Revisiting RAIM

Fred Simonds

Thursday, July 22, 2021 at 11:36 AM ET

Verified

Key Takeaways:

RAIM (Receiver Autonomous Integrity Monitoring) independently assesses GPS position integrity by comparing multiple satellite signals to detect and correct errors, crucial for ensuring accuracy and filling gaps before the main GPS control system responds to issues.
It operates with Fault Detection (FD) or the more advanced Fault Detection and Exclusion (FDE) capabilities, which are significantly enhanced when integrated with WAAS (Wide Area Augmentation System) integrity signals.
Pilots using non-WAAS GPS must perform preflight and en-route RAIM checks for availability, while WAAS users are generally exempt if coverage is confirmed, with future Advanced RAIM (ARAIM) aiming to further improve reliability and reduce manual checks.

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Receiver Autonomous Integrity Monitoring is a mouthful, but it’s descriptive. RAIM independently assesses the integrity of positions reported by a GPS receiver.

RAIM is essential because half a dozen error sources can result in position errors ranging from negligible to unsafe. RAIM detects and, in some cases, corrects these errors. Only then can a pilot know the GPS is accurate.