Runway

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This article is about airport runways. For information on fashion model runways, see catwalk.

Image:ChennaiAirport.jpg A runway is a strip of land on an airport, on which aircraft can take off and land. Runways may be a prepared surface (often asphalt or concrete) or an unprepared surface (grass, dirt, or gravel).

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Orientation and dimensions

Runways are generally numbered according to the magnetic direction in which they point, rounded to the nearest ten degrees and then divided by ten. Each digit is pronounced separately for clarity in radio communications. For example, Runway Three Six would be aligned in roughly a 360 degrees direction (i.e. magnetic north), Runway Nine would be used for a runway with a 94 degree-alignment, and Runway One Seven for 168 degrees. Each runway can be used in either direction, and hence has two numbers. Runway One Zero becomes Runway Two Eight when used in the opposite direction. Runways in North America that lie within the Northern Domestic Airspace are, because of the magnetic north pole, usually numbered according to true north.

In United States civil aviation, numbers for runways less than 100° are often given as single digits; e.g. Runway Nine or Runway Four Right. In United States military and ICAO operations, numbers for runways less than 100° include the leading "zero", e.g. Runway Zero Two or Runway Zero One Left.

If there is more than one runway pointing in the same direction (parallel runways), each runway is identified by appending Left, Center and Right to the number — for example, Runways One Five Left (15L), One Five Center (15C), and One Five Right (15R). Runway Two Left (2L) becomes Runway Two Zero Right (20R) when used in the opposite direction.

At large airports with more than three parallel runways (for example, at Los Angeles International Airport in Los Angeles, California or Hartsfield International Airport in Atlanta, Georgia), some runway identifiers are shifted by 10 degrees to avoid the ambiguity that would result with more than three parallel runways. In Los Angeles, this system results in Runways Six Left, Six Right, Seven Left, and Seven Right, even though all four runways are exactly parallel (approximately 69 degrees).

For fixed wing aircraft it is advantageous to perform take-offs and landings into the wind to reduce takeoff roll and reduce the ground speed needed to attain flying speed. Larger airports usually have several runways in different directions, so that one can be selected that is most nearly aligned with the wind. Airports with one runway are often constructed to be aligned with the prevailing wind.

Runway dimensions vary from as small as 800 feet (240 m) long and 25 feet (8 m) wide in smaller general aviation airports, to 16,000 feet (4,800 m) long and 300 feet (100 m) wide at large international airports built to accommodate large passenger jets. Runway dimensions are measured in feet in the United States and Canada, and meters are used elsewhere in the world.

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"Sections" of a runway

Image:Runway diagram.png

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Blast pads

Image:Runway diagram, Blast pad.png

Blast pads or stopways are often constructed just before the start of a runway where jet blast produced by large planes during the takeoff roll can erode the ground and eventually damage the runway. They may also be constructed as emergency space for aborted take-offs.

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Displaced threshold

Image:Runway diagram, Displaced threshold.png

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Runway lighting

At bigger airports, runways use a standard lighting system to allow night landings. Seen from a landing plane, the runway starts with a strip of green lights at the near end and stops with a strip of red lights at the far end. The runway itself is framed with white elevated edge lights, as opposed to the blue elevated edge lights of a taxiway. The centerline is often indicated by white lights, which may be coded alternately white and yellow and then purely yellow nearing the far end of the runway. Furthermore, many runways equipped with instrument landing systems feature touchdown zone lighting. This consists of rows of white light bars on either side of the centerline over the first 30 feet of the runway. The sides of the runway are marked by lines of bright white lights. Larger runways may have another line of dimmer white lights running down the centerline. According to Transport Canada's regulations, the runway-edge lights must be visible for at least 2 miles.

The lights must be arranged such that:

  • the minimum distance between lines is 75 feet, and maximum is 200 feet;
  • the maximum distance between lights within each line is 200 feet;
  • the minimum length of parallel lines is 1400 feet;
  • the minimum number of lights in the line is 8.
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Runway markings

There are various runway markings and signs on any given runway. Larger runways have a distance remaining sign (black box with white numbers). This sign uses a single number to indicate the thousands of feet remaining, so 7 will indicate 7,000 feet remaining. The runway threshold is marked by a line of green lights.

Image:RunwayDiagram.png

Some airports/airfields (particularly uncontrolled ones) are equipped with Pilot Controlled Lighting, so that pilots can temporarily turn on the lights when they need them. This avoids the need for automatic systems or staff to turn the lights on at night or in other low visibility situations. This also avoids the costs of having hundreds of lights on for extended periods.

Of course not all airports have lighted runways, and runways may not be marked at all. At small, particularly private airfields, there may be nothing more than a windsock, if that.

There are three types of runways:

  • Visual runways (found at small airstrips) do not provide an instrument-based landing procedure - pilots must be able to see the runway to use it
  • Non-precision runways (found at smaller airports) provide horizontal position guidance - via radio beacons - to planes on instrument approach
  • Precision runways (found at medium and large size airports), which provide both horizontal and vertical guidance for instrument approaches.
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Visual Runways

Visual Runways are usually just a strip of grass, gravel, or unmarked asphalt or concrete. They may also be marked asphalt or concrete. There are no markings on a visual runway; it is usually just threshold markings, numbers, and centerlines.

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Non-precision runways

Often used at small-medium size airports, non-precision runways are always marked. They consist of threshold markings, numbers, centerlines, and sometimes an aiming point.

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Precision runways

Precision runways, found at medium and large size airports, consist of, in order, a blast pad/stopway (optional), threshold, number, centerline, one 3-stripe touchdown zone (All countries) or two three stripe touchdown zone (All except US), aiming point, two 2-stripe touchdown zones (All countries) or one 2-stripe touchdown zone (All except US), and two 1 stripe touchdown zones.

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Notes

  • In Canada, Australia, Japan, and the United Kingdom, all touchdown zones for precision runways are one-stripe.
  • In Australia, precision runways consist of only one 1-stripe touchdown zone, aiming point, and one 1-stripe touchdown zone. Furthermore, all non-precision and visual runways have no aiming point.
  • Some European countries replace the aiming point with a 3-stripe touchdown zone.
  • Runways may have one end with Precision markings and the other end with Non-Precision. Many real world airports do not install precision guidance equipment on both ends, in order to save money. Runways with only one Precision end can install the full set of touchdown zones, even if some are past the midpoint. If a runway has Precision markings on both ends, touchdown zones within 270m of the midpoint are omitted, to avoid pilot confusion over which end the marking belongs to.
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Active runway

Image:ORD airport map.PNG The active runway is the runway at an airport that is in current use for takeoffs and landings. Since takeoffs and landings are usually done as close as "into the wind" as possible, wind direction generally determines the active runway (or just the active in aviation slang).

Selection of the active runway, however, depends on a number of factors. At an uncontrolled airport (one with no control tower), pilots usually select the runway most nearly aligned with the wind, but they are not obliged to use that particular runway. For example, a pilot arriving from the east may elect to land straight in to an east-west runway despite a minor tailwind or significant crosswind, in order to expedite his arrival, although it is recommended to always fly a regular traffic pattern to more safely merge with other aircraft.

At controlled airports, the active is usually determined by a tower supervisor. However, there may be constraints, such as policy from the airport manager (calm wind runway selection, for example, or noise abatement guidelines) that dictate an active runway selection that isn't the one most nearly aligned with the wind.

At major airports with multiple runways, the active could be any of a number of runways. For example, when O'Hare (ORD) is landing on 27R and 32L, departures use 27L and 32R, thus making four active runways. When they're landing on 14R and 22R, departures use 22L and 9L, and occasionally a third arrival runway, 14L, will be employed, bringing the active runway count to five.

At major airports, the active runway is based on existing weather conditions (visibility and ceiling, as well as wind, and runway conditions such as wet/dry or snow covered), efficiency (ORD can land more airplanes on 14R-22R than they can on 27R-32L), traffic demand (when a heavy departure rush is scheduled, a runway configuration that optimizes departures vs arrivals may be desirable), and time of day (ORD is obliged to use Runway 9L/27R during the hours of roughly midnight to 6 a.m. due to noise abatement).

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Longest runways

Although runway length may be of some academic interest, in terms of usability for air carrier operations, a runway of at least 6,000 ft in length is usually adequate for aircraft weights below approximately 200,000 lbs. Larger aircraft including widebodies (Boeing 747, 767, and 777; McDonnel-Douglas DC-10 or MD-11; Lockheed L1011;, Airbus A-340, A-380) will usually require at least 8,000 ft at sea level and somewhat more at higher altitude airports. International widebody flights may also have landing requirements of 10,000 ft or more and takeoff requirements of 13,000+ ft.

At sea level, 10,000 ft can be considered an adequate length to accommodate virtually any aircraft. For example, at ORD, when landing simultaneously on 22R and 27L or parallel 27s, it is routine for arrivals from the Far East who would normally be vectored for 22R (7,500 ft) or 27R (8,000 ft) to request 27L (10,000 ft). It is always accommodated, although occasionally with a delay.

Some of the longest runways include:


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See also

cs:Vzletová a přistávací dráha de:Startbahn es:Pista de aterrizaje fr:Piste (aéroport) id:Landas pacu nl:Startbaan no:Rullebane ja:滑走路 pt:Pista de pouso e decolagem ru:Взлётно-посадочная полоса fi:Kiitotie zh:跑道 (航空)

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