Why Runways Have Numbers — And Why They Sometimes Change
A number between 01 and 36 identifies every runway in the world. This number corresponds to the runway’s magnetic heading, rounded to the nearest ten degrees.
For example:
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Runway 09 points east (90°)
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Runway 18 points south (180°)
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Runway 27 points west (270°)
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Runway 36 points north (360°, not 0°)
Since runways can be used in both directions, each end receives its own designation. The opposite end of Runway 15, for instance, becomes Runway 33 (180° apart).
To avoid confusion in radio communications, pilots pronounce each digit separately — “runway one-five,” not “runway fifteen.”
Parallel Runways
Many major airports have multiple runways aligned in the same direction, known as parallel runways.
To distinguish between them, the letters L, C, and R — standing for Left, Center, and Right — are added after the number.
For example, an airport with three parallel runways might have 09L, 09C, and 09R.
At huge airports with four or more parallel runways, identifiers are sometimes adjusted by one digit to avoid duplicates. Examples include Los Angeles (LAX), Atlanta (ATL), Dallas-Fort Worth (DFW), Denver (DEN), and Orlando (MCO).
Take Dallas/Fort Worth International Airport (KDFW), for example — it has five parallel runways, designated 17L, 17C, 17R, 18L, and 18R, all aligned along a magnetic heading of approximately 175.4°.
View KDFW on AirNav Radar
When Earth Itself Changes the Numbers
Runway numbers aren’t permanent. Because Earth’s magnetic field slowly shifts over time, a runway’s magnetic heading can gradually change as well.
When that drift becomes significant — typically by 5 degrees or more — airports must update the runway designation to match the new magnetic heading.
This has happened at several airports worldwide. For instance:
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Geneva Airport (GVA) changed from 05/23 to 04/22
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London Stansted Airport (STN) made the same adjustment overnight
So next time you see a runway number, remember — it’s not just a label. It’s a snapshot of how our planet’s magnetic field lines up with the runways guiding aircraft safely to and from the sky.
