Final answer:
The NAV autotune function is accessed via the aircraft's Flight Management System (FMS) or navigation radio panel and is used to automatically select and tune navigation frequencies for the flight.
Step-by-step explanation:
The NAV autotune function is typically a feature in aircraft navigation systems and is accessed via the aircraft's Flight Management System (FMS) or the navigation radio panel, depending on the specific aircraft type. The purpose of NAV autotune is to automatically select and tune the correct navigation frequencies required for a flight plan. Thus, it simplifies pilot workload by having the system manage frequency changes during a flight. Pilots would use the FMS interface or a dedicated NAV control panel to enable the feature, which then handles the tuning based on the programmed route or the phase of the flight.