Definition
A precision instrument approach that uses a Ground-Based Augmentation System (GBAS) to provide GPS corrections and integrity data to the aircraft, enabling lateral and vertical guidance to a runway with accuracy comparable to an ILS. A single GBAS ground station at an airport supports GLS approaches to multiple runways by broadcasting correction signals via VHF data link to suitably equipped aircraft.
Plain English
A landing approach where the airplane follows GPS-based guidance to the runway, with a ground station at the airport sending corrections that make the GPS accurate enough to fly down to landing minimums.
Context Anchor
Seen on instrument approach charts, in avionics approach menus, and in FAA material discussing GBAS approach operations.
Derivation
GLS originally stood for GNSS Landing System (GNSS = Global Navigation Satellite System). It was renamed GBAS Landing System to make it clear that the precision comes from the ground-based augmentation, not from the satellites alone. Knowing this helps explain why the ground station at the airport is what makes the approach possible.
Why Pilots Care
It provides a precision landing option at airports without traditional ILS infrastructure, expanding access in low-visibility conditions while maintaining high accuracy.
Intuition Check
A GLS approach is not just any GPS-based approach. It specifically uses airport-based GBAS equipment to improve the satellite guidance for that runway.
Example Sentence 1
The crew briefed the GLS approach to Runway 28R, noting that they would tune the GBAS channel rather than an ILS frequency.
Example Sentence 2
After the GBAS station uplink, the aircraft captured the GLS approach path and continued to a stabilized landing.