Airliner


An airliner is a type of aircraft for transporting passengers and air cargo. Such aircraft are most often operated by airlines. Although the definition of an airliner can vary from country to country, an airliner is typically defined as an airplane intended for carrying multiple passengers or cargo in commercial service. The largest of them are wide-body jets which are also called twin-aisle because they generally have two separate aisles running from the front to the back of the passenger cabin. These are usually used for long-haul flights between airline hubs and major cities. A smaller, more common class of airliners is the narrow-body or single-aisle. These are generally used for short to medium-distance flights with fewer passengers than their wide-body counterparts.
Regional airliners typically seat fewer than 100 passengers and may be powered by turbofans or turboprops. These airliners are the non-mainline counterparts to the larger aircraft operated by the major carriers, legacy carriers, and flag carriers, and are used to feed traffic into the large airline hubs. These regional routes then form the spokes of a hub-and-spoke air transport model.
The lightest of short-haul regional feeder airliner type aircraft that carry a small number of passengers are called commuter aircraft, commuterliners, feederliners, and air taxis, depending on their size, engines, how they are marketed, region of the world, and seating configurations. The Beechcraft 1900, for example, has only 19 seats.

History

Earliest specifications

When the Wright brothers made the world's first sustained heavier-than-air flight, they laid the foundation for what would become a major transport industry. Their flight in 1903 was just 11 years before what is often defined as the world's first airliner. These airliners have had a significant impact on global society, economics, and politics.
In 1913, Igor Sikorsky developed the first large multi-engine airplane, the Russky Vityaz, refined into the more practical Ilya Muromets with dual controls for a pilot plus copilot and a comfortable cabin with a lavatory, cabin heating and lighting.
The large four-engine biplane was derived in a bomber aircraft, preceding subsequent transport and bomber aircraft.
Due to the onset of World War I, it was never used as a commercial airliner.
It first flew on December 10, 1913 and took off for its first demonstration flight with 16 passengers aboard on February 25, 1914.
In 1915, the first airliner was used by Elliot Air Service. The aircraft was a Curtiss JN-4, a small biplane which was used mainly in World War I as a trainer. Later, it was also used as a tour and familiarization flight aircraft in the early 1920s.

Interwar period

In 1919, after World War I, the Farman F.60 Goliath, originally designed as a long-range heavy bomber, was converted for commercial use into a passenger airliner. It could seat 14 passengers from 1919, and around 60 were built. Initially, several publicity flights were made, including one on 8 February 1919, when the Goliath flew 12 passengers from Toussus-le-Noble to RAF Kenley, near Croydon, despite having no permission from the British authorities to land.
Another important airliner built in 1919 was the Airco DH.16; a redesigned Airco DH.9A with a wider fuselage to accommodate an enclosed cabin seating four passengers, plus pilot in an open cockpit. In March 1919, the prototype first flew at Hendon Aerodrome. Nine aircraft were built, all but one being delivered to the nascent airline, Aircraft Transport and Travel, which used the first aircraft for pleasure flying, and on 25 August 1919, it inaugurated the first scheduled international airline service from London to Paris. One aircraft was sold to the River Plate Aviation Company in Argentina, to operate a cross-river service between Buenos Aires and Montevideo.
Meanwhile, the competing Vickers converted its successful WWI bomber, the Vickers Vimy, into a civilian version, the Vimy Commercial. It was redesigned with a larger-diameter fuselage, and first flew from the Joyce Green airfield in Kent on 13 April 1919.
The world's first all-metal transport aircraft was the Junkers F.13, also from 1919, with 322 built.
The Dutch Fokker company produced the Fokker F.II and then the F.III. These aircraft were used by the Dutch airline KLM when it reopened an Amsterdam-London service in 1921. The Fokkers were soon flying to destinations across Europe, including Bremen, Brussels, Hamburg, and Paris. They proved to be very reliable aircraft.
The Handley Page company in Britain produced the Handley Page Type W as the company's first civil transport aircraft. It housed two crew in an open cockpit and 15 passengers in an enclosed cabin. Powered by two Napier Lion engines, the prototype first flew on 4 December 1919, shortly after it was displayed at the 1919 Paris Air Show at Le Bourget. It was the world's first airliner to be designed with an on-board lavatory.
Meanwhile, in France, the Bleriot-SPAD S.33 was a great success throughout the 1920s, initially serving the Paris-London route, and later on continental routes. The enclosed cabin could carry four passengers with an extra seat in the cockpit.
By 1921, aircraft capacity needed to be larger for the economics to remain favourable. The English company de Havilland, therefore built the 10-passenger DH.29 monoplane, while starting work on the design of the DH.32, an eight-seater biplane with a less powerful but more economical Rolls-Royce Eagle engine. Owing to the urgent need for more capacity, however, work on the DH.32 was stopped and the DH.34 biplane was designed, accommodating 10 passengers. The Fokker trimotor was an important and popular transport, manufactured under license in Europe and America.
Throughout the 1920s, companies in Britain and France were at the forefront of the civil airliner industry, often considerably aided by government subsidies.
In America, the Ford Trimotor was an important early airliner. With two engines mounted on the wings and one in the nose, and a slabsided body, it carried eight passengers and was produced from 1925 to 1933. It was used by the predecessor to Trans World Airlines, and by other airlines long after production ceased. Pan Am opened up transoceanic service in the late 1920s and early '30s, based on a series of large seaplanes – the Sikorsky S-38 through Sikorsky S-42.
By the 1930s, the airliner industry had matured and large consolidated national airlines were established with regular international services that spanned the globe, including Imperial Airways in Britain, Lufthansa in Germany, KLM in the Netherlands, and United Airlines in America. Multi-engined aircraft were now capable of transporting dozens of passengers in comfort.
In Britain, the de Havilland Dragon was a successful aircraft during the 1930s. Its simple design used a plywood box fuselage. It could carry six passengers, each with of luggage, on the London-Paris route on a fuel consumption of just 13 gal per hour. The wing panels outboard of the engines could be folded for storage. The type was attractive as a short-haul, low-capacity airliner and was soon in service worldwide. British production of the DH.84 ended when it was replaced on the assembly line by the more powerful and elegant de Havilland Dragon Rapide.
appeared in 1935
The first modern-looking, sleek metal airliners also came into service in the 1930s. In the United States, the Boeing 247 and the 14-passenger Douglas DC-2 flew, and in 1935, the more powerful, faster, 21–32 passenger Douglas DC-3 appeared. DC-3s were produced in quantity for World War II and sold as surplus afterward. The Douglas DC-3 was a particularly important airplane, because it was the first airliner to be profitable without a government subsidy.
Long-haul flights were expanded during the 1930s as both Pan American Airways and Imperial Airways competed in the provision of transatlantic travel using flying boats such as the British Short Empire and the American Boeing 314. This prefigured the dramatic growth of transatlantic travel in the postwar period.

The postwar era

United Kingdom

In the United Kingdom, the Brabazon Committee was formed in 1942 under John Moore-Brabazon, 1st Baron Brabazon of Tara to investigate the future needs of the British Empire's civilian airliner market. The study was an attempt at defining in broad overview, the impact of projected advances in aviation technology, and to forecast the global needs of the postwar British Empire and Commonwealth in the area of air transport, for passengers, mail, and cargo. The crucial problem that the planners faced was that an agreement had been reached between the United States and the United Kingdom in 1942 to split responsibility for building multi-engine aircraft types for British use: the US would concentrate on transport aircraft, while the UK would concentrate on their heavy bombers. This decision meant that the United Kingdom would be left at the close of the war with little experience in the design, manufacture, and final assembly of transport aircraft.
The final report called for the construction of four general designs studied by the committee and members of the state-owned airlines British Overseas Airways Corporation and later British European Airways. The first three designs were piston-powered aircraft of varying sizes for different markets, while the Type IV design, at the urging of Geoffrey de Havilland, whose company was involved in development the first jet fighters, was for a jet-powered 100-seat design.
The Type I design, after a brief contest, was given to the Bristol Aeroplane Company, building on submissions they had made during the war for a "100 ton bomber". This evolved into the creation of the Bristol Brabazon.
The Type II process was complicated by the proposition of Vickers that a move to the newly developed turboprop power should be made. The specification was, therefore, split in two, with the conventional piston design going to the eventual de Havilland Dove and Airspeed Ambassador. The revolutionary VC.2 Viceroy, first flown in 1948, was the first turboprop design anywhere. The Type III requirement was developed as the Avro Tudor.
The Type IV for the jet-powered aircraft went to de Havilland and became, in 1949, the world's first jet airliner, the Comet. It featured an aerodynamically clean design with four de Havilland Ghost turbojet engines buried in the wings, a pressurised fuselage, and large, square windows. For the era, it offered a relatively quiet, comfortable passenger cabin and showed signs of being a commercial success at its 1952 debut. However, a year after entering commercial service, the Comets began suffering problems, with three of them breaking up during mid-flight in well-publicised accidents. This was later found to be due to catastrophic metal fatigue, not well understood at the time, in the airframes. The Comet was withdrawn from service and extensively tested to discover the cause. Rival manufacturers, meanwhile, heeded the lessons learned from the Comet while developing their own aircraft. Although sales never fully recovered, the improved Comet 2 and the prototype Comet 3 culminated in the redesigned Comet 4 series which debuted in 1958 and had a productive career of over 30 years.
This disaster, coupled with the fact that the UK's domestic market was much smaller than the US's, meant that by the 1960s, it was increasingly clear that the UK had lost the airliner market to the US, and later designs like the BAC 1-11, Vickers VC10, and Hawker Siddeley Trident although successful would be unable to win a substantial part of it back again. Another committee was formed to consider supersonic designs, STAC, and worked with Bristol to create the Bristol 223 design for a 100-passenger transatlantic airliner. However, this was going to be so expensive to produce that the effort was later merged with similar efforts in France to create the Concorde supersonic airliner.

United States

The United States, conversely, gained a huge advantage in design and production in the airline industry in the years leading up to the war, but many of the developments were put off until after the war as the manufacturing efforts were placed on the war effort. The advancements that the United States made in this industry were in large part due to the cooperation of the airlines discussing what they desired with the airliner manufacturers.
DC-6, Stapleton Airport, Denver, September 1966
Soon after the war, though, Douglas made a large advancement with the DC-4; although this could not cross the Atlantic at every point, it was able to make a nonstop flight from New York to the United Kingdom. Due to the war going on, the first batch of these planes went to the U.S. Army and Air Forces, and was named the C-54 Skymaster. Some of these used in the war were later converted for the airline industry, along with the passenger and cargo versions that were placed on the market once the war ended. Douglas later developed a version of this plane that was pressurized and five feet longer; this redesigned plane became the DC-6; these DC-6s were grounded for six months to rectify a few safety issues that were causing in-flight fires.
Soon after the DC-4, Lockheed developed the distinctive triple-tail Constellation. An aviation breakthrough, it was the first commercially successful pressurized airliner, allowing it to fly higher than other airliners. Its fuselage was some 127 inches wider than the DC-4s. Drafted by the military in World War II, it experienced a similar late entry into the civilian airline industry. Safety concerns grounded it for six months soon after it entered service while problems were investigated and repaired.
In 1947, the Boeing 377 Stratocruiser entered the industry with a completely different design from Douglas and Lockheed aircraft. Based on the C-97 Stratofreighter military transport, it had a double deck and pressurized fuselage. Luxury and a 100-passenger capacity distinguished it from its rivals. While 900 C-97s were supplied to the military, only 55 were produced for civil aviation.
The American companies had done a great job of advancing the status of transcontinental travel, but the aging fleet of DC-3s had to be addressed. Convair decided that they were going to address this market, and began producing the Convair 240, which was a 40-person fully pressurized plane. Including two that were equipped with jet-assisted take-off units, 566 of these planes flew. Convair later developed the Convair 340, which was slightly larger and could accommodate between 44 and 52 passengers, and 311 of this model were produced. Finally, Convair created a Convair 440, which had small modifications, including much better soundproofing than the previous models. Convair experienced competition from the Martin 2-0-2 and Martin 4-0-4, but in general was able to control this market, as the 2-0-2 had safety concerns and was unpressurized, and the 4-0-4 only sold around 100 units.
The United States was dominant in this industry for several reasons, including a large domestic market for these planes. The market also worked in the United States' favor as the American companies began to build pressurized airliners. During the postwar years, engines became much larger and more powerful, and safety features such as deicing, navigation, and weather information were added to the planes. Lastly, the planes produced in the United States were more comfortable and had superior flight decks than those produced in Europe.

France

In the postwar years, France developed a few significant airliners, some of these being planes that could land on water; part of the reason the French companies were so focused on these flying boats is that in 1936, the French Air Ministry requested transatlantic flying boats that could hold at least 40 passengers. Only one model from this request was ever put into service. The first set of these were three Latécoère 631's that Air France purchased and put into service in July 1947. However, two of these planes crashed, and the third plane was soon removed because of safety concerns. Later, the SNCASE SE.161 Languedoc was a much more successful plane, with 40 of them being placed into service through Air France. The French also developed the Breguet 763 Deux Ponts, which first flew in February 1949. This was a double-decker transport airliner that ended up being used for both people and cargo. This four-engined plane could be used to hold large amounts of cargo or 97 passengers. After a long silence, France then created the Caravelle, the world's first short- to midrange jet airliner. Subsequent French efforts were part of the Airbus pan-European initiative.

USSR

Soon after the war, most of the Soviet fleet of airliners consisted of DC-3s or Lisunov Li-2s. These planes were in desperate need of replacement, and in 1946, the Ilyushin Il-12 made its first flight. The Il-12 was very similar in design to American Convair 240, except was unpressurized. In 1953, the Ilyushin Il-14 made its first flight, and this version was equipped with much more powerful engines. The main contribution that the Soviets made in regards to airliners was the Antonov An-2. This plane is a biplane, unlike most of the other airliners, and sold more units than any other transport plane.

Types

Wide-body airliners

The largest airliners are wide-body jets, also called twin-aisle aircraft because they generally have two separate aisles running from the front to the back of the passenger cabin. Aircraft in this category are the Boeing 747, Boeing 767, Boeing 777, Boeing 787, Airbus A300/A310, Airbus A330, Airbus A340, Airbus A350, Airbus A380, Lockheed L-1011 TriStar, McDonnell Douglas DC-10, McDonnell Douglas MD-11, Ilyushin Il-86, and Ilyushin Il-96. These aircraft are usually used for long-haul flights between airline hubs and major cities with many passengers.

Narrow-body airliners

A smaller, more common class of airliners is the narrow-body or single-aisle aircraft. These smaller airliners are generally used for medium-haul flights with fewer passengers than their wide-body counterparts. Currently produced narrow-body airliners include the Airbus A220 and A320, Boeing 737, Embraer E-Jet, and Tupolev Tu-204/214.
Out-of production aircraft include the McDonnell Douglas DC-9 and its derivatives MD-80/MD-90 series and Boeing 717, using the same cabin cross-section as the Boeing 737, the 757, 727, and 707, its competitor the Douglas DC-8 or the Tupolev Tu-154, Ilyushin IL-18, and the Ilyushin IL-62.
Future narrow-body airliners include the Comac C919 and Irkut MC-21.

Regional, short-haul, and feederliner aircraft

s typically seat fewer than 100 passengers and may be powered by turbofans or turboprops. These airliners are the non-mainline counterparts to the larger aircraft operated by the major carriers, legacy carriers, and flag carriers, and are used to feed traffic into the large airline hubs or focus cities. These particular routes may need the size of a smaller aircraft to meet the frequency needs and service levels customers expect in the marketed product offered by larger airlines and their modern narrow- and wide-body aircraft. Therefore, these short-haul airliners are usually equipped with lavatories, stand-up cabins, pressurization, overhead storage bins, and reclining seats, and have a flight attendant to look after the in-flight needs of the passengers during point-to-point transit routes.
Because these aircraft are frequently operated by smaller airlines that are contracted to provide passengers from smaller cities to hub airports for a "major" or "flag" carrier, regional airliners may be painted in the liveries of the major airline for which they provide this "feeder" service, so the regional airlines may offer and market a seamless transition between the larger airline to smaller airline.
Typical aircraft in this category include the Bombardier CRJ and Embraer ERJ regional jets along with the Bombardier "Q" series, ATR 42/72 and Saab 340/2000 turboprop airliners.

Commuterliners used by regional airlines and air taxi operators

The lightest of short-haul regional feeder airliner type aircraft that carry 19 or fewer passenger seats are called commuter aircraft, commuterliners, feederliners, and air taxis, depending on their size, engines, how they are marketed, region of the world, and seating configurations. The Beechcraft 1900, for example, has only 19 seats. Depending on local and national regulations, a commuter aircraft may not qualify as an airliner and may not be subject to the regulations applied to larger aircraft. Members of this class of aircraft normally lack such amenities as lavatories and galleys, and typically do not carry a flight attendant as an aircrew member.
Other aircraft that may fall into this category are the Fairchild Metro, Jetstream 31, and Embraer EMB 110 Bandeirante. The Cessna Caravan and Pilatus PC-12 are single-engined turboprops, sometimes used as small airliners, although many countries stipulate a minimum requirement of two engines for aircraft to be used as airliners.
Twin piston-engined aircraft made by Cessna, Piper, Britten-Norman, and Beechcraft are also in use as short-haul, short-range, commuter-type aircraft.

Engines

Until the beginning of the Jet Age, piston engines were common on propliners such as the Douglas DC-3. Nearly all modern airliners are now powered by turbine engines, either turbofans or turboprops. Gas turbine engines operate efficiently at much higher altitudes, are more reliable than piston engines, and produce less vibration and noise. The use of a common fuel type – kerosene-based jet fuel – is another advantage. Prior to the Jet Age, the same or very similar engines commonly were used in civilian airliners and military aircraft. In recent years, divergence has occurred, so that is of the same engine on military type and civilian type aircraft is unusual. Those military aircraft which do share engine technology with airliners are typically transports or tanker types.

Airliner variants

Some variants of airliners have been developed for carrying freight or for luxury corporate use. Many airliners have also been modified for government use as VIP transports and for military functions such as airborne tankers, air ambulance, reconnaissance, as well as for troop-carrying roles.

Configuration

Modern jetliners are usually low-wing designs with two engines mounted underneath the swept wings. The Boeing 747 and Airbus A380 are the only airliners in production which are too heavy for just two engines. Smaller airliners sometimes have their engines mounted on either side of the rear fuselage. Numerous advantages and disadvantages exist due to this arrangement. Perhaps the most important advantage to mounting the engines under the wings is that the total aircraft weight is more evenly distributed across the wingspan, which imposes less bending moment on the wings and allows for a lighter wing structure. This factor becomes more important as aircraft weight increases, and no in-production airliners have both a maximum takeoff weight more than 50 tons and engines mounted on the fuselage. The Antonov An-148 is the only in-production jetliner with high-mounted wings, which reduces the risk of damage from unpaved runways.
Except for a few experimental or military designs, all aircraft built to date have had all of their weight lifted off the ground by airflow across the wings. In terms of aerodynamics, the fuselage has been a mere burden. NASA and Boeing are currently developing a blended wing body design in which the entire airframe, from wingtip to wingtip, contributes lift. This promises a significant gain in fuel efficiency.

Current manufacturers

The major manufacturers with airliners currently in production include:
The narrow-body and wide-body airliner market is dominated by Airbus and Boeing, and the regional airliner market is mostly split between ATR Aircraft, Bombardier Aerospace, and Embraer.
Setting up a reliable customer support network, ensuring uptime, availability and support 24/7 and anywhere, is critical for the success of airliner manufacturers.
Boeing and Airbus are ranked 1 and 2 in customer satisfaction for aftermarket support by a survey by Inside MRO and Air Transport World, and this is a reason why Mitsubishi Aircraft Corporation purchased the Bombardier CRJ program.
It is an entry barrier for new entrants like the Xian MA700 and Comac C919, with no credible previous experience with the MA60, or the Irkut MC-21 after the Sukhoi Superjet 100.

Notable airliners

ModelFirst flightNet ordersDeliveriesBacklogMTOW typ. seatsRange
Airbus A22016/09/201360.8-67.6116-1412,950-3,200
Airbus A320 family 22/02/198775.5-97124-2063,200-4,000
Airbus A330/A330neo02/11/1992242-251247-2876,350-8,150
Airbus A35014/06/2013280-316325-3668,100-8,400
Airbus A38027/04/20053312301015755448,200
Boeing 737 NG/737 MAX09/02/199770.1-88.3126-1882,935-3,825
Boeing 747-808/02/2010214484108,000
Boeing 767-300F20/06/1995300233671853,255
Boeing 777-300ER/F/777X24/02/2003349.7-351336-4007,370-8,700
Boeing 78715/12/2009227.9-250.8242-3306,430-7,635

Fleet

The airliner fleet went from 13,500 in 2000 to 25,700 in 2017: 16% to 30.7% in Asia/Pacific, 34.7% to 23.6% in USA and 24% to 20.5% in Europe.
In 2018, there were 29,398 airliners in service: 26,935 passenger transports and 2,463 freighters, while 2,754 others were stored.
The largest fleet was in Asia-Pacific with 8,808, followed by 8,572 in North America, 7,254 in Europe, 2,027 in Latin America, 1,510 in Middle East and 1,347 in Africa.
Narrowbody are dominant with 16,235, followed by 5,581 Widebodies, 3,743 Turboprops, 3,565 Regional jets and 399 Others.
Model2018201720162015
Airbus A320 family6,8386,5166,041
Boeing 737 NG5,9685,5565,115
Boeing 7771,3871,3191,258
Airbus A3301,2141,1691,093
Boeing 737 Classic/original8909311,006
Boeing 767744738762
Boeing 787696554422288
Boeing 757689688737
Boeing 717/MD-80/90/DC-9607653668
Boeing 747489503558

Model2018201720162015
Embraer E-jets1,2351,1401,102
ATR42/72950913886
Bombardier Q400506465451
Bombardier Dash 8-100/200/300374395424
Bombardier CRJ700/900/1000762747696
Bombardier CRJ100/200516557558
Embraer ERJ 145 family454528606
Beechcraft 1900-100/200/300328338347
de Havilland Canada DHC-6 Twin Otter270266268
Saab 340225231228

By the end of 2018, there were 1,826 parked or in storage jetliners out of 29,824 in service : 1,434 narrowbodies and 392 widebodies, down from 9.8% of the fleet at the end of 2012 and 11.3% at the end of 2001.

Market

Since it began, the jet airliner market had a recurring pattern of seven years of growth followed by three years of deliveries falling 30–40%, except a steady growth from 2004 due to the economic rise of China going from 3% of world market in 2001 to 22% in 2015, expensive jet fuel till 2014 stimulating old jets replacement allowed by low interest rates since 2008, and strong airline passenger demand since.
In 2004, 718 Airbus and Boeings were delivered, worth $39.3 billion; 1,466 are expected in 2017, worth $104.4 billion and 1,990 are forecast in 2020, worth $138.3 billion : a growth by 3.5 from 2004 to 2020 is unprecedented and highly unusual for any mature market.
In 2016, the deliveries went for 38% in Asia-Pacific, 25% in Europe, 22% in North America, 7% in Middle East, 6% in South America and 2% in Africa. 1,020 narrowbodies were delivered and their backlog reach : 4,991 A320neo, A320ceo; 3,593 737 Max, 835 737NG, 348 CSeries, 305 C919 and 175 MC-21; while 398 widebodies were delivered : 137 Dreamliners and 99 B777 for
Boeing against 63 A330 and 49 A350 for Airbus, more than 2,400 widebodies were in backlog, led by the A350 with 753 then the Boeing 787 with 694.
The most important driver of orders is airline profitability, itself driven mainly by world GDP growth but also supply and demand balance and oil prices, while new programmes by Airbus and Boeing help to stimulate aircraft demand.
In 2016, 38% of the 25 years old airliners had been retired, 50% of the 28 years old : there will be 523 aircraft reaching 25 years old in 2017, 1,127 in 2026 and 1,628 in 2041.
Deliveries rose by 80% from 2004 to 2016, they represented 4.9% of the fleet in 2004 and 5.9% in 2016, down from 8% previously.
Oil prices and airshow orders are trending together.

Storage, scrapping and recycling

Storage can be an adjustment variable for the airliner fleet: as Jan–Apr 2018 RPKs are up by 7% over a year and FTKs up by 5.1%, the IATA reports 81 net aircraft went back from storage in April.
It is the second month of storage contraction after eight of expansion and the largest in four years, while new aircraft deliveries fell slightly to 448 from 454 due to supply-chain issues and in-service issues grounding others.
Retirements were down by 8% and utilization up by 2%, according to Canaccord Genuity, driving used aircraft and engines values up while MRO shops have unexpected demand for legacy products like the PW4000 and GE CF6.

Cabin configurations and features

An airliner will usually have several classes of seating: first class, business class, and/or economy class. The seats in more expensive classes are wider, more comfortable, and have more amenities such as "lie flat" seats for more comfortable sleeping on long flights. Generally, the more expensive the class, the better the beverage and meal service.
Domestic flights generally have a two-class configuration, usually first or business class and coach class, although many airlines instead offer all-economy seating. International flights generally have either a two-class configuration or a three-class configuration, depending on the airline, route and aircraft type. Many airliners offer movies or audio/video on demand. Cabins of any class are provided with lavatory facilities, reading lights and gaspers. Larger airliners may have a segregated rest compartment reserved for crew use during breaks.

Seats

The types of seats that are provided and how much legroom is given to each passenger are decisions made by the individual airlines, not the aircraft manufacturers. Seats are mounted in "tracks" on the floor of the cabin and can be moved back and forth by the maintenance staff or removed altogether. Naturally the airline tries to maximize the number of seats available in every aircraft to carry the largest possible number of passengers.
Passengers seated in an exit row usually have substantially more legroom than those seated in the remainder of the cabin, while the seats directly in front of the exit row may have less legroom and may not even recline. However, passengers seated in an exit row may be required to assist cabin crew during an emergency evacuation of the aircraft opening the emergency exit and assisting fellow passengers to the exit. As a precaution, many airlines prohibit young people under the age of 15 from being seated in the exit row.
The seats are designed to withstand strong forces so as not to break or come loose from their floor tracks during turbulence or accidents. The backs of seats are often equipped with a fold-down tray for eating, writing, or as a place to set up a portable computer, or a music or video player. Seats without another row of seats in front of them have a tray that is either folded into the armrest or that clips into brackets on the underside of the armrests. However, seats in premium cabins generally have trays in the armrests or clip-on trays, regardless of whether there is another row of seats in front of them. Seatbacks now often feature small colour LCD screens for videos, television and video games. Controls for this display as well as an outlet to plug in audio headsets are normally found in the armrest of each seat.

Overhead bins

The overhead bins, also known as overhead lockers or pivot bins, are used for stowing carry-on baggage and other items. While the airliner manufacturer will normally specify a standard version of the product to supply, airlines can choose to have bins of differing size, shape, or color installed. Over time, overhead bins evolved out of what were originally overhead shelves that were used for little more than coat and briefcase storage. As concerns about falling debris during turbulence or in accidents increased, enclosed bins became the norm. Bins have increased in size to accommodate the larger carry-on baggage passengers can bring onto the aircraft. Newer bin designs have included a handrail, useful when moving through the cabin.

Passenger service units

Above the passenger seats are Passenger Service Units. These typically contain reading lights, air vents, and a flight attendant call light. On most narrowbody aircraft, the flight attendant call button and the buttons to control the reading lights are located directly on the PSU, while on most widebody aircraft, the flight attendant call button and the reading light control buttons are usually part of the in-flight entertainment system. The units frequently have small "Fasten Seat Belt" and "No Smoking" illuminated signage and may also contain a speaker for the cabin public address system. On some newer aircraft, a "Turn off electronic devices" sign is used instead of the "No Smoking" sign, as smoking isn't permitted on board the aircraft anyway.
The PSU will also normally contain the drop-down oxygen masks which are activated if there is a sudden drop in cabin pressure. These are supplied with oxygen by means of a chemical oxygen generator. By using a chemical reaction rather than a connection to an oxygen tank, these devices supply breathing oxygen for long enough for the airliner to descend to thicker, more breathable air. Oxygen generators do generate considerable heat in the process. Because of this, the oxygen generators are thermally shielded and are only allowed in commercial airliners when properly installed – they are not permitted to be loaded as freight on passenger-carrying flights. ValuJet Flight 592 crashed on May 11, 1996, as a result of improperly loaded chemical oxygen generators.

Cabin pressurization

Airliners developed since the 1940s have had pressurized cabins to enable them to carry passengers safely at high altitudes where low oxygen levels and air pressure would otherwise cause sickness or death. High altitude flight enabled airliners to fly above most weather systems that cause turbulent or dangerous flying conditions, and also to fly faster and further as there is less drag due to the lower air density. Pressurization is applied using compressed air, in most cases bled from the engines, and is managed by an environmental control system which draws in clean air, and vents stale air out through a valve.
Pressurization presents design and construction challenges to maintain the structural integrity and sealing of the cabin and hull and to prevent rapid decompression. Some of the consequences include small round windows, doors that open inwards and are larger than the door hole, and an emergency oxygen system.
To maintain a pressure in the cabin equivalent to an altitude close to sea level would, at a cruising altitude around, create a pressure difference between inside the aircraft and outside the aircraft that would require greater hull strength and weight. Most people do not suffer ill effects up to an altitude of, and maintaining cabin pressure at this equivalent altitude significantly reduces the pressure difference and therefore the required hull strength and weight. A side effect is that passengers experience some discomfort as the cabin pressure changes during ascent and descent to the majority of airports, which are at low altitudes.

Cabin climate control

The air bled from the engines is hot and requires cooling by air conditioning units. It is also extremely dry at cruising altitude, and this causes sore eyes, dry skin and mucosa on long flights. Although humidification technology could raise its relative humidity to comfortable middle levels, this is not done since humidity promotes corrosion to the inside of the hull and risks condensation which could short electrical systems, so for safety reasons it is deliberately kept to a low value, around 10%. Another problem of the air coming from the ventilation is that fumes from components in the synthetic oils can sometimes travel along, causing passengers, pilots and crew to be intoxicated. The illness it causes is called aerotoxic syndrome.

Baggage holds

Airliners must have space on board to store "checked" baggage – that which will not safely fit in the passenger cabin.
Designed to hold baggage as well as freight, these compartments are called "cargo bins", "holds", or occasionally "pits". Occasionally baggage holds may be referred to as cargo decks on the largest of aircraft. These compartments can be accessed through doors on the outside of the aircraft.
Depending on the aircraft, baggage holds are normally inside the hull and are therefore pressurized just like the passenger cabin although they may not be heated. While lighting is normally installed for use by the loading crew, typically the compartment is unlit when the door is closed.
Baggage holds on modern airliners are equipped with fire detection equipment and larger aircraft have automated or remotely activated fire-fighting devices installed.

Narrow-body airliners

Most "narrow-body" airliners with more than 100 seats have space below the cabin floor, while smaller aircraft often have a special compartment separate from the passenger area but on the same level.
Baggage is normally stacked within the bin by hand, sorted by destination category. Netting that fits across the width of the bin is secured to limit movement of the bags. Airliners often carry items of freight and mail. These may be loaded separately from the baggage or mixed in if they are bound for the same destination. For securing bulky items "hold down" rings are provided to tie items into place.

Wide-body airliners

"Wide-body" airliners frequently have a compartment like the ones described above, typically called a "bulk bin". It is normally used for late arriving luggage or bags which may have been checked at the gate.
However, most baggage and loose freight items are loaded into containers called Unit Load Devices, often referred to as "cans". ULDs come in a variety of sizes and shapes, but the most common model is the LD3. This particular container has approximately the same height as the cargo compartment and fits across half of its width.
ULDs are loaded with baggage and are transported to the aircraft on dolly carts and loaded into the baggage hold by a loader designed for the task. By means of belts and rollers an operator can maneuver the ULD from the dolly cart, up to the aircraft baggage hold door, and into the aircraft. Inside the hold, the floor is also equipped with drive wheels and rollers that an operator inside can use to move the ULD properly into place. Locks in the floor are used to hold the ULD in place during flight.
For consolidated freight loads, like a pallet of boxes or an item too oddly shaped to fit into a container, flat metal pallets that resemble large baking sheets that are compatible with the loading equipment are used.

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