Definition
A pre-flight check performed by a GPS receiver, or by an external service, that forecasts whether enough satellites will be available and properly positioned at the destination — at the planned arrival time — to allow the receiver to verify the integrity of its own position information. RAIM stands for Receiver Autonomous Integrity Monitoring. A successful RAIM prediction is required before a pilot may rely on a non-WAAS GPS as the primary means of navigation for an instrument approach.
Plain English
Before flying an instrument approach using a non-WAAS GPS, the pilot checks ahead of time whether enough GPS satellites will be visible at the destination, at the expected arrival time, for the GPS to trust its own position. If the check passes, the GPS approach can be flown. If it fails, the pilot must plan a different approach.
Context Anchor
Seen during IFR GPS flight planning, especially before using GPS as the main navigation source or flying a GPS approach.
Derivation
RAIM means Receiver Autonomous Integrity Monitoring — the receiver checks itself. A 'prediction' here is simply a forecast: looking ahead to see whether that self-check will work at the time and place it will be needed.
Why Pilots Care
It confirms GPS navigation will meet integrity requirements for IFR operations, preventing reliance on position data that could become unreliable due to poor satellite geometry.
Grounding Statement
Before departure, the pilot is asking: when I get there, will the GPS have enough satellite information to catch a problem with itself?
Intuition Check
RAIM prediction is not a guarantee that GPS will work perfectly. It is a calculated look-ahead that says whether the GPS is expected to have enough satellite coverage to monitor its own reliability.
Example Sentence 1
Before departure, the pilot ran a RAIM prediction for the planned arrival time and confirmed the GPS approach into the destination would be available.
Example Sentence 2
A marginal RAIM prediction prompted the pilot to load an ILS backup approach in case satellite coverage dropped below required levels.