What indication does the RMU provide when UHF GUARD is activated?

When UHF GUARD is activated, the RMU provides a clear indication by displaying "GUARD" as the mode annunciation. This helps pilots quickly recognize that they are monitoring the UHF GUARD frequency, which is crucial for emergency communications and ensuring that they remain aware of any distress calls or emergency broadcasts occurring on that frequency. The display serves as a visual confirmation of the selected mode, aiding in operational readiness and safety during flight.

In contrast, the other choices do not accurately reflect the functions of the RMU in this situation. Although some systems may have alert indicators, the specific indication for UHF GUARD is the mode annunciation of "GUARD." There is no automatic frequency change involved with the activation of UHF GUARD, nor is there a lack of indication when the feature is activated. This clear mode annunciation is a vital feature for maintaining situational awareness while in flight.