I used the search engine but could only see this problem solution for Nvidia cards with a NVnACER tool.

How do I force Vertical sync with my Ati 4870 card?
When looking around with my track ir I see horizontal tearing.

motoadve:

I have a ATI Radeon 4870 X2 and am running Vista 32-bit.  If your system is like mine, then simply selecting "vsync always on" in Catalyst Control Center will not force vsync on in FSX.

My solution was to install Ray Adams ATI Tray Tools (search Google - it is easily found).  In addition to setting it for "vsync always on" in 3D settings, you also need to make sure that you select 2X or 3X in the "Temporal AA" box.

Others have reported success enabling the "Force vsync (Vista workaround)" option on ATI Tray Tools' "Direct3D Tweaks" tab (which can be found if you set up a Game Profile for FSX).  D3D Overrider in RivaTuner does this as well.  However, I cannot use these tweaks on my system because they prevent FSX from launching for some reason.  In any event, I was able to force vsync in FSX through the 3D settings in ATI Tray Tools as explained above.  Good luck.