PAPI

PAPI (Precision Approach Path Indicator) is a visual aid consisting of four light units positioned beside the runway that provide glide slope guidance to pilots on approach. Each unit shows either red or white depending on the aircraft angle relative to the desired approach path.

• 4 white lights = too high
• 3 white, 1 red = slightly high
• 2 white, 2 red = on correct path
• 1 white, 3 red = slightly low
• 4 red lights = too low

The standard PAPI glide path angle is 3 degrees. PAPI is visible from 3-5 miles during the day and up to 20 miles at night. A two-unit version is called APAPI (Abbreviated PAPI).