Delta alum came to campus prior to winter break for an info session. Applications were due right before the end of the semester and one-on-one phone interviews were held in early January. First-round interview is pretty straightforward. Standard behavioral questions, then a discussion on what you know of/how interested you are in the airline industry. There's a small 'case' that you can't really prepare for, but it's not difficult to answer.
Second-round interviews take place a month and a half later onsite in Atlanta. The entire process starts and ends in one day, so you're up early to be flown in and you're back on the plane by 5PM. The day starts with a presentation, then you have four interviews, some time to talk to a buddy, and you get back on the plane and fly home.
Of the four interviews, one is a more in-depth (and numerical) airline case. One's a review of your resume. The other two are behavioral in nature and have focuses on working in teams and working with data.
I went to Super Day with three other students from my school. None of us received offers or were given any feedback from any of the people we interviewed with.