VASI

VASI (Visual Approach Slope Indicator) is a system of lights beside the runway that provides visual descent guidance to pilots on approach. VASI typically uses two sets of light bars:

• White over white: Too high
• Red over white: On correct path (3 degrees)
• Red over red: Too low

VASI has been largely replaced by PAPI at most airports, as PAPI provides more precise guidance. However, VASI installations still exist at many airports worldwide.