The opposite end of the runway always differs by 180 degrees, so it’s numbered 18 higher or lower. For example, Runway 9-27 is oriented east-west.

You might be thinking that the numbers on this diagram are backwards. On a handheld compass, south is 180 degrees (so 18 in runway terms) and west is 270 (27). But the “W” is numbered 9 because the runway number is connected to the direction the plane is traveling. So if you’re on runway 9, then you’re heading east (90 degrees on a compass). Runway 36 means you’re moving north, and so on.

Most runways can typically be used in either direction, depending on prevailing winds. Furthermore, each runway end is identified separately. Therefore, an aircraft taking off easterly on Runway 9-27 would be considered to be utilizing Runway 9 for departure.

Many large airports have parallel runways, which requires further designation of each runway. For example, Boston, Massachusetts’ Logan International Airport (pictured) has two pairs of parallel runways. One is Runway 4L-22R and the other 4R-22L. The ”L” and ”R” designate the relative position (left or right) of each runway respectively when approaching/facing its direction. A small number of airports have three parallel runways—the runway in the middle gets a “C” for center.

During airport operations, runway number designations are pronounced individually. For example, Runway 4L-22R would be pronounced by air traffic control as “Flight 123, you are cleared to land on Runway Four Left” or alternatively “…Two Two Right,” if cleared to land the opposite direction. This level of enunciation ensures clear communication and enhances safety.

So the next time you travel by air plane and the pilot announces that you’ll be taking off on runway 27, you'll know that you’re traveling due west.

Enjoy your flight!