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Visual Approach Slope Indicator (VASI)

Visual Approach Slope Indicator (VASI)

  • VASI installations are the most common visual glide path systems in use.
  • The VASI provides obstruction clearance within 10° of the runway extended runway centerline, and to four nautical miles (NM) from the runway threshold.
  •   The VASI consists of light units arranged in bars.
  •  There are 2-bar and 3-bar VASIs. The 2-bar VASI has near and far light bars and the 3-bar VASI has near, middle, and far light bars.
  • Two-bar VASI installations provide one visual glide path which is normally set at 3°.
  • The 3-bar system provides two glide paths, the lower glide path normally set at 3° and the upper glide path. degree above the lower glide path.
  • The basic principle of the VASI is that of color differentiation between red and white.
  •  Each light unit projects a beam of light, a white segment in the upper part of the beam, and a red segment in the lower part of the beam. The lights are arranged so the pilot sees the combination of lights shown in to indicate below, on, or above the glide path.

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