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 day and night.

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.

If an aircraft is on the correct approach path, the pilot will see two red and two white light indicators. If the aircraft approach is too high, an increased number of white light indicators will be seen. If the approach is too low, the pilot will see an increased number of red light indicators and must take corrective action to enable a safe landing in the designated part of the runway.