Precision Approach Path Indicator
As an additional aid to a precision approach, glide path guidance is provided during the visual phase (after DH) by the PAPI lighting system.
This consists of 4 light units showing either red or white light through precision defined angles.
Each light unit is set to a different mid angle and below that angle shows red and above shows white. The overall effect is to give a reference to the median angle which is set to the required glide path (e.g. 3°).
ICAO define PAPI as “A wing bar of 4 lights uniformally spaced”.
