Allows the pilot to establish and maintain an exact glide path to the runway for the final landing approach phase, right to the touchdown point during daytime and nighttime.

The system consists of four light units equally spaced at the side of the runway, adjacent to the origin of the glide path. The nominal glide slope angle is midway between the central pair of the four units. The PAPI emits two high powered beams of light, the lower part is red and the top part white.