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 aircraft intended for carrying multiple passengers or cargo in commercial service.
The largest airliners are wide-body jets. These aircraft are frequently called twin-aisle aircraft because they generally have two separate aisles running from the front to the back of the passenger cabin. These aircraft are usually used for long-haul flights between airline hubs and major cities with many passengers.
A smaller, more common class of airliners is the narrow-body or single-aisle aircraft. These smaller airliners 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 (light aircraft, list of light transport aircraft) 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.
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
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 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 (“feed”) passengers from smaller cities to hub airports (and reverse) 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” (DASH-8) series, ATR 42/72 and Saab 340/2000 turboprop airliners.
Commuterliners used by regional airlines and air taxi operators
The lightest (light aircraft) 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 aircrsft 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 (for example, the Vickers VC10, Lockheed L-1011, Boeing 707), air ambulance (USAF/USN McDonnell Douglas DC-9), reconnaissance (Embraer ERJ 145, Saab 340, and Boeing 737), as well as for troop-carrying roles.
Configuration
Modern jetliners are usually low-wing designs with two engines mounted underneath the swept wings (turboprop aircraft are slow enough to use straight wings). The Boeing 747 and Airbus A380 are the only airliners in production which are too heavy (more than 400 tons maximum takeoff weight) 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 (usually seen in military transport aircraft), 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:
Airbus (France/Germany/Spain/United Kingdom)
Antonov (Ukraine)
ATR Aircraft (France/Italy)
Boeing (United States)
Bombardier Aerospace (Canada)
Comac (China)
Embraer (Brazil)
Let Kunovice (Czech Republic)
Mitsubishi Aircraft Corporation (Japan)
United Aircraft Corporation (Russia, includes Tupolev, Yakovlev, Sukhoi, Ilyushin, and others)
Xi’an Aircraft Industrial Corporation (China)
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.
Notable airliners
Boeing 247 – the first design to incorporate modern features such as all-metal construction and retractable landing gear
Douglas DC-3 – still in service more than 80 years after its debut, it is generally regarded as one of the most significant transport aircraft ever made
Boeing 307 – one of the first airliners to be pressurized and have the ability to fly into the stratosphere
Douglas DC-6 – originally developed as a military transport, it was reworked for passenger service after World War II, a role it continues to perform today
Boeing 377- developed soon after World War 2, from the C-97 Stratofreighter, this was a luxurious double-decker airliner with a pressurized cabin.
Vickers Viscount – the first turboprop airliner to enter service
Lockheed Constellation – a distinctive triple-tailed piston-engined airliner of the 1950s, it was one of the last large propeller-driven airliners
De Havilland Comet – the world’s first jetliner to reach mass production, early crashes informed vital design lessons
Antonov An-2- best selling transport airliner up to the point it was built.
Tupolev Tu-104 – the first turbojet airliner to provide sustained service, and the sole jetliner operating in the world between 1956 and 1958
Boeing 707 – the first United States-built jetliner to enter production
Tupolev Tu-124 – the first turbo-fan powered airliner
Douglas DC-8 – launched after the Boeing 707, it nevertheless established Douglas in the airliner market, and continues to serve as a cargo aircraft to this day
Sud Aviation Caravelle – the first jetliner with rear mounted engines. It is also the first airliner to perform a CAT III landing (low visibility)
Tupolev Tu-154 – standard medium-range airliner for Russia (and others), carried half of all Soviet air traffic since 1972 with 1015 built; the fastest airliner in service
Ilyushin Il-62 – standard long-range airliner for Russia (and others) for three decades, first flight 1963; still in service
Douglas DC-9 – production of it and successive variants nearly reached 2,500
Boeing 737 – the best-selling jet airliner in the history of aviation
Hawker Siddeley Trident The first airliner to make an automated blind landing whilst in service
Tupolev Tu-144 – the first supersonic transport aircraft constructed in the Soviet Union
Concorde – an Anglo-French supersonic transport, it remains the only supersonic aircraft to sustain a regular passenger service
Boeing 747 “Jumbo Jet” – an iconic aircraft, it was the world’s largest passenger airliner between 1969 and 2005. It was also the first widebody jet airliner to enter service, introducing many features that became standard in current jetliners like high-bypass turbofans.
McDonnell Douglas DC-10 – a trijet competitor to the widebody 747
Lockheed L-1011 TriStar – a trijet competitor to the Boeing 747 and the similarly sized DC-10. Lockheed’s last entry into commercial aircraft manufacturing.
Airbus A300 – the world’s first twinjet widebody
Airbus A320 – pioneered the use of fly-by-wire technology
Antonov An-225 Mriya “Mriya” – the world’s largest and heaviest aircraft. Only one example built, it is used for carrying oversized payloads. It is also the only airliner with six engines
Boeing 777 – the first airliner designed entirely by computer, without physical mockups
Airbus A380 “Superjumbo” – the world’s largest passenger airliner from 2005 onwards
Boeing 787 Dreamliner – the world’s first jet airliner to make use of composite materials for most of its construction
In production aircraft
| Model | First flight | Net orders | Deliveries | Backlog | MTOW (t) | typ. seats | Range (nmi) |
|---|---|---|---|---|---|---|---|
| Airbus A220 | 16/09/2013 | 355 | 18 | 337 | 60.8-67.6 | 108-130 | 3,100-3,300 |
| Airbus A320 family | 22/02/1987 | 13160 | 7658 | 5505 | 68-95 | 107-206 | 3,110-4,000 |
| Airbus A330 | 02/11/1992 | 1631 | 1328 | 303 | 242 | 247-287 | 6,350-7,500 |
| Airbus A350 | 14/06/2013 | 856 | 114 | 742 | 259-308 | 276-366 | 7,950-8,245 |
| Airbus A380 | 27/04/2005 | 317 | 216 | 101 | 575 | 544 | 8,200 |
| Boeing 737 NG/Boeing 737 MAX | 09/02/1997 | 10660 | 6257 | 4403 | 70.1-88.3 | 126-188 | 2,935-3,515 |
| Boeing 777-200LR/300ER/Boeing 777X | 24/02/2003 | 1369 | 944 | 425 | 347.5-351 | 301-400 | 7,370-8,700 |
| Boeing 787 | 28/11/2008 | 1265 | 591 | 674 | 227.9-250.8 | 242-330 | 6,430-7,635 |
Market
The airliner fleet went from 13,500 in 2000 to 25,700 in 2017: 16% to 30.7% in Asia/Pacific (2,158 to 7,915), 34.7% to 23.6% in USA (4,686 to 6,069) and 24% to 20.5% in Europe (3,234 to 5,272).
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 $138.3 billion (constant 2017 dollar values): a growth by 3.5 from 2004 to 2020 is unprecedented and highly unusual for any mature market.
| Manufacturer | 2016 orders and deliveries | 2018-2022 projections | ||||
|---|---|---|---|---|---|---|
| deliveries | values ($bn) | net orders | backlog | deliveries | values ($bn) | |
| Boeing | 726 | 57.8 | 563 | 5,660 | 4,779 (43.6%) | 756.5 (51.1%) |
| Airbus | 685 | 45.5 | 711 | 6,845 | 4,388 (40.0%) | 648.1 (43.8%) |
| Embraer | 108 | 2.9 | 39 | 444 | 498 (4.5%) | 21.1 (1.4%) |
| Bombardier | 81 | 1.9 | 162 | 437 | 486 (4.4%) | 25.7 (1.8%) |
| ATR | 73 | 1.5 | 36 | 236 | 391 (3.6%) | 9.5 (0.6%) |
| Other | 31 | 0.5 | 72 | 1,080 | 430 (3.9%) | 19.2 (1.3%) |
| Total | 1,704 | 110.1 | 1,583 | 14,702 | 10,972 | 1,480 |
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 10891: 4,991 A320neo, 644 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 (65%) against 63 A330 and 49 A350 for Airbus, more than 2,400 widebodies were in backlog, led by the A350 with 753 (31%) then the Boeing 787 with 694 (28%).
Largest in service mainline fleet
| Model | 2017 | 2016 | 2015 |
|---|---|---|---|
| Airbus A320 family | 6,838 | 6,516 | 6,041 |
| Boeing 737 NG | 5,968 | 5,556 | 5,115 |
| Boeing 777 | 1,387 | 1,319 | 1,258 |
| Airbus A330 | 1,214 | 1,169 | 1,093 |
| Boeing 737 Classic/original | 890 | 931 | 1,006 |
| Boeing 767 | 744 | 738 | 762 |
| Boeing 757 | 689 | 688 | 737 |
| Boeing 717/MD-80/90/DC-9 | 607 | 653 | 668 |
| Boeing 787 | 554 | 422 | 288 |
| Boeing 747 | 489 | 503 | 558 |
| Model | 2017 | 2016 | 2015 |
|---|---|---|---|
| Embraer E-jets | 1,235 | 1,140 | 1,102 |
| ATR42/72 | 950 | 913 | 886 |
| Bombardier CRJ700/900/1000 | 762 | 747 | 696 |
| Bombardier CRJ100/200 | 516 | 557 | 558 |
| Bombardier Q400 | 506 | 465 | 451 |
| Embraer ERJ 145 family | 454 | 528 | 606 |
| Bombardier Dash 8-100/200/300 | 374 | 395 | 424 |
| Beechcraft 1900-100/200/300 | 328 | 338 | 347 |
| de Havilland Canada DHC-6 Twin Otter | 270 | 266 | 268 |
| Saab 340 | 225 | 231 | 228 |
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.
Forecasts
For 2018-2037, Airbus forecasts 37,400 new airliners overs 100 seats for US$5.8 trillion: 28550 below 230 seats for $3.2trn, 8830 above for $2.6 trn. Forecast International plan a production of 29,407 large commercial jets from 2018 through 2032, valued $4.73 trillion, rising from 1,607 yearly in 2018 to 2,086 in 2029: Boeing should produce 14,085 (47.9%), Airbus 13,590 (46.2%) plus 641 A220-300s.
Between 2018 and 2037, Boeing forecasts 42,730 deliveries for $6,350 billion : 2,320 Regional jets for $110 billion, 31,360 single-aisles for $3,480 billion and 9,050 Widebodies for $2,760 billion including freighters. Flightglobal predicts 46,460 deliveries between 2018 and 2037, 65% single-aisles, worth $3.1 trillion including $1.29 for twin-aisles: Asia-Pacific 23%, North America 20%, China 19%, Europe 16%, Latin America 8%, Middle East 7%, Russia 4% and Africa 3%.
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 (132 recalled and 51 stored) 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 (which may be referred to as coach class or tourist class, and sometimes has a separate “premium” economy section with more legroom and amenities). 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 (this is standard in first and business class on many international flights and may be available on economy). 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 (and therefore most profitable) number of passengers.
Passengers seated in an exit row (the row of seats adjacent to an emergency exit) 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 (for evacuation safety reasons). 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 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[when?] 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 (PSU). These typically contain reading lights, air vents, and a flight attendant call light. On most narrowbody aircraft (and some Airbus A300s and A310s), 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.
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 (or, more accurately, pressurized hulls including baggage holds) 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 10,000 m (33,000 ft), 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 1,800–2,500 m (5,900–8,200 ft), 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 (unto which the oil lubrication system of the engines is hooked up) 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 (ULDs), 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.
Source from Wikipedia