Runway

Runway

In aviation, a runway is a long, flat surface for aircraft to land and take off. Runways can be made from many materials, such as asphalt, concrete, or natural surfaces like grass, dirt, gravel, ice, sand, or salt. While some people use the word “tarmac” for runways, very few runways are actually made from tarmac.

Special areas on water are used for seaplanes and are called waterways. Today, most places measure runway lengths in meters, but in North America, people often use feet to talk about these lengths.

History

In January 1919, aviation pioneer Orville Wright said that airplanes needed clear places to land. But making these places was expensive and needed regular care.

In 1919, the United States Army Air Service made rules for where planes could land. At first, most planes could land in any direction on grassy fields. But as planes got bigger and needed stronger tires, these fields were not useful anymore. By 1928, Ford Airfield became the first U.S. airport with runways made of concrete. After that, many big airports did the same.

Design

The main idea when building a runway is to point it in the direction the wind usually blows. This helps airplanes take off and land safely. When airplanes land against the wind, they need less runway space and can land more easily.

Runways are given numbers from 01 to 36 based on the direction they point. For example, a runway numbered 09 points east, and a runway numbered 18 points south. A runway can be used in both directions, so runway 15 can also be called runway 33 when used the other way.

Declared distances

Runway sizes can be very different. Small runways at local airports might be only 245 meters long and 8 meters wide. Big international airports can have runways that are 5,500 meters long and 80 meters wide, to handle large jets. There is an enormous runway at Edwards Air Force Base in California, measuring 11,917 meters by 274 meters, built for the Space Shuttle.

When talking about how far planes can take off or land, there are special terms used:

• Takeoff Run Available (TORA) – This is the part of the runway that is ready for a plane to use when it takes off.
• Takeoff Distance Available (TODA) – This includes the takeoff run plus any extra space called a clearway, if there is one. The clearway must be within the airport limits.
• Accelerate-Stop Distance Available (ASDA) – This is the takeoff run plus any extra space called a stopway, if there is one.
• Landing Distance Available (LDA) – This is the part of the runway that is ready for a plane when it lands.
• Emergency Distance Available (EMDA) – This is the landing distance or takeoff run plus a stopway.

Sections

There are rules for marking runways.

• The runway thresholds are marks that show where a plane can start or finish taking off and landing normally.

• The runway safety area is a clear, smooth area around the runway to keep planes safe.

• The runway is the part between the thresholds, with special marks and numbers, but without extra areas at the ends.

• Blast pads are built before the start of a runway to protect it from strong winds from big planes taking off.

• Stopways, also called overrun areas, are built at the end of runways to help planes stop if they go too far. Blast pads and stopways look similar and both have yellow marks, but stopways are stronger and meant for stopping planes, while blast pads are weaker and not for landing or taking off. An engineered materials arrestor system (EMAS) might also be there, painted in a similar way, but it is not part of a stopway.

• Displaced thresholds are used for moving around the airport, taking off, and landing, but not for landing normally. They exist because of things like obstacles or noise rules. They are marked with white arrows leading to where landing can start. Landings on displaced thresholds are only allowed in special cases.

• Relocated thresholds are like displaced thresholds. They mark parts of the runway that are closed for repair or maintenance. This closed part can be used for moving around but not for taking off or landing. A common way to show a relocated threshold is with a big white line across the runway.

• Clearway is an area past the end of the runway, controlled by the airport. It has no tall obstacles and a gentle slope. It can be added to the runway length when calculating how far a plane can take off. For example, if a paved runway is 2,000 metres long and there are 400 metres of clearway, the total takeoff distance is 2,400 metres. This lets bigger planes take off with more weight.

Markings

Most big runways have special signs to help pilots. These signs show how far a plane is from the end of the runway. For example, a sign showing the number 7 means there are 7,000 feet left.

Runways can be different depending on their size and what they are used for. Small airstrips might just be a strip of grass or gravel, and often don’t have many markings. Bigger airports have runways with many lines and lights to help planes land and take off.

Lighting

Runway lights help airplanes take off and land safely, especially when it's dark or hard to see. These lights line the runway and can change color to show where the airplane should go.

Runway lights include special lights at the ends of the runway, lights along the sides, and lights in the middle. Some lights flash, and others stay on steady. These lights help pilots see where they are during takeoff and landing. Airports use these lights to make sure airplanes can land safely, even in bad weather.

Safety

Runways can sometimes have problems, called safety incidents. One type is when a plane leaves the runway in the wrong place, called a runway excursion.

Another kind of incident happens when something or someone gets onto the runway when they shouldn’t, called a runway incursion. Sometimes a plane might try to land or take off on the wrong runway, which is called runway confusion.

Surface

The material used to build a runway depends on its use and the local ground. Big airports often use concrete for their runways because it lasts a long time. If the ground is unstable, asphalt is used because it can be fixed more easily. Smaller airports might use grass or salt flats for their runways.

When designing runways, engineers test the ground to decide how thick the pavement should be. For large planes, the pavement can be very thick. Engineers think about many things like the type of plane and the materials used. Special drainage systems are put under runways to keep them dry and in good shape.

Length

Main article: List of longest runways

Runways must be long enough for planes to take off and land safely. Smaller planes need runways that are at least 1,800 meters (about 5,900 feet) long. Bigger planes with many passengers usually need runways that are at least 2,400 meters (about 7,900 feet) long. Very big planes that fly internationally may need runways that are even longer — sometimes 3,200 meters (about 10,500 feet) or more for landing, and 4,000 meters (about 13,000 feet) for taking off.

The length needed can change depending on where the airport is. For example, at sea level, a runway that is 3,200 meters long can handle almost any plane. Some airports, like O'Hare International Airport, sometimes use longer runways when needed. Hot weather or high altitude can also affect how long a runway needs to be for planes to take off safely.