Also found this online:
https://www.fsmissioneditor.com/product/prepar3d-mission-editor-2/
Thanks Brad. I've just acquired a copy of it. Playtime ...
Well, I was excited to get the program, but spent the rest of the day and night trying to get it to work. No joy. The program couldn't find my P3dv4 install initially, until I found settings for v4 in the "compatibility" settings for the projects. I set that to 4 and the program started finding and reading airports and models, etc. So I thought, Great!! It's gonna work now. But it doesn't finish, it crashes to desktop with no error messages at all. It is a port over from FSX, and built by a former ACES member of MS. The documents still refer to FSX, not P3d. I couldn't find any more help than if I were dealing with MS. So sad.
I wanted to build missions again, but it's not happening with this program (yet). I wish it would show the error or issue it has that causes the CTD, not just disappear.
It cost me $28 to find out the program has issues. I should have tried it before buying the thing. I never do.