Wide Area Augmentation System (WAAS)

The Wide Area Augmentation System
FAA Photo

The Wide Area Augmentation System (WAAS) is perhaps the most valuable tool for pilots today. Currently, it is the most precise location-providing service available in North America. The Federal Aviation Administration (FAA) has teamed with the Department of Transportation (DOT) to implement the WAAS throughout the aviation industry, making flying more efficient and safe for users.

What is WAAS? 

WAAS is an abbreviation for Wide Area Augmentation System, which is a fancy way of saying it's a system that uses widely-spaced ground stations to correct satellite ambiguities, improving upon the already-precise satellite system in North America.

With satellite errors corrected, users can increase location accuracy, putting WAAS-enabled operations within FAA limits for certain navigational uses -- specifically, precision instrument approach procedures.

What's Wrong With Regular Old GPS?

Regular old GPS is a great navigational aid. In fact, GPS is probably the most error-proof NAVAID on the market. Yet the system, like all systems, has its insufficiencies.

GPS data is vulnerable to a few different errors, including timing errors, disturbances from the ionosphere and satellite orbit errors. These errors aren't likely to cause many significant problems, but they are the reason that regular old GPS signals aren't accurate enough for use with precision instrument approaches.

Typical GPS alone doesn't meet the FAA's requirements for both vertical and horizontal navigational accuracy for precision approach procedures. A GPS with WAAS capabilities, however, exceeds those accuracy standards, making it possible for pilots to fly a precision approach with a WAAS-enabled GPS receiver.

How Does WAAS Work?

The wide area augmentation system uses 25 ground-based stations across the United States to monitor satellites. There are two Wide Area Master Stations and 23 Wide Area Reference Stations.

Satellite data is collected at the reference stations and sent to a master station. At the master station, that regular old GPS data is augmented and corrected.

This adjusted data is sent back to the stationary satellites through an uplink station, where it is broadcast to WAAS-enabled GPS receivers as position data.

Practical Use of WAAS

The main benefit to the wide area augmentation system is greatly improved accuracy. Traditional GPS is accurate to 15 meters. WAAS-enabled GPS accuracy is less than three meters 95 percent of the time.

Along with accuracy comes the ability to utilize Localizer Performance with Vertical Guidance (LPV) approaches, making the national airspace system more efficient altogether. With WAAS abilities, aircraft that might otherwise be required to fly to an alternate location in low visibility now have the ability to land with lower weather minimums utilizing an LPV approach, which means fewer delays and lower costs overall.

Improved accuracy also creates the opportunity for lower separation minimums and more direct routes for aircraft.

Finally, with WAAS in use at many airports nationwide, a large amount of money can be saved on equipment cost alone. Traditional radio navigation aids, such as the ILS and MLS require expensive equipment and costly maintenance to operate. With new precision approaches available with WAAS, such as the LPV approach, older navigational equipment like VORs will no longer be necessary to install or maintain.

As a part of the FAA's NextGen program, LPV approaches are currently available at about 3,000 airports. LPV approaches will be available at all remaining eligible runways by 2016.