What is required for the navigation radios to be selected to Auto tune?

The requirement for the navigation radios to be selected to Auto tune is that the needles must display white. In the context of avionics and navigation systems, the color of the needles on the radio tuning indicators provides essential information about the system's state. White needles signify that the frequency can be auto-tuned and that the system is ready to switch to the selected navigation source. This feature is particularly important for ensuring that navigation is precise and reliable during flight operations.

Other considerations, such as the conditions (clear weather) or different needle colors (such as green or standby), do not have a direct role in enabling the Auto tune function for navigation radios. Understanding the function and condition of the needle display is crucial for pilots to operate the navigation systems effectively.