Originally Posted by
TheBusFlyer
My question might sound stupid…but you wrote -If the thrust lever is here , the required N1 should be this value.
If TMS/FMC are already doing the maths for the target N1 to be achieved, why is EEC trying to figure out what is the N1 value ? Why can’t TMS/FMC just send the target directly to the EEC?
From what I understand, TMS/FMC are doing the maths to figure out what’s the target N1. Behind they position the thrust levers. Given their position, EEC also does the maths using different parameters + TLA to figure out the required N1…sounds a bit redundant. Also implies that TMS/FMC know the EEC parameters (Mach, pressure etc) as well to position the thrust levers correctly.
AFAIK the FMC doesn’t send anything to the EEC, it just computes the appropriate N1 for the mode that it is in and displays/demands this. If, say, the TAT is in error (this happens in ICI) then the wrong values for the ambient conditions will be calculated which could lead to a significant under/over N1 command for what actually exists outside. The engines and the FMC get environmental variables but they are not from the same sources, hence the possibility for disparity and alternate mode.