FAA Instrument Rating Airplane (IRA)Navigation SystemsMedium
A pilot planning an RNAV (GPS) approach checks the RAIM prediction for the destination and finds that RAIM will be unavailable for a 10-minute window centered on the estimated time of arrival. What should the pilot do?
- APlan an alternate means of navigation, adjust the arrival time, or select a different approach not dependent on GPS integrity
- BFly the approach as planned since RAIM only affects en route navigation
- CDescend below the minimum en route altitude to improve satellite geometry
- DDisregard the prediction, since WAAS receivers do not require RAIM
Show answer & explanationAnswer & explanation
Correct answer: A. Plan an alternate means of navigation, adjust the arrival time, or select a different approach not dependent on GPS integrity
If RAIM is predicted to be unavailable at the ETA, the pilot cannot ensure GPS integrity monitoring for the approach and must plan accordingly—delaying arrival, choosing a different approach, or using an alternate means of navigation not reliant on GPS.
Why the other options are wrong
- B. RAIM prediction is specifically important for approach and terminal operations, not just en route.
- C. Altitude changes do not resolve satellite geometry/RAIM outages.
- D. WAAS receivers still rely on integrity monitoring; a prediction outage still matters if WAAS coverage/RAIM is unavailable.
RAIM Prediction
Receiver Autonomous Integrity Monitoring (RAIM) verifies GPS signal integrity; pilots must check RAIM availability before flying GPS-based approaches, especially without WAAS augmentation.
- RAIM outage predictions can be checked via GPS receiver, flight planning tools, or ATC
- If RAIM unavailable, alternate navigation or approach must be planned
- WAAS avionics have their own integrity checks but coverage can still be affected
Memory trick: 'No RAIM, no game—delay or divert.'