Approach Lights (SBFT)
The PAPI (Precision Approach Path Indicator) is used as a visual guide,
which provides approach path guidance for non-precision approach runways.
These lights are visually seen at least 3 miles during the daylight hours
and up to 20 miles during the night. These lighting systems are arranged
in a horizontal row of four lights, which are located on the left side of the runway.
The VASI (Visual Approach Slope Indicator) is very similar to the PAPI, which also provides approach slope guidance. The VASI lights are arranged as a two bar lighting system. They can also, be seen 3 miles during the daylight hours and up to 20 miles during the night.
When on an approach path using a PAPI or slope with a VASI, either lighting system will indicate two white and two red, which is usually a 3-degreeapproach path, but not always the case. Some airports may have a much steeper approach path, such as at Steamboat Springs, CO (KSPS) which has a 7.75-degree approach path due to terrain. Other light combinations will indicate when either slightly high/low or even, too high or too low. The more white lights you see the higher you are, and the more red lights you see the lower.
If you are on final approach to land at any airport, and you as the pilot are
referencing the PAPI or VASI to insure safe obstacle clearance. You just begin
to see the on glide path or on approach slope lights. Then suddenly you notice one
of the lights is indicating incorrectly, for an example one red one white two red
lights or vice versa. As goes for a VASI lighting system.
Day or night
Weather – n/a
What has happened? What should you do?
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As good practice, pilots should utilize either lighting system. PAPI’s and VASI’s are a good safe visual reference and should be used when available to avoid ground obstacles such as trees, power lines, etc. especially during night flights, hazy VFR conditions or other optical illusions.