high pressure compressor, and Pratt and Whitney the high pressure turbine and combustor.
Although unducted fan technology would have offered several advantages, it would not have been available and certified until much later in the decade and had not been operationally proven, leaving questionable airline and passenger acceptance of a still-experimental concept.
Thus without choice, McDonnell-Douglas combined its proven DC-9 and MD-80 foundation with the new IAE turbofans, launching the MD-90 program on November 14, 1989 and paving the way, as its numerical nomenclature indicated, for its entry into service during the next decade.
The initial MD-90-10, a 114-passenger counterpart to the MD-87 for hot-and-high deployment, and the MD-90-20, a designation reserved for potential, full-size MD-80 retrofits, were not, in the event, built, leaving the MD-90-30 as its first production version.
Featuring a 4.6-foot forward plug to counterbalance the increased engine weight, the aircraft offered a new, 141.2-foot fuselage and 152.7-foot overall length as compared to the MD-88.
Formed by means of modular construction techniques, it was the result of subassemblies provided by Alenia, AeroSpace Technologies of Australia, Dassault Aerospatiale, CASA, Chengdu Aircraft Industrial Corporation (CAC), and Shanghai Manufacturing Factory (SAMF), and delivered to Salt Lake City before being transported to the combined, MD-80 and MD-90 production line in Long Beach, California.
The strengthened, 107.10-foot MD-80 wing, with a 1,209-square-foot area, 24 degrees of sweepback at the quarter chord, and an aspect ratio of 9.6, retained its predecessor’s tri-section leading edge slats, double-slotted training edge flaps, and spoilers, which could be used as air brakes and lift dumpers.
Utilizing the enlarged, 40.2-foot tailplane of the MD-87, the MD-90 had a 30-foot, 7 ¼-inch overall height. In order to counteract the pitch axis motion created by the elongated fuselage and heavier engines, powered elevators with dual actuators and manual reversion were introduced.
Power was provided by two 25,000-thrust-pound, cascade thrust reverser-equipped IAE V2525-D5 turbofans, which were attached by means of a new pylon and were fed by 5,840 US gallons of fuel.
The aircraft was ground-supported by a dual-wheeled, hydraulically actuated, tricycle undercarriage, equipped with carbon wheel brakes (for a 400-pound weight savings) and provisioned with a digital antiskid system.
Aircraft access was provided by four doors: a 34-by-72-inch forward, left passenger door; a 27-by-48-inch forward, right service door; a 27-by-60-inch aft, left service door; and a 27-by-72-inch tail passenger door with an integral, ventral airstair. Four 20-by-36-inch overwing emergency exists were also provided.
An updated, two-person, electronic flight instrument system (EFIS) cockpit, based upon the MD-88’s, featured a flight management system (FMS), a digital flight guidance system (DFGS), an auxiliary control system (ACS), an advanced inertial reference system, and a new air data computer.
Introducing a “new look” cabin with 12-percent larger-and lighted-overhead storage compartments equipped with full-grip handrails, the MD-90 standardly featured two forward, right, and two aft, left vacuum lavatories. Although its exit-limited capacity remained the 172 of the MD-80, its larger cabin could accommodate two additional seat rows, providing increased comfort. A typically mixed class interior entailed 153 passengers, while a tri-class one included 12 seats at a 36-inch pitch, 14 at a 32-inch pitch, and 132 at a 31-inch pitch. A 163 all-coach arrangement entailed 19 seats at a 32-inch pitch and 144 at a 31-inch pitch, all in a five-abreast, two-three configuration.
Lower-deck baggage and cargo holds, accessed by three starboard doors, collectively offered 1,300 cubic feet of space.
The MD-90 offered AlliedSignal variable-speed, constant frequency electrical generators, a new environmental control system, and a 565-shp AlliedSignal GTCP131-9D auxiliary power unit (APU), which had an 8,000-hour life.
With an 88,171-pound operating weight, 156,000-pound maximum take off weight, and 142,000-pound landing weight, the MD-90-30 could carry a 41,829-pound payload and had a 2,085-nautical mile range with 153 passengers.
Piloted by Crew Chief Test Pilot William Jones, Test Pilot G. R. “Bear” Smith, and Flight Test Engineer Barry McCarthy, the MD-90-30 prototype, registered N901DC, took to the air for the first time on February 22, 1993.
“The… MD-90,” according to McDonnell-Douglas, “is an advanced mid-size, medium-range airliner that serves the needs of travelers and airlines today and well into the 21st century. The aircraft, one of the quietest large commercial jetliners in the skies, belongs to the twin-jet family of aircraft that started with the DC-9 and includes the… 717 and MD-80… (It) was designed to be technically and economically competitive by incorporating many cost-effective technologies. It offers an advanced flight deck, including an electronic fight instrument system (EFIS), a full flight management system (FMS), a state-of-the-art inertial reference system, and LED dot-matrix displays for engine and system monitoring.”
Its second prototype, registered N902DC and used for avionics and systems tests and automatic landings, first flew on August 27, or three weeks ahead of schedule, while the first production aircraft took to the skies on September 20 of the following year, joining what would become a 1,450-flight, 1,906-hour flight test program, which culminated with FAA type approval two months later, on November 16.
Launch customer Delta, which had placed a 31-firm and 106-optioned order, took delivery of the first MD-90-30 (N902DA) on February 24 of the following year in Atlanta, the 2,094th aircraft in the DC-9/MD-80 family built.
Commenting during the hand over, Ronald W. Allen, Delta Air Lines Chairman, President, and Chief Executive Officer, said, “From the start, we participated in writing the specifications for this aircraft in anticipation of where our industry and our company are headed.”
Although it offered considerable commonality with its existing MD-88s, Delta had calculated an annual, $200,000 fuel savings due its IAE engines over that achieved by its predecessor’s JT8Ds.
It was inaugurated into revenue service on the Dallas-Newark sector on April 1, 1995.
Other major operators included Alaska Airlines (20 firm and 20 options), Japan Air System (10 and 10), International Lease Finance Corporation (15 and 15), Reno Air, China Northern, China Eastern, EVA Airways, Uni Airways, KTHY, Grand China Airlines, and Saudi Arabian Airlines, the first of which inaugurated it into European service on November 1 of the following year. By March of 1997, 46 aircraft were operated by ten carriers.
The type’s design service life, of 90,000 hours and 60,000 landings, was significantly greater than the 50,000 hours and 50,000 landings of the comparable MD-83.
Several other versions were either built or proposed.
The MD-90-30ER, for example, was intended, as its designation suggests, for extended ranges with an optional, 565-US gallon auxiliary fuel tank. Launch customer AMC Aviation of Egypt took delivery of the first of two ordered, registered SU-BMQ, on September 24, 1997.
The MD-90-30T resulted from the Trunkliner Program with China, whose agreement, signed on June 25, 1992, originally stipulated three MD-82s, 17 MD-82Ts, and 20 MD-90-30Ts, and the gradual transference of skills and components for ultimate license-building. Although fewer airframes emerged from Chinese production lines than the initial-and ambitious-contract had covered, these aircraft featured quad-wheeled main undercarriage units.
The higher-capacity, but unbuilt MD-90-40, for 180 passengers, was planned with forward, 190-inch and aft, 95-inch fuselage plugs.
And the MD-90-50 was optimized for airlines requiring increased range. Powered by two 28,000 thrust-pound IAE V2528-D5 turbofans, it introduced a 565-US gallon auxiliary fuel tank installed in the lower deck hold, reducing its volume to 822 cubic feet, but increasing its fuel capacity to 6,405 US gallons. With a 33,500-pound payload, 172,500-pound gross weight, and 150,000-pound maximum landing weight, it had a 3,022-nautical mile range.
The addition of two doors would have circumvented the aircraft’s otherwise 172-seat exit-limited capacity with the MD-90-55, a high-density derivative for up to 187 passengers.
Despite the fact that the MD-90 represented the pinnacle of McDonnell-Douglas twin-jet evolution, with the original DC-9 and the subsequent MD-80 having provided worldwide service for some three-and-a-half decades, its technological success proved counter to the manufacturer’s financial one. Having quickly lost ground to both Airbus Industrie and Boeing, it was all-too-aware that the progressive stretches of its three basic DC-8, DC-9, and DC-10 pure-jet products had failed to keep pace with the all-new airliners its competitors had intermittently offered, and to do so now would have cost it many times its worth, which was an unfeasible proposition.
Buoyed by a buyout from Boeing, its fiercest US rival during the jet age, it relegated itself to becoming the Douglas Products Division of the Boeing Commercial Airplane Company after the acquisition had been consummated on August 4, 1997, and the MD-90, for all its merits, was withdrawn from production in 2000 after only 114 aircraft had been built, now rendered superfluous by Boeing’s own-and competing-737-700 and -800 short- to medium-range twin-jet product line.