A Satellite Based Augmentation System (SBAS) is a primary air navigation system that provides augmented accuracy and integrity to a Global Navigation Satellite Systems (GNSS) navigation signal such as used by the U.S. Global Positioning System (GPS). GNSS alone is considered a supplemental air-navigation system. An SBAS provides improved service availability over a wide area and is a more reliable navigation service than GNSS alone.
The internationally cooperative standards for SBAS were published as the Standards and Recommended Practices (SARPs) Annex 10 by the International Civil Aviation Organization (ICAO), a specialized agency of the United Nations. The ICAO is chartered to provide globally interoperable SBAS aviation standards that describe the principles and practices of international air navigation.
The ICAO SARPs foster the planning and development of international air transport systems that support SBAS interoperability and SBAS avionics technology interchangeability. The SARPs establish that the introduction of new GNSS navigation elements should include evaluation of the navigation systems with respect to four essential criteria:
These specific criteria define the standards for Approach with Vertical guidance (APV), the ICAO term for an SBAS approach classification that allows the use of stabilized descent using vertical guidance.
The Interoperability Working Group (IWG), made up of SBAS providers around the world, provides the forum to allow the coordinated development of interoperable SBAS systems andcommon aircraft avionics receiver technology that enable aircraft to easily transition from one SBAS system to the next.
As technology evolves both groups provide guidance and planning objectives to maintain seamless global operations as systems expand, are enhanced, or as new SBAS systems are implemented.