What is the function of a visual approach slope indicator (VASI)?

A visual approach slope indicator (VASI) is designed specifically to provide pilots with visual guidance to help them maintain the correct glide slope as they approach for landing. This system typically consists of a series of lights that indicate whether the aircraft is above, below, or on the proper glide path to the runway.

By using the colors emitted from the VASI system, pilots can visually ascertain their approach angle. For instance, a configuration often uses red and white lights, where red typically indicates that the aircraft is below the glide slope, and white indicates that the aircraft is on or above the glide slope. This tool aids significantly in ensuring a safe and stable descent, particularly during conditions where visibility may be compromised.

The other options do not pertain to the primary function of a VASI. For example, traffic patterns around an airport are managed through air traffic control and not displayed by a VASI system. Runway availability is communicated through air traffic control and airport signage, rather than being indicated by a VASI. Lastly, measuring distance to the runway is typically accomplished through systems like distance measuring equipment (DME) or GPS and is not a feature of the VASI. Thus, the contribution of the VASI remains uniquely centered on glide slope indication during the