Plain English Meaning

A runway light system with three rows of lights instead of two. It gives two different correct approach paths -- a lower one for normal aircraft and a higher one for big jets where the pilot sits far above the wheels.

Full Definition

A Visual Approach Slope Indicator system that uses three rows of light bars instead of the standard two, providing two distinct glide paths to the runway. The near and middle bars form a lower glide path (typically 3°) intended for most aircraft, while the middle and far bars form a higher glide path (typically 3.25°) intended for high cockpit aircraft such as wide-body jets, where the pilot's eye is far above the landing gear and a higher approach is needed to ensure adequate .