What Is RAIM and How Does It Affect Approach Operations?
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Monitors and verifies integrity and geometry of tracked GPS satellites
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Notifies the pilot when satellite conditions do not provide the necessary coverage to support a certain phase of flight
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Ascertains whether the number of available satellites is sufficient to satisfy requirements at a destination
For RAIM to work correctly, the GPS receiver must track at least five satellites. A minimum of six satellites is required to allow RAIM to eliminate a single corrupt satellite from the navigation solution.
RAIM ensures that satellite geometry allows for a navigation solution calculation within a specified protection limit (2.0 NM for oceanic and en route, 1.0 NM for terminal, and 0.3 NM for non-precision approaches). Without RAIM, GPS position accuracy cannot be monitored. If RAIM is not available when crossing the FAF, the pilot must fly the missed approach procedure.