No Cockpit Glass

I have a plane converted from FS9. It has extremely low cockpit glass (almost invisible). I used a Hex Editor and looked at the mdl file. It calls out three glass files (glass_l.bmp, glass_d.bmp and glass_t.bmp). In the texture folder there is only a glass_t.bmp. How can I fix the textures up so the glass shows up OK? What do each of the three bmp's do? Thanks, regards, Bob.