Apologies if this has been posted already, but I just noticed this on the UK AA site:
New Check-In Location At London Heathrow Terminal 3
We're relocating our check-in facilities at Heathrow Terminal 3 on 1st June.
All Main Cabin (Economy) passengers will be able to check-in at Zone F.
<redacted for current accuracy>
Our exclusive FlagshipSM Check-In for First and Business Class passengers remains at Zone H. AAdvantage Executive Platinum® and oneworld Emerald passengers are also able to use FlagshipSM Check-In at Zone H.
Look out for signage at the airport, which will direct you to our new check-in facilities.
======================MODERATOR NOTE=====================
Airport Information & Ticket Counters (LHR) American Airlines operates from Terminal 3 at London Heathrow Airport (LHR). If your flight is operated by Iberia or British Airways please check the right terminal before proceeding to the airport. Here's your simple guide to set your trip off to a flying start.
Check-In: We have several check-in options available:
- Online Check-In is available from 24 hours and up to 2 hours before your flight departure time
- Check-in desks are located in Terminal 3, Zone F
- Self-service check-in machines are located in Terminal 3, Zone F
- Flagship Check-In for First Class and Business Class passengers is located in Zone H, in the forecourt of Terminal 3
- Ticket Counter Location & Opening Hours
Open Daily from 06:30 to 18:15pm
Saturdays Only – 06:30 to 16:15pm
Codeshare Flight Information: Even when your ticket has an AA flight number, your flight may be on a oneworld® or codeshare partner. To find out if you are travelling on a partner carrier please look for the words, "Operated by…" on your ticket. For codeshare partners terminal location and opening hours please refer to your flight operating carrier.
Link to UK airport information (LHR and MAN)
Link to video about Flagship Check-in, Admirals Club, Flagship Lounge and Arrivals Lounge. It's an overview, and not definitive about who is allowed to use which facility; for that information, please visit the appropriate thread.