Definition
A precision approach and landing system that uses GPS signals corrected by a ground-based augmentation system (GBAS) to guide an aircraft along a defined glidepath and centerline to a runway. A GBAS station at the airport monitors GPS signals, calculates corrections, and broadcasts them by VHF data link to aircraft on approach, producing approach guidance with accuracy comparable to an ILS.
Plain English
GLS is a way of flying a precision approach to a runway using GPS, with extra signals from a ground station at the airport to make the GPS accurate enough for landing.
Context Anchor
Seen on instrument approach charts, in aircraft navigation systems, and during approaches to runways that are approved for GLS use.
Derivation
Built from three ideas: 'Ground Based' (the corrections come from equipment on the ground at the airport), 'Augmentation' (it adds to, or improves, the basic GPS signal), and 'Landing System' (it provides guidance all the way down to the runway). Augmentation comes from Latin augere, 'to increase' — here it means making GPS more accurate and trustworthy than it is on its own.
Why Pilots Care
It enables precision approaches at airports lacking traditional ILS infrastructure, expanding safe landing options in poor weather.
Intuition Check
GLS is not the same as an ILS, and it is not simply a ground beam leading to the runway. The aircraft gets its basic position from satellites, while the airport ground station improves that position enough for approach guidance.
Example Sentence 1
The crew briefed the GLS approach to Runway 28R, noting that the procedure required an aircraft and avionics capable of receiving GBAS corrections.
Example Sentence 2
The airport added GLS capability to support lower landing minimums without installing an ILS.