Hi Ubaid,
so I got everything to work as intended. I can't tell which scenerie caused the problem but I would like to explain which ones I removed. So I removed every freeware scenerie even the "high quality" ones like Mister X and ZDP. I also removed every 3rd party library.
Over the next days I'll reinstall the Mister X and ZDP sceneries and the respective libraries to see it the aircrafts still works with them.
If it's OK for you I would like to keep you updated in this thread and if you need any more infos from my side do not hesitate to contact me.
BTW is it possible that the custom navdata caused the problem. It looks like it is the final step to load the aircraft.
I wish you all the best and a happy new year in advance and thanks again for your help 🙂