Definition
A satellite-based augmentation system (SBAS) developed by the FAA that improves the accuracy, integrity, and availability of GPS signals across a wide geographic area. WAAS uses a network of ground reference stations to monitor GPS satellite signals, calculate corrections for errors such as ionospheric delay and satellite clock drift, and broadcast those corrections to aircraft via geostationary satellites. The result is GPS positioning precise enough to support instrument approaches with vertical guidance down to LPV minimums, often as low as 200 feet above the runway.
Plain English
A system that makes regular GPS much more accurate and trustworthy for flying. Ground stations watch the GPS satellites, work out any small errors, and send corrections up to the aircraft so the pilot can rely on GPS for precise approaches, including ones with vertical guidance down to near the runway.
Context Anchor
Pilots encounter WAAS when using an approved GPS navigator, especially when selecting or flying GPS-based instrument approaches.
Derivation
Augmentation' comes from the Latin augmentare, 'to increase' or 'add to.' WAAS literally adds to GPS — it doesn't replace it. The 'wide area' part distinguishes it from local systems (like GBAS) that cover only a single airport; WAAS covers most of North America from one network.
Why Pilots Care
Enables LPV approaches with vertical guidance at thousands of airports that lack traditional ILS equipment, increasing access to precision landings and improving safety.
Grounding Statement
WAAS is best pictured as a correction layer added on top of GPS so the aircraft receiver has a more accurate and more closely checked position.
Intuition Check
WAAS is not a separate navigation system that replaces GPS. It is an added system that improves GPS for aviation use.
Example Sentence 1
Because the aircraft was equipped with a WAAS-certified GPS, the pilot was able to fly the LPV approach into the small rural airport that had no ILS.
Example Sentence 2
WAAS corrections allowed the aircraft to meet the required navigation performance for the RNAV arrival into the airport.