You all surely have seen the numbers at the beginning of airport runways and wondered how they are assigned. Contrary to what many may think, airport runways are not numbered in sequence. That means that the first runway built is not going to be runway number one. So how are airport runway numbers assigned?
How Are Airport Runway Numbers Assigned?
The number of each runway is assigned according to the direction relative to the earth’s magnetic north pole. For those who might not know, the magnetic north pole of the planet doesn’t coincide with the geographical north pole.
According to the direction to the magnetic north pole, every runway at an airfield is assigned a number from 01 to 36. These two digits are the first two numbers of the runway’s direction.
For instance London Heathrow’s runway 09L will have a heading of 090 degrees. This is a first indication to pilots on approach that they are heading in the right direction towards the correct runway.
What About Runways Used in 2 Directions?
Many runways, actually most, runways in the world are used in two directions. What happens to the numeration of these runways?
For numbering purposes they will be treated as 2 distinct runways. For instance staying with the Heathrow example, runway 09L when used in the opposite direction becomes 27R.
You’ll just need to add 18 to any given landing strip number to have its number when used in the opposite heading. But why did the letter after the number change?
What About The Letters?
The letters L/C/R are used when an airport has multiple parallel runways. Keeping as an example LHR (London Heathrow), the airfield has 2 parallel runways.
It would create quite a bit of confusion, let alone be extremely dangerous, if both runways were to have the same number. Without any other distinction both runways would be numbered 09/27.
This is why L will be used for runways on the left side of an airfield and R for those on the right. If there is a runway between these two then C, for center, will be used.