# Runway

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, gravel).

## Description

Large airports may have several runways. They are identified by the magnetic direction in which they point, rounding to the nearest ten degrees. So, for example, a runway identified with "36" would stand for a 360 degrees direction (i.e. North), "09" for 94 degrees, and "17" for 168 degrees. Each runway can be used in two directions, and hence has two numbers. Since the directions are necessarily opposite, the number of a runway can always be found by adding or subtracting 18 from the opposite runway number (whichever yields a positive number less than 37). For example runway 10 is called runway 28 when used in the opposite direction.

If in an airport there is more than one runway pointing in the same direction, the runways are identified by the letters L, C and R, for Left, Center and Right, behind the number. Such an example would be runways "15L", "15C" and "15R". In speech runways are always referred to by saying each digit of the number, followed by 'Left', 'Right' or 'Center' if necessary. The first example above would be referred to as "Runway One Five Left".

For fixed wing aircraft it as advantageous to perform take-offs and landings into the wind to achieve the maximum lift. Airports usually have several runways, running in different directions, so that this can be done for different wind directions.

## 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 3000 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.

## 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.

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.

## Active runway

An active runway is the runway at an airport that is in current use for all takeoffs and landings. Since takeoffs and landings are always done as close as "into the wind" as possible, wind direction determines the active runway (or just the active in aviation slang).

Barring elevation constraints, runways are bidirectional. For example, a west-east runway will be both "Runway 27" and "Runway 9" (derived from the compass heading divided by ten) depending on direction. If the wind if blowing from the west, the active runway will be Runway 27, as 270° points west.

## Longest runways

Some of the longest runways include:

1 Marked as "abandoned" on satellite imagery. Total pavement length including overruns is 24,085 ft. The facility's sole active runway has a length of 3651 m (11,980 ft).

2 Listed here as Chinese sources have contributed to misperceptions that it is the world's longest runway. It is billed as the world's highest airport at 4300 m (14,707 ft).