Two things missing from people's math. You can't be %99 sure he has an ace. He could have two pair of various kinds, so I really think you have to factor in at least some chance he doesn't have an A.

The other factor is that you have 3 outs to a full house. So approximately %6 of the time you'll win the whole pot, so you really have to subtract that from his chance of winning the whole pot with a flush draw.