Hi, I've been reading this thread but still I'm not sure if EU261 applies in my case.

We just came back from our HNL TP run thanks to the 2x£2014 offer, HNL-PHX(US)-BOS(US)-LHR(BA).
On the HNL-PHX leg, we were downgraded from F to Y, apparently because of a "last minute change of aircraft", but that was not true since the seatmap always showed the 12 F seat version (not the 14 seats), but I was never able to choose a seat (all appeared as blocked). US simply oversold the F cabin.

Anyway, the gate agent told me I was elegible for a partial refund, but I'm not sure under which regulations, since the airline for this segment (US) was not an EU one, although my final destination was in the EU with an EU airline (BA).

So, should I claim to BA under EU261, or to US or AA under their own terms?

Thanks.