I am uploading a corrected Avia 51 FSX version to my site for the missing textures.

I also corrected the autopilot function.

Should be ready within 30 minutes.

EDIT: Revised Avia 51 for FSX now loaded and ready for download from my website.

For those already having the FSX installed with the SCW texture that would like a corrected aircraft.cfg for the Autopilot function, it is attached.
Otherwise download the latest version that includes the SCW version and the corrected aircraft.cfg AP function.