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 angle is needed to ensure adequate threshold crossing height.
Plain English
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.
Context Anchor
Seen during visual approaches to a runway equipped with VASI lights, especially when the airport provides separate approach paths for different aircraft sizes.
Derivation
VASI comes from “visual approach slope indicator.” “Visual” means the pilot reads it by sight, “approach slope” means the downward path toward the runway, and “indicator” means it shows whether the airplane is on that path. In “3-bar,” “bar” means a row of lights, not one single light.
Why Pilots Care
Ensures proper glide slope clearance for larger aircraft to prevent runway excursions or structural contact.
Intuition Check
Do not read “3-bar” as three individual lights. In this term, a bar is a row of lights, and the three rows work together to show two possible descent paths.
Example Sentence 1
Approaching the runway in the Cessna, the pilot read the 3-bar VASI by looking only at the lower two bars and ignored the upper bar.
Example Sentence 2
Large transport aircraft often use the upper glide path provided by the 3-bar VASI system.