Which statement about RAIM is true?

• A. A system that monitors terrain features
• B. A system used to verify the usability of GPS signals and warns the pilot of any navigation malfunction
• C. A system that corrects GPS time
• D. A system that broadcasts GPS corrections

Answer: (B)

RAIM is a system that checks the GPS navigation signal for integrity right in the receiver. It uses multiple satellite measurements to see if the solution is self-consistent; if a satellite or signal is faulty, RAIM will indicate that the navigation solution can’t be trusted and warn the pilot. This helps ensure you’re not relying on a compromised position or timing fix.

RAIM does not monitor terrain features—that’s a different system. It does not correct GPS time, which is determined by the satellites. It also does not broadcast GPS corrections; augmentation systems like WAAS or DGPS provide corrections.

So the statement that RAIM verifies the usability of GPS signals and warns the pilot of any navigation malfunction is the accurate description.