Precision approach path indicator ( PAPI ) is a visual aid that provides guidance information to help a pilot acquire and maintain the correct approach (in the vertical plane) to an airport or an aerodrome. It is generally located on the left-hand side of the runway approximately 300 meters beyond the landing threshold of the runway.
The ratio of white to red lights seen is dependent on the angle of approach to the runway. Above the designated glide slope a pilot will observe more white lights than red; at approaches below the ideal angle more red lights than white will be seen. For the optimum approach angle the ratio of white to red lights will remain equal throughout, for most aircraft, the exceptions being the Boeing 747 and now retired Concorde. With the 747, because the cockpit is approximately 20 feet behind the nose and much higher than other aircraft, the flight crew in a 747 will typically see one red and three white lights when they are on the glide slope. The aircrew of Concorde would see four white lights as the Concorde’s approach angle was higher than traditional aircraft.
Image for reference:-
P.S.- I am asking for this feature because I have not yet seen them in the game. Please correct me if I am wrong :)