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?


3 Answers 3


More specifically on your question:

See diagram below:

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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).

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So as you can see computers/controllers that control the A/THR are:

  • FCU
  • FMGC/S
  • EIU or EEC
  • ADR

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)

‐ Altitude

‐ 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 autothrust functions in the A320 are performed by the Flight Management and Guidance Computers, or FMGCs (what you call autopilot computers -- they indeed handle autopilot duties as well).

  • $\begingroup$ Is the FADEC part of the FMGC or additional ? $\endgroup$ Commented May 18, 2015 at 10:15
  • $\begingroup$ @PeterBourne -- the FADECs are completely separate (1 primary/1 backup per engine) $\endgroup$ Commented May 18, 2015 at 22:22

The Flight management and guidance system (FMGC) performs the following functions:

  • Autopilot
  • Flight director
  • autothrust
  • flight management

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.


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