I had a luggage issue that was ex-EU, and I submitted a complaint about it to AC, which they denied, and I objected to the denial, and they sent me a token blow-off amount, and I objected again citing my understanding of the EU law and asking them to clarify their understanding, and they wordlessly sent me a cheque for the difference. There was no "procedure" in my case, just a series of correspondences in which reference to the EU law came up.