[QUOTE
what's engine- trimming? i heard that in FADEC u dont need to do that but for HMFCU u need to make adjustment to it.
][/QUOTE]
Usually a change in the AOA of veriable pitch stator blades to more efficiently compress air and prevent an engine stall RR engines rely on bleeding air. FADEC calculates this angle or need to open/close valves and sends an electrical command to an actuator, say in the case of a CF6-50 it is done mechanically off of the FCU.