Originally Posted by
angatol
Your post is a bit confusing. If you're arriving at LHR T3 from ORD, you aren't on BA, so you'd be checking in at the AA desk in ORD. Then there's no F to PRG, and even in J there's no guaranteed priority baggage handling in CE on BA. So whatever you're trying to achieve doesn't seem fruitful.
I think...
The OP means that they're arriving at ORD T3 but departing ORD T5 on BA metal.
BA do offer priority baggage in CE.
I think the question is about getting F tags at ORD as presumably the OP is flying F TATL.