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.'
Plain English
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.
Context Anchor
Seen during final approach, especially when using visual approach slope indicator (VASI) lights to judge whether the airplane is high, low, or on the proper descent path.
Derivation
Glide comes from an old word meaning to move smoothly. Path means a route or way to follow. Together, glidepath means the smooth downward route an airplane is meant to follow toward the runway.
Why Pilots Care
Staying on glidepath keeps the aircraft clear of obstacles, ensures the proper touchdown point, and provides enough runway remaining to stop safely.
Grounding Statement
With a VASI, the usual red-over-white light pattern tells the pilot the airplane is on glidepath.
Intuition Check
Do not read “on glidepath” as simply “pointed at the runway.” It means the airplane is at the correct height on the descent path, not just lined up horizontally.
Example Sentence 1
Crossing the threshold, the VASI showed red over white, confirming we were on glidepath.
Example Sentence 2
Once the airplane was on glidepath, the pilot maintained a steady descent rate until touchdown.