Definition
A flight director and autopilot mode that captures and tracks the glideslope signal of an ILS (Instrument Landing System), commanding the pitch needed to follow the published descent path to the runway. Once armed, the system automatically captures the glideslope as the aircraft intercepts it from below and then flies the descent guidance until disengaged or until the approach is completed.
Plain English
A mode where the autopilot or flight director takes over the up-and-down part of an ILS approach, keeping the aircraft on the correct descent angle to the runway.
Context Anchor
Seen on the flight director or autopilot mode display during an ILS approach.
Derivation
“Glideslope” combines glide (a steady descent without added power) and slope (an angled path). The mode is named after the radio beam it follows — an angled signal, typically about 3 degrees, projected upward from beside the runway.
Why Pilots Care
Provides precise vertical guidance needed for safe landings in low visibility or at night.
Intuition Check
Do not read G/S here as groundspeed. In this flight director context, G/S means glideslope guidance for descending toward the runway.
Example Sentence 1
After intercepting the localizer, the crew watched the flight director annunciate G/S as the aircraft captured the glideslope and began the descent to the runway.
Example Sentence 2
With G/S mode engaged the flight director commanded a steady descent rate that kept the aircraft on the proper approach path.