Definition
G/S is the vertical guidance component of an Instrument Landing System (ILS). It transmits a narrow radio beam, typically angled about 3 degrees upward from the runway touchdown zone, that an aircraft follows down to the runway during an instrument approach. On a flight director display, the G/S indication shows the aircraft's position relative to this descent path.
Plain English
G/S is the radio signal that tells a pilot whether they are on the correct downward angle to land. If the aircraft drifts above or below the proper descent path, the G/S indicator shows it, and the flight director cues the pilot to correct.
Context Anchor
Seen on flight director and instrument approach displays during an ILS approach, where it provides vertical guidance for the descent.
Derivation
From 'glide,' meaning a steady controlled descent without added power, and 'slope,' meaning an inclined path. Together it describes the angled descent path the aircraft glides along to reach the runway.
Why Pilots Care
Following the G/S keeps the aircraft clear of obstacles and aligned for a safe landing on the intended runway surface.
Intuition Check
G/S here does not mean groundspeed. In this flight director context, G/S means glideslope: vertical guidance for the approach.
Example Sentence 1
Once established on the localizer, the pilot intercepted the G/S and began a stable descent toward the runway.
Example Sentence 2
When the G/S signal was lost, the crew executed a missed approach.