CF34-8E
FADEC Full Authority Digital Electronic Control
Dual Channel
In line and cross monitored
independent power supply with backup supply from AC electrical system
inputs
Thrust Lever Angle from RVDTs
stop switch signal
weight on wheels
engine id
application id
air data (total air temperature, altitude, mach number)
bleed system configuration discrete
electronic N1 trim
Take Off Data Settings and Thrust Rating System data
discrete inputs (start, ignition, windshear warning, ice detector, fire handle, maintenance requests)
weight on wheels and wheelspeed data
aircraft monitored propulsion system parameters (oil quantity, oil temperature, fuel temperature, oil pressure, N1 vibe, N2 vibe, thrust reverser)
aircraft configuration data (landing gears position, flaps position)
fault status information on aircraft systems
radio altimeter
P0 (Static Px)
P3 (HP Comp outlet Px)
N1
N2
T2 (Inlet temp)
T45 (ITT)
VG position
OBV position
Ignition
Various signals to and from the Fuel Metering Unit
The signals from the AC are transmitted to each FADEC via an ARINC data bus.
The FADEC can use cross engine inputs in case of data failure.
Channel failures will result in automatic channel swap
Dual channel failures (FADEC critical Fault) will shut down the engine with an ENG FAIL message
The pilot or autothrottle move the thrust levers. The position is sensed and sent to the FADEC. This signal along with all the other inputs is used to set an N1 target.
There are flat spots in the Thrust lever range that act like switch positions. e.g.
Idle flat- The FADEC sets the appropriate idle thrust based on all the other inputs. (there are 4 idles)
CON flat- FADEC sets continuous thrust.
TOGA Flat - the FADEC sets Take Off thrust based on the inputs from the Take off data set and other inputs, or Go Around thrust.
MAX- FADEC sets Reserve Thrust and signal other AC systems to configure. i.e. Bleed air off.
Input from the Automatic Take Off Thrust control system will modify the TOGA flat to give reserve thrust in case of engine failure or windshear based on other AC inputs.
This is just a summary. The tech description is over 100 pages long. The AOM has about 2 pages dedicated to the FADEC.
I presume this thread was started to help understand what may have happened to the 777. Without an full understanding of it's FADEC it's folly to guess what happened.