[ Military ] Open Question : What is the difference between a army flight engineer and a army crew chief?

I read on ehow that 15u chinook mechanics are called flight engineers and the 15t blackhawk mechanics are called crew chiefs, is this true? Of course I know this is not when a soldier first enlist in the chosen mos but eventually with time they can try for a slot. So is there a difference between the two and is door gunner training available for both of these jobs or do they usually get another mos to do this?