Figure 4-12 -- Visual approach slope indicator light units.
For more complete information on the VASI system, refer to the Aeronautical
Information Manual (AIM).
Precision Approach Path Indicator
With the Precision Approach Path Indicator (PAPI), the pilot sees a single row of either
two or four lights. PAPI lights are normally installed on the left side of the runway. PAPI
lighting configurations and meanings are depicted in Figure 4-13.
Figure 4-13 -- Precision approach path indicator.
If more lights are seen as red by the pilot, the aircraft is too low. If more lights are seen
as white by the pilot, the aircraft is too high. Navy requirements indicate that PAPI
should be installed when entire VASI systems require replacement.