What are the RAIM tolerances for En Route navigation?

The choice of ±2 NM as the RAIM (Receiver Autonomous Integrity Monitoring) tolerance for En Route navigation is based on the standards set for navigation accuracy within this phase of flight. During the En Route segment, aircraft are typically flying at altitude and have a greater distance to cover, which permits a wider tolerance in position accuracy.

The ±2 NM tolerance provides a balance between navigational precision and operational efficiency, allowing pilots to utilize the navigation system effectively while maintaining safety margins. This tolerance is designed to ensure that the aircraft remains well within the designated airspace and can safely navigate along the planned route, even with minor discrepancies that can arise from various factors affecting GPS signals.

In contrast, acceptable tolerances in other phases of flight, such as terminal or approach, are usually stricter to allow for more precise maneuvering as aircraft prepare for landing, which would explain why those choices may not align with RAIM requirements during the En Route phase.