You need to download a program called DXTBmp and to inverse the alpha map ;)
I am sure this is correct but this method is not so easy to the non computer minded person and probably do not have a clue as to what you are talking about. Having never messed around with bitmap editors this is not as simple as you make it out to be.
some might need a little more information. 8-)
Then I sugest you pop on over to:
http://www.sim-outhouse.com/sohforums/index.php?
And go to the FSX forum. There were a couple of threads recently that addressed this
"SP2 induced" problem for that particular aircraft as well as others.
I believe there were links to some replacement prop textures in one of the
threads. A simple matter of copying a new prop texture into each "texture"
folder....
That said, even many replacement prop textures, although fixing the SP2 inducded
opaque pros will still show SP2 induced problems where the prop disc will become
totally transparent ( invisable ) when viewed with clouds and some scenery objects
behind the disc. I THINK they look OK from within the VC. Just about every FS9
aircraft imported into FSX will exhibit SP2 induced problems that were NOT present
in FSX RTM or SP1. SP2 PORKED most FS9 aircraft

Paul