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Check to see if a visual or electronic glide slope is available before departing to your
destination. Although visual glide slope indicators are installed at most airports, it is
important to note that they may be installed at only one runway end. Also, there are many
variations. Some of the not-so-common indicators include the Tricolor System, Pulsating
System,Alignment of Element System, and the Three-bar VASI.
- Tri-color System. Tri-color visual approach slope indicators normally
consist of a single light unit projecting a three-color visual approach path into
the final approach area of the runway upon which the indicator is installed.
The below glide path indication is red, the above glide path indication is amber,
and the on glide path indicator is green. These types of indicators have a useful
range of approximately one-half to one mile during the day and up to five miles at night.
Note: Since the tri-color VASI consists of a single light source which could
possibly be confused with other light sources, pilots should exercise care to properly
locate and identify the light signal.
- Pulsating Systems. Pulsating visual approach slope indicators normally
consist of a single light unit projecting a two color visual approach into the final
approach area of the runway upon which the indicator is installed. The on-glide path
indication is a steady white light. The slightly below-glide path indication is a steady
red light. If the aircraft descends further below the glide path, the red light
starts to pulsate. The above glide path is a pulsating white light. The pulsating rate
increases, as the aircraft gets further above or below the desired glide slope. The useful
range of this system is about four miles during the day and up to ten miles at night.
- Alignment of Element Systems. Alignment of elements systems are installed on
some small general aviation airports and are a low-cost system consisting of painted panels,
normally black, white or fluorescent orange. Some of these are lighted for night use. The
useful range of these systems is about three-quarters of a mile.
- Three-bar VASI. Three bar VASI installations provide two visual glide paths.
The lower glide path is normally set at three degrees while the upper glide path, provided
by the middle and far bars, is normally 1/4 degree higher. The higher glide path is intended
for use only by high cockpit aircraft (Boeing 747,DC10) to provide a sufficient threshold
crossing height.
Note: Although normal glide path angles are three degrees, angles at some
locations may be as high as 4.5 degrees to give proper obstacle clearance. Pilots
of high performance aircraft are cautioned that use of VASI angles in excess of 3.5
degrees may cause an increase in runway length required for landing and rollout. |
