Definition
A precision approach and landing system that uses GPS signals corrected and enhanced by a ground station at the airport. The ground station measures errors in the GPS signals it receives and broadcasts correction data to aircraft on a VHF datalink, allowing them to fly precise approaches comparable to a Category I, II, or III ILS without needing the traditional ground-based localizer and glideslope transmitters.
Plain English
A landing system that takes regular GPS signals, fixes the small errors in them using a ground station at the airport, and sends those corrections to your aircraft so you can fly an accurate approach all the way down to the runway.
Context Anchor
Seen in flight plan equipment codes, aircraft equipment descriptions, avionics approach selections, and some instrument approach procedures.
Derivation
Ground-Based because the correction equipment is installed on the airport, not on a satellite. Augmentation because it adds to (augments) the standard GPS signals to make them accurate enough for landing. The result is a system that does the job of an ILS using GPS as its foundation.
Why Pilots Care
It supports precision approaches at airports that lack an ILS, increasing landing options in low visibility.
Analogy
Imagine a small local helper station on the airport grounds that constantly checks the satellites and whispers corrections to the plane so its GPS becomes accurate enough to land by.
Intuition Check
Do not read “landing system” as meaning the airplane lands itself. GBAS landing system provides precise guidance; the pilot or approved aircraft automation still flies and manages the approach.
Example Sentence 1
The crew briefed the GLS approach, confident the GBAS landing system would provide ILS-equivalent guidance to the runway.
Example Sentence 2
On the approach briefing the crew verified that the GBAS landing system was providing guidance to the runway threshold.