Those huge white numbers at the beginning of the track are not randomly assigned. They have a meaning. There is a logical and simple system related to the direction of takeoff or landing to assign the numbers of the runways.
What do the track numbers mean?
The runway numbers are actually a reference to the nearest magnetic heading of the runway. The runway heading is rounded to the nearest 10 degrees and zero is removed. This number is assigned to the track.
Be careful, the angles are measured with respect to magnetic north, not geographic north.
Besides that, if there are several parallel tracks we will also use lyrics.
Let’s see an example with the runways of the Adolfo Suárez Madrid-Barajas Airport.
What we would do is stand at the foot of the track with a compass and measure the direction of the track. That runway heading is rounded to the nearest 10° and we then drop the last 0 to get a two-digit identifier.
The resulting number is the track number, but if we have two parallel tracks we will put L (left) on the left and R (right) on the one on the right.
When there are 3 parallel tracks, the middle track uses the letter C. If there are more than 3 parallel tracks, a simple rule is followed. The next series of clues will have their final digit changed to 1 to avoid any confusion. For example, 28L, 28C, 28R, and 29.
In this way we obtain tracks 36L, 36R, 32L and 32R. Of course, we must bear in mind that the tracks have two directions, so in the end we have:
The tracks are oriented based on the prevailing trend of the wind; the land; noise reduction and nearby residential areas; the local topography; existing infrastructure and other factors.
Is there a track 0?
You should not find any tracks numbered as “0” or “00”. Any runway pointing to magnetic north will receive the designator “36” (as in 360 degrees). This will also correspond to the headings read by both ATC and the pilot. For this reason, when a plane is flying north, it is always said to be flying on a heading of “three-six-zero”, and never “zero-zero-zero” degrees.
Why do the tracks change numbers?
If you are familiar with a certain airport, you may notice that every several years the runway numbers change.
This is because magnetic north does not stay constant, it moves slightly over time.
If magnetic north drifts far enough that the runway heading doesn’t match the nearest 10°, it’s time to change the numbers so they do.