First and foremost, everyone there is really nice. They fly you to the CLT the night before your interview (stay at the homestead) there will many others there from PDT, in fact I should be there. Feel free to ask questions everyone is really helpful. You will take the 6 a.m. bus to the U.S. Airways training center Mr. Trout will gather you up and take you to the class room where you will take a 50 question ATP style test. Read the gauges they are accurate, go over jepp plates, IFR procedures and weather. If I remember correctly there is also a few 121 regs. They give you plenty of time to complete the test then they will call out the ones who do not pass.
You will then be giving an approach plate and a document that tells you what they expect from you during the sim. The dash-8 sim is always full so you will fly a King Air PCATD.
Lastly they will call you in for the HR interview, for me it was Mr. Trout and one other guy. They may or may not ask some technical questions they did ask me a few, but they were easy and just evolved Jepp plates.
Remember relax and have fun.