Plain English Meaning

The aircraft is descending at the right angle to land where it should. The VASI lights tell the pilot this with one red light above one white light.

Full Definition

The condition in which an aircraft on final approach is tracking the correct vertical descent angle to the runway touchdown zone. On a Visual Approach Slope Indicator (VASI), this is shown by the upwind (far) bar appearing red and the downwind (near) bar appearing white -- commonly described as 'red over white.'

Context Anchor

Seen during final approach, especially when using visual approach slope indicator (VASI) lights to judge whether the is , , or on the proper .