Final answer:
Pressing the guarded NAV button on an RMP panel quickly switches the aircraft's navigation system back to a primary or preset source, acting as a safeguard for navigational integrity.
Step-by-step explanation:
When you press the guarded NAV button on an RMP (Radio Management Panel), it typically serves as a safeguard function. This button is often used in aviation to quickly switch the navigation system back to a primary or preset navigation source. For instance, if an aircraft is equipped with multiple navigation systems and one becomes unreliable, the pilot can press the guarded NAV button to revert to the default navigation source, ensuring continued safe operation.