Definition
A flight director and autopilot mode that automatically engages when the aircraft intercepts the ILS glideslope from below, transitioning the system from altitude hold (or whatever vertical mode was active) to tracking the glideslope signal down to the runway.
Plain English
When the aircraft is flying level toward the runway and crosses the descending glideslope beam, the autopilot/flight director switches itself over and starts following that beam down for the approach.
Context Anchor
Seen on the flight director or autopilot mode display during an Instrument Landing System approach, usually as the aircraft reaches the glide path from below.
Derivation
Capture' here means the system has detected and locked onto the glideslope signal — like a sensor 'catching' the beam as the aircraft flies into it. The word emphasizes that the transition is automatic, not pilot-commanded.
Why Pilots Care
It provides precise vertical path control during instrument approaches, reducing pilot workload and improving landing accuracy in low visibility.
Intuition Check
“Capture” does not mean the airplane physically grabs anything. It means the guidance system has recognized the glide path and switched into a mode that follows it.
Example Sentence 1
After intercepting the localizer, the pilot armed the approach mode and watched for glideslope capture as the beam came alive.
Example Sentence 2
The pilot monitored the glideslope capture mode to confirm the autopilot was tracking the beam correctly before continuing the approach.