Basically, it involves downloading a program called DXTBmp from
http://www.mnwright.btinternet.co.uk/pr ... dxtbmp.htm, finding and opening up the glass texture, using the program to export the alpha channel to your image editor, changing it to black, saving it, refreshing the alpha channell within the DXTBmp, saving it, and putting it back into the aircraft texture folder.
Also, always make a backup of the texture file before you edit it