Know about PAPIs

How to read PAPI lights

A PAPI light system will consist of either two or four lights, which will either be red or white depending on the angle of the plane’s approach. This is how to read a four-light PAPI system:

Four white lights: the plane is much too high
Three white lights and one red light: the plane is slightly too high
Two white lights and two red lights: the plane is on the correct glideslope
Three red lights and one white light: the plane is slightly too low
Four red lights: the plane is much too low
A two-light PAPI system simplifies this:

Two white lights: the plane is too high
One white light and one red light: the plane is on the correct glideslope
Two red lights: the plane is too low
Although a system with four lights provides a pilot with a more granular insight into how much they need to adjust, both types will ultimately help ensure the pilot’s angle of approach is correct.