During the terminal phase, when RAIM loss occurs, what must ATS do?

• A. There is RAIM loss or loss of GNSS integrity
• B. RAIM loss for more than 2 minutes
• C. No reporting is required
• D. Only report if RAIM is restored within 1 minute

Answer: (A)

RAIM is the mechanism that checks the trustworthiness of the GPS/navigation signal. In the terminal phase, any RAIM loss means GNSS integrity is compromised, so pilots can’t rely on GPS for precise guidance. When this happens, ATS must report that there is RAIM loss or a loss of GNSS integrity. This notification is essential so pilots know to use alternative navigation methods or non-GNSS procedures and so ATC can maintain safe operations. The reporting isn’t about a specific duration or only about restoration; integrity loss is a condition that should be communicated as soon as it’s detected.