Definition
A satellite-based augmentation system developed by the FAA that improves the accuracy, integrity, and availability of GPS signals over a wide geographic area. WAAS uses a network of ground reference stations to monitor GPS signals, calculate correction data, and broadcast those corrections to aircraft via geostationary satellites. The result is GPS positioning accurate enough to support precision-like instrument approaches with vertical guidance down to LPV minima.
Plain English
A system that makes GPS signals far more accurate and reliable for aircraft, so pilots can fly approaches that bring them lower to the runway using GPS alone.
Context Anchor
Seen on RNAV instrument approach charts, in GPS equipment capability, and when determining which GPS-based approach minimums an aircraft is allowed to use.
Derivation
Wide Area refers to the system covering a continent-sized region rather than a single airport. Augmentation means adding to or strengthening something — in this case, strengthening the basic GPS signal by adding correction data to it.
Why Pilots Care
It provides vertical guidance on many GPS approaches, allowing lower landing minimums at airports without an ILS.
Intuition Check
WAAS is not a separate replacement for GPS. It is a system that improves GPS by adding correction and reliability information.
Example Sentence 1
Because the aircraft was equipped with a WAAS-capable GPS receiver, the pilot was able to fly the LPV approach into the small regional airport.
Example Sentence 2
With WAAS active the GPS unit displayed glidepath guidance all the way to the runway.