Definition
A cockpit instrument display, typically a horizontal needle on the course deviation indicator, that shows the aircraft's vertical position relative to the published glideslope of an Instrument Landing System (ILS) approach. The needle deflects up when the aircraft is below the glideslope and down when above, with the centered position indicating the aircraft is on the correct descent path to the runway.
Plain English
A needle in the cockpit that tells you whether you are too high, too low, or right on the correct downward path to the runway during an instrument approach.
Context Anchor
Seen on navigation instruments during instrument approaches, especially when flying an ILS approach to a runway.
Derivation
Glideslope combines glide (a steady descent without engine power thrust producing climb) and slope (an inclined surface or path). Indicator comes from Latin indicare, to point out. Together it is the instrument that points out where the aircraft sits on the sloping descent path to the runway.
Why Pilots Care
Keeps the descent path stable so the aircraft touches down at the right point on the runway instead of landing short or floating long.
Intuition Check
The glideslope indicator does not show how far you are from the runway. It shows whether you are vertically above, below, or on the descent path.
Example Sentence 1
As the glideslope indicator came alive, the pilot reduced power and began the final descent toward the runway.
Example Sentence 2
Keeping the glideslope indicator centered all the way to the runway produced a smooth touchdown in low ceilings.