tricolor visual approach slope indicator

A system of lights to indicate the correct glide slope when making an approach to a runway. It consists of a single light unit projecting a three-color visual approach path. The below–glide path indication is red, the above–glide path indication is amber, and the on–glide path indication is green. The indicator has a useful range of 1/2 to 1 mile during the day and 5 miles at night, depending upon visibility conditions. Since the tricolor VASI consists of a single light source, which could possibly be confused with other light sources, pilots should exercise care to properly locate and identify the light signal. When the aircraft descends from green to red, the pilot may see a dark amber color during the transition.

Note: When the aircraft descends from green to red, the pilot may see a dark amber color during the transition from green to red.