Are you curious about how pilots line up their aircraft perfectly with the runway? Or maybe you're starting your own aviation journey towards becoming a pilot. Either way, learning all about the different runway lighting systems will benefit you greatly.
In this article we'll explore everything there is to know about VASI lights.
Let's start learning more about them!
SUMMARY
-
VASI lights are used to help pilots maintain the proper glide slope during landings.
-
Red and white light signals provide high-contrast guidance.
-
PAPI systems are newer, but VASI remains widely used at many airports.
What is a VASI Light?
If you look to the left-side of the runway and see 4 lights in sets of 2's, more than likely, it's VASI.
Visual Approach Slope Indicator (VASI) is a system of lights located near the runway threshold. It helps pilots maintain the proper glide path during an approach.
The purpose of VASI is to reduce the risk of you landing too short or making the mistake of overshooting the runway.
VASI's system usually is made up of two or three bars of lights. These are called the:
-
Near bar.
-
Middle bar.
-
Far bar.
Each bar contains light units arranged in sets of 2, 4, 6, 12, or 16.
With Visual Approach Slope Indicator, the most common is the two-bar setups with near and far bars.
Glide Path Options
-
Two-bar VASI: Provides a single glide path, usually set at 3 degrees.
-
Three-bar VASI: Offers two glide paths:
-
Lower glide path: Near and middle bars, typically at 3 degrees.
-
Upper glide path: Middle and far bars, 3.25 degrees, for high cockpit aircraft.
-
The great thing about VASI is that its glide paths provide visual descent guidance while making sure that you have obstacle clearance up to 4 nautical miles (NM) from the runway threshold and within 10 degrees of the runway centerline.
How Do VASI Lights Help?
VASI gives you, the pilot, immediate visual feedback. You can see the lights clearly from a distance while on final and determine if you're too high or too low.
VASI systems are meant to reduce the likelihood of you experiencing a hard landing, a missed approach, or a runway overrun.
This visual aid really is beneficial since you can make corrections well before reaching the runway. The system’s red and white color differentiation allows you to instantly assess your position:
-
Below Glide Path: Both bars appear red.
-
On Glide Path: The near bar appears white, and the far bar appears red.
-
Above Glide Path: Both bars appear white.
To simplify and make it clear: when aligned correctly with a two-bar VASI system, the lights will show red on the top bar and white on the bottom bar.
This configuration is commonly referred to as “red over white” and is an easy way for pilots to confirm they’re on the proper glide slope.
These simple color combinations are designed to provide you with simple and clear visual cues during your approach to land.
Additional Considerations
-
In some locations, VASI glide path angles can be steeper than the standard 3 degrees. They can reach up to 4.5 degrees for proper obstacle clearance. Pilots flying high-performance aircraft have to be extra cautious with steeper angles since they can increase their landing and rollout distances.
-
The VASI system does not provide lateral course guidance, which is something that is typically offered by runway lights or markings.
What's the Difference Between PAPI and VASI Lights?
PAPI (Precision Approach Path Indicator) lights and VASI lights can help to serve a similar purpose but they differ in both their configuration and design.
-
Configuration
-
VASI lights use two or three light bars placed horizontally.
-
PAPI lights use a single row of four lights placed horizontally.
-
-
Precision
-
PAPI systems offer finer resolution with four light units for these indications: “4 white” (too high), “3 white lights/1 red” (slightly high), “2 white/2 red” (on slope), “3 red/1 white” (slightly low), "4 red lights" (too low).
-
VASI lights are simpler, showing either “high,” “on slope,” or “low.”
-
-
Visibility
-
PAPI lights’ single-row setup is much easier to locate visually from the air.
-
VASI lights’ multi-bar setup can be a bit more effort to interpret for pilots unfamiliar with the system.
-
Either way, both of these systems are highly useful at guiding you from the skies to the runway for a visual approach landing.
How to Read 3-Bar VASI Lights
A 3-bar VASI system provides additional guidance for larger aircraft, which have a steeper approach angle compared to smaller planes such as Cessna 172's.
Visual Interpretations of 3-Bar VASI Systems
-
Below Both Glide Paths: All three bars appear red.
-
On Lower Glide Path: The near bar appears white, and the middle and far bars appear red.
-
On Upper Glide Path: The near and middle bars appear white, and the far bar appears red.
-
Above Both Glide Paths: All three bars appear white.
Basically this: All bars red? You’re too low. All bars white? You’re too high.
The additional bar in a 3-bar VASI gives you a higher glide path angle for high-cockpit aircraft while maintaining the standard glide slope for smaller aircraft.
Placement and Coverage
A VASI runway lighting system with 2, 4, or 6 light units are usually installed on one side of the runway, typically the left.
Larger systems with 12 or 16 lights are placed on both sides. This is designed so that you have visibility from 3-5 miles during the day and up to 20 miles or more at night.
Frequently Asked Questions
-
What does a fully white VASI signal mean?
You are too high above the glide slope.
-
Why are VASI lights red and white?
The colors provide clear, high-contrast signals that are easily noticeable.
-
Can VASI systems be used in all weather conditions?
They are visible in most conditions but may be less effective in extremely low visibility, for example heavy fog.
-
How far out can VASI lights be seen?
Typically, they are visible from about 3-5 miles during the day and up to 20 miles or more at night.
-
Do all airports have VASI lights?
Not all; some use PAPI systems or other visual guidance tools.
-
Are VASI systems being replaced by newer technology?
While newer systems like PAPI are more common, VASI remains widely used.
Takeaway
Now that you are equipped with the knowledge of how VASI works, try looking for these systems the next time you're coming in on your final approach at your local FBO.
Fly safe!
Interested in Aviation Lighting Systems?
Our guides are designed to help!
-
Cockpit Lights: How to Choose the Right Set for Flying at Night
-
The 11 Light Gun Signals All Pilots Must Know (And How to Respond)
Did you find this article helpful?
Do you think we missed an important interview question? Let us know in the comments below!
