The helicopter Visual Approach Slope Indicator (VASI) is a system of lights on the side of an airport runway threshold that provides visual descent guidance information during approach. These lights may be visible from up to 8 kilometres (5.0 mi) during the day and up to 32 kilometres (20 mi) or more at night. was developed as a landing aid for helicopter flight. It is specially designed to accommodate the helicopter’s steep angles of descent and deliberate speeds.
Three Color Design
Three wide horizontal beams of different colored light are projected in fan shaped array into the incoming flight pattern. The top beam (yellow) indicates a too high altitude of approach. The center beam (green) is the correct altitude and the lower beam (red) is a too low altitude. By staying within the green (correct altitude) light beam, the correct slope is maintained to touchdown. An ideal control for training students.
Normal Beam Dimensions
At a distance of one half mile: the green beam (correct altitude) is 300 feet high; the yellow beam (too high altitude) is 565 feet high; the red (too low) beam is 265 feet high. All of the three beams are 900 feet wide, on each side of vertical. The dimensions of this pyramid shaped cone of colored beams may be varied and ordered to accommodate special landing problems. Special color arrangements such as red on top, clear in the center and red of the bottom, are also available.
Visibility
Optical elements, combined with special color filters, provide clear color visibility. The VASI may be seen for up to one half-mile in daylight and up to one mile at night.
Height Settings
The VASI is easily adjusted. Normal height settings for the bottom of the green (correct altitude) beam range from 0° to as high as 15°. A 1/2° vernier scale provides accurate positioning. Heavy pressure screws are provided to secure the settings in place.
Light Source
The VASI has an energy efficient LED light source. The VASI is powered by 120 VAC or it may be ordered to operate from other inputs, if desired.
Installation and Maintenance
The VASI is normally placed on the border of the landing area on the near side, facing into the landing pattern. It has a low profile, being 12 inches high, 8 inches wide and 16 inches long and is constructed of heavy cast aluminum that is weathertight and finished in orange polyester powder coating.
