Runways: Airport Layout And Design Explained

The layout of airport runways is influenced by several factors, including geographic features, wind patterns, and airport traffic. The direction of the runway is crucial as aircraft typically take off and land into the wind or with a headwind. Additionally, geographic features such as mountains or hills can impact the runway's orientation to ensure safe approaches and departures. The size of the airport and the volume of air traffic also play a role in determining the number and configuration of runways. While older airports may have intersecting runways, modern airports tend to favour parallel runway configurations to increase arrival and departure rates.

Wind direction

The layout of airport runways is dictated by several factors, one of the most important being wind direction and intensity. Airplanes are most stable when taking off and landing directly into the wind. This is because a headwind increases lift during takeoff, requiring a shorter runway distance, and provides additional drag during landing, aiding in slowing the aircraft. Therefore, runway directions are largely chosen based on the average local wind directions. Airports with a single runway are often constructed to be aligned with the prevailing wind. Airports with multiple runways are usually built in a parallel configuration to allow for simultaneous departures and arrivals.

Runways are aligned to take advantage of prevailing winds, which blow from a single direction. As most winds in the continental United States blow from west to east, most runways are oriented approximately in that direction. However, there are exceptions, such as in central Kansas and Oklahoma, where runways are oriented in a north-south direction due to the prevailing winds.

The naming of runways also takes into account wind direction. Runways are named by a number between 01 and 36, which is generally the magnetic azimuth of the runway's heading in decadegrees. For example, a runway facing east, or heading 090°, becomes runway 09 (or 9). If there is more than one runway pointing in the same direction, they are identified by appending left (L), centre (C), or right (R) to the end of the runway number to indicate its position relative to the others.

When choosing which runway to use, air traffic controllers consider various variables, including wind direction and intensity, visibility, runway length, and aircraft type. They aim to select the safest and most efficient runway configuration for the prevailing conditions.

Terrain and obstacles

The presence of natural obstacles, such as mountain ranges or hills, can influence the direction and layout of runways. Designers may opt to construct runways in a way that avoids these obstacles, ensuring that aircraft approaches and departures are not compromised. For example, if a mountain range is located to the north of an airport, runways may be oriented in an east-west direction to facilitate safer take-offs and landings.

In some cases, man-made obstacles, such as buildings or structures, may also impact runway layout. Airports located near populated areas may direct departures and arrivals away from the towns to minimise noise pollution. Additionally, obstacles located just before the runway, such as buildings or terrain features, can result in a displaced threshold. This means that the beginning section of the runway may not be suitable for landings, but can still be used for taxiing, takeoff, and landing rollout.

To ensure safe take-off and climb, runway analysis is performed, taking into account guidelines from organisations like the FAA (Federal Aviation Administration) and ICAO (International Civil Aviation Organization). These guidelines provide methods for obstacle analysis, helping to determine the necessary clearance for aircraft operations. By considering terrain and obstacles, runway designers and operators can maintain safe and efficient airport operations.

Runway width and length

The length of a runway is a critical factor in ensuring the safety and efficiency of aircraft operations. It directly affects an aircraft's ability to speed up for takeoff and slow down for landing. The length of a runway can significantly impact flight operations, and the processes of taking off and landing an aircraft are critical phases that depend heavily on the design and condition of airport runways. Therefore, it is important to make accurate calculations taking into account runway length, surface condition, and environmental factors.

The length of a runway is determined by several factors, including the size of the airport, the type of aircraft expected to land there, the elevation of the airport, and the weather conditions. The larger the aircraft, the longer the runway required. For instance, a runway catering to Boeing 737s and international flights might be 150 feet wide and 10,000 feet long, whereas a runway catering to only general aviation aircraft might be 50 feet wide and 3,000 feet long. Larger aircraft, including wide-bodies, will usually require at least 7,900 to 8,000 feet at sea level and somewhat more at higher altitudes.

The average length of a runway at major commercial airports is usually between 8,000 and 13,000 feet. In contrast, runways on aircraft carriers are significantly shorter, typically around 1,000 to 1,200 feet long. These runways are designed for military jets, which use catapult systems for takeoff and arresting wires for landing. A runway of at least 6,000 feet in length is usually adequate for aircraft weights below approximately 200,000 lb.

The width of a runway is also important and is determined by the size, popularity, use, and commercialism of the airport. The width of a runway can vary, commonly from 75 feet wide at smaller airports to 200 feet at larger facilities. Larger runways accommodate higher speeds and larger aircraft, which require more room to reach takeoff velocity and to slow down upon landing.

Runway naming

The naming of runways follows a strict set of guidelines. Firstly, directionality is dictated on a magnetic 360-degree scale, with north's heading being 360°, east's 090°, south's 180°, and west's 270°—like a compass. The runway's name is then determined by the magnetic azimuth of the runway's heading in decadegrees, with runways named by a number between 01 and 36. For example, a plane taking off from runway 09 faces east, into an "east wind" blowing from 090°.

When two or more runways face the same direction, they receive the labels Left, Right, or Center. For example, in Fort Lauderdale, there are two runways oriented toward a heading of 100°, so they are both runway 10. The runway on the left is identified as 10L (or 10 Left), while the other is identified as 10R. If there are more than three runways that point in the same direction, like in Atlanta, the runways are simply named using an adjacent heading, with the north runways identified as 26R and 26L, the middle two as 27L and 27R, and the southernmost runway as 28.

Runways with non-hard surfaces, like small turf airfields and waterways for seaplanes, may use a standard numerical scheme or traditional compass point naming. For example, Ketchikan Harbor Seaplane Base uses the names Waterway E/W for its runways. Airports with unpredictable water currents, like Santa Catalina Island's Pebbly Beach Seaplane Base, may use the name Waterway ALL/WAY to denote the lack of a designated landing direction.

Runway lighting

Runway lights are almost direct replacements for runway markings that are only visible during the day. The lights offer visual guidance to pilots, enabling safe and efficient airport operations during takeoff, landing, and taxiing. These lights typically indicate the runway edge, threshold, centre line, and touchdown zone. Runway lights are spaced at defined intervals, with specific colour combinations and brightness levels conveying different meanings.

High-Intensity Runway Lights (HIRLs) and Medium-Intensity Runway Lights (MIRLs) are the brightest lights and are spaced a maximum of 200 feet apart. Low-Intensity Runway Lights (LIRL) are also used in certain situations. On instrument runways, the lights change to yellow for the last 2,000 feet or half the runway length, whichever is shorter, indicating a caution zone for landing or takeoff.

Runway End Identifier Lights (REIL) are another type of lighting system. These are flashing lights on each side of the runway threshold, helping pilots identify the runway, especially in reduced visibility conditions or when surrounded by bright city lights. Precision instrument runways at larger airports may also have centre line lights installed, spaced 50 feet apart, aiding pilots in keeping their aircraft aligned during takeoff and landing. These lights change to red and white for the last 3,000 feet of the runway and then turn red for the final 1,000 feet, warning pilots of the approaching end.

The Visual Approach Slope Indicator (VASI) is a system of lights that provides visual descent guidance during the approach to a runway. These lights are visible from 3 to 5 miles during the day and up to 20 miles or more at night. VASI installations consist of multiple light units arranged in bars, providing visual glide paths for aircraft.

Frequently asked questions