What is indicated by red lights on the VASI system?

Red lights on a Visual Approach Slope Indicator (VASI) system specifically indicate that the aircraft is too low in relation to the ideal glidepath for landing. The VASI system provides pilots with visual cues to help ensure that they approach the runway at the correct descent angle. When the pilot sees red lights, it signals that they need to increase their altitude to align with the proper glidepath for a safe landing. This is crucial for maintaining safe vertical separation during the approach phase, ensuring that the aircraft does not land too low and potentially risk a mishap or runway incursion.