I am from Chicago and looking at a flight home from Barcelona that connects at Heathrow. There is a plane change and the time between flights is only 70 min. It is all on American (codeshare with BA). Is that enough time? Do I have to go through customs/passport control/security at Heathrow? Thanks!
Check the flights and see if they land at and depart from the same terminal. BA flights to/from Barcelona go from T3 but I don't know if that applies to American. Even if you stay in the same terminal, you will go through ssecurity again before boarding the flight to the US. If you have to transfer terminals, you can follow the signs to "flight connections" and stay "airside" so you do not have to go through immigration/passport control. There is a free bus that takes you between terminals. This assumes you either have carry on bags or have checked them through. Once you know the terminals you can check the Heathrow website for the legal connect times and how to best do it. http://www.heathrowairport.com/heathrow-airport-guide/flight-connections
I found the Heathrow connection help page
http://www.heathrowairport.com/heathrow-airport-guide/flight-connections but the flights I'm looking at don't come up when I search for which terminal they arrive/depart (they are in October, so maybe that's too far ahead to know), but it looks like they give the min connection time as 75-105 minutes unless you are connecting in the same terminal. Even then they give the min as 60 minutes. I didn't think there was a later flight out of Heathrow for the same price, but now I see the otherwise same itinerary with a 2:50 layover between flights. I'll go with that one.