FAA Instrument Flight Instructor (FII)Instruments and SystemsHard
While conducting a GPS-based instrument approach in actual instrument conditions, the receiver annunciates a loss of RAIM prior to the final approach fix. The most appropriate action is to
- Areduce airspeed and continue since RAIM only affects enroute navigation accuracy
- Bexecute the missed approach procedure since GPS integrity can no longer be assured
- Cdisregard the annunciation since WAAS receivers do not require RAIM
- Dcontinue the approach using the autopilot's inertial reference as backup
Show answer & explanationAnswer & explanation
Correct answer: B. execute the missed approach procedure since GPS integrity can no longer be assured
RAIM (Receiver Autonomous Integrity Monitoring) verifies that sufficient satellite geometry exists to detect a position error. A loss of RAIM prior to the FAF means GPS position integrity can no longer be guaranteed for the approach, so the pilot must not continue relying on GPS guidance and should execute the missed approach or revert to another approved means of navigation.
Why the other options are wrong
- A. RAIM directly affects approach-level position integrity, not just enroute accuracy, so continuing is not appropriate.
- C. WAAS-equipped receivers use an equivalent integrity function; a loss of integrity annunciation still requires action, not disregard.
- D. General aviation autopilots typically lack a certified inertial backup capable of maintaining approach-level accuracy without RAIM.
RAIM (Receiver Autonomous Integrity Monitoring)
RAIM is a GPS receiver function that checks satellite signal redundancy to detect and warn of position errors, essential for safely flying GPS-based instrument approaches.
- Requires adequate satellite geometry (usually 5+ satellites)
- Loss of RAIM before FAF requires aborting the GPS approach
- WAAS provides an equivalent integrity function (satellite-based augmentation)
- Pilots should check RAIM prediction during preflight planning
Memory trick: No RAIM, no aim — go missed, don't guess.