Bob I am not disputing your situation with the Cadiz scenery, but I would like to understand Roby's FSX install path, because in my understanding this does not work. I can say that in all my years of playing with sceneries that i've never encountered a situation where files are mutually exclusive.
For the sake of argument, I will disagree

.
Me too, I run W7 and have my FSX in C:\windows\Program Files (86)\Microsoft games, etc.
Bob was kind enough to send me his files and I do not have any problems. The aircraft sits on the water and no CTD's or whatever.
I must therefore conclude that there is another file active that makes the aircraft sit on a flatten of another scenery that I do not have and so does not interfere with this one.
View attachment 29213
Totally understood, except for whatever part we or I am misunderstanding, but I am game to explore the anomaly. First off, I know that there is no known cure for Windows DEP besides circumventing it. The easiest and most direct way that I know of is to move the files and execute data outside it's area of focus. It can be an intermittent problem because events within the simulator trigger DEP, to my understanding. You can specifically allow FSX but when a .dll performs a task, you are not given the opportunity to allow it so the procedure fails and FSX crashes. It would seem that if FSX is being run from within C:\windows\Program Files (86)\Microsoft games, you have done something else to circumvent DEP and that it would be something you would remember. Perhaps you have a hacked version of W7? I'm not making any sort of accusation and I totally trust your understanding and expertise in these matters, however the sheer volume of hits in my Google search should substantiate this is no small matter. So great a matter actually, that in the absence of any errant flattens or afcads and whatever you did to make it work Roby, the proposed fix is about as easy as a continued search and the biggest harm is that it would disrupt the install/activation path of any payware, which could also be corrected.
Ok as to slew levitation. I just ran a test and I was mistaken in my assertion, only the avatar model I use levitates in slew mode
all the time. However I observed a very peculiar situation with the P3D default F35 that may provide clues to your situation. I think the issue is the aircraft air or model file and I'll show you why, first the avatar in external and in slew mode to demonstrate:
See what I mean? It happens all the time everywhere and I use it to place scenery. I think also some of my own creation models do the same thing but it is not something I am asserting or checking. Now onto the F35. The default start external view is not exactly identical to the slew view, in that you can see more of the center line above the cockpit. What is very noticeable is the view immediately upon exiting slew mode, the nose noticeably dips then rises to rest
almost as if a weight got deposited in the cockpit, hidden vents become exposed and much more of the center line is visible than in the other images. This is something anyone can confirm. First default start, then slew and then the first instant after exiting slew:
I also tried the experiment in a freeware helicopter I use and the result was similar to the F35 but less dramatic. Overall I would conclude that it is the "pilot" that becomes levitated, probably by becoming weightless, but that is just a guess. Therefore there is something about the situation you encounter where it causes the airplane to be weightless itself or be levitated by the act of the pilot becoming levitated.