Definition
A ground-based system that improves the accuracy, integrity, and availability of GPS signals in the local area around an airport. A GBAS reference station receives GPS signals, calculates corrections, and broadcasts those corrections by VHF data link to aircraft within roughly 23 nautical miles, allowing precision approach guidance down to and including Category I minimums (and, where approved, lower).
Plain English
Equipment on the ground at or near an airport that listens to GPS, works out small errors in the signals, and sends a corrected version to nearby aircraft so they can fly very accurate approaches.
Context Anchor
Seen in approach and landing procedures that use satellite-based guidance at airports equipped with this service.
Derivation
Augmentation' comes from the Latin augmentare, meaning to increase or add to. The system 'augments' raw GPS by adding correction data, making the position fix more trustworthy than GPS alone.
Why Pilots Care
It delivers ILS-like vertical and lateral guidance using GPS at airports where installing and maintaining an ILS would be impractical, expanding access to precision approaches.
Grounding Statement
Picture airport equipment at a known surveyed spot checking satellite position information and sending nearby aircraft a better, locally corrected version to use.
Intuition Check
Do not read “augmentation” as a separate replacement navigation system. Here it means the ground equipment improves and checks satellite navigation information before the aircraft uses it.
Example Sentence 1
The crew briefed a GBAS approach to Runway 28R, noting that the corrections would be received from the airport's ground station via VHF.
Example Sentence 2
After the controller cleared the flight for the GBAS approach, the crew confirmed the Ground Based Augmentation System signal was received and the approach mode armed.