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Airports
The first airports were simply grass fields (airfields) but as aircraft became heavier, paved runways were developed. This also meant that airplanes could land and take off in all weather conditions. Over the years airports have become bigger and busier with elaborate terminal buildings to improve passenger comfort. The world’s biggest airport is now considered to be Atlanta, with Heathrow airport generally recognized as the world’s biggest international airport, though it faces serious competition from Charles de Gaulle (Paris), Frankfurt and Schipol (Amsterdam).
Airports are sometimes referred to as aerodromes, though this term is considered old-fashioned and often implies a small airport. The term airstrip is used when not much more than a small basic runway is provided (often used by the military).
In recent years there has been considerable controversy concerning the environmental impact of increasing traffic at large airports. Noise pollution is a particularly controversial issue, and expanding existing airports or building new ones is becoming increasingly difficult in many parts of the world.
Organization
Airports are divided into landside and airside areas. Airside areas are where the airplanes can be found. These include runways and taxiways, as well as stands, where aircraft are parked for providing direct access to the terminal building through an air bridge or jetway. The airside area also includes the apron, where several aircraft may park at a distance from the terminal building (buses then take passengers to and from the aircraft).
Access to all airside areas is subject to tight security controls. Landside areas, on the other hand, which include shops, restaurants, car parks and check-in areas, are more accessible to the general public.
Air Traffic Control (ATC) is usually provided from a control tower situated on-site. At major airports ATC is separated into ground control (responsible for aircraft and all other vehicles using the apron and taxiways) and tower control (responsible for aircraft landing and taking off on the runways). Approach control handles aircraft which have just taken off or are about to land. En-route traffic is controlled at an area control centre, which can be situated anywhere, as the aircraft are only visible on a controller’s radar screen.
Runways
Small airports may have only one runway but most major airports have several. When a new airport is built or an existing one expanded, runway layout is of primary concern. Runways need to be laid out to make optimum use of the prevailing winds because aircraft need to take off and land directly into the wind if possible. Crosswinds can be a dangerous hazard. Assuming that the airport will be busy, the layout should also be efficient, ideally allowing runways to be used at the same time. A further important consideration is the way in which local resident communities will be disturbed by noise.
The three main runway configurations are parallel runways, open-V runways (they diverge but do not intersect, when viewed overhead the shape is a ‘V’), and intersecting runways. The latter two types are relevant in locations where the direction of the prevailing wind changes.
Runways are labelled depending on their direction relative to the magnetic compass. This number is clearly indicated at the end of each runway. If a runway is labelled 09 at its starting point (runway threshold) because it runs due east (90°), then it will be labelled 27 at the other end which is the runway threshold should the pilot need to land in a westerly direction (270°). All runways are thus designated by two numbers the difference between which is 18. For example, on runway 13-31 pilots can either land or take off with a heading of 130° or 310°.
At international airports all runways must have ground markings and standardized lighting according to agreed international standards. The threshold and direction of a runway should be clearly marked as well as the touchdown zone and distance markers at various points to show a pilot how much runway is left. The centre line should also be clearly visible as well as the runway exits leading to taxiways. Standardized lighting is as follows:
• Green threshold lights mark the beginning of a runway.
• Red lights mark the end of a runway.
• White or yellow lights mark the edges of a runway.
• Blue lights indicate taxiways.