scope:

GENERAL

Introduction. An SBAS augments core satellite constellations by providing ranging, integrity and correction information via geostationary satellites. The system comprises a network of ground reference stations that observe satellite signals and master stations that process observed data and generate SBAS messages for uplink to the geostationary satellites, which broadcast the SBAS messages to the users.

By providing extra ranging signals via geostationary satellites and enhanced integrity information for each navigation satellite, SBAS delivers higher availability of service than the core satellite constellations.

SBAS coverage and service areas. It is important to distinguish between SBAS coverage areas and service areas. An SBAS coverage area is defmed by GEO satellite signal footprints. Service areas for a particular SBAS are established by a State within an SBAS coverage area. The State is responsible for designating the types of operations that can be supported within a specified service area. Different SBAS service areas may overlap. When this occurs and when an FAS data block is available, it identifies which SBAS service provider(s) may be used for approach operations using GNSS APV I and II performance levels. Receiver standards dictate that such approaches cannot be flown using data from more than one SBAS service provider, ,but de-selection is possible for these approaches. When an F AS data block is not available, the minimum avionics requirements permit the use' of any SBAS service proyider and permit the mixing of information from more than one SBAS service provider for en-route, terminal and LNA V approach procedures.

SBAS coverage area. SBAS avionics should function within the coverage area of any SBAS. States or regions should coordinate through ICAO to ensure that SBAS provides seamless global coverage and that aircraft do not suffer operational restrictions. If a State does not approve the use of some or all SBAS signals for en-route, terminal and SBAS LNAV approach operations, pilots would have to de-select GNSS altogether, since receiver standards do not permit de-selection of a particular SBAS for these operations. It is not expected that APV I or II operations are available within the coverage area other than in specifically desib'1lated service areas.

SBAS service area. Near the edge of the SBAS service area, several outages of vertical guidance a day at a specific location could occur. Although these outages are of short duration, they could totally overburden the NOT AM system. As a resul!, the State may elect to defme different SBAS service areas for different levels of SBAS service. SBAS en-route service requirements are much less stringent than those of the SBAS vertically guided approach service.