How Do Runways Get Their Numbers?

Runways can mark either the beginning or the end of a journey, both literally and symbolically. These paved strips have a special placed in certain passengers’ hearts, as, for some of us, either takeoff or landing is our favorite part of a flight. While on your travels, you may have noticed that each runway is marked with a number at either end. But how exactly are these decided?

Runway Lukla Airport
Runway 24 at the legendary Tenzing-Hillary Airport in Lukla, Nepal. Photo: Getty Images

Based on compass bearings

Those of us who have ever listened to excerpts from air traffic control conversations will know that, in terms of which direction pilots are meant to fly in, they are instructed to fly on three-digit ‘headings.’ These numbers refer to the direction’s compass bearing relative to true north.

For example, a heading of 180 would represent following a path 180 degrees from true north – in other words, directly south. Correspondingly, runways are numbered using a similar logic, albeit with a slight difference. Specifically, they are designated using their heading in decadegrees. This measurement sees its heading divided by 10.

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Southampton airport
Runways are numbered based on the compass bearing they point toward. Photo: Getty Images.

As such, rather than being numbered 1-360, they use a simplified 1-36 scale. As The Points Guy observes, this means that, for a runway designated as 04, this could have a bearing of anywhere between 35 and 45 degrees. Sometimes, a runway’s designation may even change. For example, a shift in the position of the Earth’s magnetic North Pole saw London Stansted renumber its runway from 05/23 to 04/22 in July 2009, according to the BBC.

Letters for parallel runways

But what happens when an airport has two runways that run parallel to each other on the same compass bearing? Of course, to have multiple runways with the same designation would be very confusing, not to mention dangerous. Thankfully, there is a way around this conundrum. In the case of two parallel runways, these landing strips will also be designated either ‘L’ or ‘R’.

These letters represent whether the runway is on the left or right-hand side of the pair. For example, London Heathrow‘s runways are 09L/27R and 09R/27L. When a third runway comes into the equation, the middle strip is designated with a ‘C,’ meaning ‘center.’ Three of Frankfurt‘s four runways are parallel, with the middle being numbered as 07C/25C.

Heathrow generally uses one runway for departures and the other for arrivals. Photo: Getty Images

Other designations

Some particularly large airports even have four or more parallel runways. In these instances, the ‘C’ designation is not enough to separate all four landing strips. As such, airports will sometimes renumber a pair of runways by a factor of one to avoid confusion.

For example, although Los Angeles International has four parallel runways, these are numbered in two pairs. Specifically, these are 6L/24R and 6R/24L, along with 7L/25R and 7R/25L. Finally, Honolulu International in Hawaii even has a ‘W’ suffix on its runways 4W/22W and 8W/26W. This informs pilots that it is a water-based runway for use by seaplanes.

Did you know how runways are numbered? Which is your favorite runway to take off from or land on? Let us know your thoughts in the comments.