Definition
An area navigation instrument approach procedure that uses GPS satellite signals corrected by the Wide Area Augmentation System (WAAS) to provide lateral and, where published, vertical guidance to a runway. WAAS corrections improve GPS accuracy and integrity enough to support approaches with vertical guidance, including LPV and LNAV/VNAV minima, in addition to lateral-only LNAV minima.
Plain English
It is an instrument approach flown using GPS, where extra correction signals from ground stations make the GPS signal accurate enough to follow a published path down to the runway, often with both side-to-side and up-and-down guidance.
Context Anchor
Seen on RNAV (GPS) approach charts and in instrument flying when selecting the correct approach type and minimums in a WAAS-capable GPS unit.
Derivation
RNAV stands for area navigation, meaning the aircraft can fly a direct path between any two points rather than following ground-based navigation stations. WAAS stands for Wide Area Augmentation System, a network of ground stations that monitor GPS signals and broadcast corrections through geostationary satellites. Together the term describes a GPS approach made more accurate and reliable by these corrections.
Why Pilots Care
It provides precision-approach capability at thousands of runways that have no ILS, raising safety margins and airport access in low visibility.
Grounding Statement
Think of WAAS as an added correction and checking service that helps the GPS navigator know more precisely where the airplane is during the approach.
Intuition Check
WAAS does not turn every GPS approach into a precision approach. It only allows the pilot to use the WAAS-supported minimums that are published and available for that approach.
Example Sentence 1
With a WAAS-capable navigator on board, the pilot briefed the RNAV (GPS) approach using WAAS to Runway 27 and selected the LPV minima line.
Example Sentence 2
With the aircraft WAAS-equipped, the crew flew the published glidepath on the RNAV (GPS) approach using WAAS down to the published minimums.