VASI (Visual Approach Slope Indicator)

VASI (Visual Approach Slope Indicator) is a visual approach aid that provides glidepath guidance using two bars of lights (near and far) that appear red or white depending on the aircraft's position. It is the predecessor to PAPI and is still installed at many airports worldwide.

• White over white = too high ("white over white, you'll fly all night")
• Red over white = on glidepath ("red over white, you're all right")
• Red over red = too low ("red over red, you're dead")
• Standard 2-bar VASI provides one visual glidepath, typically 3°
• 3-bar VASI provides two glidepaths — the upper one for larger aircraft with higher eye-to-wheel height