A visual approach slope indicator is a series of two or three sets of lights arranged around runways to aid aircraft landing. Each VASI light set has between two and 16 bulbs. The lights are designed so that when viewed from a particular angle, they appear to be either red or white. Both light sets appear white when the aircraft is too high, and this tells the pilot they need to make an altitude correction. Likewise, both sets appear red when the aircraft is too low. One set appears white and the other set appears red when the aircraft altitude is optimal.
Locate the start of the runway landing area. Some runway landing areas do not start until after a displacement threshold. Ensure landing runway start corresponds to area regulations.
Measure a position at least 10 feet (3 meters) to the runway's side. Position the first set of assembled VASI lights here. Fix to the turf per instructions. Pilot training dictates these lights mark the start of the runway. Convention puts these lights to the left of the runway from the pilot's perspective.
Measure a distance of 20 feet (seven meters) down the runway. Ensure this position is at least 10 feet (3 meters) from the runway. Position the second set of lights at this position and fix to the turf per instructions.
Mark a position 20 feet (7 meters) further down the runway from the second sets of lights. Ensure this position is at least 10 feet (3 meters) from the runway. Install a third set of VASI lights here and fix to the turf per instructions.
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