Research. Research. Research.
There are numerous posts here on typical questions asked at phase 3.
I've never been there and I can tell you that, from what I read here, they might ask you what routes the airlines operate to and from, their current aircraft, maybe their management, how do you think one particular airline compares with the other, what should that airline do to compete more successfully, and also they might ask you which airline you'd like to work for and why.
Don't want to sound like I've been through it all and I know a lot about it, but at least do make a better effort if you want to ace the CTC interview.