Editing Runway (section)

==Design==

=== Orientation ===
The primary consideration in determining runway orientation is the prevailing wind direction, in lieu of spatial constraints or obstructions that may prevent optimal alignment. To mitigate the occurrence of crosswind operations which are more challenging and dangerous, runways at airports are designed to align with the wind’s direction. Utilizing runways oriented with the wind direction also allows for aircraft to take-off and land into the headwind, reducing the length of runway used during operations. Taking off and landing into the wind increases the relative air speed of the aircraft to create more lift; this allows aircraft to reach take-off velocity with a shorter amount of ground roll and also allows aircraft to land with a slower ground speed. To determine the prevailing wind directions, analysis of a [[wind rose]] is used before constructing airport runways.<ref>{{cite web |url=http://www.enviroware.com/windrose-pro-for-airports-runway-design |title=WindRose PRO for airports runway design |website=Enviroware  |access-date=2012-02-24}}</ref>

[[File:China lake.jpg|thumb|Triangular runway pattern at Armitage Field, [[Naval Air Weapons Station China Lake]]]]
Originally in the 1920s and 1930s, airports and air bases (particularly in the United Kingdom) were built in a triangle-like pattern of three runways at 60° angles to each other. The reason was that aviation was only starting, and although it was known that wind affected the runway distance required, not much was known about wind behaviour.{{cn|date=January 2024}} As a result, three runways in a triangle-like pattern were built, and 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.<ref>{{Cite web|url=https://aviation.stackexchange.com/questions/61396/when-and-why-was-runway-07-25-at-kai-tak-removed|title=Airport - when and why was runway 07/25 at Kai Tak removed?}}</ref> 

===Naming===
[[File:Runway 22.svg|thumb|left|upright|Runway 22]]
[[File:Runway landing designator marking-Numbers.svg|thumb|upright|left|Font and size of numbers and letters]]

Runways are named by a number between 01 and 36, which is generally the [[Compass#How a magnetic compass works|magnetic]] [[azimuth]] of the runway's [[heading (navigation)|heading]] in [[deca-|deca]][[Degree (angle)|degrees]]. This heading differs from [[true north]] by the local [[magnetic declination]]. A runway numbered 09 points east (90°), runway 18 is south (180°), runway 27 points west (270°) and runway 36 points to the north (360° rather than 0°).<ref>[http://www.faa.gov/air_traffic/publications/ATpubs/AIM/Chap2/aim0203.html Federal Aviation Administration Aeronautical Information Manual, Chapter 2, Section 3 Airport Marking Aids and Signs part 3b] {{webarchive|url=https://web.archive.org/web/20120118165015/http://www.faa.gov/air_traffic/publications/atpubs/aim/Chap2/aim0203.html |date=2012-01-18 }}</ref> When taking off from or landing on runway 09, a plane is heading around 90° (east). A runway can normally be used in both directions, and is named for each direction separately: e.g., "runway 15" in one direction is "runway 33" when used in the other. The two numbers differ by 18 (= 180°). For clarity in radio communications, each digit in the runway name is pronounced individually: runway one-five, runway three-three, etc. (instead of "fifteen" or "thirty-three").

[[File:ORD Airport Diagram.svg|thumb|upright|[[FAA]] airport diagram at [[O'Hare International Airport]]. The two 14/32 runways go from upper left to lower right, the two 4/22 runways go from lower left to upper right, and the two 9/27 and three 10/28 runways are horizontal.]]
A leading zero, for example in "runway zero-six" or "runway zero-one-left", is included for all ICAO and some [[United States armed forces|U.S.&nbsp;military]] airports (such as [[Edwards Air Force Base]]). However, most U.S.&nbsp;[[civil aviation]] airports drop the leading zero as required by FAA regulation.<ref>{{cite book | title = FAA Advisory Circular AC 150/5340-1L - Standards for Airport Markings | chapter=Chapter 2.3.e.(2) | chapter-url = http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/1022266 | page=17 | quote=A single-digit runway landing designation number is never preceded by a zero.}}</ref> This also includes some military airfields such as [[Cairns Army Airfield]]. This American anomaly may lead to inconsistencies in conversations between American pilots and controllers in other countries.

Military airbases may include smaller paved runways known as "assault strips" for practice and training next to larger primary runways.<ref>{{Cite web|url=https://www.amc.af.mil/News/Article-Display/Article/146910/new-assault-landing-strip-opens-in-wyoming-mcchord-c-17-makes-first-landing/|title=New assault landing strip opens in Wyoming; McChord C-17 makes first landing}}</ref> These strips eschew the standard numerical naming convention and instead employ the runway's full three digit heading; examples include [[Dobbins Air Reserve Base]]'s Runway 110/290	and [[Duke Field]]'s Runway 180/360.<ref>{{cite web|title=Duke Field (Eglin AF Aux Nr 3) Airport|publisher=Airnav.com|date=July 16, 2020|url=https://www.airnav.com/airport/KMGE|access-date=August 5, 2020}}</ref><ref>{{cite web|title=Dobbins Air Reserve Base|publisher=Airnav.com|date=July 16, 2020|url=https://www.airnav.com/airport/KEGI|access-date=August 5, 2020}}</ref>

Runways with non-hard surfaces, such as small turf airfields and waterways for [[seaplane]]s, may use the standard numerical scheme or may use traditional [[Compass rose|compass point]] naming, examples include [[Ketchikan Harbor Seaplane Base]]'s Waterway E/W.<ref>{{cite web|title=Ketchikan Harbor Seaplane Base
|publisher=Airnav.com|date=July 16, 2020|url=https://www.airnav.com/airport/5KE|access-date=August 8, 2020}}</ref><ref name=ac15035/> Airports with unpredictable or chaotic water currents, such as [[Santa Catalina Island (California)|Santa Catalina Island]]'s Pebbly Beach Seaplane Base, may designate their landing area as Waterway ALL/WAY to denote the lack of designated landing direction.<ref>{{cite web|title=Pebbly Beach Seaplane Base|publisher=Airnav.com|date=July 16, 2020|url=https://www.airnav.com/airport/L11|access-date=August 5, 2020}}</ref><ref name=ac15035/>

===Letter suffix===
[[File:15R-33L - Aeropuerto de Madrid-Barajas - detail.jpg|thumb|left|Runway sign at [[Madrid-Barajas Airport]], Spain]]

If there is more than one runway pointing in the same direction (parallel runways), each runway is identified by appending left&nbsp;(L), center&nbsp;(C) and right&nbsp;(R) to the end of the runway number to identify its position (when facing its direction)—for example, runways one-five-left&nbsp;(15L), one-five-center&nbsp;(15C), and one-five-right&nbsp;(15R). Runway zero-three-left&nbsp;(03L) becomes runway two-one-right&nbsp;(21R) when used in the opposite direction (derived from adding 18 to the original number for the 180° difference when approaching from the opposite direction). In some countries, regulations mandate that where parallel runways are too close to each other, only one may be used at a time under certain conditions (usually adverse [[weather]]).

At large airports with four or more parallel runways (for example, at [[O'Hare International Airport|Chicago O'Hare]], [[Los Angeles International Airport|Los Angeles]], [[Detroit Metropolitan Wayne County Airport|Detroit Metropolitan Wayne County]], [[Hartsfield-Jackson Atlanta International Airport|Hartsfield-Jackson Atlanta]], [[Denver International Airport|Denver]], [[Dallas/Fort Worth International Airport|Dallas–Fort Worth]] and [[Orlando International Airport|Orlando]]), some runway identifiers are shifted by 1 to avoid the ambiguity that would result with more than three parallel runways. For example, in Los Angeles, this system results in runways 6L, 6R, 7L, and 7R, even though all four runways are actually parallel at approximately 69°. At [[Dallas/Fort Worth International Airport]], there are five parallel runways, named 17L, 17C, 17R, 18L, and 18R, all oriented at a heading of 175.4°. Occasionally, an airport with only three parallel runways may use different runway identifiers, such as when a third parallel runway was opened at [[Phoenix Sky Harbor International Airport]] in 2000 to the south of existing 8R/26L—rather than confusingly becoming the "new" 8R/26L it was instead designated 7R/25L, with the former 8R/26L becoming 7L/25R and 8L/26R becoming 8/26.

Suffixes may also be used to denote special-use runways. Airports that have seaplane waterways may choose to denote the waterway on charts with the suffix W; such as [[Daniel K. Inouye International Airport]] in [[Honolulu]] and [[Lake Hood Seaplane Base]] in [[Anchorage, Alaska|Anchorage]].<ref>{{cite web|title=Daniel K Inouye International Airport|publisher=Airnav.com|date=July 16, 2020|url=https://www.airnav.com/airport/PHNL|access-date=August 5, 2020}}</ref> Small airports that host various forms of air traffic may employ additional suffixes to denote special runway types based on the type of aircraft expected to use them, including [[STOL]] aircraft (S), [[Glider (aircraft)|glider]]s (G), [[rotorcraft]] (H), and [[ultralight aviation|ultralight]]s (U).<ref name=ac15035>[https://www.faa.gov/documentLibrary/media/advisory_circular/150-5200-35/150_5200_35.pdf FAA AC 150/5200-35]</ref> Runways that are numbered relative to [[true north]] rather than magnetic north will use the suffix T; this is advantageous for certain airfields in the far north such as [[Thule Air Base]] (08T/26T).<ref>[http://ww1.jeppesen.com/documents/aviation/business/ifr-paper-services/intro-USA.pdf Jeppesen Airport Chart Legend]</ref>

===Renumbering===
Runway designations may be changed over time as the Earth's magnetic field shifts and their headings shift with it. This is more common at higher latitudes: for example, [[Fairbanks International Airport]] in [[Alaska]] renames runways roughly every 24 years, most recently in 2009.<ref>{{Cite web |date=2017-11-16 |title=Airport Runway Names Shift with Magnetic Field |url=https://www.ncei.noaa.gov/news/airport-runway-names-shift-magnetic-field |access-date=2025-02-10 |website=National Centers for Environmental Information (NCEI) |language=en}}</ref> In northern Canada,<ref>{{Cite web |date=26 December 2024 |title=Designated Airspace Handbook |url=https://www.navcanada.ca/en/dah20241226.pdf |access-date=10 February 2025 |publisher=[[NAV CANADA]] |page=200 |format=PDF}}</ref> runways are designated based on true north, which avoids the need to update them.<ref>{{Cite web |date=October 31, 2024 |title=Requirements for Navigation in Northern Domestic Airspace and Polar Regions |url=https://www.navcanada.ca/en/cnop-9.0-31-oct-2024.pdf |access-date=10 February 2025 |publisher=[[NAV CANADA]] |page=56 |format=PDF}}</ref> [[Nav Canada]], Canada's air navigation service provider, has advocated for an industry-wide switch to true north.<ref>{{Cite web |title=NAV CANADA Switching to TRUE: Pulling away from magnetic north |url=https://www.navcanada.ca/en/news/blog/switching-to-true-pulling-away-from-magnetic-north.aspx |access-date=2025-02-10 |website=www.navcanada.ca |language=en}}</ref>

As runways are designated with headings rounded to the nearest 10°, some runways are affected sooner than others; e.g. a hypothetical Runway&nbsp;23 with a heading of 226° would only have to shift to 224° to become Runway&nbsp;22. Because magnetic drift itself is slow, these changes are uncommon, and not welcomed, as they require accompanying changes in [[aeronautical chart]]s and descriptive documents. When a runway designation does change, it is often done at night, especially at major airports, because [[taxiway]] signs need to be changed and the numbers at each end of the runway need to be repainted to the new runway designators.{{Citation needed|date=February 2025}} In 2009 for example, [[London Stansted Airport]] in the United Kingdom changed its runway designation from 05/23 to 04/22 during the night.<ref>{{Cite web |date=2009-07-06 |title=Stansted Airport changes the name of its runway |url=https://www.dunmowbroadcast.co.uk/news/21684003.stansted-airport-changes-name-runway/ |access-date=2025-02-10 |website=Dunmow Broadcast |language=en}}</ref>