Shooters, please help me out of this!

Can u guys help me out of these please? Its "in mourning" chapter where I found my lack at most. I'm getting tired to play almost 20x in this singled mission. after roman was killed, Lil Jacob asking to do me a favor which is to find the person whose responsible behind the dead cousin tragedy. ok, I'm going straight to the core point in which Lil Jacob got the chopper to chase Dimitri and his follower, also by helicopter to get the revenge. then Niko has to operate the chopper to track down Dimitri. the thing is I didnt know how to operate this kind of stuff and end up with crashing to the building around. why is that so hard to control the chopper in the mean time I'm good at handling a heli before. is it anything that I didnt complete? or theres any other way to handle the diffrent heli that I should know? please shooter. I'm stuck at this mess