The visual approach slope indicator (VASI) is a system of lights on the side of an airport runway threshold that provides visual descent guidance information during approach. These lights may be visible from up to 8 kilometres (5.0 mi) during the day and up to 32 kilometres (20 mi) or more at night.
Basic visual approach slope indicators consist of one set of lights set up some 7 metres (23 ft) 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 from. 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 by Precision approach path indicators (PAPIs), which are closer together and therefore more efficient to site 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
Red over White, you're alright.
Red over Red, you're dead.
White over Red, unsaid / you're under head. ("White over red" isn't actually possible unless the VASI installation is badly off, or else if you're upside down on final.)
Video Visual approach slope indicator
See also
- Leading lights, similar aid to navigation
- Pilot controlled lighting (PCL)
- Precision approach path indicator (PAPI)
- Runway end identifier lights (REIL)
- Runway edge lights (HIRL, MIRL, LIRL)
- Approach lighting system (ALS)
Maps Visual approach slope indicator
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
Source of the article : Wikipedia
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