The visual approach slope indicator (VASI) and precision approach path indicator (PAPI) are light systems on the side of a runway threshold that provide visual descent guidance information during approach. Here are the particulars of the different types of path-lighting systems:
Everything Explained: VASI Light Systems
Key Takeaways:
- Visual approach slope indicators (VASI, PAPI, Tricolor, Pulsating) provide critical visual descent guidance for aircraft approaching a runway, typically establishing a 3-degree glidepath and ensuring obstruction clearance within 4 nautical or statute miles.
- VASI systems offer one or two glidepaths (the latter for high-cockpit aircraft) and are visible from 3-5 miles during the day, while PAPI systems use a single row of lights with similar visibility.
- More specialized systems include Tricolor, which uses red, green, and amber lights for path indication with a shorter range (up to 5 miles at night), and Pulsating (PVASI/PLASI) systems, which use steady or pulsating white/red lights whose rate indicates deviation from the ideal glidepath, offering a useful range of up to 10 miles at night.
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