The
Garmin 430
 An Introduction to Aviation GPS

                   

Wide Area Augmentation System

 

What's WAAS?

WAAS stands for Wide Area Augmentation System. It is an FAA enhancement to the Global Positioning System allowing for much higher accuracy in positioning.

GPS uses a constellation of 24 orbiting satellites. WAAS monitors these satellites with  a series of ground stations in North America. Ground processing calculates very high quality updates to their timing. These updates are relayed to WAAS-enabled receivers via two satellites in geosynchronous (stationary) orbit.

Because of the increased accuracy, WAAS-enhanced GPS receivers may be used for all phases of flight. Additionally they can be used for precision approaches in much the same fashion that the radio-based ILS is used. WAAS has been designed and is being built to provide performance comparable to Category 1 ILS.

To summarize, WAAS provides several advantages. First, the geosynchronous satellites provide additional ranging signals into the WAAS enabled receiver, increasing GPS system coverage and availability. Since WAAS monitors and corrects variations in the GPS positioning, the system is much more accurate with smaller alert limits. This smaller integrity limit supports the current generation of GPS approaches, Localizer Performance with Vertical guidance (LPV). Another advantage is that it allows WAAS-equipped users to flight plan and file for alternate airfields with GPS-based approaches.