You don't have to use any 3D software to make scenery. The 3D modeling programs are only for if you wish to add 3D models to an airport (or any other structure).
If you do indeed wish to make models for your scenery, there is already a plug-in for AC3D. You can use it free for 30 days then it's fairly cheap compared to 3DS Max.
Thank you drHotwing1, if you don't add any 3d modelling like in cities and Airports then it will be just a flat photo is this correct?
Not so much flat since there is an elevation model built in, but in the sense of there not being anything except the aerial imagery then yes, that's correct.
