VASI (Visual Approach Slope Indicator)

A visual glidepath indicator system consisting of two sets of light bars (near and far) positioned beside the runway approach end. When on the correct approach path, the near bars appear white and the far bars appear red. If the pilot is too high, both bars appear white; if too low, both appear red. VASI provides a visual glidepath of approximately 3 degrees and is being gradually replaced by PAPI at many airports.