What alert might indicate that the backup UHF is in manual frequency mode?

When the backup UHF radio is set to manual frequency mode, it typically does not generate any alerts or warnings. This is intentional, as the system is designed so that the pilot can operate the radio without distraction, allowing them to focus on frequency changes without an active alert system.

In manual mode, the pilot manually selects frequencies, so there’s no automatic indication like a flashing light or continuous beep that would typically accompany other modes that require attention. Therefore, having no alerts indicated reflects the operation of the backup UHF radio in this specific mode, allowing the pilot to assume control without interruptions.

In contrast, alerts that might signal issues or require immediate attention would typically present themselves when the radio is functioning incorrectly or in a different operational mode.