Plans are loaded in IF10 to build a flight, or a plan might be loaded mid-flight into FSX by the FMC or loaded manually, this is noted by IF10 and changes are made accordingly.
A subject came up about plans with no airport destination:
IF10 is aware of any plans you file along the way and the weather system generates weather wherever you go, even across the oceans.
Plan with-no-destination
FSX loads the 'plan with-no-destination' without question, but if you look in the FSX map, you'll see the route does not go to an airport. Without an airport destination with runway, ATC ends at the last waypoint.
However when loading a plan to build a flight, IF10 Flight Planner correctly loads the 'plan with-no-destination', and reports the destination is an unknown airport. IF10 does suggest to try a re-index which might help locate the missing airport, but I'm stopping that now as unnecessary, at least during flight plan loading to make flights.
Since we are loading a plan we want IF10 to make a flight of it faithfully, IF10 has to faithfully load the waypoint list (since some folk might want to land at a Nav site with a chopper, for example).
IF10 goes on to build the flight, and plan, to the last waypoint in the plan file waypoint list. This flight loads in FSX and the route in the FSX MAP window ends at the last waypoint, as is expected.
During the sim and loading another plan, some functions require an actual airport as the endpoint. In these circumstances IF10 compares the last waypoint in the waypoint list, to the destinationlla in the plan, and if the destinationlla is different, or is an airport, IF10 "Prefers" the destinationlla.
When building flights from these 'plan with-no-destination' files, I've made the flight planner assume the destination in the plan header is preferred as the final destination.