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I have heard about auto-thrust yet I still don't know what it is. Can someone please explain to me what it is?

I know that I can just Google this up, but I was hoping that a community which revolves around aviation would be able to answer my question.

I did end up using Google to do some preliminary research and I found this definition:

An autothrottle (automatic throttle) allows a pilot to control the power setting of an aircraft's engines by specifying a desired flight characteristic, rather than manually controlling the fuel flow.

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In its basic form, it is just like the cruise control in a car.*

Here is a photo of the autopilot control panel on a Boeing 777. Note the "IAS 200" window on the left:

enter image description here

IAS stands for "indicated airspeed". When engaged, this setting tells the auto-thrust to adjust engine power to maintain 200 knots of airspeed.

Just like a car, when you go uphill you need more gas to maintain a constant speed, and when you go downhill you give it less gas. If the downhill is steep enough, you may have to use some brakes to maintain a constant speed.

Same thing happens when a plane pitches up to climb or pitches down to descend. Airspeed, vertical speed and engine power are closely related - changing any one will impact the remaining two. This is the fundamental of how planes fly, and likely your first ground school lesson if you learn to become a pilot. Auto-thrust is a component of the autopilot system which manages engine power. Note that I used constant airspeed as an example in the previous paragraph: advanced autopilots have many modes, and it can be set to maintain constant vertical speed instead of airspeed. But in all cases, auto-thrust manages engine power.

* Well said TomMcW

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  • $\begingroup$ It is worth noting that many aircraft are not equipped with auto-thrust or auto-throttles, including many of those with sophisticated autopilots. $\endgroup$
    – J Walters
    Feb 7, 2017 at 22:15
  • $\begingroup$ @JonathanWalters I wouldn't call those autopilots "sophisticated" then. And I'd say it's pretty common. Surely it is rare in GA, but on the passenger side, I'd bet at least 8 out of 10 flights you can book at major airlines is flown on an aircraft with auto-thrust. $\endgroup$
    – kevin
    Feb 7, 2017 at 22:24
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    $\begingroup$ I was thinking specifically of the Garmin GFC 700 as an example. I suppose there could be good reason to not call it sophisticated, but I would and others in the industry do. $\endgroup$
    – J Walters
    Feb 7, 2017 at 22:47
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    $\begingroup$ @JonathanWalters the autopilot (and FMC) on Airbus and Boeing can do de-rated takeoffs, fuel economy management, descend energy management, auto-trim etc. I'd say these are the things that are missing, but then I agree many autopilots are very capable even without auto-throttle. $\endgroup$
    – kevin
    Feb 7, 2017 at 23:06

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