the author (daemotron) of FSE / XFSE says: This is a bug in the Challenger, not XFSE. The check resulting in the error message about airborne refueling does not use any position or time related information, it simply compares the fuel on board NOW to the fuel on board stored a second ago. You're not the first to report this error message with the Challenger; the root cause must be that under certain circumstances, the fuel on board data ref (sim/flightmodel/weight/m_fuel) is not reliably updated by HotStart. Therefore, I kindly ask you to file a bug report with them. Nothing I can do about my end, and I doubt it has anything to do with the date line (though this hint might help them sort out their stuff).