Runway approach lighting systems play an integral role in airline safety. What are the different types of approach lighting systems in use at airports?
The types of runway approach lighting systems serve distinct purposes for planes making a landing. These types include threshold lighting, sequenced flashing lights, alignment indicator lights, and bars.
These lighting aids at airports help make it easier for pilots to land planes safely. Each type of approach lighting serves a somewhat different purpose, depending on the circumstances.
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Why Runway Approach Lighting is Important
One thing that many people unfamiliar with the aviation world are unaware of is that many airport approaches are designed so pilots don’t see the runway. However, the approach lights are what the pilot is supposed to see.
Most lighting systems have been designed to guide pilots to a height of about 100 feet above the runway. The geometry of the lights makes it possible for pilots to see the runway at that point.
Threshold and Centerline Lighting
Threshold lighting goes across a runway to a distance of about 45 ft from the edges. These lights are on five-foot centers and may be up to 10 feet from the landing surface.
These lights are designed to separate the usable runway and a displaced threshold. Threshold lights appear in all Series A approach lighting systems.
Centerline lights use rows of five lights that are 100 ft apart and measure 13.5 ft in width. The glide slope measurement determines how far these lights extend from the threshold.
When glide slopes are 2.75 ft or more, the centerline lights can extend 2,400 ft. For a lesser grade slope, the lights can extend 3,000 ft.
Military airfields may have layouts that allow for different spacing. The extension can be as short as 2,000 ft in a military field setting.
Sequenced Flashing Lights
Sequenced flashing lights have a pattern that flashes toward the threshold at twice-per-second intervals. These lights stop at the 1,000 ft roll bar.
High-intensity approach lighting systems are for runways that rely on instrument approaches and landings.
Pilots will see the sequenced flashers 1/2 to 3/4 mi from the touchdown location. Ideally, pilots should be 300 ft above ground level (AGL).
At the 1,000 ft roll bar, which puts pilots about 1/3 mi or 2,000 ft from touching down, pilots will begin to descend for the approach. Most pilots are 100 feet above ground level at this point.
Sequenced flashers are also used in non-precision approaches. These lights are visible about 2,000 ft or 1/3 mi from aircraft touchdown. Like high-intensity systems, these lights require pilots to be about 100 ft AGL.
Medium-intensity approach lighting systems may also incorporate sequenced flashers in spots where pilots could have trouble identifying the approach area.
Omnidirectional sequenced flashing lights may feature a configuration of seven lights on the runway. These lights offset the need for circling and provide clear visuals for non-precision landings.
Alignment Indicator Lights
Runway alignment indicator lights are also known as RAILS. These approach lights are also a type of sequenced flashers.
Because of the 200 ft spacing, RAILS extend beyond centerline lights. These lights may also be used in conjunction with centerline lights.
Runway end identifier lights also play a crucial role in approach lighting. These lights’ most important role is easy identification of a runway’s end.
These lights have a lateral placement at each runway threshold side. Synchronized flashing lights help provide a signal that is easy for pilots to see.
End identifier lights may face a single direction or be omnidirectional. The goal is to ensure that pilots know where the runway ends.
Bars Used in Runway Approach Lighting
Visual approach slope indicators are some of the most common approach lights used in a bar formation. These lights work through red and white color differentiation.
Each of these lights uses a red upper beam and a red lower beam. This light combination allows some of the greatest visibility for pilots, especially if landing under challenging conditions.
Another common usage of bars similar to visual approach slope indicators is a precision approach path indicator. These lights consist of two or four units placed in a single row.
Visibility is one of the most significant benefits that these lights offer. The lights are visible for up to 20 mi at night.
Roll bars provide essential support, with two bars placed outside the centerline light at 1,000 ft. These bars give dimension to landings that might be missing from the centerline lights alone.
Some runways may use 500 ft roll bars. These bars are more likely to be in use during weather conditions that make it easier to lose sight of the 1,000 ft bars.
Side row bars start at the last 1,000 ft of the runway and consist of red lights. When descending below 100 ft, these bars or termination bars will be in view to help you land safely.
Termination bars also have red lights, appearing 200 ft from the end of the runway and on either side of the centerline. Pilots must be able to see these bars if descending under 100 ft, or they must be able to see the actual runway.
Wing bars are a type of approach lighting you may see when a lateral landing becomes necessary. Most of these lights will be red, making them easy to spot.
What Are Some Important Things to Know About Approach Lighting?
The most important thing to remember is that approach lighting systems are standardized. These configurations are designed to prevent costly and deadly aviation disasters.
Many of the approach lights, particularly sequence flashing lights, have intensity controls. These controls are used on pilot requests for higher or lower-intensity lighting.
Runway status lights may be responsive to real-time airport traffic at busier airports. When approaching a busier airport, keeping this possibility in mind is helpful.
How Are Lighting Systems Controlled?
The Air Traffic Control Tower (ATCT) customarily controls the approach lighting. In locations without a control tower, control of the lighting is up to the Flight Service Station (FSS).
Intensity controls for approach lights can be adjusted per pilot request. There may also be intensity controls possible for sequenced flashing lights.
When Can Lighting Be Pilot-Controlled?
Select airports provide options for pilots to control the approach lighting. The way to activate these controls is by keying the microphone on the plane.
The circumstances where pilot control is often available include:
- Airports without specified lighting hours
- Locations without an ATCT or FSS
- During hours when the FSS or ATCT are closed
- Specified hours at the airport’s discretion
Regardless of the number of airport runways, lighting systems use a common radio frequency. The most typical frequency is the common traffic advisory frequency (CTAF), although some airports may use a different frequency.
The lights will turn off after 15 minutes when pilot-controlled, making this a good scenario to avoid with a short final. If you turn the lights on before you enter the pattern and refresh them with each downward leg, you’ll be in good shape on your approach.
Different combinations of lights can be pilot-controlled with Federal Aviation Administration (FAA) approval. Approach lighting always takes precedence over any of the types of lighting present.
How Do Pilots Activate Pilot-Controlled Lighting?
Pilots will need to key the microphone seven, five, or three times. Keying the microphone seven times is usually initially suggested.
You can key five or three times for a lower intensity. If you start keying when entering the final approach, you are sure to have access to the lighting when you most need it.
How Long Has Approach Lighting Been Around?
Approach lighting as we know it today dates back to the years following World War II. The Arcata–Eureka Airport in California was the site of early work on these lighting systems.
The conditions that these systems were designed for include:
- Nightime landings
- Rainy conditions
- Heavy fog
The original approach lighting systems comprised 38 towers topped with natural gas lights. These systems had a row of 17 towers on each side of the runway for a 3,500 visual approach.
When the Navy started developing strobe lights, natural gas-powered lighting became obsolete. By 1956, strobe lighting was standard at many of the larger airports.
How Does the Usage of Current Approach Lighting Impact Safety?
The most critical criteria in how airports use approach lighting include the number of aircraft in use, the type of operations going on, and the runway design.
Although the approach lighting system plays a role in enabling safer landings, the criteria used to address the approach lighting used at an airport does not directly address safety after a crash or other incident.
One of the many responsibilities that airport officials face is keeping surrounding communities, in addition to pilots, passengers, and crew members, safe during regular airport operations.
Many larger airports in urban areas have grown to the extent that more of the airport area reaches into populated areas. One of the challenges that airports face is how to balance these concerns.
When present, approach lighting systems make it easier for pilots to transition from instrument to visual flight while preparing to land. Making this transition as smooth as possible eliminates the chances of overrunning or overshooting during the landing and leading to injury.
Despite the critical role that approach lighting plays in safety, there is a risk of damage to the structural and electrical components during landings. The FAA uses criteria that help minimize the risk of these types of incidents.
How Can Pilots Best Make Use of Approach Lights?
Pilots ought to make use of the fact that approach lights provide orientation as well as measurement. You’ll have an accurate idea of where you are in relation to the touchdown area, as well as the distance.
You can always benefit from remembering that the ATCT can turn the lights up or down as needed or take the initiative yourself when permitted. Although airports may use different varieties of lights, they all serve an essential purpose.
What are the different types of approach lighting systems?
There are many types of approach lighting used in airports, ranging from sequenced flashers to bars. These lights may feature low, medium, or high intensity as needs require.
What is the definition of a simple approach lighting system?
Simple approach lighting includes a row of lights on the extended center line of the runway. These lights will form a crossbar that stops short of the threshold.
What does Approach Lighting System (ALS) mean in an aviation context?
ALS refers to signal lights in a configuration beginning with the landing threshold and extending into the approach area. The distance for non-precision runways is 1,400-1,500 ft and 2,400-3,000 ft for precision instrument runways.
What does the approach lighting system do?
The approach lighting system enables pilots to see the runway after dark, as the markings are not easily visible at night,
What elements make up approach lights?
Approach lights are the first lights that pilots will encounter during the landing process. The types used may include blinking, steady, unidirectional, or white lights, depending on the circumstances.
These lights are designed to be visible before the runway. Pilots will know what direction the runway is in from these lights.
There are several types of runway approach lighting that make it easier for pilots to land. Knowing what types of lights may be in use at an airport makes flights as hassle-free as possible.