Local-area 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 GPS reference receivers located at surveyed positions around the airport measure GPS deviations and calculate corrections which are sent 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 (with a D8PSK modulation type like Mode 2 of the VHF Data Link used in aeronautical radio communications) in the frequency band between 108.00 and 117.95 MHz. 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 U.S. Federal Aviation Administration, 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.

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