In a Tricolor VASI system, what does a red light signify?

In a Tricolor VASI (Visual Approach Slope Indicator) system, a red light signifies that the aircraft is below the glideslope. This color scheme is designed to provide pilots with an immediate visual indication of their vertical position relative to the ideal approach path.

When the pilot sees a red light, it indicates that they need to climb in order to reach the proper descent angle for landing. This is important for ensuring that the aircraft approaches the runway in a safe manner, avoiding obstacles that might be in the way when below the designated glide path.

In contrast, a white light would indicate that the aircraft is on or above the glideslope, which suggests that no corrective action is needed for the vertical position unless further adjustments for final approach are necessary. Understanding this color-coding helps pilots navigate safely and effectively during the critical phases of approach and landing.