Definition
The glideslope is the vertical guidance component of an Instrument Landing System (ILS). It transmits a narrow radio beam angled upward from the runway touchdown zone — typically at about 3 degrees — that the aircraft's instruments use to show whether it is on, above, or below the correct descent path to the runway.
Plain English
An invisible sloping radio beam aimed up from near the runway. The aircraft's instruments show the pilot whether they are flying along that slope, too high, or too low, so they can descend at the right angle to land.
Context Anchor
Seen on instrument approach charts and on cockpit instruments during an instrument landing system approach.
Derivation
From 'glide' (a smooth descent without engine power adding height) and 'slope' (an inclined line). Together: the inclined path along which the aircraft glides down toward the runway.
Why Pilots Care
Staying on the glideslope produces a stable, on-speed descent that lands the aircraft in the touchdown zone even when visibility is too low for visual guidance.
Grounding Statement
Picture an invisible sloping path leading down to the runway; the glideslope tells the pilot how closely the airplane is following that path.
Intuition Check
Glideslope does not mean the airplane is gliding without power. Here it means the vertical path or signal used to guide the descent to the runway.
Example Sentence 1
Cleared for the ILS approach, the pilot intercepted the glideslope and began a steady descent toward the runway.
Example Sentence 2
A full deflection of the glideslope needle told the crew they were well above the proper descent path and needed to correct immediately.