The visual approach slope indicator (VASI) is a system of

light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 t ...

s on the side of an airport

runway According to the International Civil Aviation Organization (ICAO), a runway is a "defined rectangular area on a land aerodrome prepared for the landing and takeoff of aircraft". Runways may be a man-made surface (often asphalt, concrete ...

threshold that provides visual descent guidance information during approach. These lights may be visible from up to during the day and up to or more at night. Basic visual approach slope indicators consist of one set of lights set up some from the start of the runway. Each light is designed so that it appears as either white or red, depending on the angle at which it is viewed. When the pilot is approaching the lights at the proper angle, meaning the pilot is on the glide slope, the first set of lights appears white and the second set appears red. When both sets appear white, the aircraft is too high, and when both appear red it is too low. This used to be the most common type of visual approach slope indicator system; however, it is being phased out and replaced by

precision approach path indicator A precision approach path indicator (PAPI) is a visual aid that provides guidance information to help a pilot to acquire and maintain the correct approach (in the vertical plane) to an airport or an aerodrome. It is generally located on the left- ...

s (PAPIs), which are closer together and therefore more efficient to sight and maintain. A mnemonic to remember the colors and their meaning is: : White over White, you're high as a kite / you'll fly all night / check your height / you're out of sight : Red over White, you're alright. : Red over Red, you're dead. : White over Red, unsaid / you're under head / you land on your head. ("White over red" isn't actually possible unless the VASI installation is badly off, the white and red filtered glasses on the lights were fitted upside down by accident, or else if the pilot is accidentally flying upside-down on final.)

Pulsating VASI

The pulsating visual approach slope indicator (PVASI) is a system similar in purpose to a VASI, but only consists of one piece of equipment. It indicates the pilots height on approach with a mix of red and white, steady and pulsating light. Pulsating white light indicates that the aircraft is too high, whereas steady white indicates being on glide path. Steady red light is meant to show a position only slightly below glide path, with pulsating red light being indicative of a position well below glide path. This type of system is less prevalent than other visual glide slope indicators like regular VASIs or PAPIs, as of May 2022 there were only 84 PVASIs installed at 51 airports and heliports in the United States and its territories according to

Federal Aviation Administration The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic ...

data, compared to 6730 PAPIs and 623 VASIs.{{Cite web , title=Airport Data and Information Portal , url=https://adip.faa.gov/agis/public/#/public , access-date=2022-05-09 , website=adip.faa.gov , publisher=

References

FAA Aeronautical Information Manual, Chapter 2 (Aeronautical Lighting and Other Airport Visual Aids), Section 1 (Airport Lighting Aids)

External links

FAA Aeronautical Information Manual
Airport lighting Optical communications fr:Vasi

Pulsating VASI

See also

References

External links