by Airport Industry-News
Published
19 Apr 2024
Tags
Airfield Lighting
ATG Airports Ltd
Suppliers ATG Airports Ltd
Visual Approach Slope Indicator, or VASI lights, offer a quick visual indication to pilots on final approach as to whether or not they are on the correct glideslope.
Runway VASI lights have a 2-bar or 3-bar configuration, with an array of red and white lights. Based on the visibility of the lights, pilots can immediately tell if they are too high, too low, or just right on the approach slope.
VASI stands for Visual Approach Slope Indicator, which perfectly describes the purpose of VASI lights.
On final descent into an airfield, the pilot can see the VASI lights alongside the runway, and should see a mixture of red and white lights.
If all the lights appear red, the aircraft is below the ideal glide path. If all the lights appear white, the aircraft is above the ideal glide path.
VASI lights have two common configurations:
2-bar VASI lights show two rows of two lights, in a roughly square layout. This can show three conditions:
The pilot can simply adjust altitude to keep the two bars in different colours, for an acceptable landing path.
3-bar VASI lights add a third row of two lights, creating an array two lights wide, and three lights tall:
This is useful on larger airfields, as the upper glide path is more suitable for large aircraft, whereas the lower glide path is acceptable for smaller planes.
Precision Approach Path Indicator, or PAPI lights, are a single bar of four lights that appear red or white at different viewing angles.
This can provide immediate feedback to the pilot on a total of five conditions:
While PAPI/VASI lights all provide an instant reference to pilots, PAPI lights offer the most granular information, with a total of five states relayed by just four lights. For a more visual representation of how PAPI lights work, see our popular PAPI lighting infographic.
Existing VASI lights have now largely been phased out, with PAPI lights becoming the standard across the aviation sector.
A simplified, two-light PAPI system can be used on smaller airfields, to relay whether the plane is above, below, or on the glide slope.
The smaller number of lamps used in PAPI lights can save on maintenance and running costs – and in general, VASI lights should be replaced over time, or more immediately as a matter of preference.
This article was originally published by ATG Airports.
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