Pronunciation: [vˈasi] (IPA) 
The word "VASI" is spelled with the letters V-A-S-I. In phonetic transcription, it is pronounced as /væsi/. The V sound is made by putting your top teeth on your bottom lip and blowing out, while the A sound is made by opening your mouth wide and making a short "ah" sound. The S sound is made by putting your tongue against your top teeth and hissing, and the I sound is made by raising your tongue to the roof of your mouth and saying "ee".
VASI stands for Visual Approach Slope Indicator. It is a navigational aid primarily used in aviation to assist pilots during the approach and landing phase of a flight. The VASI system helps pilots maintain the correct glide path to ensure a safe and accurate landing.
The VASI consists of a series of lights positioned on the side of the runway. These lights are typically white, although some installations may include red lights as well. The lights are arranged in two distinct sets: the upper set and the lower set. The upper set represents an optimal glide path for landing, while the lower set indicates a glide path that is too low.
Pilots approaching the runway should strive to see a combination of lights: two white lights and two red lights. This indicates that the aircraft is on the correct glide path. If the lights appear predominantly red, it indicates a low approach and the pilot should adjust the aircraft's altitude accordingly. Conversely, if the lights appear predominantly white, it indicates a high approach and the pilot should lower the aircraft's altitude.
The VASI system offers a visual reference to pilots, enabling them to make precise adjustments to their aircraft's flight path. It is especially useful during low visibility conditions, such as fog or low ceilings. By following the VASI guidance, pilots can ensure a safe and accurate approach and landing.
