Airport Visual Approach Slope Indicator Lighting

An airport lighting facility providing vertical visual approach slope guidance to aircraft during approach to landing by radiating a directional pattern of high intensity red and white focused light beams which indicate to the pilot that he is "on path" if he sees red/white, "above path" if white/white, and "below path " if red/red. Some airports serving large aircraft have three-bar Visual Approach Slope Indicators (VASI) which provide two visual glide paths to the same runway. (FAA4)