PAPI (Precision Approach Path Indicator)

It is a system of lights that are placed on the sides of the landing / takeoff runway. It consists of light boxes that provide a visual indication of an aircraft's position on the approach path associated with a particular landing/takeoff runway.

 

The approach paths vary depending on the conditions and situation of the runway, being a common value 3º.

The system consists of 4 lamps that emit a beam of light with two segments each of one colour, white (upper), red (lower).

 

The defined combinations are:

All four white lights: The aircraft is well above the path determined by the indicator.

Three white lights and one red: the aircraft is slightly above the trail.

Two white lights and two red lights: the aircraft is on the correct approach path.

Three red lights and one white: the plane is flying slightly low.

Four red lights: the plane is flying very low and must climb.