I found a way to enable free flight on Arrakis, but you have to edit a flight save (.flt flight)
All the world will be replaced by the Dune scenery, and some assets will load in the middle of the desert. By the way the mission locations are really far away from each other and scattered in the center of africa, so is not really funny flight from one location to the next.
The tutorial is in Italian but with English subtitles.
