An Airbus A320 has seven computers that control flight surfaces: two ELAC, three SEC, two FAC, and two AP (autopilot) computers.
Is there an separate computer that controls auto thrust, or is this controlled through one of the above?
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More specifically on your question:
See diagram below:
In the autothrust mode (A/THR function active), the FMGC computes the thrust, which is limited to the value corresponding to the thrust lever position (unless the alpha-floor mode is activated).
So as you can see computers/controllers that control the A/THR are:
- EIU or EEC
The **speed or Mach target may be:
‐ Selected on the FCU by the flight crew
‐ Managed by the FMGC.
EPR mode is the normal mode to control the thrust. The required EPR is set by controlling the fuel flow.
DSC-70-35-20 P 1/2
The FADEC has two mode of power setting, EPR and N1 modes. The FADEC computes the command EPR as a function of :
‐ Thrust Lever Angle (TLA)
‐ Mach number
‐ Ambient temperature
‐ Air inlet total temperature (T2) ‐ Service bleed.
Arming conditions of the A/THR are numerous. The following is a list of the most important ones:
‐ One FMGC operative
‐ One FAC operative
‐ Two ADIRS operative
‐ Two FADECs operative
‐ One channel of the FCU operative
‐ One LGCIU operative
‐ A/THR is not manually disabled (instinctive disconnect pb has not been pressed for more than 15 s).
So to summarise: FMGS computes the THR and the FADEC computes EPR and through EIU/EEC and ECU commands the fuel flow to the engines in order to give the desired EPR.
The Flight management and guidance system (FMGC) performs the following functions:
The FMGS sends the thrust commands for the autothrust function to the ECU1/EEC1 to set the thrust command on the engine 1. ECU2/EEC2 to set the thrust command on the engine 2.