PAPI Precision Approach Path Indicator
The PAPI System provides the pilot a positive visual indication of the aircraft’s position relative to the optimal glide slope during final approach to the runway.
The L-880 PAPI system consists of four units in a line or bar, each unit having two or three 200 watt lamps.
The PAPI unit produces a beam of light, the upper portion being white, the lower red. As the pilot’s vertical position changes, the color of the light as seen by the pilot changes instantaneously.
FAA: AC 150/5345-28 Current Edition: L-880 and L-881 ICAO Annex 14