Final answer:
The NAV autotune function is accessed from the Flight Management Computer (FMC), which is used to automatically select and tune navigation radios.
Step-by-step explanation:
The NAV autotune function is typically accessed from the Flight Management Computer (FMC). The FMC is a specialized computer system that uses various sensors and inputs to determine the aircraft's position and to manage the flight plan. It is part of the avionics suite of modern aircraft and is responsible for various navigational tasks. Autotune is a feature that automatically selects and tunes the navigation radios to the appropriate frequencies for the waypoints in the flight plan, making navigation more efficient and reducing pilot workload.