Which signal do small aircraft observe when using a three-bar VASI to ensure they are on glide slope?

The correct signal for small aircraft observing a three-bar Visual Approach Slope Indicator (VASI) to confirm they are on the glide slope is one red light and two white lights.

The VASI system provides visual guidance to pilots during the approach phase of flight. In the specific case of a three-bar VASI system, the configuration of lights indicates whether the aircraft is below, on, or above the ideal glide slope.

When a pilot sees one red light and two white lights, it indicates that the aircraft is on the correct glide slope for landing. This configuration means that the aircraft is at the appropriate altitude needed to maintain a safe approach to the runway.

The other configurations of lights signify different conditions. All three white lights would indicate that the aircraft is above the glide slope, while all three red lights would indicate that it is below the glide slope. This visual system is crucial for pilots to make accurate and safe approaches to landing, ensuring proper descent rates and alignment with the runway.