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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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3 Answers 3

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More specifically on your question:

See diagram below:

enter image description here

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).

enter image description here

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

  • FCU
  • FMGC/S
  • EIU or EEC
  • FADEC
  • 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.

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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).

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