An airport is a facility for handling the arrival and departure of \Taircraft\t, passengers, and freight. Today's modern passenger airports, which are the nuclei of the world's most extensive and heavily used travel network, are shaped by certain exacting requirements: sufficient space to accommodate the long runway needs of jumbo jets, as well as the hangars, terminals, parking lots, and cargo and accessory buildings necessary for efficient airport operation; sufficient highways and public transportation to allow passengers access; and sufficient distance from residential areas so that adjacent neighborhoods will not be subjected to aircraft noise. (See also \Taviation\t.) HISTORY Before World War I any spot large and level enough for a pilot to take off and land was considered an airport. The brothers Orville and Wilbur \TWright\t made do with a level cow pasture. The first experimental flights in Canada were made from the frozen surface of a lake. An old barn to house tools, a workshop, and some storage space were all that was required for early experiments in aviation. Between 1909 and 1914 the airplane swiftly gained popularity. Well-publicized world records for speed, altitude, and distance of flights were continually surpassed, and a number of national and international races were organized. Newspapers and other organizations put up substantial cash prizes for special events, which were usually staged on racetracks with large, level fields for takeoffs and landings. Europe The big bombers used in World War I had demonstrated a capability for carrying considerable loads and for operating at night, thus proving that air passenger service was theoretically feasible. Shortly after the war, a few former British military pilots acquired some surplus warplanes and refitted them for passengers. By 1919 the first London-to-Paris passenger services were inaugurated, and within the year scheduled passenger flights were offered to Amsterdam and to other cities on the Continent. By about 1928, scheduled commercial air routes crisscrossed all of Europe, and most cities had adequate airports. United States In the years after World War I, manufacturers left with large inventories of airplane parts from canceled war contracts began to produce planes for peacetime use. Small, short-hop airlines came into existence and vanished quickly; few people were willing to risk a journey in the tiny, fragile planes of the time. Charles \TLindbergh\t's transatlantic flight of 1927, however, triggered a great upsurge in public interest and generated programs in aeronautical education and research that eventually established the airplane as an effective means of mass transportation. A string of small airports and emergency fields had been established from coast to coast to service \Tairmail\t planes. During the early 1930s the first transcontinental operations were inaugurated. The first long-distance airline schedules were begun in conjunction with the existing railroad systems. Airports were sited adjacent to railroad stations, and passengers flew by day and traveled in railroad sleeping cars at night. Coast-to-coast travel time was about 48 hr by combined rail and flight. By 1932, light BEACONS and radio communication had been installed along the airways, making it possible for planes to fly through the night. Travel time became about 33 hr, with 12 to 15 stops for fuel and food. Overseas Flights In the late 1930s commercial overseas services to South America and Europe were started. The plane most widely used over water was the flying boat (a large four-engine vehicle with a watertight body that acted as a hull, allowing the plane to float), operating out of harbors on the east and west coasts (see \Tseaplane\t). It was anticipated that the flying boat would be the eventual solution for worldwide air commerce. By the end of World War II, however, further development and plans for future use of flying boats were totally abandoned, and today airport-seaport combinations are not in commercial use. TYPES OF AIRPORTS IN THE UNITED STATES Three types of airports are now in common use: government airports, operated mostly for the military; public and private airports, primarily to serve general aviation; and commercial airports, including those for domestic and foreign airline operations. Federal regulations govern their operational methods and set safety standards. Government Airports Government airports serve the U.S. Air Force, Navy, and Marine Corps, as well as \TNASA\t and various installations for research and development. They also support such special activities as the landing and recovery of space vehicles on 8-km (5-mi) desert runways. They furnish long-range jets and short-haul helicopters for presidents and foreign dignitaries. General-aviation and commercial planes are usually prohibited from using U.S. government airports, except in emergencies or when a government facility is designated a "joint use" airport. General-Aviation Airports General-aviation activities--including private flying for recreation, instruction, and business--account for 80 percent of the air-hours flown, and it is anticipated that by the 1990s the number of privately owned planes will double. Of more than 12,000 airports listed in the U.S. directories, the majority are available for general use, subject to \TFederal Aviation Administration\t (FAA) rules and regulations. General-aviation airports are often privately owned and are usually located near small cities and towns that are not along the routes of commercial airlines. In addition, most commercial airports designate specific areas for general aviation use and require all planes to be subject to the same traffic control and regulations that are imposed on commercial airline traffic. Commercial Airports Commercial airports are usually publicly owned, and operated by municipal, county, or other government agencies. The location of many modern urban airports was originally determined largely on the basis of available real estate and local politics. Before World War II, airfields in such major cities as London and New York often occupied less than 202 ha (500 acres). (By contrast, the Dallas/Fort Worth Airport in Texas has an area of more than 7,080 ha/17,500 acres; and Montreal's Mirabel Airport has more than 35,600 ha/88,000 acres in reserve, although at present it uses only about one-fifth of its total area.) As airline traffic increased in the 1950s and '60s, airports enlarged to accommodate it; the most important single change in aviation, however, was the introduction (1958) of jet planes, which made unprecedented demands on the length and strength of runways, taxiways, and ground facilities of every kind. As a result, cities with major airports enlarged them greatly or moved them into nearby rural areas. Despite the enlarging of airport facilities, many hub airports--those in large cities which serve as major transfer points--find themselves increasingly short of space. Their problems are exacerbated by the growth of the suburban areas that were relatively empty when the airports were first located there. Expanding an existing airport or building a new one is equally difficult because of population pressures, environmental issues, and the huge costs involved. In addition, at many hub airports one or two major airlines now control most of the take-off and landing time slots and the departure gates. They have no wish to see their near-monopolies disappear, a probability when new or larger facilities are built. AIRPORT FACILITIES The modern airport consists of facilities for handling airplanes: runways and taxiing areas; hangars and machine shops for plane maintenance, repair, and fueling; and traffic control towers, whose personnel track aircraft and guide them through landings and takeoffs. Passengers are received in the terminal buildings, which are connected to nearby highways and to parking facilities by access roads and which contain airline ticket counters and reception desks, baggage-handling facilities, plane-boarding gates, security-inspection devices, and such ancillary services as restaurants. In addition, airports provide special buildings and services for air freight, a business that has grown substantially in recent years. Traffic Control The most conspicuous and important structure at any airport is the \Ttraffic control\t tower. Located approximately in the center of the runway complex, it is high enough to permit a clear view of landing, takeoff, and loading areas. It contains a complex of communications and electronic surveillance gear by which the airport controllers monitor and direct all plane movements on or near the field. All commercial airlines, the military, and most general-aviation flights operate according to flight plans. Prepared by pilots before their departure, flight plans are filed with the originating airport and transmitted to the airport of destination. Flights follow predetermined routes, and reports on their progress are made from checkpoints along the airways. Control towers are advised of the estimated time of arrival (ETA) for all aircraft in their approach areas. The pilots are then given detailed landing instructions: approach routes to be followed, rate of descent, proximity of other aircraft, weather conditions, and designated landing runways. For departures, procedures are reversed. Pilots are advised what taxiways to use, what runways are available, the traffic conditions on and around the field, and the procedures to follow to reach their designated flight path at the predetermined altitude. This is particularly necessary in bad weather or at night, but such procedures are followed at all times, in the interest of maximum flight safety. In 1981 the Professional Air Traffic Controllers Organization (PATCO), the union representing all nonmilitary air traffic controllers, called a strike over issues of pay and working conditions. President Reagan declared the strike illegal and fired 11,500 controllers, replacing some of them with controllers borrowed from military airfields. At about the time of the strike, the FAA began working on plans for reducing air-traffic facilities in the future by relying more heavily on new computer capabilities, new plane-borne radar signaling devices, and new automated control systems. If its plans are carried through by the year 2000, the number of major air-traffic control centers will be reduced from 20 to 16, and of smaller flight service stations from nearly 300 to about 60. In the meantime, however, concern about air safety has grown, along with statistics indicating a pattern of overcrowding and delays on the ground and in the air at major airports, a rising number of near collisions, and a lowering of aircraft maintenance standards. In May 1986 the National Transportation Safety Board urgently recommended that the FAA reduce the number of flights at the busiest airports during peak hours, in large part because of inadequate numbers of air-traffic controllers. The FAA has also demonstrated a new computer, based in Washington, D. C., that can display the aircraft in the skies above any part of the nation. The computer will allow traffic managers at FAA headquarters to alleviate crowding anywhere in the country by rerouting or slowing planes in the air, or by delaying flights. Noise Aircraft noise became a major issue in the early 1960s, when commercial jet aircraft first came into wide use. Although those who live and work near large airports have long complained of the extraordinary burden of noise they bear, the first widely publicized controversy developed over the landing of the \TConcorde\t, the Anglo-French supersonic transport, at Kennedy International Airport in New York City on Oct. 19, 1977. Strenuous protests led to court hearings, delays, and, for a time, restricted experimental service. Today Concorde landings are limited to a few airports, and the plane is not allowed to exceed the speed of sound when it flies over the continental United States. In suits brought against airports by nearby towns or citizens' groups, the courts have generally found airport operators primarily responsible for controlling noise. Since 1976 the FAA has funded noise studies at most large airports and has issued guidelines for reducing airport noise--in addition to the existing regulations that limit the noise produced by aircraft. These guidelines recommend restrictions on airport acquisition of land and on the utilization of runways whose flight paths are over residential areas. Compliance with the FAA regulations has proven costly in terms of both money and and the availability of suitable land for airport expansion. Security \Tairplane hijacking\t has been a problem since the 1950s, and the destruction of aircraft in flight by hidden bombs has occurred several times. The December 1988 explosion over Lockerbie, Scotland, of a Pan Am passenger jet en route from London to New York City was caused by a bomb hidden in an audiocassette player. This and other terrorist attacks in the late 1980s forced airports and airlines to adopt far more stringent security measures. The demarcation of responsibility between airports and airlines is not precisely drawn. Airlines would seem to be responsible for their own passengers; airports for the security of the area and for passenger traffic in general. Israel's El Al and Air India are said to have the most rigorous airline security. Although their passenger interrogations and careful manual searches of luggage are carried out efficiently, they cause long delays and demonstrate that real security can be had only at great expense of money and time. Of airports, the Rome facility is usually ranked as the most secure. Measures taken there include searches of suspicious persons at airport entrances; interrogation and luggage search of passengers selected at random; police guarding of parked planes; and the escorting by police of passengers and passenger buses en route to the airplanes. The X-ray machines used in U.S. airports can detect guns and other metal objects, but their screens cannot show plastic explosives. The new "thermal neutron analyzer" is capable of detecting many different explosives, including those made of plastic. Its cost, however, is about $1 million per machine. Total costs for U.S. airport security improvements may eventually total $1 billion or more. The Effects of Airline Deregulation on Airports The Airline Deregulation Act of 1978 removed route-regulating authority from the Civil Aeronautics Board (CAB), leaving each airline free to choose whatever routes seemed to promise the most success and to set its own fares independent of the CAB. The years since deregulation have seen several new airlines come into existence and flourish because they offered cheaper fares or regular schedules to certain areas that had not been well served by the older, established airlines. Some older airlines have faltered, however; Braniff, which extended its routes and its capital investment too far, declared bankruptcy in 1982. The effect of deregulation on U.S. airports has not been altogether beneficial. In their scramble for the most popular routes, the airlines have overloaded the major airports--already laboring under the limitations produced by the PATCO strike--while leaving many secondary airports, once on mandatory CAB routes, without regular airline service. The federal government provides incentive subsidies for such service, but they are being gradually removed. Some small cities have sought and obtained scheduled commuter service; yet, despite a federal subsidy program to encourage small-city service, many communities are now shut out of the air-route network. At the present time a hub airport may be unable to provide "slots" (landing rights) for every airline planning to use its facilities. Some airports have been embroiled in legal actions when they attempted to restrict airport use. The use of congested hub airports by increasing numbers of private planes is also coming under question. In the coming years, air traffic inevitably will increase, and the problems of noise and lack of runway and terminal space will grow more pressing. In addition to the more obvious solutions, such as increasing the size of airports or building new ones, operators have suggested improved Instrument Flight Rule (IFR) systems to permit reduced spacing between parallel runways and shorter distances between arriving or departing aircraft, and the construction of separate, shorter runways for commuter and business aircraft. S. \TPaul\t \TJohnston\t Bibliography: Allen, R., Major Airports of the World (1979); Ashford, Norman, et al., Airport Operations (1984); Amann, Dick, Airports: Today's Small Field, Tomorrow's Neighborhood Nightmare (1981); Gesell, L. E., The Administration of Public Airports, 2d ed. (1986); Hart, Walter, Airport Terminal Design (1985); Horonjeff, Robert, The Planning and Design of Airports, 3d ed. (1983); Stratford, Alan H., Airports and the Environment (1974); Stroud, John, Airports of the World (1981); Voight, R. L., Airport Guide, 4th ed. (1986).