Welcome to the FlightGear discussions.
When you download scenery from flightgear.org, it is not initially readable
by the program. What I do is, after installing it to my desktop, I use the
fgadmin program located in C:\Program Files\FlightGear\bin\win32.
(I have a shortcut of the program on my desktop.) I do not
personally use TerraSync, but you can download it froom
After you download the tarball, you will need the 7-zip program to decompress
it. That program can be found at www.7-zip.org/
. I hope this helps.