What is the function of a Precision Approach Path Indicator (PAPI)?

The Precision Approach Path Indicator (PAPI) primarily serves to guide pilots during their approach to the runway. It does this by providing visual cues that indicate whether the aircraft is on the correct glide path for landing. The PAPI consists of a series of lights positioned alongside the runway, typically either four or two light units. The colors of the lights change based on the aircraft's altitude in relation to the prescribed approach angle.

When the pilot sees a certain combination of red and white lights, it indicates whether they are too high, too low, or on the correct path for a safe landing. This is crucial for maintaining proper approach angles, ensuring not just successful landings but also enhancing safety by improving pilots' situational awareness during critical phases of flight. Thus, while the other options may provide valuable information in their contexts, the specific function of the PAPI is to assist pilots in maintaining the correct descent path during the approach to land.