Explaining the Meaning Behind Airport Runway Digits

CGP Grey explains, in his rather frenetic manner, the purpose and the design of those seemingly random airport runway digits that are usually only seen out of a plane window.

While waiting on a plane  during taxi ’till takeoff, looking out the window, you may have noticed the giant number numbering the runway, say eight, which implies  seven others exist, at least, but this is a flight out of L.O.L. Airport, in Nevada’s desert of nothing, there’s only two runways.  

Grey then explains that, like pirates of the past, the airline industry relies on compasses to determine direction. Since airplanes are supposed to head into the wind for a smooth landing, it’s important for air traffic control to indicate at which degree of a 360° compass they should land.

The pilot can always confirm their doing it right by reading 360 on their ancient ancestor’s compass. This low-tech check is useful as a fallback because a compass can see the way even when eyes and other equipment can not. As a two-runway example…gives 315 for one end because that’s the way the pilot needs   to point and 135 at the other. Round to ten, for 320 and 140, then drop the zeros to get runways 32 and 14. On the other side. 225 and 45, round to ten again, drop the zeros for 23 and 5.  

Runway Digits Explained

Grey also explains how the magnetic pull from the magnetic North Pole can mess things up a bit, particularly since it’s not at the actual North Pole.

Runways numbers depend on where the North Pole …Okay, to find the North Pole, remember   that the Earth is a sphere that spins. …We draw a line about which this spin occurs, and name each end the North and South Pole.  Starting with these poles, we clever humans created a   square-ish co-ordinate system for our spherical earth,  …This grid is what every modern navigational system uses to get around with the GPS, global positioning, coordinates it gives.

If there is a magnetic field disruption, runway numbers must be changed. This happens more in Canada than anywhere else in the world.

Since runway numbers are derived  from the heading on a compass, when the Magnet North moves the runway numbers need to change to match. And the closer your airport is to a magnet pole, the bigger a difference its movement makes,  and thus the more frequently you need to update the number.  

Grey further delves into the properties of magnets, noting where and how magnets are formed, how they affect the Earth’s stability, and what might happen if the North and South Poles switch places.

If there’s one thing the indifferent Universe loves, it’s repeating the same patterns across scales and domains. …unlike a real electromagnet, made of stable metal, all that swirling liquid iron inside the earth is not stable. So at any moment, the field can split into multiple magnetic poles, roam randomly, or diminish entirely before flipping north to south and south to north.  Which it does every couple hundred thousand years or so,  and we have no way of predicting when. Great.  

Lori Dorn
Lori Dorn

Lori is a Laughing Squid Contributing Editor based in New York City who has been writing blog posts for over a decade. She also enjoys making jewelry, playing guitar, taking photos and mixing craft cocktails.