What is RAIM used for in GPS navigation?

• A. To compute altitude above mean sea level
• B. To determine the aircraft's vertical speed
• C. To detect corrupted satellite data and verify integrity
• D. To replace ground-based navigational aids

Answer: (C)

RAIM is all about ensuring the reliability of the GPS navigation solution. It stands for Receiver Autonomous Integrity Monitoring and uses the redundancy of satellite signals to check for errors in the GPS measurements. By comparing the observed pseudorange values from multiple satellites with the predicted ranges, the receiver can detect if one satellite is providing corrupted data. If a fault is found, the system can flag the navigation as unreliable or exclude the faulty satellite, allowing the remaining satellites to yield a trustworthy position. This focus on detecting data corruption and verifying integrity is why this option is the best choice. It isn’t about computing altitude or vertical speed, nor about replacing ground-based navigational aids.