Runway

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

Special areas on water are used for seaplanes and are called waterways. Today, most of the world measures runway lengths in meters, but in places like North America, people usually talk about these lengths in feet.

History

In January 1919, aviation pioneer Orville Wright pointed out the need for clear and well-prepared places for airplanes to land, but noted that making such surfaces was costly and needed regular care.

In 1919, based on experiences from the war, the United States Army Air Service created rules for landing fields, suggesting a special area for taking off. At first, most planes could land in any direction on grassy fields. But as planes grew bigger and needed stronger tires, these fields became less useful. By 1928, Ford Airfield became the first U.S. airport with runways made of concrete, and soon major airports followed suit.

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. But big international airports can have runways that are 5,500 meters long and 80 meters wide, to handle large jets. There is even an enormous runway at Edwards Air Force Base in California, measuring 11,917 meters by 274 meters, which was 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 and suitable 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 and suitable 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. Its length 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 large runways have special markings and signs to help pilots. These signs show how far a plane is from the end of the runway, using numbers to indicate thousands of feet left. For example, a sign showing the number 7 means there are 7,000 feet left.

Runways can be different depending on their size and the type of equipment they have. 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 guide planes during landing and takeoff.

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, which are called safety incidents. One type is when a plane leaves the runway in the wrong place, called a runway excursion. A special kind of excursion is when a plane cannot stop before the end of the runway, called a runway overrun.

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. There are also times when a plane lands before it reaches the end of the runway, called a runway undershoot.

Surface

The material used to build a runway depends on its use and the local ground conditions. Major airports often use concrete for their runways because it lasts long and needs little maintenance. However, if the ground is unstable, asphalt is used because it can be repaired more easily. Smaller airports with light planes might use grass or even salt flats for their runways.

When designing runways, engineers take samples of the ground to decide how thick the pavement should be. For big commercial planes, the pavement can be between 10 to 48 inches thick. There are different methods to design these runways, and engineers consider many factors like the type of aircraft and the materials used. To make runways last longer and perform better, special drainage systems are installed underneath to keep the pavement dry and prevent damage.

Length

Main article: List of longest runways

Runways need to be long enough for planes to take off and land safely. A runway that is at least 1,800 meters (about 5,900 feet) long works well for smaller planes. Bigger planes, like those with lots of passengers, usually need runways that are at least 2,400 meters (about 7,900 feet) long. For very big international flights that carry a lot of fuel, runways might need to be 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. Conditions like hot weather or high altitude can also affect how long a runway needs to be for planes to take off safely.