Airport, Taxiway, and Runway Lights Explained
If you've been to any major airport at night, you've probably noticed that there are a lot of different kinds of lights, ranging from flashing white or yellow to steady red, green, and blue. Airport lighting is essential for aircraft operating at night.
Airport lights can be divided into different types: General airport lighting, taxiway lighting, runway lighting, and visual glideslope indicators.
General Airport Lighting
This first type of lighting consists of the can't-miss-it airport beacon and any warning lights on top of towers, buildings, and construction equipment. The airport beacon is a large, powerful, rotating light that's highly visible from miles away. Public-use airport beacons rotate green and white. Military airports rotate green and white but have two white lights for each green light, thus differentiating themselves from civilian airports. Heliports rotate between green, white, and yellow lights.
Pilots can easily identify an airport at night from its beacon, making it one of the easiest checkpoints for pilots when navigating on a night flight. Air traffic controllers may turn the beacon on and off as necessary, or it may be set on a timer.
Airport buildings, towers, and other tall equipment on the field will have a small, steady red beacon on top of them to aid in collision avoidance for low-flying aircraft.
There are four types of lights on the taxiway, a path for airplanes heading to or coming from a runway.
- Taxiway edge lights: These lights are blue in color and line the taxiway. Airports often have green taxiway centerline lights as well.
- Clearance bar lights: Set inside the taxiway, these lights are steady and yellow and are meant to increase the visibility of a hold position line or a taxiway intersection at night.
- Stop bar lights: These in-pavement lights are steady red and extend across the taxiway at a hold short line, the area where a taxiway meets the runway, They are meant to prevent a pilot from leaving the taxiway when their plane would be in danger of causing a collision on a runway. Once a pilot is cleared onto the runway, the air traffic controller will turn off the stop bar lights.
- Runway guard lights: A pair of two flashing yellow lights that are positioned at each side of the taxiway at the hold short line, the runway guard lights are meant to draw attention to the hold short line.
There are five different kinds of runway lights.
- Runway end identifier lights: This pair of white flashing lights, one on each side of the approach end of the runway, helps distinguish the runway from the taxiway at night.
- Runway edge lights (HIRLs/MIRLs/LIRLs): On the edges of instrument runways (those equipped with visual and electronic navigational aids and for which a straight-in landing minimum altitude has been approved), these steady lights start out white and change to yellow during the last 2,000 feet, or half the runway length, whichever is less. Then they change to red as the aircraft reaches the end of the runway. They can be high intensity (HIRLs), medium iintensity (MIRLs), or low intensity (LIRLs).
- Runway centerline lighting system (RCLS): On some precision runways—those for which there is both horizontal and vertical guidance—an RCLS is installed, with white lights spaced at 50-foot intervals on the centerline of the runway. With 3,000 feet remaining, the white lights change to alternating white and red. During the last 1,000 feet, the lights are all red.
- Touchdown zone lights: These steady white lights are placed in two rows next to the centerline, starting at 100 feet and extending to the midpoint of the runway, or 3,000 feet beyond the threshold (the designated ideal landing area), whichever is less.
- Land and hold short lights: When land and hold short operations (LAHSO) are in effect, flashing white lights may be seen across the runway at the hold short line. During LAHSO, air traffic control may require a pilot who has just landed to hold their position to keep clear an intersecting runway or taxiway or some other designated point on a runway.
- Runway status lights: This group of lights includes runway entrance lights, the takeoff hold light array, runway intersection lights, and the final approach runway occupancy signal. These lights assist in informing pilots and ground vehicle operators when it's safe to enter or cross a runway. They work in conjunction with surveillance systems (like ADS-B) and are fully automated.
Visual Glide Slope Indicators
Visual glide slope indicators are meant to give pilots a visual guide during their descent to help maintain a stabilized approach. They come in two types, visual approach slope indicators (VASIs) and precision approach path indicators (PAPIs), each of which has multiple types of arrangements and both of which give pilots a good idea whether they're on the glide path for a stable approach.
- VASIs: These are bars of lights on the side of the runway that give pilots a visual indication of whether their aircraft is too high or too low on the approach. VASIs can be made up of 2, 4, 6, 12, or 16 lights, are commonly located on two bars—near and far—and provide an indication for a 3-degree glide slope, the typical approach path for a landing. In a common two-bar VASI system, a pilot should see two red lights on the higher, far bars and two white lights on the lower, near bars. If all lights on the near and far bars are red, the pilot is too low. If all lights on the near and far bars are white, the pilot is too high. Pilots use the saying "red over white, you're all right" regarding VASIs.
- PAPIs: These sets of lights are arranged horizontally and typically include four lights that can be red or white, depending on where the aircraft is in the glide slope. A PAPI system is usually located on the left side of the runway. When all four lights are white, the aircraft is too high. As the plane, descends onto the glide path, the lights on the right side will begin to turn red. When an aircraft is on the precise glide path, the two left lights will be white and the two right lights will be red. When three or more lights are red, the aircraft is too low.