What is required for 3D position and integrity monitoring using RAIM?

For 3D position and integrity monitoring using RAIM (Receiver Autonomous Integrity Monitoring), the correct requirement is the necessity for at least 5 satellites. This is because RAIM requires a minimum of 5 satellites to not only determine a precise 3D position (latitude, longitude, and altitude) but also to assess the integrity of the navigation signals being received.

With 4 satellites, a receiver can calculate a 3D position, but it does not have enough information to check for any potential errors within those signals. By incorporating a fifth satellite, the system can compare the data from the additional satellite to the other four, enabling the identification and exclusion of faulty signals. This capability to monitor integrity is crucial for ensuring the accuracy and reliability of navigation in aviation.

Therefore, while more satellites can enhance the robustness of the position solution and integrity monitoring, a minimum of 5 satellites is essential for effective RAIM functionality. Options citing fewer than 5 satellites do not provide the necessary data redundancy required for effective integrity monitoring.