Page |1 RUNWAY ORIENTATIONAccording to the International Civil Aviation Organization (ICAO) a runway is a"defined rectangular area on a land aerodrome prepared for the landing and takeoff ofaircraft".The orientation of the runway is an important consideration in airport planning anddesign. The correct runway orientation maximizes the possible use of the runwaythroughout the year accounting for a wide variety of wind conditions.FAA and ICAOregulations establish rules about runway orientation and their expected coverageRunway Location Considerations.FAA mandates identification standards for airportlayout 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 carefulexamination of prevailing wind conditions at the airport site.The challenge for thedesigner is to accommodate all of the aircraft using the facility in a reliable andreasonable manner.In navigation, all measurement of direction is performed by using the numbers of acompass. 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 runways compassdirection is indicated by a large number painted at the end of each runway. Precedingthat number are 8 white stripes. Following that number by 500 feet is the "touchdownzone" which is identified by 6 white stripes.
Page |2A runways number is not written in degrees, but is given a shorthand format. Forexample, a runway with a marking of "14" is actually 140 degrees. A runway with amarking of "31" has a compass heading of 310 degrees. For simplicity, the FAA roundsoff the precise heading to the nearest tens. For example, runway 7 might have a preciseheading 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 endof 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 dueeast is 90 degrees ("9"). All runways follow this directional layout. This runway would bereferred to as "Runway 9-27" because of its east-west orientation.
Page |3The FAA includes over 20 different runway layouts in their advisory materials. There are4 basic runway configurations with the rest being variations of the original patterns. Thebasic runway configurations are the following:A) Single runwayThis is the simplest of the 4 basic configurations. It is one runway optimally positionedfor prevailing winds, noise, land use and other determining factors. During VFR (visualflight rules) conditions, this one runway should accommodate up to 99 light aircraftoperations per hour. While under IFR (instrument flight rules) conditions, it wouldaccommodate between 42 to 53 operations per hour depending on the mix of traffic andnavigational aids available at that airport.
Page |4B) Parallel runwaysThere are 4 types of parallel runways. These are named according to how closely theyare placed next to each other. Operations per hour will vary depending on the totalnumber of runways and the mix of aircraft. In IFR conditions for predominantly lightaircraft, the number of operations would range between 64 to 128 per hour.
Page |5If there is more than one runway pointing in the same direction (parallel runways), eachrunway 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).C) Open-V runwaysTwo runways that diverge from different directions but do NOT intersect form a shapethat looks like an "open-V" are called open-V runways. This configuration is useful whenthere 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 ofoperations per hour significantly increases. When takeoffs and landings are madetoward the two closer ends, the number of operations per hour can be reduced by 50%.
Page |6D) Intersecting runwaysTwo or more runways that cross each other are classified as intersecting runways. Thistype of configuration is used when there are relatively strong prevailing winds frommore 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 runwayscan be used simultaneously.The greatest capacity for operations is accomplished when the intersection is close to thetakeoff end and the landing threshold as shown below (with the configuration on theleft).
Page |7The capacity for the number of operations varies greatly with this runway configuration.It really depends on the location of the intersection and the manner in which therunways are operated (IFR, VFR,). This type of configuration also has the potential touse 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 aspassenger terminals, taxiways/apron configurations, circulation roads, and parkingfacilitiesThe 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 obstructionsThese are all factors in runway and airport planning. Many issues are studied beforefinal decisions on airport location and runway layout are determined.Wind Rose AnalysisAccording to FAA standards, runways should be oriented so that aircraft can takeoffand/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 calledthe 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 (normally10 years or more).On the wind rose a transparent runway template is placed to represent the proposedrunway that accommodates the size and operating characteristics of aircraft. Thetemplate is rotated around the center of the wind rose in order to search for an optimalrunway orientation. At each rotating angle, the total percentage of allowable crosswindsin the wind rose that are covered by the template is calculated, and a best angle that cangive the maximum percentage of coverage is determined.
Page |8Runway LightningAirports also use standardized lighting and ground markings to provide direction andidentification to all air and ground crews. To assist pilots in differentiating at nightbetween airport runways and freeways, airports have rotating beacon lights. Thesebeacons usually flash green and white lights to indicate a civilian airport. They arevisible from the air long before the entire airport is recognizable. To help pilots at nightquickly identify the beginning of a runway, green threshold lights line the runwaysedge. Red lights mark the ends of runways and indicate obstructions. Blue lights runalongside taxiways while runways have white or yellow lights marking their edgesICAO guidance requires that Runway lighting shall not be operated if a runway is not inuse for landing, take-off or taxiing purposes, unless such operation is required forrunway inspection or maintenance purposes. ATC are required to use whatever meansare available to them to ensure that they are aware of any lighting system.
P a g e | 11REFERENCESFAA.(1989). ‘‘Airport design.’’ FAA Advisory Circular AC 150/5300-13, Federal AviationAdministration, Washington, D.C.Wright, P.H. and Ashford, N. (1998). Transportation Engineering: Planning and Design,4th Ed., John Wiley & Sons, New York.