Definition
A local-area system that improves the accuracy, integrity, and availability of GPS signals for aircraft operating in the vicinity of an airport. A ground station at the airport receives GPS signals, compares them against its own precisely surveyed position, calculates correction data, and broadcasts those corrections by VHF data link to suitably equipped aircraft. The corrected signals are accurate enough to support precision approaches and landings.
Plain English
A system on the ground at an airport that listens to GPS signals, works out small errors, and sends corrections to aircraft nearby so their GPS becomes accurate enough to fly precision approaches.
Context Anchor
Seen in discussions of satellite navigation, instrument approaches, and airport landing systems that use ground equipment to improve satellite guidance.
Derivation
Ground-Based means the correction equipment sits on the ground at the airport, not in space or aboard the aircraft. Augmentation comes from the Latin augmentare, 'to increase or add to' -- the system adds to the raw GPS signal to make it more accurate. Together: a system on the ground that adds to GPS to make it usable for precision flying.
Why Pilots Care
It enables GPS-guided approaches with vertical guidance down to decision heights as low as 200 feet, allowing precision landings at airports that lack traditional ILS installations.
Grounding Statement
Picture ground equipment at the airport checking the same satellite signals your aircraft is using, then sending your aircraft small corrections and a warning if the signal is not safe to rely on.
Intuition Check
Ground-based does not mean the aircraft is navigating only by ground signals. Here it means ground equipment is improving satellite navigation for the aircraft.
Example Sentence 1
The airport's GBAS allowed the crew to fly a GPS-based precision approach with accuracy comparable to an ILS.
Example Sentence 2
With Ground-Based Augmentation System service available, the aircraft could fly a stabilized descent to the runway without needing an ILS signal.