FAA Airline Transport Pilot (ATM)Navigation, Air Traffic Control and ProceduresMedium
A pilot is flying an IFR flight plan and is advised by ATC to expect clearance for an RNAV (GPS) approach. The pilot notices the GPS system indicates 'RAIM NOT AVAILABLE'. What action should the pilot take?
- AProceed with the RNAV (GPS) approach, but be prepared to execute a missed approach earlier than usual.
- BContinue with the RNAV (GPS) approach as long as visual contact with the runway is established.
- CSwitch to an alternate navigation source for the approach, such as VOR or ILS, if available.
- DAdvise ATC immediately that the RNAV (GPS) approach cannot be accomplished.
Show answer & explanationAnswer & explanation
Correct answer: D. Advise ATC immediately that the RNAV (GPS) approach cannot be accomplished.
RAIM (Receiver Autonomous Integrity Monitoring) is essential for GPS navigation integrity, especially for IFR approaches. When RAIM is not available, the GPS signal integrity cannot be guaranteed, making RNAV (GPS) approaches unsafe and unauthorized.
Why the other options are wrong
- A. Executing a missed approach earlier does not resolve the fundamental issue of unreliable navigation data.
- B. Visual contact does not negate the requirement for navigational integrity during an IFR approach.
- C. While switching to an alternate navigation source is a good strategy, the immediate action is to inform ATC that the assigned approach cannot be flown due to RAIM unavailability.
RAIM (Receiver Autonomous Integrity Monitoring)
RAIM is a technology used in GPS receivers to assess the integrity of GPS signals, ensuring their accuracy for navigation, particularly for IFR operations.
- Monitors GPS signal integrity.
- Required for IFR GPS navigation, especially approaches.
- Alerts pilots if signals are unreliable.
Memory trick: RAIM's integrity shield keeps GPS on the flight path.