In which scenario is altitude information considered unreliable?

Altitude information is considered unreliable when RAIM (Receiver Autonomous Integrity Monitoring) capability is absent. RAIM is a system used in GPS technology that ensures the accuracy and integrity of GNSS (Global Navigation Satellite System) signals. When RAIM is present, the system can monitor the performance of the satellite signals and provide alerts if there is a discrepancy, thereby enhancing the reliability of altitude and positional information.

In contrast, without RAIM capability, there is no mechanism to verify the reliability of the altitude data being presented by the GPS or navigation system. This lack of integrity monitoring means that the information could be incorrect due to factors such as satellite geometry or signal errors, making it unsafe to use for altitude decisions.

The other scenarios listed may present their own challenges, but they do not directly correlate to the integrity of altitude information in the same way that RAIM absence does.