I have a Y ticket on AA that was booked via a convention/group fare. It says "valid AA only," but I wonder if UA would accept it? I know that, for example, the DL/US shuttles accept either others tickets even if the endorsement says that it is only valid on one of the carriers. This is a BOS-ORD round trip ticket. It is currently electronic, but I could print it oto paper. Has anyone ever tried this?