Runway

According to the International Civil Aviation Organization (ICAO), a **runway** is a "defined rectangular area on a land aerodrome prepared for the landing and takeoff of aircraft". 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).

## Declared distances

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 × 274 m (39,098 ft × 899 ft) lake bed runway 17/35 at Edwards Air Force Base in California – a landing site for the retired Space Shuttle.

Takeoff and landing distances available are given using one of the following terms:

TORA
**Takeoff Run Available** – The length of runway declared available and suitable for the ground run of an airplane taking off.
TODA
**Takeoff Distance Available** – The length of the takeoff run available plus the length of the clearway, if clearway is provided.
(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).
ASDA
**Accelerate-Stop Distance Available** – The length of the takeoff run available plus the length of the stopway, if stopway is provided.
LDA
**Landing Distance Available** – The length of runway that is declared available and suitable for the ground run of an airplane landing.
EMDA
**Emergency Distance Available** – LDA (or TORA) plus a stopway.
## Sections of a runway

There are 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 not overrun areas at both ends.
* **Blast pads**, also known as overrun areas or stopways, 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. **Overrun areas** are also constructed at the end of runways as emergency space to slowly stop planes that overrun the runway on a landing gone wrong, or to slowly stop a plane on a rejected takeoff or a takeoff gone wrong. Blast pads are often not as strong as the main paved surface of the runway and are marked with yellow chevrons. Planes are not allowed to taxi, take off or land on blast pads, except in an emergency.

* **Displaced thresholds** may be used for taxiing, takeoff, and landing rollout, but not for touchdown. A displaced threshold often exists because obstacles just before the runway, runway strength, or noise restrictions may make 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.

## Runway markings

There are runway markings and signs on most large runways. 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:

* Visual runways are used at small airstrips and are usually just a strip of grass, gravel, ice, asphalt, or concrete. Although there are usually no markings on a visual runway, they may have threshold markings, designators, and centerlines. Additionally, they do not provide an instrument-based landing procedure; pilots must be able to see the runway to use it. Also, radio communication may not be available and pilots must be self-reliant.
* Non-precision instrument runways are often used at small- to medium-size airports. These runways, depending on the surface, may be marked with threshold markings, designators, centerlines, and sometimes a 1,000 ft (305 m) mark (known as an aiming point, sometimes installed at 1,500 ft (457 m)). They provide horizontal position guidance to planes on instrument approach via Non-directional beacon, VHF omnidirectional range, Global Positioning System, etc.
* Precision instrument runways, which are found at medium- and large-size airports, consist of a blast pad/stopway (optional, for airports handling jets), threshold, designator, centerline, aiming point, and 500 ft (152 m), 1,000 ft (305 m)/1,500 ft (457 m), 2,000 ft (610 m), 2,500 ft (762 m), and 3,000 ft (914 m) touchdown zone marks. Precision runways provide both horizontal and vertical guidance for instrument approaches.

### National variants

* In Australia, Canada, Japan, the United Kingdom, as well as some other countries or territories (Hong Kong and Macau) all 3-stripe and 2-stripe touchdown zones for precision runways are replaced with one-stripe touchdown zones.
* In some South American countries like Colombia, Ecuador and Peru one 3-stripe is added and a 2-stripe is replaced with the aiming point.
* Some European countries replace the aiming point with a 3-stripe touchdown zone.
* Runways in Norway have yellow markings instead of the usual white ones. This also occurs in some airports in Japan, Sweden, and Finland. The yellow markings are used to ensure better contrast against snow.
* Runways may have different types on each end. To cut costs, many airports do not install precision guidance equipment on both ends. Runways with one precision end and any other type of end can install the full set of touchdown zones, even if some are past the midpoint. Runways with precision markings on both ends omit touchdown zones within 900 ft (274 m) of the midpoint, to avoid ambiguity over with which end the zone is associated.

## External links

* United States Aeronautical Information Manual – Federal Aviation Administration (published yearly)
* United States Airport/Facility Directory (d-AFD) – Federal Aviation Administration (published every 56 days)
* United States Terminal Procedures Publication/Airport Diagrams (d-TPP) – Federal Aviation Administration (published every 28 days)
* North American Powered Parachute Federation
* Visual Aids Handbook – Civil Aviation Authority