As I understood, the passenger was on time checking in (in MIA) and it was completely appropriate for the passenger to think that the bags will be checked through. So I would argue that the pax was in the check-in on time, it was the airlines fault that they didn't manage to interline luggage.
So the passenger was delayed because of the airline. And the pax got delayed on eu-bound flight. And the delay wasn't caused by extraordinary circumstances, but because of CI agent not checking the luggage through. So under those circumstances I'm still fairly certain that it would fall under the EU261.

edit: The OP said that the landing was delayed only by 2,5h, so the EU261 is out of the question anyways for this case.

The delay was on a JFK bound flight that departed from MIA, flown by AA, a non-EU carrier. EU261 wouldn't apply in any way shape or form. The fact that the passenger was connecting to an EU-bound flight doesn't trigger EU261 compensation. And it wouldn't have mattered if the OP was on BA flight numbers; it's the operating carrier that matters.

It doesn't matter what the reason why the airline in Miami chose not to check the passenger through - that flight is outside the remit of EC261

as such the passenger was required to check in in JFK ; not meeting check in times is an exception to compensation requirements

With this being a single ticket, the bags should have been checked through and passenger been ok catching the flight; it may be that some token compensation might be given by AA if the passenger has an AA account

Even so, as mentioned , even if there was entitlement, the delay was too short unless it counted as a cancellation

I realize this is not the appropriate thread but figured there's someone that could help me out. I have a 6 hour layover in T5 from BA to BA. Is it possible to transfer from T5 to T3 to use the CX lounge and then return to T5 for my flight?

Yes, it is - I did it a few weeks ago - but it's a hassle. You have to go through security twice, which especially now may take a long time, and the buses take a while too, but it is possible if you so desire. Follow signs for flight connections T3 after you land at T5. You may have to explain to the bus area staff and/or security when they see your BP that you want to use the T3 facilities, as they will see you're departing T5.

After you leave the CX lounge at T3, go towards the end of the lounge corridor (past the BA and AA lounges) and you'll find a door to flight connections back to T5.

Security theatre at the moment has been stepped up considerably. People doing "unusual" things may be cross examined in some detail.

Owing to recent events in the UK this will be looked upon with a great deal of suspicion. Would suggest dropping the idea and sticking with the T5 lounges.

Thanks for the suggestions everyone!

LAX-MIA-LHR (via AA) & LHR-MAD (via BA) Question(s)
 

Yeah, I am the bad guy as I booked this 3-leg itinerary for my wife with her +1 to ultimately arrive in Madrid. It is a Business Class ticket.

Question:

Upon arrival in LHR from MIA in the morning via AA metal ... where she has a 3+ hour layover before the LHR-MAD leg via British ... will she be able to use the American Arrivals lounge before going through "security" en route to the BA terminal?

(she will not be checking any bags, FWIW)

Or will she be forced to go through "security" and take a Bus to the BA terminal before she can use the BA lounge?

I am simply trying to give her the best guidance of how to best glide through LHR (Terminals 3 and 5 I presume) while havingthe ability to shower up before traveling thru to MAD.

Hope this question makes sense.

Thank you ...

According to the LHR maps, the Arrivals Lounge is outside of the secure area. So, it would seem that she needs to "arrive" to the UK and exit before she's able to access it. Then she would have to connect landside to T5 to make her LHR-MAD flight.

If she stayed airside and connected on the bus to T5 from T3, she would just need to do a basic security check at T5. She can then go to the BA lounge and shower there.

She can do either, but it will be simpler to just go to T5 airside and shower in one of the BA lounges there. They aren't amazing but they do the job fine.

To use the AA lounge, she will need to go through immigration at T3, which if she is a non-EU citizen can take a while, even with Fast Track. She would then get either the Heathrow Express or the Tube to T5, which run at 15m and 10m intervals respectively. Both are free, but she'd need a contactless credit/debit card or oyster card for the Tube.

When she arrives in LHR she can go through immigration (which can take a long time) and then to the AA arrivals lounge.
The AA lounge is nothing fancy or exceptional to force a stop there, IMO.

She'd be better off just taking the bus T3-T5 as soon as shelands, clear security at T5 and then head to the T5 BA lounges that have showers, food, drinks, etc, etc. The T5 BA lounges are far superior than the AA arrival lounge, IMO.

I concur so long as the T5 BA lounges are not full of people. Sometimes they are. But the same can be said of the T3 AA arrivals lounge in the early morning.

Thank you to the last four posters for clear guidance ... I will advise my wife to simply take the "Fast Pass/ Fast Track" paper they give on AA, go through that Lane, and to stay "airside and connect on the bus to T5 from T3, she would just need to do a basic security check at T5. She can then go to the BA lounge and shower there."

To get the airside buses at T3 there is no fast track - everyone queues together. Basically follow the purple signs for flight connections T5.

On arriving at T5 and going up the escalator head to the far right lane which is fast track for INT-INT connections, then follow the fast track marked esclators up to north security.

On coming out of security there is a GC lounge to the left and there are some showers in there. Otherwise head to the south lounge complex (downstairs after security and to the other end of the terminal then back up one floor, and there are showers in the elemis spa marked area off the lobby between the GF and CCR lounges.