I wonder how is designed the command chain from the throttle lever or the auto-throttle to the fuel injection in recent jetliners. I have 4 questions:

What is set by the throttle?

  • When the pilot actuates the throttle, what are they setting exactly? (I can imagine the lever position corresponds to a fuel rate, to a RPM, to a thrust value, etc).
  • Is this value a linear function of the throttle position (e.g. 73% of the full lever rotation is 73% of the maximum N1).

Is the throttle output standardized or customized for an engine model?

  • What type of output has the throttle lever: mechanical, electric, digital data?
  • Which subsystems in the engine receive the throttle output(s)?
  • Is this output customized/calibrated for an engine model, or standardized.

How are the throttle outputs processed in the engine?

  • Does the electronic engine control apply further adjustment to the throttle input?

How does the auto-throttle (auto-thrust) interact with the manual throttle?

  • Does the auto-throttle send its command directly to the engine or to the mechanical throttle?
  • Is the manual throttle position adjusted, according to the A/T output?
  • 3
    $\begingroup$ I don't understand why this is being voted down? $\endgroup$
    – Jae Carr
    Dec 8, 2015 at 20:11
  • 3
    $\begingroup$ I think these are good questions but perhaps could be improved by being more specific. These things have changed over time and are not always the same between designs. $\endgroup$
    – fooot
    Dec 8, 2015 at 20:14

2 Answers 2


Check out this Nasa powerpoint it provides a nice overview of some of the basics and how some of the systems are set up.

Does the auto-throttle send its command directly to the EEC or to the mechanical throttle?

This may vary from design to design but the Boeing 777 uses the ARNIC standard bus to send control signals to servos that physically move the throttle levers. You can read up on the ARNIC 429 data bus here.

Are the throttle levers customized/calibrated for an engine model, or are their output standardized (assuming the output is an electric signal). Does the electronic engine control apply further adjustment to the throttle input?

It seems that Rockwell Collins makes a unit that sends signals to the FADEC system instead of mechanically actuating anything.

With that in mind Im sure there are older designs out there that are closer to or a complete direct linkage from lever to engine.

Is this correction transmitted back to the throttle lever?

I dont think so, it seems that when say full throttle is applied the throttle control will remain at full and the FADEC unit will take care of spooling it up as need be. Likewise if an engine suddenly cuts out or fuel flow becomes restricted as far as I know the throttles will remain in place. Auto throttle units will however physically actuate the throttles as need be. As per the comments here it seems this is only the case in Boeing aircraft. Airbus throttles must be set to maximum setting auto-throttle is allowed to use.

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    $\begingroup$ Auto-thrust units physically actuate the thrust levers in Boeing aircraft. In Airbus aircraft they don't (the thrust levers set the maximum A/T is allowed to use). $\endgroup$
    – Jan Hudec
    Dec 8, 2015 at 21:05
  • $\begingroup$ Thanks for the many elements provided, and Nasa's overview is very helpful. $\endgroup$
    – mins
    Dec 9, 2015 at 8:46

What is set by the throttle?

For the commercial high-bypass turbofans that I am familiar with, the throttle sets a corrected N1 rpm (https://en.wikipedia.org/wiki/Corrected_speed if you aren't familar with corrected speeds). Thrust is not linear with Fan RPM, but its not too far off (for high pass turbofan anyway). This thread may help What is the relationship between thrust and engine RPM in a turbojet?

  • $\begingroup$ Good additions, thanks. $\endgroup$
    – mins
    Jan 10, 2017 at 8:57

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