XPLMSetFMSFlightPlanEntryLatLonWithId
XPLM_API void XPLMSetFMSFlightPlanEntryLatLonWithId(
XPLMNavFlightPlan inFlightPlan,
int inIndex,
float inLat,
float inLon,
int inAltitude,
const char* inId,
unsigned int inIdLength);
This routine changes the entry in the FMS to a lat/lon entry with the given coordinates. You can specify the display ID of the waypoint.