Gas Turbine FADEC

Fuel Control and Metering Systems Full Authority Authority Digital Engine Control (FADEC) ~ A category of electronic control is FADEC which takes over virtually all of the steady state and pneumatic elements of the fuel transient control intelligence and  replaces most of the hydro-mechanical and pneumatic  system.  system. valve and the power ~ A digital A digital computer controls a servo-operated fuel valve and the  power lever is only electrically connected  to  to the fuel control. pump and control valve, valve, an independent shut-off cock and a ~ The fuel The  fuel system is therefore reduced to a pump minimum of additional features necessary to keep the engine safe in the event of extensive electronic failure.

Compare the advantages of FADEC over hydromechanic mechanical al engine control: hydro -mechanical -mechanical • It requires no requires no engine trimming  • It ensures improved engine starts • It provides a provides a constant idle speed  with  with changes in atmospheric conditions and changing service bleed air requirements • It saves It  saves fuel  by  by providing improved engine bleed air management • It fully modulates the active clearance control (ACC) system (if fitted) • It provides engine limit protection by automatically limiting critical engine pressures and speeds

Fuel Control and Metering Systems FADEC (contd.) Specify the key purpose of having hav ing a two channel FADEC system: ~ two separate computers that are physically separated internally ~ Improve reliability reliability of the the engine ~ Redundancy - each channel can completely control the operation of the engine ~ Reduce flight flight crew crew workload workload reversionary ary modes: Describe reversion ~ N1 reversionary mode ~ If there is a total failure of N1 inputs to both FADECs the FADEC reverts to the “N1 Reversionary Mode” ~ In this mode the FADEC synthesizes N1 (N1 SYN) as a function of N2 and the ambient conditions ~ If for example, EPR is lost, the engine will run on its N1 settings ~ The FADEC will control the Engine by governing N2 speed ~ Engine control response times will be greater and the actual thrust output may be less accurate Specify the purpose of the “Rating” “R ating” or “Identification” “Identificatio “Identification” n” plug: ~ Most FADEC engines have multiple thrust ratings available ~ Thrust rating on a FADEC controlled engine can be changed by changing the engine rating plug ~ A 'rating plug' or 'data entry plug' plugs into the FADEC to tell it which rating to select ~ The rating plug is typically considered part of the engine and connected to the engine by a lanyard (e.g. if a FADEC is replaced due to a fault, the rating plug remains with the engine) ~ the rating is listed on the engine data plate - an engine company service bulletin is required to change it, which changes the rating plug and data plate

 Location of Rating/ID plug on the FADEC EEC