I'm sure this is a FAQ, but the search feature isn't working for me today. I was wondering: Do you earn frequent flyer miles on AA when you check in, or when you actually board the plane?

Here's a scenario where this might come up. I buy a round-trip ticket DFW-LAX. While in LA, I find out that I need to fly to Chicago before returning home. My DFW-LAX ticket is nonrefundable, so I end up not using the return LAX-DFW leg and just flying LAX-ORD-DFW.

Obviously, I get the miles for LAX-ORD-DFW. Here's my question: If I were to check in online for my original LAX-DFW leg, but then not fly, could I also get the miles for that leg? Or is there a special switch that's only flipped when I actually get on the plane, which allows me to get miles for that leg?