Airport runways are numbered based on their magnetic orientation, but due to the shifting of the Earth’s North Pole, airports worldwide have had to rename them more frequently.
How Do Airport Runways Get Their Numbers?
Airport runways are aligned with the prevailing wind directions. Each end of a runway is numbered based on the magnetic heading that pilots must follow to land.
When a pilot is flying east, the heading is 90 degrees, and when flying west, the heading is 270 degrees.
The ends of the runway are numbered according to their magnetic orientation, although it’s rounded and divided by ten for simplicity.
This means that an east-west-oriented runway has one end facing 90 degrees magnetic and designated 09, while the opposite end, facing 270 degrees magnetic, is designated 27.
When parallel runways are used at an airport, additional designations such as “L” (Left), “R” (Right), and “C” (Center) are used.
Let's look at the Hartsfield-Jackson Atlanta International Airport in Georgia as an example. The airport has five parallel runways, all of which switch between the L and R designations depending on the direction of the wind.
Runways 08L/26R and 08R/26L are oriented approximately in an east-west direction:
- End 08L/R: Magnetic orientation of about 080 degrees
- End 26R/L: Magnetic orientation of about 260 degrees
Runways 09L/27R and 09R/27L are also oriented approximately in an east-west direction:
- End 09L/R: Magnetic orientation of about 180 degrees
- End 27R/L: Magnetic orientation of about 360 degrees
It’s important to note that the northern direction corresponds to a designation of 360 degrees. However, in these examples, the orientation is predominantly east-west, and the numbering reflects the corresponding magnetic headings. Plus, the 00 designation (equivalent to a 0-degree orientation) is not used.
The Problem: The Earth's Magnetic North Is Shifting Quickly
Airplanes use compasses that point to the north magnetic pole instead of the geographic north or true north. The issue is that the magnetic poles are not fixed. They move with the movements of iron and nickel in the Earth’s core.
This movement has significantly accelerated since the 1990s, with shifts of 34 miles per year.
The rapid distortion between the magnetic and geographic poles can be challenging for pilots and air traffic controllers, who must adjust their courses according to this variance.
In this regard, they take into account their location on the planet and use the magnetic declination, which is the difference in degrees between the true north pole and the north magnetic pole, to make adjustments.
Due to this shift, the International Air Transport Association (IATA) periodically reviews the runways of all worldwide airports to determine if a numbering change is needed.
For instance, in 2009, the Fairbanks International Airport in Alaska had to rename the runway 1L-19R to 2L-20R.
The magnetic declination changes constantly and affects all airports on the planet, not just a few.
However, the airports closest to the poles have the most unusual cases. For example, a runway facing geographic north may have the 09 designation because its magnetic orientation is 90 degrees. This means that a pilot landing near the Arctic may have geographic north in front of them and magnetic north to the right.
As such, some airports in Canada use geographic north to minimize the impact of the north magnetic pole shift, which is now possible because of modern GPS systems.
Image | AENA
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