I’m a bit of a compiler fumbler, but suspect there may be a problem with the AwayPhysics.swc file.

Although I was able to compile the Away3D demo files, when trying to compile physics demos, I get errors like:
Type was not found or was not a compile-time constant: AWPDynamicsWorld.

Instead of giving a neat list of Classes, the FDT explorer it lists some 3000 cryptic items for AwayPhysics.swc in the expanded view.

Previously FDT had problems with the Nape .swc apparently due to the way it was packaged by haXe, the solution was to unzip and recompress it.

Trying the rezip method with AwayPhysics.swc ended up with a file that FTC showed as empty in the explorer expanded view.

//
The same applies to the 7/30/12 build away3d-awayphysics-core-fp11-89744b0

——Amendment 8/8/12——

I tried to compile physics demos using the AwayPhysics src files, but as apparently reported in an earlier note:
http://away3d.com/forum/viewthread/600/
You have to use AwayPhysics.swc in order to get the compiled Alcemy C++ code.
(The Alcemy SConstruct file references AwayPhysics.swc )

I reported to this issue to the FDT staff, reportedly they looked at it.