Ruth Haines
The orientation of airport runways is determined by several factors, including wind direction, safety, efficiency, and the surrounding geography. The primary consideration is usually the prevailing wind direction, as planes typically take off and land into the wind, which increases their relative airspeed and allows them to reach takeoff velocity with a shorter ground roll. Airports with unpredictable wind currents, such as seaplane bases, may not have a designated landing direction. Runways are typically numbered based on their magnetic azimuth (compass bearing) and are named using Arabic numerals. The direction a runway faces is indicated by a number between 01 and 36, with 09 pointing east, 18 pointing south, 27 pointing west, and 36 pointing north.
| Characteristics | Values |
|---|---|
| Main purpose | Landing and taking off aircraft |
| Surface | Asphalt, concrete, grass, dirt, gravel, ice, sand or salt |
| Direction | Generally parallel to the prevailing wind |
| Numbering | Based on the magnetic azimuth (compass bearing) in decadegrees |
| Naming | Runways pointing in the same direction are identified by appending left (L), centre (C) and right (R) |
| Length | Measured in meters worldwide, except in North America where feet are used |
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What You'll Learn
Runways should be parallel to the prevailing wind
When it comes to the direction that airport runways face, the primary consideration is the prevailing wind direction. This is because planes don't like taking off or landing with strong cross breezes. Therefore, runways are typically positioned to be parallel to the prevailing wind direction, or as close to it as possible. Taking off and landing into the wind allows planes to use less runway and clear traffic faster. It also increases the relative airspeed of the aircraft, creating more lift and allowing aircraft to reach takeoff velocity with a shorter ground roll.
However, this isn't always possible due to spatial constraints or obstructions. Airports with unpredictable or chaotic water currents, for example, may not have a designated landing direction. Additionally, some airports may not have been able to expand their property in the preferred direction, so they may have to put in a slightly longer runway facing a different direction.
In the early days of aviation, the layout of airports was less standardized. As a result, early airports were built with runways in different directions to accommodate various wind conditions. Modern aircraft are not as sensitive to wind direction, so for safety and efficiency, the modern practice is to build multiple parallel runways in the predominant wind direction.
The direction that a runway faces is indicated by a number from 01 to 36, which corresponds to the runway's magnetic azimuth, or compass bearing, in decadegrees. For example, a runway numbered 09 points east, while a runway numbered 18 points south. If there is more than one runway pointing in the same direction, they are identified by appending left (L), center (C), or right (R) to the end of the runway number.
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Runways should be perpendicular to the prevailing wind
The direction that airport runways face is dictated by a magnetic 360-degree scale, with north at 360°, east at 90°, south at 180°, and west at 270°. The prevailing wind direction is the primary consideration when determining runway orientation. This is because planes typically take off when facing the wind and landing into the headwind also lets the plane use less runway and clear traffic faster.
In the 1920s and 1930s, airports were built in a triangle-like pattern of three runways at 60° angles to each other. This was because, at the time, not much was known about wind behaviour. As a result, 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.
Modern aircraft are not as sensitive to wind direction as earlier aircraft, so for safety and efficiency, the modern practice is to build multiple parallel runways in the predominant wind direction. However, bigger airports will generally have perpendicular runways. This is because having parallel primary runways allows one to be used for takeoffs while the other is used for landings or extra takeoffs if needed. This cannot be done with runways that cross, as there is a much greater risk of collisions and jetwash.
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Runways should be numbered based on their magnetic azimuth
The orientation of runways is a critical aspect of airport design, with each aspect meticulously planned to optimize safety and efficiency. Runways are typically numbered based on their magnetic azimuth, or the magnetic heading they point towards in relation to magnetic north. This system of numbering is crucial for pilots, helping them align their aircraft with the correct runway during takeoff and landing.
The numbering of runways is based on rounding the compass bearing of one runway end to the nearest 10 degrees and then dropping the last digit. This results in runway numbers ranging from 1 to 36. For instance, a runway pointing towards a heading of 90 degrees will be marked as "09", with the last digit omitted for simplicity. Similarly, a heading of 180 degrees will be designated as "18", and 360 degrees (due north) as "36". The opposite end of the runway differs by 180 degrees, so its number will be 18 higher or lower. For example, if one end of a runway is numbered 9, the other end will be numbered 27.
The magnetic variations between the actual runway heading and the number painted on the runway can cause slight discrepancies. However, these variations are minimal and regularly accounted for by airport authorities. Airports with significant magnetic shifts may repaint their runway designators to maintain accuracy and ensure pilots have the most up-to-date information. For example, in 2009, Fairbanks International Airport in Alaska changed the name of runway 1L-19R to 2L-20R due to a shift in magnetic north.
The direction in which runways face is influenced by several factors, with the prevailing wind direction being the primary consideration. Aircraft take-off and landing most efficiently heading into the wind, as it provides additional lift and reduces the required runway length. As a result, airports are often designed with runways aligned to match the most common wind patterns in their region. For instance, airports in areas with consistent west-to-east winds will typically have runways oriented east-west.
In addition to wind patterns, spatial constraints, surrounding geography, and safety considerations may also influence the direction in which runways face. For instance, valleys and nearby cities may restrict runway placement. Furthermore, to ensure safety, modern airports often feature multiple parallel runways to facilitate simultaneous take-offs and landings, reducing the risk of collisions and jetwash.
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Runways should be designated with 'L', 'C', or 'R'
The orientation of runways is primarily determined by the prevailing wind direction, as planes are best able to take off when facing the wind. Spatial constraints and obstructions may also prevent optimal alignment. As such, runways are typically built parallel to the prevailing wind direction, or as close to parallel as possible.
Runways are designated with a number, which is the whole number nearest to one-tenth of the magnetic north when viewed from the direction of approach. For example, a runway pointing due east would be designated 09, while one pointing due west would be 27.
When there are multiple runways pointing in the same direction, each runway is identified by appending left (L), center (C), or right (R) to the end of the runway number. This is determined from the point of view of an observer standing at the runway threshold. For example, two parallel runways pointing east would be designated 09L and 09R, while three would be 09L, 09C, and 09R. The opposite ends of these runways would be designated with the observer's viewpoint in mind, so the opposite direction of 09L would be 27R.
Suffixes may also be used to denote special-use runways. Airports with seaplane waterways may use the suffix W, while small airports that host various forms of air traffic may use additional suffixes to denote special runway types, such as STOL aircraft (S), gliders (G), rotorcraft (H), and ultralights (U).
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Runways should be built with consideration for the surrounding geography
The construction of runways requires careful consideration of the surrounding geography. Runways are typically built to be parallel to one another for safety and efficiency, but spatial constraints or obstructions may prevent optimal alignment. For instance, valleys and cities can restrict runway placement. Airports with unpredictable water currents, such as seaplane bases, may not have a designated landing direction.
Runways are predominantly aligned to take advantage of prevailing winds, as planes are best able to take off when facing into the wind. Therefore, the direction that the wind blows the majority of the time is considered when constructing runways. Airports with multiple runways will often have a wide range of runway configurations to accommodate changes in seasonal wind directions.
Runways are numbered based on the magnetic azimuth (compass bearing) of their orientation. They are numbered from 1 to 36, with the opposite ends of the runway differing by 180 degrees and thus, being numbered 18 higher or lower. For example, a runway numbered 09 points east, while a runway numbered 18 points south.
In the early days of aviation, airports were constructed with runways pointing in every conceivable direction, with taxiways built to get aircraft from the ramp to the runway. However, as air travel grew in popularity, airports with complex runway configurations struggled to keep up with the increase in volume. As a result, modern airports tend to have multiple parallel runways to accommodate higher traffic.
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Frequently asked questions
The primary consideration when determining the direction of a runway is the prevailing wind direction. Planes are best able to take off when facing the wind and this also reduces the length of runway used.
Runways are numbered based on the magnetic azimuth (compass bearing) in which a runway is oriented. A runway facing north/360° is runway 36, east/90° is runway 09, south/180° is runway 18, and west/270° is runway 27.
When two or more runways face the same direction, they receive the labels left (L), right (R), or center (C). For example, runway 10L (10 Left) and runway 10R (10 Right).
