There is a Mac problem with the latest Quicktime upgrade 7.0.4 and importing X-Plane objects. AC3D crashes on startup.
The solution is to get the
7.0.1 re-installer from
http://www.apple.com/support/downloads/
Then if you wish you can also download the
7.0.3 update to bring Quicktime back to where it was before the latest update.
Then wait til either Andy or Ben discover what's happening or Apple releases 7.0.5 which hopefully will not crash AC3D
MIKX