Runway


In aviation, a runway is an elongated, rectangular surface designed for the landing and takeoff of an aircraft. Runways may be a human-made surface or a natural surface. Runways, taxiways and ramps, are sometimes referred to as "tarmac", though very few runways are built using tarmac. Takeoff and landing areas defined on the surface of water for seaplanes are generally referred to as waterways. Runway lengths are now commonly given in meters worldwide, except in North America where feet are commonly used.

History

In January 1919, aviation pioneer Orville Wright underlined the need for "distinctly marked and carefully prepared landing places, the preparing of the surface of reasonably flat ground an expensive undertaking there would also be a continuous expense for the upkeep."
In 1919, based on WWI experience, the United States Army Air Service published Specifications for Municipal Landing Fields. It specified an 1800 by 1800 foot square with a central 150 foot takeoff runway in the shape of a cross. Through the 1930s though, most army planes landed in any direction, subject to the prevailing winds, on circular groomed and drained turf called "all-over fields." However, tire pressures were limited to less than seventy psi in such fields. After 1935, tire pressures exceeded that limit with increased aircraft size. According to Conway, "Confronted with snow and ice removal in the north, water nearly everywhere, and the demands placed by airlines on regularity, safety, and efficient transshipment of passengers and mail, the technology of the all-over turf field became obsolete in the United States during the 1920s." In 1928, Ford Airfield became the first U.S. airport to have concrete runways, and by 1932, all major U.S. airports had runways..."

Design

Orientation

The primary consideration in determining runway orientation is the prevailing wind direction, in lieu of spatial constraints or obstructions that may prevent optimal alignment. To mitigate the occurrence of crosswind operations which are more challenging and dangerous, runways at airports are designed to align with the wind's direction. Utilizing runways oriented with the wind direction also allows for aircraft to take-off and land into the headwind, reducing the length of runway used during operations. Taking off and landing into the wind increases the relative air speed of the aircraft to create more lift; this allows aircraft to reach take-off velocity with a shorter amount of ground roll and also allows aircraft to land with a slower ground speed. To determine the prevailing wind directions, analysis of a wind rose is used before constructing airport runways.
Originally in the 1920s and 1930s, airports and air bases were built in a triangle-like pattern of three runways at 60° angles to each other. The reason was that aviation was only starting, and although it was known that wind affected the runway distance required, not much was known about wind behaviour. As a result, three runways in a triangle-like pattern were built, and the runway with the heaviest traffic would eventually expand into the airport's main runway, while the other two runways would be either abandoned or converted into taxiways.

Naming

Runways are named by a number between 01 and 36, which is generally the magnetic azimuth of the runway's heading in decadegrees. This heading differs from true north by the local magnetic declination. A runway numbered 09 points east, runway 18 is south, runway 27 points west and runway 36 points to the north. When taking off from or landing on runway 09, a plane is heading around 90°. A runway can normally be used in both directions, and is named for each direction separately: e.g., "runway 15" in one direction is "runway 33" when used in the other. The two numbers differ by 18. For clarity in radio communications, each digit in the runway name is pronounced individually: runway one-five, runway three-three, etc..
File:ORD Airport Diagram.svg|thumb|upright|FAA airport diagram at O'Hare International Airport. The two 14/32 runways go from upper left to lower right, the two 4/22 runways go from lower left to upper right, and the two 9/27 and three 10/28 runways are horizontal.
A leading zero, for example in "runway zero-six" or "runway zero-one-left", is included for all ICAO and some U.S. military airports. However, most U.S. civil aviation airports drop the leading zero as required by FAA regulation. This also includes some military airfields such as Cairns Army Airfield. This American anomaly may lead to inconsistencies in conversations between American pilots and controllers in other countries.
Military airbases may include smaller [|paved] runways known as "assault strips" for practice and training next to larger primary runways. These strips eschew the standard numerical naming convention and instead employ the runway's full three digit heading; examples include Dobbins Air Reserve Base's Runway 110/290 and Duke Field's Runway 180/360.
Runways with non-hard surfaces, such as small turf airfields and waterways for seaplanes, may use the standard numerical scheme or may use traditional compass point naming, examples include Ketchikan Harbor Seaplane Base's Waterway E/W. Airports with unpredictable or chaotic water currents, such as Santa Catalina Island's Pebbly Beach Seaplane Base, may designate their landing area as Waterway ALL/WAY to denote the lack of designated landing direction.

Letter suffix

If there is more than one runway pointing in the same direction, each runway is identified by appending left , center and right to the end of the runway number to identify its position —for example, runways one-five-left , one-five-center , and one-five-right . Runway zero-three-left becomes runway two-one-right when used in the opposite direction. In some countries, regulations mandate that where parallel runways are too close to each other, only one may be used at a time under certain conditions.
At large airports with four or more parallel runways, some runway identifiers are shifted by 1 to avoid the ambiguity that would result with more than three parallel runways. For example, in Los Angeles, this system results in runways 6L, 6R, 7L, and 7R, even though all four runways are actually parallel at approximately 69°. At Dallas/Fort Worth International Airport, there are five parallel runways, named 17L, 17C, 17R, 18L, and 18R, all oriented at a heading of 175.4°. Occasionally, an airport with only three parallel runways may use different runway identifiers, such as when a third parallel runway was opened at Phoenix Sky Harbor International Airport in 2000 to the south of existing 8R/26L—rather than confusingly becoming the "new" 8R/26L it was instead designated 7R/25L, with the former 8R/26L becoming 7L/25R and 8L/26R becoming 8/26.
Suffixes may also be used to denote special-use runways. Airports that have seaplane waterways may choose to denote the waterway on charts with the suffix W; such as Daniel K. Inouye International Airport in Honolulu and Lake Hood Seaplane Base in Anchorage. Small airports that host various forms of air traffic may employ additional suffixes to denote special runway types based on the type of aircraft expected to use them, including STOL aircraft, gliders, rotorcraft, and ultralights. Runways that are numbered relative to true north rather than magnetic north will use the suffix T; this is advantageous for certain airfields in the far north such as Thule Air Base.

Renumbering

Runway designations may be changed over time as the Earth's magnetic field shifts and their headings shift with it. This is more common at higher latitudes: for example, Fairbanks International Airport in Alaska renames runways roughly every 24 years, most recently in 2009. In northern Canada, runways are designated based on true north, which avoids the need to update them. Nav Canada, Canada's air navigation service provider, has advocated for an industry-wide switch to true north.
As runways are designated with headings rounded to the nearest 10°, some runways are affected sooner than others; e.g. a hypothetical Runway 23 with a heading of 226° would only have to shift to 224° to become Runway 22. Because magnetic drift itself is slow, these changes are uncommon, and not welcomed, as they require accompanying changes in aeronautical charts and descriptive documents. When a runway designation does change, it is often done at night, especially at major airports, because taxiway signs need to be changed and the numbers at each end of the runway need to be repainted to the new runway designators. In 2009 for example, London Stansted Airport in the United Kingdom changed its runway designation from 05/23 to 04/22 during the night.

Declared distances

Runway dimensions vary from as small as long and wide in smaller general aviation airports, to long and wide at large international airports built to accommodate the largest jets, to the huge lake bed runway 17/35 at Edwards Air Force Base in California – developed as a landing site for the Space Shuttle.
Takeoff and landing distances available are given using one of the following terms:
  • Takeoff Run Available – The length of runway declared available and suitable for the ground run of an airplane taking off.
  • Takeoff Distance Available – The length of the takeoff run available plus the length of the clearway, if clearway is provided..
  • Accelerate-Stop Distance Available – The length of the takeoff run available plus the length of the stopway, if stopway is provided.
  • Landing Distance Available – The length of runway that is declared available and suitable for the ground run of an airplane landing.
  • Emergency Distance Available – LDA plus a stopway.

    Sections

There are standards for runway markings.
  • The runway thresholds are markings across the runway that denote the beginning and end of the designated space for landing and takeoff under non-emergency conditions.
  • The runway safety area is the cleared, smoothed and graded area around the paved runway. It is kept free from any obstacles that might impede flight or ground roll of aircraft.
  • The runway is the surface from threshold to threshold, which typically features threshold markings, numbers, and centerlines, but excludes blast pads and stopways at both ends.
  • Blast pads are often constructed just before the start of a runway where jet blast produced by large planes during the takeoff roll could otherwise erode the ground and eventually damage the runway.
  • Stopways, also known as overrun areas, are also constructed at the end of runways as emergency space to stop planes that overrun the runway on landing or a rejected takeoff.
  • * Blast pads and stopways look similar, and are both marked with yellow chevrons; stopways may optionally be surrounded by red runway lights. The differences are that stopways can support the full weight of an aircraft and are designated for use in an aborted takeoff, while blast pads are often not as strong as the main paved surface of the runway and are not to be used for taxiing, landing, or aborted takeoffs. FAA Advisory Circular 150/5300-13B An engineered materials arrestor system may also be present, which may overlap with the end of the blast pad or stopway and is painted similarly.
  • Displaced thresholds may be used for taxiing, takeoff, and landing rollout, but not for touchdown. A displaced threshold often exists because of obstacles just before the runway, runway strength, or noise restrictions making the beginning section of runway unsuitable for landings. It is marked with white paint arrows that lead up to the beginning of the landing portion of the runway. As with blast pads, landings on displaced thresholds are not permitted aside from emergency use or exigent circumstance.
  • Relocated thresholds are similar to displaced thresholds. They are used to mark a portion of the runway temporarily closed due to construction or runway maintenance. This closed portion of the runway is not available for use by aircraft for takeoff or landing, but it is available for taxi. While methods for identifying the relocated threshold vary, a common way for the relocated threshold to be marked is a ten-foot-wide white bar across the width of the runway.
  • Clearway is an area beyond the paved runway, aligned with the runway centerline and under the control of the airport authorities. This area is not less than 500 ft and there are no protruding obstacles except for threshold lights provided they are not higher than 26 inches. There is a limit on the upslope of the clearway of 1.25%. The length of the clearway may be included in the length of the takeoff distance available. For example, if a paved runway is long and there are of clearway beyond the end of the runway, the takeoff distance available is long. When the runway is to be used for takeoff of a large airplane, the maximum permissible takeoff weight of the airplane can be based on the takeoff distance available, including clearway. Clearway allows large airplanes to take off at a heavier weight than would be allowed if only the length of the paved runway is taken into account.