Local reference receivers are located around an airport at precisely surveyed locations. The signal received from the GPS constellation is used to calculate the position of the LAAS ground station, which is then compared to its precisely surveyed position. This data is used to formulate a correction message which is transmitted to users via a VHF data link. A receiver on the aircraft uses this information to correct the GPS signals it receives. This information is used to create an ILS-type display for aircraft approach and landing purposes. Honeywell's CAT I system provides precision approach service within a radius of 23 NM surrounding a single airport. LAAS mitigates GPS threats in the Local Area to a much greater accuracy than WAAS and therefore provides a higher level of service not attainable by WAAS.
