Risk in the commercial aircraft business is higher than in most others. Both technological and market uncertainties are great, and the costs of launching a new model are enormous. Rolls Royce's effort to make all-composite fan blades for the Lockheed L-1011 engine failed, causing delay in the plane's introduction and ultimately the bankruptcy of both companies. Boeing's 747 got heavier and heavier throughout the development process, requiring more and more powerful engines and driving up costs. Pan Am, the 747's launch customer, Pratt & Whitney, the engine makers, and Boeing were all nearly bankrupted by the effort.
More than technological failure, failure in the market has been the source of disasters in the aircraft business. As a rule, an aircraft manufacturer needs to sell at least 500 units of a model for it to break even. Of the 26 basic airplane types introduced worldwide since the beginning of the jet age, by 1993 only 6 had sold as many as 500 (another 4 are likely to do so before their production runs end). Seven sold less than 120 copies. Only four or five have been profitable. A report by First Boston Corp. concluded that in 1984, the jet transport aircraft programs then launched had accumulated total losses of $40 billion on total sales of $180 billion (in 1984 dollars). "The essential message [of these figures] is that economic failure is the norm in the civil aircraft business.'
There is no standard taxonomy for civil aircraft. The term "Large civil aircraft" has traditionally been defined as civil aircraft with more than 100 seats and weighing over 33,000 pounds. The US Federal Aviation Administration's (FAA) long-standing definition of "large aircraft" is an aircraft with a maximum certificated takeoff weight (MTOW) of over 12,500 pounds. The aviation industry is composed of thousands of operators that conduct different types of operations in numerous different types of aircraft. Many aircraft operators are air carriers or commercial operators that offer transportation to the public for compensation or hire. Others are general aviation (GA) operators that do not offer transportation to the public. These operators often are corporate or private owners of aircraft that operate their aircraft for their own use or provide transportation for compensation or hire only to certain customers without offering transportation to the public in general.
|FAA Design Group||Wingspan|
|I||less than||49 feet|
|V||171 feet||213 feet|
|VI||214 feet||261 feet|
- OECD Category A aircraft (i.e., turbojet, turboprop, and turbo fan aircraft, with between 30 and 70 seats)
- OECD Category B aircraft (i.e., turbine-powered aircraft with fewer than 30 seats)
- OECD Category C aircraft (all other aircraft)
Airline cabins are frequently classified as narrow-body if there is a single aisle with seats on either side, or wide-body if there are two aisles with a block of seats between them in addition to the seats on the side. The number of seats abreast is affected by the aircraft width. On very small aircraft such as the Beechcraft 1900 there are only individual seats on each side of the aisle (1+1 seating). The widest narrow body aircraft such as the Airbus A320 and Boeing 737 have six abreast seating in a 3+3 layout. Asymmetrical layouts also exist, the Embraer Regional Jets have 1+2 seating while the Douglas DC-9 aircraft typically feature 2+3 seating.
In 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.
A narrow six-abreast single-aisle configuration usually has slightly less wetted area, and thus less drag, than a six-abreast twin-aisle arrangement designed for the same number of passengers. Apparently, passengers are willing to accept the single-aisle layout for short flights but prefer the more spacious wide-body design for flight times greater than several hours.
The use of the term "wide body" in describing these aircraft is derived from the interior arrangement of the passenger cabin. A typical interior cabin arrangement of a wide-body transport has first-class cabin consisting of a small four-abreast compartment in the forward part of the fuselage and a large nine-abreast tourist cabin. The tourist cabin is divided by two longitudinal aisles that run the length of the cabin. In this arrangement shown, three 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. On wide body-aircraft the center block of seats between the aisles can have as many as 5 seats on planes like the layout on some McDonnell Douglas DC-10 and Boeing 777 aircraft, although Boeing recommends the 3+3+3 over the 2+5+2 layout.
Very wide planes such as the Boeing 747 or the Airbus A380 have ten seats abreast, typically in a 3+4+3 layout, although this layout is also sometimes used as a high density layout on aircraft normally seating nine abreast, such as the 777 or DC-10. 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 is alleviated by the relatively short fuselage offered by the wide-body design for a given passenger capacity.
Section 25.815 species the minimum aisle width dimensions for transport category airplanes based on the passenger capacity. For airplanes with 20 or more passenger seats, a minimum 15-inch width at heights 25 inches or less above the main aisle floor and a minimum 20-inch width at heights greater than 25 inches above the floor must be maintained. Aisle width is measured at any point along the aisle, normal to the centerline of the aisle. The main aisle envisioned by the regulations would run in a straight line from one end of the passenger cabin to the other and would satisfy these width criteria.
Long standing FAA policy has permitted slight deviation from a straight line where there is a transition from one cabin section to another, or where there are interior features which dictate that the aisle move laterally. For example, from tourist class to first class there may be a change from five-abreast seating to four-abreast seating which moves the aisle centerline laterally. This has been accepted provided the required widths are maintained at all heights normal to the path that an individual would take. This type of offset normally occurs at one or two points in a main cabin aisle. In addition, there is no offset permitted in the aisle vertically; that is, the required 15-inch dimension must lie completely below the projected 20-inch dimension at all points along the aisle.
Successful jet transports tend to have long operational careers and are usually produced in many versions. Engine changes and improvements, changes in wing area and high-lift systems, aerodynamic and structural refinements, and modernization of onboard systems may take place during the production life of a successful aircraft type. "Stretching" is another modification technique frequently employed. In this case, the fuselage is lengthened by the addition of "barrel sections" so that the passenger capacity of the aircraft is accordingly increased.
One manner of increasing passenger space in an airplane is to increase the length of the fuselage. This process is commonly known as "stretching". Typical problems associated with "stretching" an airplane and ultimately limiting the size of the airplane are: (1) limitation of aft-body rotational clearance, (2) disproportionate growth of the lower lobe cargo space, and (3) maneuverability of the airplane around the airport. These problems occur in principle with single as well as double deck airplanes. For singledeck airplanes they become critical at a lesser increment of growth then for double deck airplanes. The Boeing 747 airplanes have an upper deck in the forward portion of the fuselage. The Stratocruiser has a lower lobe lounge. The McDonald-Douglas MD11 aircraft has a lower lobe seating option. There have been numerous large flying boats with multiple decks. Usually a double deck configuration is chosen to improve interior efficiency, sometimes utilizing space that was initially provided for other reasons. For example, the upper deck in the Boeing 747 airplanes, was the result of requiring a nose cargo door configuration. Flying boats have unique hull requirements, limiting length and therefore favoring multi-deck arrangements.
Increasing passenger space by use of an additional deck is preferred to merely increasing the length or overall size of the aircraft because it results in a shorter aircraft which is easier to maneuver around an airport. A partial upper deck is preferred because it provides a beneficial ratio of lower lobe cargo space to passenger seat space. Prior experience with the addition of an upper deck to an airplane has provided Mach number and drag penalties. However, heretofore, all upper deck additions have been either a forward partial upper deck or a full upper deck.
Sample Cross-section Dimensions and Seating Layouts
N per Max N Layout Width Height Aircraft XSection Abreast Decks inches ------------------------------------------------------------ 2 2 1 11 64 60 Lear25 2 2 1 11 65 70 DHC6 2 2 1 11 94 94 GIV 4 4 1 22 110 101 DHC7 4 4 1 22 104 104 Dash8-300 4 4 1 22 113 113 Concorde 5 5 1 23 134 134 BAC111 5 5 1 23 130 130 F100 5 5 1 23 131.5 143 MD80/717 6 6 1 33 148 - 737/757 6 6 1 33 147 - DC8 6 6 1 33 140 140 BAE146 6 6 1 33 155.5 - A320 7 7 1 232 198 217 767 7 7 1 232 186 - 7J7 8 8 1 242 222 - A300/A310/A330/A340 9 9 1 252 237 237 MD11 9 9 1 252 235 235 L1011 9 9 1 252 244 244 777 16 9 2 333/232 266 336 A3xx Study (1994) 16 10 2 343/33 256 308 747 18 10 2 343/242 266 336 A380 Coach 19 11 2 353/242 - - MD-12 (study) 19 11 2 234/242 307 373 Boeing NLA (study) 26 10 3 343/343/33 261 403 A 3-deck guess 29 12 3 343/363/232 335 403 Based on Douglas Study
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