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Yes I would say it's possible, and if on one ticket it's not necessarily a problem since you would be rebooked on to the later service anyway if you missed the earlier flight. Depends a bit on where the next flight is going to, if there is one flight a day you may want to look at this again. Also if you are put on the next flight it depends on whether there are spare seats going - and again it depends on the final destination as to the likelihood of that. VIE would normally be fine for example.
If on two tickets, OR you have checked luggage that needs to be rechecked (various rule apply here), then it's not a good idea.
T3 Flight Connections is quite slick, you can certainly do it in practical terms if the AA flight is on time or even 20 minutes late. The only slight problem is that some T3 gates are a long walk from Flight Connections.
If connecting at T3 without needing to recheck luggage then there is no passports, no customs (which is non existent in much of Europe these days) and no conformance either. There is conformance (or rather Positive Boarding) if you have to go landside to recheck luggage, which makes this journey infeasible.