Facilities on airfields that accommodate aircraft takeoff and landing operations.

The earliest runways were nothing more than small grass or dirt strips that provided room for small aircraft to land or take off. Although thousands of small runways used by small and light aircraft still exist, the heavier aircraft employed by commercial air carriers require large paved runways for their operations. The design of airport runways involves many factors that allow aircraft to perform takeoff and landing operations within aircraft performance specifications and local environmental conditions.

One of the most important characteristics of a runway is its length. Runways must have sufficient length to accommodate aircraft takeoffs and landings. Larger and heavier aircraft tend to require longer distances and, thus, longer runways, in order to accelerate to a speed high enough for liftoff. Small aircraft may require only 500 feet of runway length, whereas the largest commercial aircraft may require nearly 12,000 feet, more than 2 miles, of runway to take off. In addition to aircraft specifications, runways located at higher elevations and in warmer climates tend to be longer, as aircraft need longer distances to take off in the thinner air of hot climates and high elevations. In addition to greater runway length requirements, larger aircraft tend to require runways of greater width, so that landing gear wheels can fit on the runways. Runway widths range from as few as 50 feet to more than 200 feet. Runways are also built with shoulders, similar to those of roads, and safety areas to make sure that there are no obstructions that will be in the way of any aircraft operations.

The direction, or orientation, in which a runway is located is another important characteristic. Aircraft perform better when taking off or landing into a wind, called a headwind, than when taking off with a tailwind, with the wind behind the aircraft, or with a crosswind, with the wind blowing across the side of the aircraft. Therefore, runways are oriented so that aircraft can take off or land into the preferred wind direction. Runways that are oriented in the direction of the prevailing winds are called primary runways. Runways that are oriented in the direction of less frequent winds are called crosswind runways. Because smaller aircraft are more sensitive to crosswinds, airports that accommodate smaller aircraft tend to have multiple crosswind runways, oriented in several different directions. Airports serving larger aircraft tend to have more primary runways all oriented in the same direction, called parallel runways.

The type and amount of surface material, called pavement, used to build the runway is yet another important runway characteristic. Runways accommodating heavier aircraft tend to be constructed out of thick, rigid pavements, such as concrete. Runways accommodating smaller aircraft tend to be built out of more flexible pavements, such as asphalt. If a runway pavement cannot support the weight of an aircraft, the aircraft will not be able to perform a smooth takeoff or landing.

Runways may be operated with a variety of associated lights, signs, and markings. A runway is named by the numbers painted on each runway end. The numbers on each end of a runway describe the direction relative to magnetic north. For instance, an airport runway named 09-27 is a runway that runs east 90 degrees from magnetic north to west 270 degrees from magnetic north. Other markings on runways include centerlines and lines that help pilots make accurate landings. Some runways also have electronic landing aids that aircraft use to make precision landings in inclement weather. These runways are called instrument runways. Depending on the type of landing aids and the type of markings on the runway, the runway may either be a precision-instrument or a nonprecision-instrument runway. Runways are often also equipped with edge lights, centerline lights, and approach lights, to help pilots make accurate landings at night.

The runway threshold is defined as the beginning of the usable part of the runway for aircraft landing. Often, runways have displaced thresholds, identified by white arrows, before the threshold, to provide extra runway length for aircraft departures. Sometimes, runways have relocated thresholds, identified by yellow chevrons, which provide extra runway length for emergency landings. Relocated thresholds are not for use during normal aircraft takeoff and landing operations.

Airports often have more than one runway to handle the large numbers of aircraft that land over a period of time. Both government rules and the physical properties of flight limit the number of aircraft that can use a runway during a given period of time. The typical capacity, or maximum number of aircraft that can use a runway, is approximately sixty operations per hour. At busy airports, where more than sixty aircraft depart or land over the course of an hour, parallel runways are often operated. Government rules dictate how far apart these runways must be for them both to be used simultaneously. In cloudy, or instrument flight rules (IFR), conditions, for example, parallel runways must be 4,300 feet apart, or nearly three-quarters of a mile, in order to be used simultaneously. This is one reason why the world’s largest airports take up a large amount of land.

• Horonjeff, R., and F. McKelvey. Planning and Design of Airports. 4th ed. New York: McGraw Hill, 1994. The definitive text on airport planning and design, providing an engineering-oriented approach to runway characteristics.
• Federal Aviation Administration. Airport Design. Washington, D.C.: U.S. Department of Transportation, Federal Aviation Administration, 1994. A guide to the design and management of airports, including runways.
• Kazda, Antonín, and Robert E. Caves. Airport Design and Operation. New York: Pergamon, 2000. An encyclopedic examination of the design, construction, and management of airports, with illustrations, bibliographical references, and an index.

Airports

Commercial flight

Landing procedures

Pilots and copilots

Runway collisions

Safety issues

Takeoff procedures

Taxiing procedures

Training and education

Vertical takeoff and landing