Aviation is the most authentic example of a high-reliability industry, with every element being explicitly designed to support safety and prevent hazards. One such safety measure that is often underappreciated is the arrangement of runway lights, which are universally similar and help pilots land the aircraft in a variety of conditions. In this blog, we will discuss how runway lights are structured and how the various colors help pilots in the landing sequence.
The FAA is the governing body that creates standards for runway light arrangements in the United States. Given the efficacy of their prescribed design and the ubiquity of U.S.-operated airlines across the globe, many other countries have adopted the same layout. The seven light types in the standard FAA arrangement are as follows:
Runway Threshold Lights
The first lights that the aircraft passes upon approach are the threshold lights, which are bi-directional lights found on both sides of the runway. Since most airports support landing from both directions, these lights feature opposing red and green sides, those of which appear green on approach and red as they are passed during takeoff.
Runway Edge Lighting
Flanking either side of the runway are pairs of lights that are used to define the lateral borders. Depending on the time of day and weather conditions, the intensity of the edge lights may be increased or decreased to make them more visible to pilots. While uniformly white in most cases, airports that support instrument landing will feature bi-directional white and yellow lights to alert pilots that the runway is ending.
Runway End Identifier Lighting
Runway end identifier lights (REILs) are unidirectional lighting systems that help identify the approach side of a runway. Pilots can use these blinking-white lights to ensure they are not landing short of the runway, in addition to keeping the aircraft centered.
Runway Centerline Lighting
Placed in 50-foot intervals along the centerline of the runway, these lights help alert landing aircraft as to the end of the pavement. Runway centerline lights are white and solid until the last 3000ft of pavement. After that, they will begin to alternate between rows of red and white until the final 1000ft, at which point they are all red.
Touchdown Zone Lighting
Placed on either side of the centerline, touchdown zone lights consist of three bright white lights that aid pilots in landing flush with the ground, especially during times of decreased visibility.
Since there is typically more than one aircraft scheduled to depart in quick succession at any given time, pilots need to know where the runway borders are in order to avoid a collision. Ground support equipment operators and other vehicles that share the tarmac may also use these alternating green and yellow lights to avoid entering the runway without permission.
Precision Approach Path Indicator (PAPI) lights are unique tools that help pilots align their aircraft during the final approach. This lighting architecture consists of four lights that differ in visibility depending on the approach angle. For example, if the aircraft is approaching the runway from too high of an angle, all four lights will appear white, while the proper approach would reveal two red and two white lights.
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