FAA Flight Instructor Airplane (FIA)Navigation and AirspaceHard
A pilot is planning an IFR flight using a non-WAAS GPS receiver for an RNAV (GPS) approach. Before departure, the pilot checks for RAIM availability. What is the primary function of RAIM in this scenario?
- AIt corrects for GPS satellite clock drift errors
- BIt provides vertical guidance for precision approaches
- CIt cross-checks redundant satellite signals to detect and warn of a GPS position error
- DIt converts GPS-derived altitude into barometric altitude
Show answer & explanationAnswer & explanation
Correct answer: C. It cross-checks redundant satellite signals to detect and warn of a GPS position error
RAIM (Receiver Autonomous Integrity Monitoring) uses redundant satellite signals to verify the integrity of the GPS position solution and alerts the pilot if the position accuracy cannot be assured, which is critical for non-WAAS GPS approaches.
Why the other options are wrong
- A. Clock drift correction is handled by the GPS satellite system, not RAIM.
- B. Vertical guidance requires WAAS or baro-VNAV, not RAIM alone.
- D. RAIM does not convert altitude types; that is a separate avionics function.
RAIM (Receiver Autonomous Integrity Monitoring)
A GPS integrity monitoring function that detects satellite signal errors using redundant satellite measurements, essential for non-WAAS approaches.
- Requires minimum satellite geometry (usually 5 satellites)
- Alerts pilot if integrity cannot be assured
- Not needed when using WAAS due to built-in integrity monitoring
Memory trick: 'RAIM = Reliability Alarm In My navigation'