What should a pilot do if they see all red lights on a VASI during descent?

If a pilot observes all red lights on a VASI (Visual Approach Slope Indicator) during descent, the appropriate action is to ascend immediately. The all-red configuration indicates that the aircraft is below the optimal glide slope for landing. This signals to the pilot that they are too low, which could lead to terrain or obstacle conflicts. By ascending, the pilot can return to a safe altitude that aligns with the proper glide slope, ensuring safety during the approach to landing.

This action is crucial because maintaining the correct glide slope is essential for a safe and stable approach. The VASI serves as a visual aid to help pilots maintain the correct descent profile. Seeing all red lights suggests a dangerous situation that needs immediate correction to prevent potential accidents.