Airport Design

Airport Layout

Aviation is controlled by an agency of the United States' government known as the Federal Aviation Administration or the FAA. This agency mandates identification standards for airport layout that is meant to assist pilots in easily recognizing runways from the air and to taxi safely from the runway to the gate. From runway numbers and painted stripes to airport and runway lights and signs, the FAA regulates the National Airspace System.

compass

In navigation and surveying, all measurement of direction is performed by using the numbers of a compass. A compass is a 360° circle where 0/360° is North, 90° is East, 180° is South, and 270° is West. Runways are laid out according to the numbers on a compass. A runway's compass direction is indicated by a large number painted at the end of each runway. Preceding that number are 8 white stripes. Following that number by 500 feet is the "touchdown zone" which is identified by 6 white stripes. A runway's number is not written in degrees, but is given a shorthand format. For example, a runway with a marking of "14" is actually close to (if not a direct heading of) 140 degrees. This is a southeast compass heading. A runway with a marking of "31" has a compass heading of 310 degrees, that is, a northwest direction. For simplicity, the FAA rounds off the precise heading to the nearest tens.

For example, runway 7 might have a precise heading of 68 degrees, but is rounded off to 70 degrees.

layout of example runway

Each runway has a different number on each end. Look at the diagram below. One end of the runway is facing due west while the other end of the runway is facing due east. The compass direction for due west is 270 degrees ("27"). The compass direction for due east is 90 degrees ("9"). All runways follow this directional layout. This runway would be referred to as "Runway 9-27" because of its east-west orientation.

compass overlaid on runway to show orientation

The FAA includes over 20 different runway layouts in their advisory materials. There are 4 basic runway configurations with the rest being variations of the original patterns. The basic runway configurations are the following:

A) single runway
This is the simplest of the 4 basic configurations. It is one runway optimally positioned for prevailing winds, noise, land use and other determining factors. During VFR (visual flight rules) conditions, this one runway should accommodate up to 99 light aircraft operations per hour. While under IFR (instrument flight rules) conditions, it would accommodate between 42 to 53 operations per hour depending on the mix of traffic and navigational aids available at that airport.

 

illustration of a single runway


 

 

B) parallel runways
There are 4 types of parallel runways. These are named according to how closely they are placed next to each other. Operations per hour will vary depending on the total number of runways and the mix of aircraft. In IFR conditions for predominantly light aircraft, the number of operations would range between 64 to 128 per hour.

 

 

 

close parallel runways illustration ( intermediate parallel runways

 

far parallel runways dual line runways

C) open-V runways
Two runways that diverge from different directions but do NOT intersect form a shape that looks like an "open-V" are called open-V runways. This configuration is useful when there is little to no wind as it allows for both runways to be used at the same time. When the winds become strong in one direction, then only one runway will be used. When takeoffs and landings are made away from the two closer ends, the number of operations per hour significantly increases. When takeoffs and landings are made toward the two closer ends, the number of operations per hour can be reduced by 50%.

open V with dependent opeartions away from intersectionOpen V with dependent operations toward the intersection

D) intersecting runways
Two or more runways that cross each other are classified as intersecting runways. This type of configuration is used when there are relatively strong prevailing winds from more than one direction during the year. When the winds are strong from one direction, operations will be limited to only one runway. With relatively light winds, both runways can be used simultaneously. The greatest capacity for operations is accomplished when the intersection is close to the takeoff end and the landing threshold as shown below (with the configuration on the left).
two intersecting runways at each one's mid-point

two intersecting runways at near threshold

two intersecting runways at far threshold

 

The capacity for the number of operations varies greatly with this runway configuration. It really depends on the location of the intersection and the manner in which the runways are operated (IFR, VFR, aircraft mix). This type of configuration also has the potential to use a greater amount of land area than parallel runway configurations.

Airports also use standardized lighting and ground markings to provide direction and identification to all air and ground crews. To assist pilots in differentiating at night between airport runways and freeways, airports have rotating beacon lights. These beacons usually flash green and white lights to indicate a civilian airport. They are visible from the air long before the entire airport is recognizable. To help pilots at night quickly identify the beginning of a runway, green threshold lights line the runway's edge. Red lights mark the ends of runways and indicate obstructions. Blue lights run alongside taxiways while runways have white or yellow lights marking their edges. All these markings and lights serve to set a safety standard for all pilots to follow.

Illustration of airport lighting