If a pilot sees "red and white" on a VASI, what does it mean?

Seeing "red and white" on a Visual Approach Slope Indicator (VASI) means the pilot is on the glide slope. The VASI provides visual guidance to pilots during their approach to landing, helping them to align properly with the runway's centerline and maintain the appropriate vertical descent rate. The specific color indication of "red and white" signifies that the aircraft is at the correct altitude for a safe landing.

In practice, the VASI typically has two or four light elements, which change colors according to the aircraft's position relative to the ideal glide slope. When the lights are displaying red and white, it indicates that the aircraft is neither too high nor too low, but rather precisely aligned with the glide path – a crucial factor for a successful and safe approach to landing.

Understanding the VASI signals is essential for pilots as it directly impacts their approach and landing safety. The other options relate to different scenarios regarding the aircraft's position on the glide slope, but "red and white" specifically denotes correct positioning.