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. Pulsating white light indicates that the aircraft is too high, whereas steady white indicates being on the glide path. It indicates the pilot's height on approach with a mix of red and white, steady and pulsating light. The pulsating visual approach slope indicator (PVASI) is a system similar in purpose to a VASI, but only consists of one piece of equipment. Pilots should not mistake this area for an “above the glide path” indication. When descending below the glide path, there is a small area of dark amber. Below the glide path is indicated by red, on the glide path is indicated by green, and above the glide path is indicated by amber. AT-VASIS is an abbreviated form of T-VASIS, defined as 'ten light units arranged on one side of the runway in the form of a single wing bar of four light units with a bisecting longitudinal line of six lights.' Tri-color VASI Tri-color VASIĪ tri-color system consists of a single-light unit projecting a three-color visual approach path. T-VASIS is defined as twenty light units symmetrically disposed about the runway centre line in the form of two wing bars of four light units each, with bisecting longitudinal lines of six lights'. Simple VASIs are obsolete, having been deleted from ICAO Annex 14 in 1995, however T-VASIS and AT-VASIS are still specified. 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. 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 indicators (PAPIs), which are closer together and therefore more efficient to sight and maintain.Ī mnemonic to remember the colors and their meaning is: When both sets appear white, the aircraft is too high, and when both appear red it is too low. 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. Each light is designed so that it appears as either white or red, depending on the angle at which it is viewed. Standard VASI Standard visual approach slope indicator (circled in red) Working VASI Comparison of PAPI, VASI, and OLS meatball and datum lights (not to scale)īasic visual approach slope indicators consist of one set of lights set up some 7 metres (23 ft) from the start of the runway. 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. 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 final approach. JSTOR ( November 2012) ( Learn how and when to remove this template message).Unsourced material may be challenged and removed.įind sources: 'Visual approach slope indicator' – news Please help improve this article by adding citations to reliable sources. This article needs additional citations for verification.

Blue runway lights