is it possible to add a custom airfield to aerofly just with AC3D, without using 3Dmax or Cinema4D? Yes.
After fiddling about adding an area to aerofly I found a solution which is not very complicated.
This is probably not the 'official' way, and of course it is not perfect.
There is still plenty room for improvement, but in fact I'm quite satisfied with the current status.
Attention: I did not pay attention to runway markings, this is just a matter of bitmap textures.
So it is not a problem of the workflow, just texture work.
We can really modify the existing ground mesh with a custom mesh.
This means also, we could add slope runways by defining the mesh with a slope.
After the existing ground has been planished with our own mesh, we can place a google earth snapshot on it.
Next is the placement of a runway and define the basic lightings.
How to add an Approach Lighting System ALS is still open.
If there is some interest, I will write a tutorial and publish all original files for your own attempts.
Thanks for your attention
Btw, many thanks for ideas, testing and discussing to Ray!!!