Now and again, an airport needs to change the numerical designation of one of their runways. This is due to the magnetic shift of the earth. Last week London Luton Airport altered its runway designation, prompting a vast overnight operation.

The numbers on the end of a runway aren't something that most passengers will think about. However, these large white painted numbers serve an essential role, that of the identity of the runway. They allow the pilot to confirm that they are indeed landing on their intended runway and set the runway apart from any others that may be at the airport.

How to change the numbers

Changing the designation of a runway isn't an easy task at all. Firstly, the numbers must be switched on airport charts, and in databases. However, you also have a big issue to deal with, the numbers at the end of the runway.

It could cause some confusion if a pilot has been cleared to land on Runway 26, but he saw before him Runway 25. As such, the numbers must be replaced with the correct designation when the change occurs. This is something that London Luton Airport in the United Kingdom recently had to deal with.

Neighbouring Stansted Airport has been able to complete runway maintenance during the day due to the current lack of traffic. However, Luton opted to wait until night time to make the switch. The airport changed its runway designations at 00:00 on May 21st, and produced a short video to accompany the change:

Why change the numbers?

You may be wondering why airports change their runway designations. After all, regular pilots are aware of the current numbers as it is. However, the reason is essential.

Runways are given a destination based on their compass orientation. For example, Runway 09/27 at London City Airport runs from East to West. While the earth's geographic north pole is fixed, its magnetic north pole isn't. Indeed, in the past century, it has shifted significantly.

This means that compasses will point to a different north than they would have 100 years ago. While this will be relatively insignificant at the equator, the further north you travel, the more significant the difference will become.

As the earth's magnetic field shifts, airports renumber their runways to ensure that they match their direction. This is a change that is not needed often, and as such, last week was the first time that Luton has changed the numbers of its runway in 60 years.

Have you noticed a runway's designation change? Let us know in the comments!