GBAS is a system for the augmentation of the accuracy, integrity, continuity and availability of the information for the satellite navigation using GNSS.

The GBAS ground subsystems are RRS - Range Reference Stations, VHF Data Broadcast Station (VDB), Integrity Monitoring Station (IMS) and Processing Base Station (PBS), integrated to execute the following main functions:

The RRS (from two to four) receives the signals from the satellites that are in-view and provides the pseudo-ranges for the PBS.

The PBS processes data and calculates the pseudo-range errors, including the ranging sources availability, GBAS-related, final approach segment and atmospheric effects data, and prepares the digital messages to be sent to the aircraft through the VDB.

The IMS monitors the operational state and the integrity of the GBAS ground subsystem elements, as well as, the messages content, signals emitted by the VDB and quality of the obtained pseudo-range errors. Another IMS function is to avoid that messages containing misleading information to be sent to the aircraft.

The VDB broadcasts the GBAS messages to the aircraft that are operating inside its coverage.

GBAS is intended to support all types of approach, landing, taking off and surface operations and may support en-route and terminal operations. The supported services are:

• Category I precision approach;
• Approach with vertical guidance; and
• GBAS positioning service.