Definition
The glide slope is the vertical guidance component of an Instrument Landing System (ILS), transmitting a narrow radio beam angled upward from the runway touchdown zone — typically at 3 degrees — that an aircraft follows down to the runway. The aircraft's ILS receiver compares its position to this beam and shows the pilot whether they are above, on, or below the correct descent path.
Plain English
An invisible angled beam of radio energy that points up from near the runway. The aircraft's instruments tell the pilot whether they are tracking that beam correctly, which keeps them on the right downward path to land.
Context Anchor
Seen on instrument approach charts, cockpit approach displays, and during instrument approaches to a runway.
Derivation
Glide refers to a controlled descent with engine power reduced. Slope refers to the angle of that descent path. Together, the term describes the angled path an aircraft glides down toward the runway.
Why Pilots Care
Maintaining the glide slope keeps the aircraft on a safe, stable descent path that clears obstacles and aligns it with the runway touchdown zone in low visibility.
Grounding Statement
Picture a steady invisible ramp leading down to the runway; the glide slope helps you stay on that ramp.
Intuition Check
“Glide” does not mean the engine is off here. A glide slope is a guided descent path used during an approach to landing.
Example Sentence 1
Once established on the localizer, the pilot intercepted the glide slope and began the descent to the runway.
Example Sentence 2
A fly-down indication on the GS means the aircraft is above the proper descent path.