FAA Instrument Flight Instructor (FII)IFR Procedures and ApproachesMedium
Before departing on a flight for which the only instrument approach available at the destination is an RNAV (GPS) approach, a pilot performs a predictive RAIM check that indicates RAIM will be unavailable at the estimated time of arrival. What should the pilot do?
- APlan for an alternate means of approach guidance, since GPS-based approach guidance may not be available at the ETA
- BDepart as planned, since RAIM predictions do not apply to WAAS-enabled GPS receivers
- CDelay departure briefly and re-check RAIM, since satellite geometry has no effect on approach guidance
- DDisregard the prediction, since RAIM only affects en route GPS navigation, not instrument approaches
Show answer & explanationAnswer & explanation
Correct answer: A. Plan for an alternate means of approach guidance, since GPS-based approach guidance may not be available at the ETA
A predictive RAIM (or fault detection) unavailability forecast means the GPS receiver may not be able to provide reliable integrity monitoring for the approach at the ETA. The pilot must plan an alternate means of navigation or a different approach that does not rely on GPS.
Why the other options are wrong
- B. Even WAAS receivers can experience unavailability of the necessary integrity/augmentation service.
- C. Satellite geometry directly affects RAIM/fault detection availability, so delaying alone doesn't guarantee improvement.
- D. RAIM predictions are specifically important for approach operations, not just en route navigation.
Predictive RAIM Check
A pre-flight or pre-approach prediction of GPS Receiver Autonomous Integrity Monitoring availability; if unavailable at the ETA, GPS-based approach guidance may not be usable and an alternate plan is required.
- RAIM ensures GPS position integrity for non-precision approach use
- Predictive RAIM should be checked before flight when GPS is the sole approach means
- If unavailable, pilot must have an alternate approach or navigation method
Memory trick: 'No RAIM, No Claim' to fly the GPS approach.