Wide Area Augmentation System (WAAS)
The Wide Area Augmentation System (WAAS) is a satellite-based augmentation system (SBAS) operated by the FAA that improves the accuracy and integrity of GPS signals across North America. WAAS uses a network of ground reference stations to measure GPS errors and upload correction data to WAAS geostationary satellites, which broadcast the corrections to WAAS-capable GPS receivers.
WAAS and LPV Approaches
WAAS provides GPS accuracy of approximately 1 metre or better horizontally. This enables LPV (Localizer Performance with Vertical guidance) approaches — GPS-based precision approaches with decision heights as low as 200 ft and visibility as low as ½ SM, comparable to a CAT I ILS. LPV approaches are available at thousands of Canadian aerodromes, many of which never had an ILS.
WAAS Coverage in Canada
WAAS coverage extends across Canada south of approximately 60°N. North of 60°N, WAAS signals may be degraded or unavailable due to the geometry of the geostationary satellites relative to the high-latitude receiver. In these areas, LNAV minimums (GPS without vertical guidance) are the applicable approach type.
On the TC Written Exam
WAAS enables LPV approaches, which provide ILS-equivalent precision at GPS-equipped aerodromes. Know: WAAS improves GPS accuracy; WAAS-certified receivers are required for LPV; WAAS coverage diminishes at high latitudes.