Definition
The vertical guidance signal of an Instrument Landing System (ILS) or similar precision approach, transmitting an angled beam (typically 3 degrees) from a ground antenna near the touchdown zone that defines the correct descent path to the runway. 'Glideslope' is the term used with ILS; 'glidepath' is the equivalent term used with GLS (GBAS Landing System) and certain other precision approaches, but in everyday use the two words are treated as interchangeable.
Plain English
An invisible sloped line in the sky, sent up from the runway, that tells the pilot whether they are descending at the right angle to land. Stay on it and the descent rate is correct; drift above or below and the aircraft is too high or too low.
Context Anchor
Seen on instrument approach charts, cockpit approach guidance, and final approach descent planning.
Derivation
Glide' refers to a descending flight path with reduced power; 'slope' and 'path' both describe the angled line being followed. The two terms developed in parallel as different precision approach systems (ILS vs. GBAS) were standardized, which is why both names persist for what is essentially the same concept.
Why Pilots Care
Staying on the correct glideslope ensures proper obstacle clearance and a stable path to touchdown; deviation can lead to an unstabilized approach or missed landing.
Analogy
Think of it like an invisible ramp leading down to the runway. The aircraft is meant to stay on that ramp instead of coming in too high or too low.
Intuition Check
Do not treat glideslope and glidepath as just casual words for descending. In instrument flying, they mean a specific intended descent line, and glideslope often has the narrower meaning of an instrument landing system vertical guidance signal.
Example Sentence 1
Approaching the final approach fix, the pilot intercepted the glideslope and began a steady descent toward the runway.
Example Sentence 2
If the glidepath indicator shows full-scale deflection, the pilot must execute a missed approach.