GNSS ABAS Principles RNAV

A 3D or 4D fix from GPSGPS —Global Positioning System (USA) requires 4 satellites. RAIMRAIM —Receiver Autonomous Integrity Monitoring checks this position by using a 5th satellite. If the position from the 5th satellite does not agree, then you know something is wrong, but not whether it was the original calculated position or the 5th satellite itself. FDEFDE —Fault Detection and Exclusion uses a 6th satellite - this means that if an error is found, you now kow which of the satellite signals is in error, and can exclude it. AAIMAAIM —Air Autonomous Integrity Monitoring uses a completely different principle - using on board sensors to effectively check the position the GPSGPS —Global Positioning System (USA) has given you.