What happens to altitude information if Receiver Autonomous Integrity Monitoring (RAIM) is not available?

In the context of aircraft navigation and the use of Global Navigation Satellite Systems (GNSS), Receiver Autonomous Integrity Monitoring (RAIM) plays a crucial role in ensuring the accuracy and reliability of the position, velocity, and altitude data provided by satellite signals. When RAIM is not available, it means that the integrity checks that would normally validate the accuracy of those signals cannot be performed.

In such situations, altitude information may become unreliable. Without RAIM, there is no assurance that the data being received is accurate, which means that pilots and dispatchers should treat altitude information with caution. This uncertainty could lead to potential safety risks, as incorrect altitude data could affect the aircraft's flight profile, including clearance from terrain and safe altitude levels during various phases of flight.

The reliance on the accuracy of altitude information diminishes significantly when RAIM is unavailable, leading to the conclusion that altitude information should not be relied upon to determine the aircraft's actual altitude. The safety of an aircraft's flight operations hinges on having accurate altitude information, thus the unavailability of RAIM directly affects that reliability.