Commercial aircraft are the result of the airline requirements which shape them, attempting to fulfill, as completely and cost-effectively as possible, the particular combination of mission goals. For airliner-type aircraft, these include two primary parameters: payload, comprised of passengers, baggage, cargo, and mail, and range, which enables a carrier to offer nonstop service between specific city pairs.
Aircraft configurations are, in essence, design solutions to intended operating missions and hence vary according to fuselage length and width; wingspan, planform, and sweepback; engine type, thrust, and mounting; and horizontal and vertical tail location and size.
In the late 1970s, passenger demand had begun to eclipse the capacity of the Boeing 727, which had accommodated a maximum of 131 single-class, high-density passengers in its initial, short-fueselage -100 series and 189 in its stretched, -200 version.
Seeking to replace this venerable design on one-stop transcontinental routes with a higher-capacity tri-jet, Boeing had considered several replacements by stretching the 727-200’s fuselage, remounting two of the three engines to the wing underside, and ultimately eliminating the third engine in the vertical tail. The result, a low-wing, twin-engined, single-aisle airliner based upon the performance specifications submitted by American Airlines, Delta, and United, had been designated the 757. During this time, however, passenger acceptance of widebody aircraft had been overwhelming and many carriers had sought such a cabin cross-section on medium- as well as traditionally long-range route sectors. As a result, passenger capacity per aircraft had begun to decrease, from the 500 of the quad-engined Boeing 747, to the 350 of the tri-engined Lockheed L-1011 and McDonnell-Douglas DC-10, to the 225 of the twin-engined Airbus A-300.
With the margin between the maximum capacities of the 727-200 and the Airbus A-300 beginning to converge, many airlines had expressed interest in a small widebody which could accommodate the median of the two. The result, the 767, featured greater range and wider-cabin comfort with seven-abreast, dual-aisle coach seating for about 200, becoming the first (and thus far only) commercial airliner to deviate from the standard wide body fuselage width of previous Boeing, Lockheed, McDonnell-Douglas, and Airbus aircraft. The chosen width had offered both advantages and disadvantages. Of the advantages, it had featured less fuselage cross section-generated drag and increased cabin comfort, with most passenger seats either on the window or the aisle. Of the disadvantages, it had not been able to accommodate the now-standard LD-3 container on its lower deck in the traditional paired loading configuration and therefore had required the design of a smaller, specialized LD-2 container.
In January 1978, Boeing had expanded its Everett, Washington, production line, hitherto the sole domain of the 747, to include the new 767 design, and seven months later, on July 14, United Airlines had ordered 30 of the type, officially launching the program. First flying in prototype form on September 26, 1981, at which time orders had been received from 17 customers, the aircraft, in its initial –200 series domestic guise, received its FAA certification with the 44,300 thrust-pound Pratt and Whitney JT9D-7R high bypass ratio turbofan on July 30, 1982. The type entered scheduled service with United the following month on August 19. The aircraft was also certified with the General Electric CF6-80A powerplant on September 8 and this version entered service with Delta Air Lines. A variant with the Rolls Royce RB.211-524 engine, intended for British Airways, had also been offered.
Although initially intended for medium-range operation, the basic airframe had proven ideally suited toward larger-capacity deployment on thin, nonstop transcontinental and intercontinental sectors after being fitted with additional fuel tankage, thus able to replace previous widebody trijets. Dimensionally identical to the basic design, but certified with higher operating weights, the sub-version, designated 767-200ER…for “extended range”…had entered service on March 26, 1984.
The basic 767 fuselage, initially designed for increased capacity “stretchability,” had been lengthened by some 20.1 feet, accommodating 40 additional passengers. Although it had retained the original wingspan, the new version, designated 767-300, had been intended for higher-capacity transcontinental routes and had been first rolled out on January 30, 1986. Certified nine months later in September, it had entered scheduled service on September 25.
Mating the newly-elongated fuselage of the -300 series with the extended range capabilities of the -200ER, Boeing had produced the -300ER with increased-thrust engines, additional fuel capacity, and minor structural strengthening. Recording a 50,000-pound gross weight increase, the 767-300ER, numerically the most popular version with 505 aircraft having been sold, had featured a 2,000-mile range increase, entering scheduled service on February 19, 1988.
The final version, the 767-400ER, had incorporated technology designed for the already-in-service 777-200. Accommodating some 409 single-class passengers in a 21-foot longer fuselage and featuring a 14-foot greater wingspan with highly swept, raked wing tips, the 400,000-pound version had sat on a higher main undercarriage in order to retain take off rotation angles. The aircraft, with a remodeled passenger interior, had closed the gap between its smaller -300 series 767 and its larger 777 design. Although it had offered numerous advancements, it had appeared after most of the market had already ordered previous 767, A-330, and A-340 versions, not entering service until August 20, 2000, and therefore had only been operated by Continental, which had ordered 16, and Delta, which had ordered 21.
All aircraft incorporate several design-shaping characteristics.
The Boeing 767, for example, had replaced the 727 with a larger capacity, widebody design, retaining gate and ramp compatibility at smaller, 727-like airports, and had been optimized for the tri-jet’s one-stop transcontinental routes. Because of parallel 757 development, it had been able to minimize its development costs.
A narrower fuselage cross-section than that used by previous widebody aircraft had resulted in a reduction in parasite drag and a twin-aisle cabin, in which passengers had never been more than one seat away from the window or the aisle. Composite construction had been used in most of the flight surfaces, particularly the fixed wing leading edge panel, the spoilers, the ailerons, the fixed wing trailing edge panel, the undercarriage doors, the elevators, and the rudder, and the airframe had utilized advanced, light-weight aluminum alloy construction.
A supercritical wing, one the aircraft’s key design features, had resulted in a high aspect ratio, an aft-loaded section, the development of more lift for less drag than any previous airfoil, a 22% thicker wing than that used by any previous-decade commercial airliner, a lighter and simpler structure, and more wing-integral fuel tank capacity.
Powered by two high bypass ratio turbofans, in which a higher percentage of the engine’s thrust is produced by the cooler, inner core-bypassing air, it had featured lower specific fuel consumption, a reduced noise footprint, lower maintenance costs, and high reliability.
A two-person cockpit crew, following the trend created by the Airbus A-300, had reduced crew costs, and the aircraft’s common pilot type rating with that of the narrow-body Boeing 757 had ensured greater crew scheduling flexibility to carriers which had operated both types.
Inherent fuselage stretchability and existing wing and tail capability had enabled the manufacturer to offer increased-capacity versions and these, coupled with its extended range twin-engine operations certification, had enabled it to offer a viable DC-10 and L-1011 alternative with one fewer engine and cockpit crew member, significantly reducing operating costs.
Although sales of the Boeing 767 had dwindled by 2008, the type, currently being replaced by Boeing’s own 787, had sold some 950 aircraft of all versions to well over 100 worldwide airlines.