Definition
A self-checking function built into a GPS receiver that verifies the integrity of the position information it is producing. RAIM compares signals from the available GPS satellites and detects when one of them is providing faulty data. To work, RAIM requires a minimum number of satellites in view with suitable geometry; if that minimum is not met, RAIM is unavailable and the GPS position cannot be guaranteed reliable for navigation.
Plain English
RAIM is the GPS receiver's way of checking its own work. It looks at the satellite signals it is using and asks, 'Do these all agree?' If one satellite is giving bad information, RAIM can spot it and warn the pilot. If there aren't enough satellites in view to perform the check, RAIM tells the pilot it can't guarantee the position is accurate.
Context Anchor
Seen in instrument flying when using GPS for en route navigation, arrivals, or GPS-based approaches.
Derivation
Receiver — the GPS unit in the aircraft. Autonomous — done on its own, without help from outside. Integrity — trustworthiness of the data. Monitoring — continuous checking. Together: the receiver checks the trustworthiness of its own GPS signals, by itself, in real time.
Why Pilots Care
It alerts the pilot if GPS accuracy drops below safe limits, preventing reliance on faulty position data during instrument flight.
Grounding Statement
RAIM is the receiver asking, “Do these satellite signals agree well enough for me to trust this position?”
Intuition Check
Integrity here does not mean honesty or personal character. It means the GPS position has been checked and is reliable enough for the intended navigation use.
Example Sentence 1
Before departing on the IFR flight, the pilot ran a RAIM prediction to confirm GPS integrity would be available at the destination during the planned arrival window.
Example Sentence 2
Loss of RAIM capability during the flight forced the pilot to switch to an alternate navigation method.