FAA Instrument Rating Airplane (IRA)IFR Procedures and ChartsMedium
A pilot's aircraft is equipped with a non-WAAS IFR-approved GPS receiver. Before departing on a flight that will conclude with an RNAV (GPS) approach, an active NOTAM indicates that a GPS satellite is out of service. What action should the pilot take regarding this approach?
- ARequest radar vectors only, since GPS approaches cannot be flown with any satellite outage
- BDisregard the NOTAM since ATC automatically monitors satellite integrity for all IFR flights
- CPerform a RAIM prediction check using the receiver's prediction function or another approved method for the approach time and location
- DFile a different destination airport since the approach is automatically unusable
Show answer & explanationAnswer & explanation
Correct answer: C. Perform a RAIM prediction check using the receiver's prediction function or another approved method for the approach time and location
Non-WAAS GPS receivers rely on Receiver Autonomous Integrity Monitoring (RAIM) to detect satellite geometry problems. When a satellite outage is NOTAM'd, the pilot must verify RAIM availability for the approach using the receiver's prediction capability or an approved external tool before relying on GPS guidance for the approach.
Why the other options are wrong
- A. Incorrect — one satellite outage does not automatically preclude use of GPS approaches.
- B. Incorrect — ATC does not monitor RAIM; this is the pilot's responsibility.
- D. Incorrect — the approach may still be usable if RAIM prediction shows adequate coverage.
RAIM Prediction
A check performed by non-WAAS GPS receivers (or via other approved tools) to confirm sufficient satellite geometry exists to detect navigation errors during a planned approach.
- Required when satellite outages are NOTAM'd for non-WAAS GPS
- WAAS receivers generally do not require RAIM prediction
- Pilot responsibility, not an ATC function
Memory trick: No WAAS? Always Ask 'RAIM Ready?'