Airport

An airport is a facility where aircraft can take off and land. At the very minimum, an airport consists of one runway (or helipad), but other common components are hangars and terminal buildings. Apart from these, an airport may have a variety of facilities and infrastructure, including fixed base operator services, air traffic control, passenger facilities such as restaurants and lounges, and emergency services. A military airport is known as an airbase in North American terminology (other countries may use the term airfield or air station in current parlance or aerodrome in 1930s parlance). The terms airfield and airstrip may also be used to refer to a facility that has nothing more than a runway.

Airport operations

Outside the terminal, there is a large team of people who work in concert to ensure aircraft can land, take off, and move around quickly and safely. These processes are largely invisible to passengers, but they can be extraordinarily complex at large airports.

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Air traffic control

Air traffic control (or ATC) is system whereby ground-based controllers direct aircraft movements, usually via radio. This coordinated oversight facilitates safety and speed in complex operations where traffic moves in all three dimensions. Air traffic control responsibilities at airports are usually divided into two main areas: ground and tower.

Related Topics:
Controllers - Radio

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Ground Control is responsible for directing all ground traffic in designated "movement areas," except the traffic on runways. This includes planes, baggage trains, snowplows, grass cutters, fuel trucks, and a wide array of other vehicles. Ground Control will instruct these vehicles on which taxiways to use, which runway they will use (in the case of planes), where they will park, and when it is safe to cross runways. When a plane is ready to take off it will stop short of the runway, at which point it will be turned over to Tower Control. After a plane has landed, it will depart the runway and be returned to Ground Control.

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Tower Control controls aircraft on the runway and in the controlled airspace immediately surrounding the airport. Tower controllers use radar to identify and accurately locate an aircraft's position in three-dimensional space. They coordinate the sequencing of aircraft in the traffic pattern and direct aircraft on how to safely join and leave the circuit. Aircraft which are only passing through the airspace must also contact Tower Control in order to be sure that they remain clear of other traffic and do not disrupt operations.

Related Topics:
Tower - Controlled airspace - Radar

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Traffic pattern

Smaller airports and military airfields use a traffic pattern to assure smooth traffic flow between departing and arriving aircraft. Generally, this pattern is a circuit consisting of five "legs" that form a rectangle (two legs and the runway form one side, with the remaining legs each form another side). Each leg is named (see diagram), and ATC directs pilots on how to join and leave the circuit. Traffic patterns are flown at one specific altitude, usually 1000 ft AGL. Most traffic patterns are left-handed, meaning all turns are made to the left. Right-handed patterns do exist, usually because of obstacles such as a mountain or to reduce noise for local residents. The predetermined circuit helps pilots look for other aircraft, and helps reduce the chance of a mid-air collision.

Related Topics:
AGL - Mountain

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At extremely large airports, a circuit is not usually used. Rather, ATC schedules aircraft for landing while they are still hours away from the airport. Airplanes can then take the most direct approach to the runway and land without worrying about interference from other aircraft. While this system keeps the airspace free and is simpler for pilots, it requires detailed knowledge of how aircraft are planning to use the airport ahead of time and is therefore only possible with large commercial airliners on pre-scheduled flights. The system has recently become so advanced that controllers can predict whether an aircraft will be delayed on landing before it even takes off; that aircraft can then be delayed on the ground, rather than wasting expensive fuel waiting in the air.

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Navigational aids

Before takeoff, pilots usually check an Automatic Terminal Information Service (ATIS) for information about airport conditions where they exist. The ATIS contains information about weather, which runway and traffic patterns are in use, and other information that pilots should be aware of.

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When flying, there are a number of aids available to pilots, though not all airports are equipped with them. A VASI helps pilots fly a perfect approach for landing once they have found the airport. Some airports are equipped with a VOR to help pilots find the direction to the airport, VORs are often accompanied by a DME to determine the distance to the airport. In poor weather, pilots will use an Instrument Landing System to find the runway and fly the correct approach, even if they cannot see the ground.

Related Topics:
VASI - VOR - DME - Instrument Landing System

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Larger airports sometimes offer Precision Approach on Radar (PAR). The aircraft's horizontal and vertical movement is tracked via radar, and the controller tells the pilot his position relative to the approach slope. Once the pilots can see the runway lights, they may continue with a visual landing.

Related Topics:
Precision Approach on Radar - Approach slope

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Guidance signs

Airport guidance signs provide direction and information to taxiing aircraft and airport vehicles and assist in safe and expedient movement of aircraft. Smaller airports may have few or no signs, relying instead on airport diagrams and charts.

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There are two classes of signage at airports, with several types of each:

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Operational guidance signs

• Location signs - yellow on black background. Identifies the runway or taxiway currently on or entering.
• Direction/Runway Exit signs - black on yellow. Identifies the intersecting taxiways the aircraft is approaching, with an arrow indicating the direction to turn.
• Other - Many airports use conventional traffic signs such as stop and yield signs throughout the airport.

Mandatory instruction signs

Madatory instruction signs are white on red. They show entrances to runways or critical areas. Vehicles and aircraft are required to stop at these signs until the control tower gives clearance to proceed.

Related Topics:
Red - Control tower

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• Runway signs - White on a red. These signs simply identify a runway intersection ahead.
• Frequency Change signs - Usually a stop sign and an instruction to change to another frequency. These signs are used at airports with different areas of ground control.
• Holding Position signs - A single solid yellow bar across a taxiway indicates a position where ground control may require a stop. If a two solid yellow bars and two dashed yellow bars are encountered, this indicates a holding position for a runway intersection ahead; runway holding lines must never be crossed without permission. At some airports, a line of red lights across a taxiway is used during low visibility operations to indicate holding positions.

Lighting

Many airports have lighting that help guide planes using the runways and taxiways at night or in rain or fog.

Related Topics:
Lighting - Fog

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On runways, green lights indicate the beginning of the runway for landing, while red lights indicate the end of the runway. Runway edge lighting is white lights spaced out on both sides of the runway, indicating the edge. Some airports have more complicated lighting on the runways including lights that run down the centerline of the runway and lights that help indicate the approach. Low-traffic airports may use Pilot Controlled Lighting to save electricity and staffing costs.

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Along taxiways, blue lights indicate the taxiway's edge, and some airports have embedded green lights that indicate the centerline.

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Wind indicators

Planes take-off and land into the wind in order to achieve maximum performance. Wind speed and direction information is available through the ATIS or ATC, but pilots need instantaneous information during landing. For this purpose, a windsock is kept in view of the runway.

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Safety management

Air safety is an important concern in the operation of an airport, and almost every airfield includes equipment and procedures for handling emergency situations. Commercial airfields include one or more emergency vehicles and their crew that are specially equipped for dealing with airfield accidents, crew and passenger extractions, and the hazards of highly flammable airplane fuel. The crews are also trained to deal with situations such as bomb threats, hijacking, and terrorist activities.

Related Topics:
Air safety - Emergency vehicle - Accident - Fuel - Bomb threat - Hijacking - Terrorist

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Potential airfield hazards to aircraft include debris, nesting birds, and environmental conditions such as ice or snow. The fields must be kept clear of debris using cleaning equipment so that loose material doesn't become a projectile and enter an engine duct. Similar concerns apply to birds nesting near an airfield, and crews often need to discourage birds from taking up residence. In adverse weather conditions, ice and snow clearing equipment can be used to improve traction on the landing strip. For waiting aircraft, equipment is used to spray special deicing fluids on the wings.

Related Topics:
Bird - Ice - Snow

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During the 1980s, a phenomenon known as microburst became a growing concern due to accidents caused by microburst wind shear. (For example, see Delta Air Lines Flight 191.) Microburst radar was developed as an aid to safety during landing, giving two to five minutes warning to aircraft in the vicinity of the field of an microburst event.

Related Topics:
1980s - Microburst - Accidents - Wind shear - Delta Air Lines Flight 191

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