Ground-based augmentation system

The local-area augmentation system (LAAS) is an all-weather aircraft landing system based on real-time differential correction of the GPS signal. Local reference receivers located around the airport send data to a central location at the airport. This data is used to formulate a correction message, which is then transmitted to users via a VHF Data Link. A receiver on an aircraft uses this information to correct GPS signals, which then provides a standard instrument landing system (ILS)-style display to use while flying a precision approach. The FAA has stopped using the term LAAS and has transitioned to the International Civil Aviation Organization (ICAO) terminology of ground-based augmentation system (GBAS). While the FAA has indefinitely delayed plans for federal GBAS acquisition, the system can be purchased by airports and installed as a Non-Federal navigation aid. The ground-based augmentation system (GBAS) with aviation standards identified in International Civil Aviation Organization (ICAO) Standards and Recommended Practices (SARPS), Annex 10 on radio-frequency navigation provides international standards for augmentation of GPS to support precision landing. The history of these standards can trace back to efforts in the United States by the Federal Aviation Administration to develop a Local Area Augmentation System (LAAS). Many references still refer to LAAS, although the current international terminology is GBAS and GBAS Landing System (GLS). GBAS monitors GNSS satellites and provides correction messages to users in the vicinity of the GBAS station. The monitoring enables the GBAS to detect anomalous GPS satellite behavior and alert users in a time frame appropriate for aviation uses. The GBAS provides corrections to the GPS signals with a resulting improvement in accuracy sufficient to support aircraft precision approach operations. For more information on how GBAS works, see GBAS-How It Works. Current GBAS standards only augment a single GNSS frequency and support landings to Category-1 minima.