Instrument Rating Checkride Practice Test

To perform a RAIM (Receiver Autonomous Integrity Monitoring) function, a GPS receiver must have access to at least five satellites. RAIM is crucial for ensuring the integrity of the GPS signal by monitoring the accuracy of the satellite data received. With five satellites in view, the receiver can check the consistency of the signals, which allows it to detect any potential errors in the satellite navigation data.

RAIM functions by comparing the measurements from the satellites; with five satellites, the receiver can identify which satellite might be providing incorrect information by analyzing discrepancies. This level of redundancy is what enables the system to maintain a high level of reliability in providing positional information.

With fewer than five satellites, the receiver wouldn't have enough data points to effectively perform this function, which is essential for safe navigation under instrument flight rules. Using four satellites alone may provide a position fix, but it lacks the necessary data for RAIM—thus not fulfilling the requirements for integrity monitoring in critical phases of flight.