Connecting thru Heathrow

If this is on one ticket, you will not have to go through immigration or customs.

What airline are you flying from Amsterdam to London as AA does not fly this route?

If it's British Airways, you will arrive at Terminal 5 and depart from Terminal 3. (Assuming it really is an AA flight and not an AA codeshare with BA.)

So the questions are...

Is this one ticket or two separate tickets?

Will you have checked luggage?

Is your flight from Heathrow really on American or a codeshare with British Airways?

Plug in your flight information at this website and you will get step by step instructions on what to do:

http://www.heathrow.com/flight-connections

If this is one ticket, you follow the purple "Flight Connections" signs. You will stay airside and be driven over to Terminal 3 free of charge. (No immigration or customs.) If you have checked luggage it will be automatically sent to your next flight. Just make sure you have the boarding passes for the continuing flight.

It depends if it’s one ticket or not. Once you confirm that people can advise on whether you need an ETA or not.

Minimum connection time at Heathrow which involves a Terminal 5 to Terminal 3 transfer is 90 minutes. Within T5 (or for that matter T3) it is currently 75 minutes.

This suggests that either the flight to Chicago is actually on British Airways from T5 or this could be a cobbled together itinerary or that the timings have changed. Knowing the flight numbers would most likely sort this out what is going on.

You are all correct. Although I'm buying it thru AA (it's on hold right now), I will be flying W/ British Airways from Amsterdam to Heathrow and then onto Chicago. The 1st flight # is AA7104 & 2nd leg is AA7017. Knowing this, what would your answer be?
We will probably have checked luggage

Unless something changes, you would be in and out of Terminal 5.

Are you purchasing this all on 1 ticket, not separate tickets?

FYI Unless you have high status, if you want to select your seat assignment in advance you will need to purchase them in addition to the airfare. Otherwise you'll be assigned whatever seats are left during check-in. Biz class seat assignments on BA can be pricey.

Put your flight info in on the link Frank provided and it should tell you what you do.

You may find it easier to deal with the BA flight numbers. They are BA 431 AMS-LHR and BA 299 LHR-ORD.

Use the flight connections link I posted earlier in the thread. You will not have to go through immigration or customs, you will have to go through security, your bags should automatically be transferred between flights and you won't have to change terminals.

You also won't need an ETA.

If you want to choose your seats ahead of time, you will need the BA record locater as you can only get seats from them and not American. (Think of AA as a travel agent in this case. All they do is sell you the ticket. BA does everything else.) To get that call AA and ask for it.

If your booking your tickets through AA they will provide both the AA record locater and the BA record locater in your confirmation email.

I flew through Heathrow this week and a few weeks ago, the first time with carry-on only and the second time with a checked bag. Both times the flights were continuous bookings on BA, in and out of Terminal 5. The walking distances aren't a big problem, but security can be slow. Liquids have to go into a little bag they provide. I'm estimating that once I reached the security checkpoint, it took 15 to 20 minutes to get through.

If your booking your tickets through AA they will provide both the AA record locater and the BA record locater in your confirmation email.

That's new. The last time I flew an AA codeshare on BA was before the pandemic when you had to call BA. I stopped flying BA across the pond because of the extra fees to get a seat (in business class.) and to use FF miles.

I now use them, and my Avios points, to fly within Europe.