Search

Wednesday, December 14, 2011

Airports

In this post, I'm going to tell you all about airports and their various uses.

An airport is a location where aircraft such as fixed-wing aircraft, helicopters, and blimps take off and land. Aircraft may be stored or maintained at an airport. An airport consists of at least one surface such as a runway for a plane to take off and land, a helipad, or water for takeoffs and landings, and often includes buildings such as control towers, hangars and terminal buildings.
Larger airports may have fixed base operator services, seaplane docks and ramps, air traffic control, passenger facilities such as restaurants and lounges, and emergency services. A military airport is known as an airbase or air station.

Infrastructure


The passenger terminal buildings atIncheon International Airport, Incheon, South Korea
Smaller or less-developed airports—which represent the vast majority—often have a single runway shorter than 1,000 m. Larger airports for airline flights generally have paved runways 2,000 m or longer. Many small airports have dirt, grass, or gravel runways, rather than asphalt or concrete.
In the United States, the minimum dimensions for dry, hard landing fields are defined by the FAR Landing And Takeoff Field Lengths. These include considerations for safety margins during landing and takeoff. Heavier aircraft require longer runways.
The longest public-use runway in the world is at Qamdo Bangda Airport in China. It has a length of 5,500 m. The world's widest paved runway is at Ulyanovsk Vostochny Airport in Russia and is 105 m wide.
As of 2009, the CIA stated that there were approximately 44,000 "... airports or airfields recognizable from the air" around the world, including 15,095 in the US, the US having the most in the world.


Airport structures


The exterior of  Tan Son Nhat International Airport, Ho Chi Minh City ,Vietnam. The airport will soon be replaced by Long Thanh International Airport as the main airport of Ho Chi Minh City

View of the East Atrium at Orlando International Airport, Orlando, U.S., with a Hyatt Regency hotel within the terminal structure

Infrastructure of an airport
Airports are divided into landside and airside areas. Landside areas include parking lots, public transportation train stations,tank farms and access roads. Airside areas include all areas accessible to aircraft, including runways, taxiways, ramps and tank farms. Access from landside areas to airside areas is tightly controlled at most airports. Passengers on commercial flights access airside areas through terminals, where they can purchase tickets, clear security check, or claim luggage and board aircraft through gates. The waiting areas which provide passenger access to aircraft are typically called concourses, although this term is often used interchangeably with terminal.

The apron from the top floor observation room, Halifax International Airport, Canada
The area where aircraft park next to a terminal to load passengers and baggage is known as a ramp (or "the tarmac"). Parking areas for aircraft away from terminals are called aprons.
Airports can be towered or non-towered, depending on air traffic density and available funds. Due to their high capacity and busy airspace, many international airports have air traffic control located on site.
Airports with international flights have customs and immigration facilities. However, as some countries have agreements that allow travel between them without customs and immigrations, such facilities are not a definitive need for an international airport. International flights often require a higher level of physical security, although in recent years, many countries have adopted the same level of security for international and domestic travel.
Some airport structures include on-site hotels built within or attached to a terminal building. Airport hotels have grown popular due to their convenience for transient passengers and easy accessibility to the airport terminal. Many airport hotels also have agreements with airlines to provide overnight lodging for displaced passengers.
"Floating airports" are being designed which could be located out at sea and which would use designs such as pneumatic stabilized platform technology.



Cargo and freight services

In addition to people, airports move cargo around the clock. Cargo airlines often have their own on-site and adjacent infrastructure to transfer parcels between ground and air. Cargo Terminal Facilities International airports need areas where export cargo has to be stored after customs clearance and prior to loading on the aircraft. Similarly import cargo that is offloaded needs to be in bond before the consignee decides to take delivery. Areas have to be kept aside for examination of export and import cargo by the airport authorities. Designated areas or sheds may be given to airlines or freight forward ring agencies. Every cargo terminal has a landside and an airside. The landside is where the exporters and importers through either their agents or by themselves deliver or collect shipments while the airside is where loads are moved to or from the aircraft. In addition cargo terminals are divided into distinct areas - export, import and interline or transhipment


Support services

Aircraft maintenance, pilot services, aircraft rental, and hangar rental are most often performed by a fixed base operator (FBO). At major airports, particularly those used as hubs, airlines may operate their own support facilities.
Some airports, typically military airbases, have long runways used as emergency landing sites. Many airbases have arresting equipment for fast aircraft, known as arresting gear (not to be confused with arresting a person) – a strong cable suspended just above the runway and attached to a hydraulic reduction gear mechanism. Together with the landing aircraft's arresting hook, it is used in situations where the aircraft's brakes would be insufficient by themselves.


Airport access

Many large airports are located near railway trunk routes for seamless connection of multimodal transport, for instance Frankfurt Airport, Amsterdam Airport Schiphol, London Heathrow Airport, London Gatwick Airport and London Stansted Airport. It is also common to connect an airport and a city with rapid transit, light rail lines or other non-road public transport systems, for instance the AirTrain JFK at John F. Kennedy International Airport in New York and the Silver LineT at Boston's Logan International Airport by the Massachusetts Bay Transportation Authority (MBTA). Such a connection lowers risk of missed flights due to traffic congestion. Large airports usually have access also through controlled-access highways ('freeways' or 'motorways') from which motor vehicles enter either the departure loop or the arrival loop.


Airport operations


Air traffic control

The majority of the world's airports are non-towered, with no air traffic control presence. However, at particularly busy airports, or airports with other special requirements, there is an air traffic control (ATC) system whereby controllers (usually ground-based) direct aircraft movements via radio or other communications links. 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 at least two main areas: ground and tower, though a single controller may work both stations. The busiest airports also have clearance deliveryapron control, and other specialized ATC stations.


Ground Control 

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 takeoff 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.
Tower Control controls aircraft on the runway and in the controlled airspace immediately surrounding the airport. Tower controllers may use radar to locate an aircraft's position in three-dimensional space, or they may rely on pilot position reports and visual observation. 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.


Traffic pattern

Left-hand circuit pattern
All airports use a traffic pattern (often called a traffic circuit outside the U.S.) 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 forming three more sides). 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 800 or 1,000 ft (244 or 305 m) above ground level(AGL). Standard 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 traffic flow smoothly because all pilots know what to expect, and helps reduce the chance of a mid-air collision.
At extremely large airports, a circuit is in place but not usually used. Rather, aircraft (usually only commercial with long routes) request approach clearance while they are still hours away from the airport, often before they even takeoff from their departure point. Large airports have a frequency called Clearance Delivery which is used by departing aircraft specifically for this purpose. This then allows airplanes to take the most direct approach path 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.


Navigational aids

There are a number of aids available to pilots, though not all airports are equipped with them. A Visual Approach Slope Indicator (VASI) helps pilots fly the approach for landing. Some airports are equipped with a VHF omnidirectional range (VOR) to help pilots find the direction to the airport. VORs are often accompanied by a distance measuring equipment (DME) to determine the distance to the VOR. VORs are also located off airports, where they serve to provide airways for aircraft to navigate upon. In poor weather, pilots will use an instrument landing system (ILS) to find the runway and fly the correct approach, even if they cannot see the ground. The number of instrument approaches based on the use of the Global Positioning System (GPS) is rapidly increasing and may eventually be the primary means for instrument landings.
Larger airports sometimes offer precision approach radar (PAR), but these systems are more common at military air bases than civilian airports. 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.


Guidance signs


Airport guidance signs provide direction and information to taxiing aircraft and airport vehicles. Smaller airports may have few or no signs, relying instead on airport diagrams and charts.
There are two classes of signage at airports, with several types of each:


Operational guidance signs


Location sign for a taxiway.

Direction sign to taxiway Bravo.
  • 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


No entry sign.
Mandatory 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.
  • Runway signs – White text on a red background. 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 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. An "interrupted ladder" type marking with an "ILS" sign in white on red indicates a holding position before an ILS critical area.


Lighting


Flood lights in front of the control tower at Sialkot International Airport, Pakistan
Many airports have lighting that help guide planes using the runways and taxiways at night or in rain or fog.
On runways, green lights indicate the beginning of the runway for landing, while red lights indicate the end of the runway. Runway edge lightingconsists of 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 (an Approach Lighting System, or ALS). Low-traffic airports may use Pilot Controlled Lighting to save electricity and staffing costs.
Along taxiways, blue lights indicate the taxiway's edge, and some airports have embedded green lights that indicate the centerline.
  • Obstruction Lighting
    • Used to mark hazards
    • Gives pilots a visual aid (usually creates a lane)
    • Meant to be visible to pilots and not a disturbance to people on ground


Weather observations

Weather observations at the airport are crucial to safe takeoffs and landings. In the US and Canada, the vast majority of airports, large and small, will either have some form of automated airport weather station, whether an AWOS, ASOS, or AWSS, a human observer or a combination of the two. These weather observations, predominantly in the METAR format, are available over the radio, through Automatic Terminal Information Service (ATIS), via the ATC or the Flight Service Station.
Planes take-off and land into the wind in order to achieve maximum performance. Because pilots need instantaneous information during landing, a windsock is also kept in view of the runway.


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 aviation fuel. The crews are also trained to deal with situations such as bomb threats, hijacking, and terrorist activities.

NASA air safety experiment (CID project)
Hazards to aircraft include debris, nesting birds, and reduced friction levels due to environmental conditions such as ice, snow, or rain. Part of runway maintenance is airfield rubber removal which helps maintain friction levels. The fields must be kept clear of debris using cleaning equipment so that loose material does not become a projectile and enter an engine duct. 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.
Many airports are built near open fields or wetlands. These tend to attract bird populations, which can pose a hazard to aircraft in the form of bird strikes. Airport crews often need to discourage birds from taking up residence.
Some airports are located next to parks, golf courses, or other low-density uses of land. Other airports are located near densely-populated urban or suburban areas. In the 1980s, a conflict arose in San Jose, California, when a plane attempting to land at Reid-Hillview Airport (built in the 1930s) collided with a Macy's department store at the Eastridge Center. Many local residents tried to get the airport shut down, even though it had been there for fifty years: their neighborhoods (and the mall) were about a decade old.
An airport can have areas where collisions between airplanes on the ground tend to occur. Records are kept of any incursions where airplanes or vehicles are in an inappropriate location, allowing these "hot spots" to be identified. These locations then undergo special attention by transportation authorities (such as the FAA in the US) and airport administrators.
During the 1980s, a phenomenon known as microburst became a growing concern due to aircraft accidents caused by microburst wind shear, such as 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 a microburst event.
Some airfields now have a special surface known as soft concrete at the end of the runway (stopway or blastpad) that behaves somewhat like styrofoam, bringing the plane to a relatively rapid halt as the material disintegrates. These surfaces are useful when the runway is located next to a body of water or other hazard, and prevent the planes from overrunning the end of the field.
========================================================================


No comments:

Post a Comment