As the new MSFS sim is rising, the old models become interesting as well – why design everything from the beginning, when the objetcts already exists.
Thanks to modelConverterX (https://www.scenerydesign.org/modelconverterx/) you can do this even without having the original gmax-file – so you can take the bgl oder mdl-files instead and convert it to .obj format.
As the current blender (2.8x) importer fails for me I had to convert once more – this time open die .obj in Windows 10 3d-Viewer – now you can check the export and again save as .glb – With this format importing into blender with gITF2 (.glb/.gltf) works like a charm.