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RUNWAY ORIENTATION

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".

The orientation of the runway is an important consideration in airport planning and design. The correct runway orientation maximizes the possible use of the runway throughout the year accounting for a wide variety of wind conditions.FAA and ICAO regulations establish rules about runway orientation and their expected coverage Runway Location Considerations.FAA mandates identification standards for airport layout that is meant to assist pilots in easily recognizing runways.

Ideally, all aircraft operations on a runway should be conducted against the wind. Unfortunately, wind conditions vary from hour to hour thus requiring a careful examination of prevailing wind conditions at the airport site.The challenge for the designer is to accommodate all of the aircraft using the facility in a reliable and reasonable manner.

In navigation, all measurement of direction is performed by using the numbers of a compass. A compass is a 360° circle where 0/360° is North, 90° is East, 180° is South, and 270° is West, as shown in figure.

Runways are laid out according to the numbers on a compass. A runway's compass direction is indicated by a large number painted at the end of each runway. Preceding that number are 8 white stripes. Following that number by 500 feet is the "touchdown zone" which is identified by 6 white stripes.

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A runway's number is not written in degrees, but is given a shorthand format. For example, a runway with a marking of "14" is actually 140 degrees. A runway with a marking of "31" has a compass heading of 310 degrees. For simplicity, the FAA rounds off the precise heading to the nearest tens. For example, runway 7 might have a precise heading of 68 degrees, but is rounded off to 70 degrees.

Each runway has a different number on each end. Look at the diagram below. One end of the runway is facing due west while the other end of the runway is facing due east. The compass direction for due west is 270 degrees ("27"). The compass direction for due east is 90 degrees ("9"). All runways follow this directional layout. This runway would be referred to as "Runway 9-27" because of its east-west orientation.

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The FAA includes over 20 different runway layouts in their advisory materials. There are 4 basic runway configurations with the rest being variations of the original patterns. The basic runway configurations are the following:

A) Single runwayThis is the simplest of the 4 basic configurations. It is one runway optimally positioned for prevailing winds, noise, land use and other determining factors. During VFR (visual flight rules) conditions, this one runway should accommodate up to 99 light aircraft operations per hour. While under IFR (instrument flight rules) conditions, it would accommodate between 42 to 53 operations per hour depending on the mix of traffic and navigational aids available at that airport.

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B) Parallel runwaysThere are 4 types of parallel runways. These are named according to how closely they are placed next to each other. Operations per hour will vary depending on the total number of runways and the mix of aircraft. In IFR conditions for predominantly light aircraft, the number of operations would range between 64 to 128 per hour.

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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 Two Left (02L), Two Center (02C), and Two Right (02R).

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C) Open-V runwaysTwo runways that diverge from different directions but do NOT intersect form a shape that looks like an "open-V" are called open-V runways. This configuration is useful when there is little to no wind as it allows for both runways to be used at the same time.

When the winds become strong in one direction, then only one runway will be used. When takeoffs and landings are made away from the two closer ends, the number of operations per hour significantly increases. When takeoffs and landings are made toward the two closer ends, the number of operations per hour can be reduced by 50%.

D) Intersecting runwaysTwo or more runways that cross each other are classified as intersecting runways. This type of configuration is used when there are relatively strong

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prevailing winds from more than one direction during the year. When the winds are strong from one direction, operations will be limited to only one runway. With relatively light winds, both runways can be used simultaneously.

The greatest capacity for operations is accomplished when the intersection is close to the takeoff end and the landing threshold as shown below (with the configuration on the left).

The capacity for the number of operations varies greatly with this runway configuration. It really depends on the location of the intersection and the

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manner in which the runways are operated (IFR, VFR,). This type of configuration also has the potential to use a greater amount of land area than parallel runway configurations.

Factors Affecting Runway Orientation :

The direction of the runway controls the layout of the other airport facilities, such as passenger terminals, taxiways/apron configurations, circulation roads, and parking facilities

The following factors should be considered in locating and orienting a runway:

Wind Airspace availability Environmental factors (noise, air and water quality) Obstructions to navigation Air traffic control visibility Wildlife hazards Terrain and soil considerations Natural and man-made obstructions

These are all factors in runway and airport planning. Many issues are studied before final decisions on airport location and runway layout are determined.

Wind Rose Analysis

According to FAA standards, runways should be oriented so that aircraft can takeoff and/or land at least 95 percent of the time without exceeding the allowable crosswinds (Wright 1998). An approach often used in determining the runway orientation is called the wind rose method. The method uses a wind rose template to arrange velocity, direction, and frequency of wind occurrences within a certain period of time (normally 10 years or more). 

On the wind rose a transparent runway template is placed to represent the proposed runway that accommodates the size and operating characteristics of aircraft. The template is rotated around the center of the wind rose in order to search for an optimal runway orientation. At each rotating angle,

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the total percentage of allowable crosswinds in the wind rose that are covered by the template is calculated, and a best angle that can give the maximum percentage of coverage is determined.

Runway Lightning

Airports also use standardized lighting and ground markings to provide direction and identification to all air and ground crews. To assist pilots in differentiating at night between airport runways and freeways, airports have rotating beacon lights. These beacons usually flash green and white lights to indicate a civilian airport. They are visible from the air long before the entire airport is recognizable. To help pilots at night quickly identify the beginning of a runway, green threshold lights line the runway's edge. Red lights mark the ends of runways and indicate obstructions. Blue lights run alongside taxiways while runways have white or yellow lights marking their edges

ICAO guidance requires that Runway lighting shall not be operated if a runway is not in use for landing, take-off or taxiing purposes, unless such operation is required for runway inspection or maintenance purposes. ATC are required to use whatever means are available to them to ensure that they are aware of any lighting system.

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Runway Markings

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REFERENCES

FAA.(1989). ‘‘Airport design.’’ FAA Advisory Circular AC 150/5300-13, Federal Aviation Administration, Washington, D.C.

Wright, P.H. and Ashford, N. (1998). Transportation Engineering: Planning and Design, 4th Ed., John Wiley & Sons, New York.