A runway (RWY) is a strip of land at an airport on which aircraft can take off and land and forms part of the maneuvering area. Runways may be a man-made surface (often asphalt, concrete, or a mixture of both) or a natural surface (grass, dirt, gravel, ice, or salt).
By extension, the term has also come to mean any long, flat, straight area, such as that used in fashion shows.
Runways are given a number between 01 and 36. This indicates the runway's heading: A runway with the number 36 points to the north (360°), runway 09 points east (90°), runway 18 is south (180°), and runway 27 points west (270°). Thus, the runway number is one tenth of the runway centerline's magnetic azimuth, measured clockwise from the magnetic declination.
A runway can be used in two directions, which means the runway has two names: "runway 33" and "runway 15". The two numbers always differ by 18 (= 180°).
For clarity in radio communications, each digit is pronounced individually: runway three six, runway one four, etc. A leading zero, for example in "runway zero six" or "runway zero one left", is included for International Civil Aviation Organization (ICAO) and some United States military airports (such as Edwards Air Force Base). However in the United States at most civil aviation airports, the leading zero is often dropped: "runway niner" (the number nine is pronounced "niner" to avoid confusion with the spoken number "five") or "runway four right". 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. It is very common in a country such as Canada for a controller to clear an incoming American aircraft to, for example, Runway 04, and the pilot read back the clearance as Runway 4. In flight simulation programs those of American origin might apply U.S. usage to airports around the world. For example Runway 05 at Halifax will appear on the program as the single digit 5 rather than 05.
Runway designations change over time because the magnetic poles slowly drift on the Earth's surface and the magnetic bearing will change. Depending on the airport location and how much drift takes place, it may be necessary over time to change the runway designation. As runways are designated with headings rounded to the nearest 10 degrees, this will affect some runways more than others. For example, if the magnetic heading of a runway is 233 degrees, it would be designated Runway 23. If the magnetic heading changed downwards by 5 degrees to 228, the Runway would still be Runway 23. If on the other hand the original magnetic heading was 226 (Runway 23), and the heading decreased by only 2 degrees to 224, the runway should become Runway 22. Because the drift itself is quite slow, runway designation changes are uncommon, and not welcomed, as they require an accompanying change in aeronautical charts and descriptive documents. When runway designations do change, especially at major airports, it is often changed overnight as taxiway signs need to be changed and the huge numbers at each end of the runway need to be repainted to the new runway designators. In July 2009 for example, London Stansted Airport in the United Kingdom changed its runway designations from 05/23 to 04/22 overnight.
If there is more than one runway pointing in the same direction (parallel runways), each runway is identified by appending Left (L), Center (C) and Right (R) to the number — for example, Runways One Five Left (15L), One Five Center (15C), and One Five Right (15R). Runway Zero Three Left (03L) becomes Runway Two One Right (21R) when used in the opposite direction (derived from adding 18 to the original number for the 180 degrees when approaching from the opposite direction).
At large airports with more than three parallel runways (for example, at Los Angeles, Detroit Metropolitan Wayne County, Hartsfield-Jackson Atlanta, Denver, and Dallas-Fort Worth), some runway identifiers are shifted by 10 degrees 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 exactly parallel (approximately 69 degrees). At Dallas-Fort Worth, there are five parallel runways, named 17L, 17C, 17R, 18L, and 18R, all oriented at a heading of 175.4 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 245 m (804 ft) long and 8 m (26 ft) wide in smaller general aviation airports, to 5,500 m (18,045 ft) long and 80 m (262 ft) wide at large international airports built to accommodate the largest jets, to the huge 11,917 m (39,098 ft) x 274 m (899 ft) lake bed runway 17/35 at Edwards Air Force Base in California - a landing site for the Space Shuttle.
Two runways pointing in the same direction are classed as dual or parallel runways depending on the separation distance. In some countries, flight rules mandate that only one runway may be used at a time under certain conditions (usually adverse weather) if the parallel runways are too close to each other.
(The clearway length allowed must lie within the aerodrome or airport boundary. According to the Federal Aviation Regulations and Joint Aviation Requirements (JAR) TODA is the lesser of TORA plus clearway or 1.5 times TORA).
The first runway lighting appeared in 1930 at Cleveland Municipal Airport (now known as Cleveland Hopkins International Airport) in Cleveland, Ohio.. A line of lights on an airfield or elsewhere to guide aircraft in taking off or coming in to land or an illuminated runway is sometimes also known as a flare path.
Runway lighting is used at airports which allow night landings. Seen from the air, runway lights form an outline of the runway. A particular runway may have some or all of the following.
According to Transport Canada's regulations, the runway-edge lighting must be visible for at least 2 mi (3 km). Additionally, a new system of advisory lighting, Runway Status Lights, is currently being tested in the United States.
The edge lights must be arranged such that:
Control of Lighting System Typically the lights are controlled by a control tower, a Flight Service Station or another designated authority. Some airports/airfields (particularly uncontrolled ones) are equipped with Pilot Controlled Lighting, so that pilots can temporarily turn on the lights when the relevant authority is not available. 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 cost of having the lighting system on for extended periods. Smaller airports may not have lighted runways or runway markings. Particularly at private airfields for light planes, there may be nothing more than a windsock beside a landing strip.
There are runway markings and signs on any 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 ft (2,134 m) remaining. The runway threshold is marked by a line of green lights.
There are three types of runways:
Several terms fall under the flight safety topic of runway safety, including incursion, excursion, and confusion.
Runway excursion is an incident involving only a single aircraft where it makes an inappropriate exit from the runway. This can happen because of pilot error, poor weather, emergency, or a fault with the aircraft. Overrun is a type of excursion where the aircraft is unable to stop before the end of the runway. An example of such an event is Air France Flight 358 in 2005. Further examples can be found in the overruns category. Runway excursion is the most frequent type of landing accident, slightly ahead of runway incursion. For runway accidents recorded between 1995 and 2007, 96% were of the 'excursion' type.
Runway event is another term for a runway accident.
Runway incursion involves a first aircraft, as well as a second aircraft, vehicle, or person. It is defined by the U.S. Federal Aviation Administration (FAA) as: "Any occurrence at an aerodrome involving the incorrect presence of an aircraft, vehicle or person on the protected area of a surface designated for the landing and take off of aircraft."
Runway confusion involves a single aircraft, and is used to describe the error when the aircraft makes "the unintentional use of the wrong runway, or a taxiway, for landing or take-off".
The U.S. FAA publishes an annual report on runway safety issues, available from the FAA website. New systems designed to improve runway safety, such as Airport Movement Area Safety System (AMASS) and Runway Awareness and Advisory System (RAAS), are discussed in the report. AMASS prevented the serious near-collision in the 2007 San Francisco International Airport runway incursion.
Runway condition is also an important paramater related to meterological conditions and air safety.
According to the JAR definition, a runway with water patches or that is flooded is considered to be contaminated.
The choice of material used to construct the runway depends on the use and the local ground conditions. For a major airport, where the ground conditions permit, the most satisfactory type of pavement for long-term minimum maintenance is concrete. Although certain airports have used reinforcement in concrete pavements, this is generally found to be unnecessary, with the exception of expansion joints across the runway where a dowel assembly, which permits relative movement of the concrete slabs, is placed in the concrete. Where it can be anticipated that major settlements of the runway will occur over the years because of unstable ground conditions, it is preferable to install asphaltic concrete surface, as it is easier to patch on a periodic basis. For fields with very low traffic of light planes, it is possible to use a sod surface. Some runways also make use of salt flat runways.
For pavement designs, borings are taken to determine the subgrade condition, and based on the relative bearing capacity of the subgrade, the specifications are established. For heavy-duty commercial aircraft, the pavement thickness, no matter what the top surface, varies from 10 in (250 mm) to 4 ft (1 m), including subgrade.
Airport pavements have been designed by two methods. The first, Westergaard, is based on the assumption that the pavement is an elastic plate supported on a heavy fluid base with a uniform reaction coefficient known as the K value. Experience has shown that the K values on which the formula was developed are not applicable for newer aircraft with very large footprint pressures.
The second method is called the California bearing ratio and was developed in the late 1940s. It is an extrapolation of the original test results, which are not applicable to modern aircraft pavements or to modern aircraft landing gear. Some designs were made by a mixture of these two design theories.
A more recent method is an analytical system based on the introduction of vehicle response as an important design parameter. Essentially it takes into account all factors, including the traffic conditions, service life, materials used in the construction, and, especially important, the dynamic response of the vehicles using the landing area.
Because airport pavement construction is so expensive, every effort is made to minimize the stresses imparted to the pavement by aircraft. Manufacturers of the larger planes design landing gear so that the weight of the plane is supported on larger and more numerous tires. Attention is also paid to the characteristics of the landing gear itself, so that adverse effects on the pavement are minimized. Sometimes it is possible to reinforce a pavement for higher loading by applying an overlay of asphaltic concrete or portland cement concrete that is bonded to the original slab.
Post-tensioning concrete has been developed for the runway surface. This permits the use of thinner pavements and should result in longer concrete pavement life. Because of the susceptibility of thinner pavements to frost heave, this process is generally applicable only where there is no appreciable frost action.
Runway pavement surface is prepared and maintained to maximize friction for wheel braking. To minimize hydroplaning following heavy rain, the pavement surface is usually grooved so that the surface water film flows into the grooves and the peaks between grooves will still be in contact with the aircraft tires. To maintain the macrotexturing built into the runway by the grooves, maintenance crews engage in airfield rubber removal or hydrocleaning in order to meet required FAA friction levels.
The active runway is the runway at an airport that is in use for takeoffs and landings. Since takeoffs and landings are usually done as close to "into the wind" (see headwind) as possible, wind direction generally determines the active runway (or just the active in aviation vernacular).
Selection of the active runway, however, depends on a number of factors. At a non-towered airport, 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 is not 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 are 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 weather conditions (visibility and ceiling, as well as wind, and runway conditions such as wet/dry or snow covered), efficiency (ORD can land more aircraft on 14R/32L than they can on 9L/27R), 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).
A runway of at least 6,000 ft (1,829 m) in length is usually adequate for aircraft weights below approximately 200,000 lb (90,718 kg). Larger aircraft including widebodies will usually require at least 8,000 ft (2,438 m) at sea level and somewhat more at higher altitude airports. International widebody flights, which carry substantial amounts of fuel and are therefore heavier, may also have landing requirements of 10,000 ft (3,048 m) or more and takeoff requirements of 13,000 ft (3,962 m)+.
At sea level, 10,000 ft (3,048 m) can be considered an adequate length to land virtually any aircraft. For example, at O'Hare International, when landing simultaneously on 22R and 27L or parallel 27R, it is routine for arrivals from the Far East which would normally be vectored for 22R (7,500 ft (2,286 m)) or 27R (8,000 ft (2,438 m)) to request 27L (10,000 ft (3,048 m)). It is always accommodated, although occasionally with a delay.
An aircraft will need a longer runway at a higher altitude due to decreased density of air at higher altitudes, which reduces lift and engine power. An aircraft will also require a longer runway in hotter or more humid conditions (see density altitude). Most commercial aircraft carry manufacturer's tables showing the adjustments required for a given temperature.
A runway (also abbreviated to RWY) is a strip of land on an airport, on which aircraft can take off and land. Runways may be a man-made surface (often asphalt, concrete, or a mixture of both) or a natural surface (grass, dirt, or gravel).