Definition
A self-checking function inside a GPS receiver that confirms the satellite signals it is using are accurate enough to support an instrument approach. Approach RAIM uses a tighter accuracy tolerance than the RAIM used during enroute or terminal flight, because an approach demands more precise position information. If the receiver cannot verify signal integrity to that approach-level standard, it must alert the pilot, and the GPS approach cannot legally be flown.
Plain English
Before flying a GPS approach, the receiver checks whether it has enough good satellite signals to trust its own position to approach-level accuracy. If it doesn't, it warns the pilot and the approach can't be used.
Context Anchor
Seen during IFR flight planning when a pilot plans to use GPS for a departure, route segment, arrival, or instrument approach and must confirm that GPS integrity will be available.
Derivation
Receiver autonomous' means the GPS receiver does the check by itself, on board, without help from a ground station. 'Integrity monitoring' means watching the quality of the signal to make sure it can be trusted. 'Approach' is added to specify the stricter version of the check used during instrument approaches.
Why Pilots Care
Confirms GPS can safely support the approach; loss of RAIM may require an alternate procedure or missed approach.
Analogy
It is like the GPS doing its own cross-check before you trust it. If the signals do not agree well enough, it warns you that the position information should not be relied on for that operation.
Intuition Check
“Autonomous” does not mean the airplane flies by itself. Here it means the GPS receiver checks the reliability of its own satellite navigation information without outside help.
Example Sentence 1
During preflight, the pilot checked approach RAIM availability for the planned arrival time at the destination and found it would be available throughout the approach window.