How does a PAPI function?

A Precision Approach Path Indicator (PAPI) functions by helping pilots maintain a safe glide path during the landing approach. It consists of a series of lights positioned alongside the runway that project visual cues to indicate whether the aircraft is on the correct approach path.

When a pilot approaches the runway, they observe the PAPI lights, which can typically show red and white colors. If the pilot sees more white lights, it indicates that they are too high on approach, while more red lights indicate that they are too low. The goal is to see a balanced mixture of red and white lights, which signifies that the aircraft is on the ideal glide path for landing.

Utilizing the PAPI effectively is crucial for ensuring a safe landing, as it provides immediate visual feedback that can help prevent issues related to altitude during the critical phase of landing. This makes option B the correct answer. In contrast, the other options, such as indicating runway length, measuring wind direction, or indicating distance to the runway, do not describe the primary function of a PAPI.