Editing Airfield traffic pattern (section)

== Wind direction ==
Pilots prefer to take off and land facing into the wind. This has the effect of reducing the aircraft's speed over the ground (for a given airspeed), thus reducing the length of runway required to perform either maneuver.

An exception to this rule is at airports where the runway is on a severe [[slope]], such as alpine airports ([[altiport]]s). In these instances, takeoffs are usually made downhill and landings uphill regardless of wind direction with the slope aiding in [[acceleration]] and deceleration. Another exception is at airports with mountains at one end.

Many airfields have runways facing a variety of directions. The purpose of this is to provide arriving aircraft with the best runway to land on according to the wind direction. Runway orientation is determined from historical data of the prevailing winds in the area. This is especially important for single-runway airports that do not have the option of a second runway pointed in an alternative direction. A common scenario is to have two runways arranged at or close to 90 degrees to one another, so that aircraft can always find a suitable runway.  Almost all runways are reversible, and aircraft use whichever runway in whichever direction is best suited to the wind. In light and variable wind conditions, the direction of the runway in use might change several times during the day, or there may be a preferred “calm wind runway”, possibly because it’s longer.<ref>{{cite web
 | url =https://www.faa.gov/documentLibrary/media/Advisory_Circular/150_5300_13_chg17_cons_p2.pdf
 | title =Airport Design: Wind Analysis
 | date =30 September 2000
 | website =Federal Aviation Administration
 | access-date =4 June 2021}}</ref>