Sorry, but that's incorrect. While the local map only displays the navaids that are within the boundaries of the loaded tiles, the nav radios are NOT restricted to tuning navaids only within those same loaded tiles. Want to test it out? … Select an airport. Using Skyvector or whatever, choose a navaid (i.e.. VOR) that is outside the loaded tiles (but not too far) when at that airport. Open up the earth_nav.dat file and locate that navaid. Change the range of the navaid so that it is farther than the distance that the navaid is from the airport (again, use Skyvector as necessary to measure). Load up X-plane (with the stock C172) and put the aircraft at the selected airport. Tune the nav radio to the frequency of the selected navaid. Voila!… the VOR gauge will be ALIVE! So, while you may not be happy with the default "distance" for some of the navaids in X-Plane, they are ALL "available" to the nav radio(s) regardless of what tiles are loaded.