An approach slope indicator system consisting of four light units situated on the left side of the runway in the form of two wing bars referred to as the upwind and downwind wing bars. The aircraft is on slope if the upwind bar shows red and the downwind bar shows white, too high if both bars show white, and too low if both bars show red. Some aerodromes serving large aircraft have three-bar VASIS, which provide two visual glide paths (GP) to the same runway. The VASIS can be situated so as to provide three types of eye-to-wheel height (EWH): V1 (10 ft), V2 (25 ft) and V3 (25 ft and 45 ft).