WAAS User Segment

WAAS
Title	WAAS User Segment
Author(s)	GMV.
Level	Basic
Year of Publication	2011

The Wide Area Augmentation System (WAAS) is the United States Satellite Based Augmentation System. The programme, started in 1992, is being carried out by the Federal Aviation Agency (FAA) and is specially developed for the civil aviation community. The system, which was declared operational in late 2003, currently supports thousands of aircraft instrument approaches in more than one thousand airports in USA and Canada. WAAS service area includes CONUS, Alaska, Canada and Mexico. The WAAS programme is continuously in evolution; two development phases have been already covered, a third is in progress, and there are plans to improve the capability of the system in parallel with the evolution of the SBAS standards towards a dual-frequency augmentation service.

WAAS User Segment

The WAAS user segment consists in the GNSS receivers that combine GPS information with the SBAS signal-in-space broadcast by the WAAS GEO satellites. As such, the user segment is not under the control of the WAAS service provider, FAA, and it is driven by the GNSS application market. Although the prime target of WAAS is the civil aviation user community, most of GPS receivers nowadays can be configured to receive and process WAAS signal-in-space (SIS), so they can benefit from the enhanced accuracy and/or integrity offered by WAAS.

WAAS users include any aircraft with approved SBAS avionics using a SBAS-enabled GPS receiver. The WAAS user equipment shall be compliant (certified) against several standards, i.e. RTCA MOPS DO 229 (see article SBAS Standards). The civil aviation certified equipment is in the highest rank with respect its cost. There exist a large number of certified receivers manufacturers worldwide, including:

• GARMIN
• Honeywell
• Rockwell Collins
• Universal Avionics
• CMC Electronics
• Avidyne

Aircraft Supplemental Type Certificates (STC) have been issued by the FAA for an important number of aircraft models equipping WAAS-compliant avionics, including, among others, aircraft from Boeing, Bombardier, Cessna, Embraer, Falcon, Hawker... Other certificates are in progress including airplanes from other companies such as Airbus or Lockheed Martin.

Aircraft equipped with WAAS compliant avionics may take benefit from the more than 2000 LPV/LP approaches approved in USA and Canada airports (see the article WAAS Services).

The non-safety-of-life devices comprise low cost, general purpose GPS equipment that uses the WAAS signal-in-space (SIS) to provide the user with an enhanced accuracy performance in comparison with the one provided by a standalone GPS device. In comparison with the certification requirements of the safety-of-life user equipment, the general-purpose equipment is not necessarily compliant with the RTCA MOPS DO 229 processing rules, but might only make use of the processing algorithms that render the accuracy corrections provided by the SBAS SIS.