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The European Airbus A380 is the world's largest and broadest passenger aircraft

A wide-body aircraft is a large airliner with a fuselage diameter of 5 to 6 metres (16 to 20 ft), with twin aisles. Passengers are usually seated 7 to 10 abreast. For comparison, a traditional narrow-body airliner has a diameter of 3 to 4 metres (10 to 13 ft), a single aisle, and seats arranged 2 to 6 abreast. Typical wide-body aircraft can accommodate between 200 and 600 passengers, while the largest narrow-bodies carry about 280. Freight or cargo wide-bodies also exist.

Boeing 747, the first wide-body, operated by Pan American, with a fuselage diameter of 256 inches in the constant section

Following the success of the Boeing 707 (with 148 inch fuselage) and Douglas DC-8 (with 163 inch fuselage) in the late 1950s, airlines began asking for larger aircraft to meet the rising demand for air travel. Engineers were faced with many challenges as airlines wanted more seats, more range, and lower operating cost. One of the most significant difficulties was selecting a fuselage configuration suitable for more than 200 passengers.

Early jet aircraft like the 707 and DC-8 seated passengers either side of a single aisle, with no more than 6 seats per row. Larger aircraft would have to be longer, higher (i.e. double-deck) or wider in order to accommodate the proposed passenger numbers. Engineers realized that lengthening the fuselage would have resulted in aircraft that would be too long to be handled by airports, while having two decks caused difficulties meeting emergency evacuation regulations which were extremely challenging with the technology available at the time. This left a wider fuselage as the best option: by adding a second aisle, as many as 10 seats across could be accommodated.^[1]

The Airbus A300 introduced in 1972 was the first twin-engined wide body

The first true wide-body airliner was the four-engined Boeing 747; it debuted in 1969 and remained the largest in passenger service till the 25th October 2007 when the Airbus A380 entered commercial service. The main deck of the 747 features twin aisles and seating 10-abreast, while the upper deck "hump" seats 6-abreast along a single aisle. Its fuselage is 256 inches in diameter.

Other wide-bodies soon followed, including the McDonnell Douglas DC-10 and the Lockheed L-1011 Tristar, with 237 inch diameter fuselage. In 1974, Airbus introduced the Airbus A300, the first twin-engined wide-body. Subsequent commercial wide-bodies include:

An example of a widebody Lockheed L-1011 TriStar in a trijet configuration of Royal Jordanian Airlines in this shortlived early 1980s livery

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Two wide-body designs are in development or testing:

• Boeing 787 (2008) - first aircraft to utilize monolithic composite fuselage, replacement for the Boeing 767. The outside diameter of its fuselage is 227 inches.
• Airbus A350 (2012-2013) - replacement for the Airbus A330/A340 line

Cross section of the Airbus A380. Note the twin aisles on both decks

Airbus A300 fuselage cross-section, showing the passenger compartment above and cargo containers below. On display at the Deutsches Museum in Munich, Germany.

Although a wide-body aircraft has a larger frontal area than a narrow-body of equivalent capacity, and thus greater form drag, it has several advantages:

• Lower ratio of surface area to volume, and thus (for equal volume) lower frictional drag.
• Twin aisles accelerate loading and unloading/evacuation relative to a single aisle
• Wider fuselage reduces the overall length of the aircraft, improving ground maneuverability and reducing the risk of tail strikes.
• Greater under-floor freight capacity.
• More structurally efficient than narrow-bodies for large aircraft
• The British and the Russians proposed aircraft similar in configuration to the Vickers VC-10 and Boeing 717, but with a wide-body fuselage. The Three-Eleven project never got off the drawing board while the Russian Il-86 wide-body gave way to a more conventional engine on wing-mounted design, most likely due to the inefficiencies of mounting such large powerplants off the aft fuselage.

Aircraft are categorised by ICAO according to the amount of wake turbulence they produce. Because wake turbulence is generally related to the weight of an aircraft, these categories are based on weight—aircraft with a maximum certificated take-off weight of 300,000 lb (136,000 kg) or more are classed as Heavy, those between 15,500 lb and 300,000 lb (7,000 kg and 136,000 kg) are classed as Medium, and those below 15,500 lb (7,000 kg) are classed as Light. Due to their weight, all current wide-body aircraft are categorised as Heavy.

The wake turbulence category is used to guide the separation of aircraft—a Heavy category aircraft will require greater separation behind it than a Medium category, which in turn requires more separation than a Light category. In some countries, such as the USA, it is a requirement to suffix the aircraft's call sign with the word "heavy" when communicating with ATC in the Terminal Radar Area. If the aircraft is on an ARTCC (Air Route Traffic Control Center Frequency), they are not required to say "heavy" at the end of the callsign. For example, flight UAL342 operated by United Airlines using a wide bodied aircraft would use the call sign "United 342 Heavy" while in the USA.

• [1] official boeing company website]

1. ^ Irving, Clive (1994). Wide Body: The Making of the Boeing 747. Coronet. ISBN 0 340 59983 9.