For the group you are given some exercise where you have to work together with the others, agree for a common solution to reach a goal, etc. Let's say they tell you you have 15 minutes to decide where to open a new base and why.
The interview with HR is more about your personality, why you want to join, what motivates you etc. They will ask you some questions about handling delicate situations (you see a captain drinking in the pub and you're flying the next morning together - what do you do?), or some questions to throw you off guard and see how you react under stress.