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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?

user2617804
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    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. – GremlinWranger Dec 08 '22 at 13:43
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    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. – tml Dec 08 '22 at 14:00
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    Simply said - you don't need it, as on the normal throttles you can grip both with no problems. Second - you can use it to "walk the throttle" by adjusting only one while using the second as a reference/hold. – tsg Dec 08 '22 at 14:46
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    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". – FreeMan Dec 08 '22 at 17:04
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    If I'm not mistaken, engine start is generally one at a time. – WPNSGuy Dec 08 '22 at 18:14
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    "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. – TypeIA Dec 09 '22 at 05:29
  • https://www.reuters.com/article/idUSN01319038 Sriwijaya Air 182, AF091. .. – user2617804 Dec 09 '22 at 08:07
  • If there is any safety case against something, there has to be a really good reason for adopting it. This seems to lack any good reasons, and to have potential to cause several different safety problems. That makes it a bad idea. – John Dallman Dec 10 '22 at 19:58

2 Answers2

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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.

John K
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  • Why make fine adjustments? – user2617804 Dec 09 '22 at 08:07
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    To avoid crashing the airplane? – Fattie Dec 09 '22 at 11:42
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    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. – John K Dec 09 '22 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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    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). – FreeMan Dec 08 '22 at 17:01
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    @FreeMan it's almost like there is a soft physical lock made up of the pilot's hand, auto-releasing as required. Ergonomics FTW. – Chris H Dec 08 '22 at 21:33
  • As simple as a bar behind the throttles with a spring loaded with one button press to release the bolt. – user2617804 Dec 09 '22 at 08:10
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    @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. – Fattie Dec 09 '22 at 11:41
  • Pilots are not compareable to drivers- a clean motion to use one throttle could be trained in and its not even compulsory to use- takeoff could be indivdual throttle control- high demand landing situation and inflight are the real risky situations So you also hate the trim release button, the TOGA and the direction control pull. – user2617804 Dec 10 '22 at 04:47
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    @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. – ilkkachu Dec 10 '22 at 12:26
  • sorry @user2617804 , really it just makes no sense. the reason they are separate, is for an extremely important safety reason. (as has been explained on here many time.) nothing more needs be said really. they're separate for a critical safety reason. it would be absurd/bizarre to link them for literlaly no reason. – Fattie Dec 10 '22 at 21:20
  • hi @ilkkachu It has nothing at all to do with that. It was simply an example that you would never, in a million years as it were, add some sort of lock on an immediately-needed safety device. – Fattie Dec 10 '22 at 21:21
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    There you go, @ChrisH, they are actually locked! By the pilot's hand. ;) Excellent point. – FreeMan Dec 12 '22 at 12:38