After you get a flight plan, you can use both Doppler System or CIVA INS. My favourite is the first one because the second seems to me a little tedious to use, because you must insert each waypoint coordinates (LAT and LON) before and during flight. The system is limited up to 9 waypoints (0 - 8). So, if your flight plan has a lot of them (long haul flight), you must constantly insert the new ones in the INS "carousel". Give it a try in both systems and make your choice.

Pinatubo.