Relax
I interviewed there recently. I wore a suit. The focus of the interview was on customer service and whether or not you would be someone that they want to sit within 12" of for the better part of 8 days. There was a lot of TMAAT where you: offered excellent customer service; dealt with a really bad day; etc. There were also questions about scenarios around interpersonal challenges. Have a few strengths and weaknesses ready for both you as a person and abilities as a pilot.
Oh, and by the way, I was offered the job on the spot.
Good luck!