Wide-Body / Twin Aisle Aircraft

Four families of aircraft made up the fleet of wide-body transports that began operation on airlines throughout the world in the 1970's. These aircraft are the Boeing 747, the McDonnell Douglas DC-10, and the Lockheed L-1011, which were manufactured in the United States, and the Airbus A-300, produced by a consortium of European countries. All were expected to continue in service for the foreseeable future. In addition to these aircraft, the Soviet Union developed a large four-engine wide-body transport. This aircraft, the Ilyushin 86, first flew on December 22, 1976, and airline operations began in 1980. China is a late entrant to this market, with a COMAC C929 possibly flying after 2020.

The use of the term "wide body" in describing these aircraft is derived from the interior arrangement of the passenger cabin. Consider first the arrangement of the cabin of a "narrow-body" transport such as the 707 or 727. The cabin is divided into a small first-class compartment with four-abreast seating and a large tourist-class cabin with six-abreast seating. A single aisle runs the entire length of the cabin with three seats located on either side. For an aircraft of large passenger capacity, the fuselage of the narrow-body type tends to become very long, which, in turn, may dictate a long, heavy landing gear in order to permit the desired rotation angle on takeoff without scraping the rear end of the fuselage on the runway. The long aisle also causes lengthy delays in passenger loading and difficulty for the cabin attendants in serving meals and refreshments.

In a wide-body transport, the first-class cabin consists of a small four-abreast compartment in the forward part of the fuselage and a large seven-abreast tourist cabin. The tourist cabin is divided by two longitudinal aisles that run the length of the cabin. In the particular arrangement shown, two seats are located on either side of the aircraft next to the windows, and three seats are disposed about the centerline of the cabin with an aisle on either side. Some wide-body aircraft are designed to accommodate as many as 10-abreast seats. Current high-density versions of the Boeing 747, for example, may seat as many as 550 passengers in a 10-abreast arrangement.

For large-capacity aircraft, the double-aisle arrangement offers easy passenger loading and simplifies the serving problem for the cabin attendents. The design may also offer the passenger somewhat wider seats and a feeling of greater spaciousness. The landing-gear problem previously referred to is alleviated by the relatively short fuselage offered by the wide-body design for a given passenger capacity.

The large-diameter fuselage of the wide-body aircraft is often cited as a source of increased skin friction drag. The bulky appearance of these aircraft is no doubt responsible for this viewpoint. Actually, the ratio of wetted area to wing area for wide- and narrow-body aircraft of the same passenger capacity and wing loading may not be greatly different because of the shorter length of the wide-body aircraft.

The wide-body jet transports introduced in the 1970's are characterized by two other distinguishing features. First, these aircraft are very large in comparison with earlier jet transports. For example, one version of the Boeing 747, the largest of the wide-body aircraft, is certified at a maximum takeoff gross weight in excess of 800,000 pounds. Although the wide-body concept was originally applied only to very large aircraft, new designs for use in the 1980's utilize the wide-body concept in aircraft of the 707 weight category.

A second distinguishing feature of the wide-body transports is the type of engines used to power them. All the aircraft are powered by very large engines of high bypass ratio. Because of the high bypass ratio and high compressor pressure ratio of these engines, the values of their cruise-specific fuel consumption are about 20 percent lower than earlier low-bypass-ratio engines such as the Pratt & Whitney JT3D. Another outstanding feature of these engines is their relatively low noise levels, as compared with earlier engines, even though the thrust produced by the new engines is significantly higher than values typical of the earlier ones. The low-noise-level characteristic of the high-bypass-ratio engines results from an improved understanding of the mechanism of noise generation, as influenced by engine design, and through the use of new sound-absorbing materials in various parts of the inlets and other flow passages.

In other respects, the wide-body aircraft, as compared with earlier jet transports, have only evolutionally technical refinements. The widespread use of sophisticated, high-speed computational equipment has resulted in more refined aerodynamic and structural design and in improved machine control in manufacturing. As a result of more sophisticated analysis techniques and new developments in transonic aerodynamics, some improvements may be found in wing and airfoil design. Basically, however, the aerodynamic design of the wide-body aircraft is similar to the preceding generation of aircraft. Again, in the area of structural design, no radical innovations are to be found. All the aircraft use fully powered flight control systems, and all employ sophisticated auto pilots and other onboard systems.

The combination of large passenger capacity, more efficient and quieter engines, and more sophisticated detail design has resulted in transport aircraft that are safe, reliable, environmentally acceptable, and, from the airlines' viewpoint, profitable. From the passengers' viewpoint, the aircraft are fast, convenient, and relatively comfortable, and they offer reasonable fares.

Challengers such as Airbus waited in the wings, backed with governmental commitments that far exceeded American support to the industry. Founded in 1965 as a consortium of European countries, Airbus used massive government subsidies and private investors to develop its first plane. The Airbus had important innovations: it flew on two engines with two pilots, instead of three engines and three pilots. This reduced fuel consumption and lowered per flight operating costs. In 1967, the first A300 appeared-a 320-seat, twin-engine airliner. In 1988, Airbus captured 23 percent of the world market, and in 1999, for the first time, it received more orders for airplanes than Boeing did.

With a first flight date in September 1981, the Boeing 767-200 entered airline service in the late summer of 1982. The Boeing 767-200 is a 290-passenger, double-aisle, wide-body airliner designed to replace the aging Boeing 707 and McDonnell Douglas DC-8 transports used on domestic and foreign medium range route segments. Although of conventional configuration, the detailed aerodynamic design of the 767-200 is highly refined, as might be expected by the nearly 25 000 hours of wind-tunnel time required in the development of the aircraft. To place this wind-tunnel effort in perspective, 14 000 and 4000 wind-tunnel hours were expended in developing the Boeing 747 and 727, respectively.

The flight length categorisation has changed over the years and is not set in stone.Short-haul is now considered to be any flight with a distance under 3,000nm (5,600km). A medium-haul flight is between 3,000 and 6,000nm (5,600-11,100km) while a long-haul flight is for a distance of above 6,000nm. The Boeing 777-200LR is the longest-range airliner currently in production with a maximum range of 9,400nm [20,000 km].

About 50% of all widebody passenger scheduled sectors flown in 2013 were shorter than 2,500nm, while 70% are under 4,000nm. Less than 0.4% of these sectors exceed 8,000nm. Yet with the exception of the A330, all widebody aircraft offered by Airbus and Boeing today are designed with 8,000nm-plus range.

De-regulation, consumer demand for higher frequencies and the development of higher-capacity and increasingly efficient single-aisle models led to older-generation twin-aisle types such as the Airbus A300/A310 and Boeing 767 being squeezed off most short/medium-haul routes in Europe and North America. Some regional markets in Asia continue to sustain widebody operations, but the low-cost model is increasingly taking hold, led by the rampant growth of predominantly narrowbody operators. Asia continues to see extensive use of widebodied aircraft on short and medium-haul services. These aircraft are largely servicing trunk routes with high passenger demand.

In the wake of Boeing’s decision to abandon its proposed 787-3 development, which was primarily aimed at the Japanese domestic market, the Chicago-based giant and rival Airbus have concentrated on offering re-certifications of long-range widebodies with lower operating weights, derated engines and extended cyclic maintenance intervals designed to make the “misuse” of these aircraft more economically palatable for operators. A major advantage for airlines and financiers is the ability to retain the flexibility to re-activate their aircraft with their full range capability at later date by paying a fee to the manufacturer.