For some passengers (and indeed pilots and cabin crew as well!), they signify moments of excitement. For others, they are simply a necessary means to an end. No matter which category of traveler you fall under, there is absolutely no denying that flying as we know it would not be possible without the humble runway. Let's take a closer look at the multi-faceted nature of aviation's unsung heroes.

Different surfaces and terrains

Starting off at the most basic level possible, what is it that makes a runway a runway? The International Civil Aviation Organisation (ICAO) defines one as "a defined rectangular area on a land aerodrome prepared for the landing and take-off of aircraft." This may seem like a rather broad characterization, but, of course, it has to be, as the world's runways generally have a huge degree of variety to them.

Some are made of layers of compact snow, like the Ice Runway at McMurdo Sound, used by the US Antarctic Program. Others consist of sand, like at Barra Airport in Scotland, where planes land on a beach at low tide. Others are so short that pilots often can't pick up enough speed to take off and have to drive the plane off of a cliff and take flight during the drop, like at Matekane Airstrip in Lesotho.

Want answers to more key questions in aviation? Check out the rest of our guides here!

Lukla Airport Nepal Runway In Fog
Photo: pendakisolo/Shutterstock

One of the world's most famous runways can be found in Lukla, Nepal. As picture above, this also takes aircraft off a cliff and into spectacular scenery. Thankfully, most airport runways come in more standard varieties than those mentioned above. However, there are, of course, big differences in lengths and construction.

The long and the short

The world's longest runway is located at 4,334 meters (14,219 feet) above sea level at Qamdo Bamda Airport (BPX) in Tibet, and measures an impressive 5,500 meters (18,045 feet) in length. At the other end of the scale, the world's shortest commercial runway is located at Juancho E. Yrausquin Airport (SAB) on the tiny Caribbean island of Saba. It has a length of 400 meters (1,312 feet).

Meanwhile, if an airport is to be capable of welcoming larger widebody jets, it generally needs to provide a runway of at least 2,400 meters (7,874 feet) at sea level. Longer runways are required at higher altitudes as it takes aircraft longer to generate the required speed to take off in such conditions. This is a key reason behind the fact that Denver International Airport (DEN) has such long runways.

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Southwest Airlines Boeing 737 Denver
Photo: Don Mammoser | Shutterstock

Runways also need to be able to withstand significant loads, as the world's busiest airports can have planes landing every 40 seconds. Although they are often referred to as "tarmac," runways are very seldom actually built from this material. Instead, they are usually constructed from concrete or asphalt, as explained here.

The runway's surface is often grooved to make sure that an aircraft's wheels can gain traction, as well as in order to prevent aquaplaning. The latter occurs if a layer of water was to build up between the wheels and the runway's surface.

Routine maintenance typically has to be an overnight affair

Runways must be kept in tip-top shape at all times. Routine maintenance can be performed overnight when there are no scheduled landings or departures.

Denver Airport Snow Removal
Photo: Denver International Airport

This includes the re-painting of markings or numbers, repairing cracks and resealing joints, or cutting surrounding grass. However, occasionally, the airport may need to close the runway entirely, for instance, to renew the top surface. This can take several weeks, as was the case in Lagos, Nigeria earlier this year.

How are they numbered?

To help pilots navigate safely, airport runway markings are standardized. Every runway in the world has two numbers on it. These are between 1 and 36, corresponding to compass directions, and painted at opposite ends.

The first shows the magnetic heading of the runway's azimuth in decadegrees, whereas the second one is the opposite direction, 180 degrees from the first. They are always rounded to the nearest ten degrees, with the final digit dropped.

An Aerial View of London Stansted Airport Runway 04.
Photo: London Stansted Airport

Of course, if an airport has parallel runways, this means that the runways will have the same numbers as each other. They will then be designated a letter as well in order to avoid confusion, namely L, C, or R, signifying Left, Center, or Right.

Meanwhile, as the Earth's magnetic field is shifting by about 60 km (37 miles) per year, this means that runways often need to be renumbered and renamed. For example, in 2018, Geneva Airport changed its runway numbers. It replaced close to 100 sign panels and used about 150 kg (331 lbs) of paint in the process.

The importance of navigational accuracy

The FAA usually checks the readings every five years. However, as late as 2019, the north magnetic pole began moving away from Canada towards Siberia much faster than researchers had expected. This was driven by liquid iron moving about in the Earth's core and caused scientists to change the model one year early.

Ryanair Boeing 737 On Gran Canaria Runway
Photo: Masi Perez/Shutterstock

As such, it is vitally important that runway numbers are kept up to date. Normally, an experienced pilot should be able to tell if the airport hasn't replaced them in time. However, when this is not the case, it can have dire consequences.

For example, in August 2006, Comair flight 5191, marketed as a Delta Connection service, crashed after the pilots failed to pick up on cues that they were on the wrong runway at Blue Grass Airport in Lexington, Kentucky. Instead of using the assigned runway 22, they tried to take off from runway 26, 40 degrees off. Out of the 50 people onboard, only one, the flight's first officer, survived.

Runway incursions

When an aircraft (or other vehicle or person) is on a runway without permission, this is called a runway incursion. These can be of three different categories: operational incidents, pilot deviations, or vehicle/pedestrian deviations.

Chicago O'Hare Airport Aerial View
Photo: EQRoy/Shutterstock

Operational incidents occur when an air traffic controller's action results in two or more aircraft ending up too close to one another. This is also the category for an aircraft being cleared to land or take off on a closed runway.

On the other hand, if a pilot fails to comply with an air traffic controller's instruction, such as crossing a runway without clearance, this is classified as a pilot deviation. Vehicle and pedestrian deviations are any movements by either one on the airport's taxiways or runways without having obtained prior ATC clearance.

O'Hare tops the list with eight runways

The title of most runways in the world belongs to Chicago O'Hare Airport (ORD), which boasts an impressive eight landing strips. Simple Flying took a closer look at other airports with many runways, which you can read about here.

What else do you think is noteworthy about runways? Which is your favorite to land on or take off from? Let us know your thoughts and experiences in the comment section!

Source: ICAO