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A physical lock so one throttle can control all of them. Sure there would be circumstance to disconnect it such as engine failure and possibly wind shear but there really too many instances of pilots and occasionally system failures causing one engine to not track other engine(s) output and at very least cause a significantly increased workload and contribute to severe accidents. So what isn't it physically interlocked?

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    $\begingroup$ Does there need to be a better reason than 'every single engine failure now becomes a twin engine failure because you have to take both throttles to zero'? This will indeed avoid problems associated with asymmetric thrust but replaces them with some other rather substantial ones. $\endgroup$ Dec 8, 2022 at 13:43
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    $\begingroup$ And even more for something like the B-52, with eight engines, and (if I understand correctly) throttles that aren't physically coupled. One would think it is quite easy for the pilot to accidentally lose grip of the leftmost or rightmost throttle when trying to move them in synchrony. $\endgroup$
    – tml
    Dec 8, 2022 at 14:00
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    $\begingroup$ Most twin-engine prop aircraft run with the throttles slightly offset all the time to eliminate the "thrum" of props beating the wind every so slightly out of rhythm. There are many twin-engine props used today as "passenger airliners". $\endgroup$
    – FreeMan
    Dec 8, 2022 at 17:04
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    $\begingroup$ If I'm not mistaken, engine start is generally one at a time. $\endgroup$
    – WPNSGuy
    Dec 8, 2022 at 18:14
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    $\begingroup$ "there really too many instances of ..." can you back up this assertion (with statistics or concrete examples)? I believe such cases are extremely rare to the point of being practically nonexistent. Locks are a (bad) solution without a problem. $\endgroup$
    – TypeIA
    Dec 9, 2022 at 5:29

2 Answers 2

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The problem with physical locks:

A locking device can fail "on" (same reason carbureted piston engines use primer systems instead of chokes) so you are stuck with both/all levers ganged together, which can be a problem in an engine fire situation. So it's out of the question for that reason alone.

The other one is, except with the latest FADEC engines, the throttle/thrust lever is a mechanical connection with rigging allowances, connected to a hydromechanical (with electronic trimming on newer engines) fuel control system. Much of the time the two levers are not perfectly matched when Torque or N1 or EPR values are matched (often it's just from having a low time engine on one side and a high time engine on the other side).

Another minor factor is when moving the levers in small increments, you "walk" them along which makes it much easier to make very fine adjustments, which you couldn't do if they are locked.

So overall, there are safety show stoppers, and the concept isn't really desirable operationally.

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  • $\begingroup$ Why make fine adjustments? $\endgroup$ Dec 9, 2022 at 8:07
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    $\begingroup$ To avoid crashing the airplane? $\endgroup$
    – Fattie
    Dec 9, 2022 at 11:42
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    $\begingroup$ You are often tweaking the levers to make tiny changes. Say on an approach you are 6kt fast, you need to make a very small thrust reduction, then wait for the result. That's how you avoid chasing the thrust/speed all over the place. Walking them back makes that much easier. You're using one lever as an anchor to rotate your hand to make a tiny movement in the other, then vice versa. $\endgroup$
    – John K
    Dec 9, 2022 at 13:56
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Most "passenger airliners" are twin engine and are operated with the auto-throttle system engaged (managing throttle movement) throughout most of the flight.

A "physical lock" would seemingly provide no benefit in addition to, or in place of, an auto-throttle system. It would also, for one example, negatively impact engine failure flight crew procedures by requiring the "lock" to be released/removed when confirming and identifying the failed engine.

Also, a person's hand on twin throttles covers both throttles at the same time without difficulty. Even four engine aircraft like a B747 has throttles that can be moved with a single hand.

There are many reasons why having a "physical lock" between the throttles on modern passenger airliners would not be beneficial, and would be an impediment under certain circumstances.

B757 Thottles B757 Throttles (source: This previous A.S.E question)

B747 Throttles B747 Throttles (source: This question on Quora)

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    $\begingroup$ It's almost like they designed them to be moved in unison with one hand on purpose! TBH, I'd expect that the extra time required to remove a physical lock (even if it were only a flip-catch of sorts) would be extremely detrimental in an emergency (like one engine out on final approach in a strong crosswind). $\endgroup$
    – FreeMan
    Dec 8, 2022 at 17:01
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    $\begingroup$ @FreeMan it's almost like there is a soft physical lock made up of the pilot's hand, auto-releasing as required. Ergonomics FTW. $\endgroup$
    – Chris H
    Dec 8, 2022 at 21:33
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    $\begingroup$ @user2617804 - that would be a profoundly horrible idea. Imagine on your car, if, there was a small catch on the brake pedal "for convenience". When you had to use the brake pedal, you had to release the catch, and then use the brake pedal. $\endgroup$
    – Fattie
    Dec 9, 2022 at 11:41
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    $\begingroup$ @Fattie, just the minor difference that brake pedals are usually operated by foot, probably with a shoe on, and the throttle levers by hand. There's a rather significant difference between the fine motor skills of the two appendages. $\endgroup$
    – ilkkachu
    Dec 10, 2022 at 12:26
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    $\begingroup$ There you go, @ChrisH, they are actually locked! By the pilot's hand. ;) Excellent point. $\endgroup$
    – FreeMan
    Dec 12, 2022 at 12:38

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