A runway (RWY) is a strip of land on an airport, on which aircraft can take off and land. Runways may be a man-made surface (often asphalt, concrete, or a mixture of both) or a natural surface (grass, dirt, or gravel).

Orientation and dimensions

Runways are generally numbered according to their magnetic heading (the takeoff direction it is "pointing towards"). The runway number is the whole number nearest one-tenth the magnetic azimuth of the centerline of the runway, measured clockwise from the magnetic north. Each digit is pronounced separately for clarity in radio communications. For example, Runway Three Six would be aligned in roughly a 360 degrees direction (magnetic north), Runway Nine would be used for a runway with a 94 degree-alignment (close to magnetic east), and Runway One Seven for 168 degrees. Each runway can be used in either direction, and hence has two numbers, each 180° apart. Thus, Runway One Zero (100°) becomes Runway Two Eight (280°) when used in the opposite direction and Runway One Eight (180°) becomes Runway Three Six (360°). Runways in North America that lie within the Northern Domestic Airspace are, because of the magnetic north pole, usually numbered according to true north.

In International Civil Aviation Organization (ICAO) and some United States military (such as Edwards Air Force Base) airports, numbers for runways less than 100° include the leading "zero", for example, Runway Zero Two or Runway Zero One Left. However in the United States at most civil aviation airports, numbers for runways less than 100° are often given as single digits; for instance, Runway Nine or Runway Four Right. 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. It is very common in a country such as Canada for a controller to clear an incoming American aircraft to, for example, Runway 04, and the pilot read back the clearance as Runway 4. Users of flight simulation programs may note that those of American origin might apply U.S. usage to airports around the world. For example Runway 05 at Halifax (CYHZ) will appear on the FS program as the single digit 5 rather than 05.

Runway designations do change over time. Because the magnetic poles slowly drift on the Earth's surface, but the runways stay fixed, the magnetic bearing will change. Depending on the airport location and how much drift takes place, it may be necessary over time to change the runway designation. As runways are designated with headings rounded to the nearest 10 degrees, this will affect some runways more than others. For example,if the magnetic heading of a runway is 276 degrees , it would be designated Runway 28. If the magnetic heading changed upwards by 5 degrees, the Runway would still be Runway 28. If on the other hand the original magnetic heading was 284 (Runway 28), and the heading increased by only two degrees to 286, the runway should become Runway 29. Because the drift itself is quite slow, runway designation changes are relatively uncommon, and not welcomed, as they do require an accompanying change in a wide range of navigational and descriptive documents.