B777 EEC functions
Hi
Premetting i am not a B777 driver so go easy on me, i have a few questions regarding the engine fuel system and the EEC.
As far as i understand pressurized fuel from the engine fuel sov is delivered into the metering unit or EEC controlling the thrust output of the engine by modulating the fuel flow to the engine based on inputs from the thrust levers and based upon a number of parameters.
The EEC can operate either in the normal mode or in the alternate mode.
When operated in the normal mode the EEC modulates the ff so as to control the N1 based on inputs from the thrust levers. Besides fuel metering the EEC will also provide reference/target N1 or EPR computed by the FMC; red line based on environmental conditions, maximum N1 or EPR based on environmental conditions and corresponding to max thrust available as the thrust levers are advanced to the mechanical stop, N1 and N2 or N1, N2 and N3 overspeed protection based on the engines preventing the computed red line from being exceeded when the TL's are advanced to the mechanical stop reducing the ff to the engine and triggering an EICAS message; overboost protection and idle selection - minimum or approach.
Should any of the requied inputs become unavailable the system will revert to an alternate mode - either soft or hard.
Now what is the difference between overspeed protection and max N1/EPR?
What is exactly overboost - is it some kind of compressor stall protection?
What are the required inputs?
What functions do u loose when in the alternate modes - other then overboost protection in the hard mode, if i am not mistaken?
Many thanks
Baobab