Definition
A precision approach and landing system that uses a Ground-Based Augmentation System (GBAS) to correct GPS satellite signals, providing the lateral and vertical guidance an aircraft needs to fly an approach down to the runway. A ground station near the airport monitors GPS signals, calculates corrections, and broadcasts them by VHF data link to suitably equipped aircraft, which use the corrected data to fly a defined approach path.
Plain English
GLS is a way of using GPS to fly an instrument approach. A station on the airport checks the GPS signals, fixes any small errors, and sends the corrections to the aircraft so the pilot can follow an accurate path down to the runway.
Context Anchor
Seen on approach charts, in aircraft navigation systems, and in clearances for a GLS runway approach.
Derivation
Built from GBAS (Ground-Based Augmentation System) plus 'Landing System.' 'Augmentation' means adding to or improving something — here, improving raw GPS by correcting its errors from the ground. The name tells you exactly what it does: a landing system that uses ground-based help to make GPS accurate enough for precision approaches.
Why Pilots Care
Offers an alternative to traditional ground-based systems, often supporting lower landing minimums and continued operations when other aids are unavailable.
Intuition Check
GLS is not simply ordinary GPS guidance. It uses satellite navigation together with airport ground equipment that checks and improves the signal for precision approach guidance.
Example Sentence 1
Cleared for the GLS Runway 27 approach, the crew selected the approach in the FMS and followed the guidance down to minimums.
Example Sentence 2
ATC cleared the flight for the GLS 09 when the ILS was out of service.