What is the function of the VASI system during an approach?

The VASI, or Visual Approach Slope Indicator, is designed to provide pilots with visual cues about their glide path during an approach to landing. Its primary function is to indicate whether an aircraft is on the correct descent trajectory towards the runway.

When a pilot approaches a runway equipped with a VASI system, the lights are visible from a distance and change color based on the aircraft's position relative to the ideal glide path. Specifically, if the pilot is on the correct glide slope, the lights will indicate a certain color combination, representing "on glide path." If the lights show a different combination, they will indicate whether the aircraft is too low or too high. This visual feedback allows pilots to make necessary adjustments to their descent, ensuring a safe and accurate approach, which is crucial for a smooth landing.

This function is vital during instrument approaches, especially in conditions where visibility may be reduced. The VASI allows pilots to maintain the appropriate descent profile without relying solely on instruments, enhancing situational awareness. The other options, which refer to navigation guidance, wind conditions, or runway alignment, do not pertain to the specific purpose of the VASI system.