Three-bar VASIs provide two visual glidepaths. The lower glidepath is provided by the near and middle bars and is normally set at 3 degrees; the upper glidepath, provided by the middle and far bars, is normally 0.25 degrees higher. This higher glidepath is intended for use only by high-cockpit aircraft to provide a sufficient threshold crossing height. Although normal glidepath angles are 3 degrees, angles at some locations may be as high as 4.5 degrees to give proper obstacle clearance. This system provides safe obstruction clearance within ±10 degrees of the extended runway centerline and 4 nm from
the runway threshold.