I've checked this out for you. It's easy enough to fix it yourself. You will need DXTBmp if you don't already have it.
http://www.mwgfx.co.uk/programs/dxtbmp.htmRun DXTBmp & open C160_disco-elica.bmp (in the Transall_C-160\texture folder).
Double-click on the Alpha channel image at top right to send it to editor.
Select the bucket fill tool & change the palette index to something like 20. The image should change from white to black.
Exit your graphics editor saving changes when prompted.
Back in DXTBmp click Alpha > Refresh Alpha.
Finally click File > Save As > Extended Bitmap. Select DX3 format in the 'Save as type' box & click Save. Overwrite the original file when prompted.
Check it out in FSX. If it works you can paste a copy of the modified texture into the Texture.1 folder.
Note: As this is an FS9 model it won't make it fully compatible with FSX.
Before:

After:
