Definition
The ability of a GPS receiver to independently verify the integrity of the satellite signals it is using for navigation. A RAIM-capable receiver continuously cross-checks signals from multiple satellites and warns the pilot if the position information cannot be trusted to meet the accuracy required for the current phase of flight. RAIM capability is required for a GPS receiver to be approved for IFR navigation, and pilots can perform a pre-flight RAIM prediction to confirm adequate satellite coverage will exist along the planned route at the expected time of arrival.
Plain English
It is the GPS receiver's built-in ability to check its own work and tell the pilot if the position it is showing is reliable enough to be used for navigation.
Context Anchor
Seen when planning or using GPS for IFR navigation, especially before relying on GPS for an instrument approach.
Derivation
Receiver Autonomous Integrity Monitoring -- 'autonomous' (from Greek, meaning self-governing) means the receiver does the checking on its own, without help from ground stations or other systems. 'Integrity' here means trustworthiness of the signal, not absence of damage. Together: the receiver checks the trustworthiness of its own signals by itself.
Why Pilots Care
It confirms reliable GPS position data for safe navigation when no external integrity source is available.
Grounding Statement
Before a GPS approach, the receiver needs enough usable satellite signals to compare them and catch a bad position indication.
Intuition Check
RAIM capability does not mean the GPS position is guaranteed to be perfect. It means the receiver can check whether the position is trustworthy enough and warn you if it is not.
Example Sentence 1
Before filing the IFR flight plan, she ran a RAIM prediction to confirm RAIM capability would be available at her destination during the approach.
Example Sentence 2
Loss of RAIM capability during flight requires the pilot to switch to an alternate navigation source.