I'm another person known by my middle name. It's not just flights/tickets. Almost every organisation I know assume without asking that using my first name is correct. One of the few who asked was my dentist whose records now have my full name but they know I am known by my second name.
The one I find most irritating is banks. I have to keep reminding people to make out cheques to my first name or initial and at least a couple of times a year someone forgets and my bank won't process it. They used to; there was a way of recording alternative names that cheques could be made payable to. They claim it's all to do with money laundering.
In the end, I've learned to live with it. Any form of travel booking (trains, planes, hotels, cars, ferries etc etc) now go in the form first name/last name. If someone on the phone tries to use my first name I just tell them I don't use that name and after some embarresment and confusion on their part we end up with Mr Hartington.