Not a chance.
As Doug said no computer on the market today will do that.
The weak link is the graphics card. Those are laptop video cards in the iMac. Just not up to the job. It has a Passmark score of 4956... about on par with a GTX 760. A GTX 980 is 9704... nearly double the power. And IT won't do NEAR 50 fps.
Doug's suggestion won't work, as the video cards cannot be changed in an iMac. The other issue is that you will likely not be able to find Windows drivers for that graphics card. At least that was the issue in past iMacs I've tried to run under Boot Camp.
All that said... SURE you can run FSX on it. Just don't expect unrealistic frame rates. My experience was that it ran better on the Mac than on a Windows machine. And that screen is BEAUTIFUL. But in reality it is just a big laptop with a pretty screen.