kmw510

MCP VS Thumbwheel direction

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Does anybody know the reasoning behind having the mcp vertical speed thumbwheel rotate in the opposite direction? Up is pointing down and down is pointing up. I don't think they would have designed it that way unless there was specific reasoning associated with aircraft operation or some human factors issue.

 

Kevin Wilson

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it is the same with the trim buttons on the Yoke. Moving down moves the nose up, moving up moves nose down.

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Don't think of the VS wheel as up and down.   Think of it as forward and back,  like a trim switch... then it makes sense. 

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16 hours ago, kmw510 said:

Does anybody know the reasoning behind having the mcp vertical speed thumbwheel rotate in the opposite direction? Up is pointing down and down is pointing up. I don't think they would have designed it that way unless there was specific reasoning associated with aircraft operation or some human factors issue.

Literally everything else in the plane works this way:

  1. Yoke: A pull back is essentially a roll of the 'wheel' back towards you - nose up
  2. Trim: A roll of the wheel back towards you - nose up
  3. Trim buttons: A pull back/down is essentially a roll of the 'wheel' back towards you - nose up
  4. VS Knob: A roll of the wheel back towards you - nose up

So, I would turn the question around:
What reasoning is going on in your mind where the opposite case would be 'logical'?

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2 hours ago, scandinavian13 said:

What reasoning is going on in your mind where the opposite case would be 'logical'?

You want the nose to go up/down - trim button up/down. V/S climb/descent - wheel up/down. Makes sense too imo, got me confused initially too.

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2 hours ago, scandinavian13 said:

Literally everything else in the plane works this way:

  1. Yoke: A pull back is essentially a roll of the 'wheel' back towards you - nose up
  2. Trim: A roll of the wheel back towards you - nose up
  3. Trim buttons: A pull back/down is essentially a roll of the 'wheel' back towards you - nose up
  4. VS Knob: A roll of the wheel back towards you - nose up

So, I would turn the question around:
What reasoning is going on in your mind where the opposite case would be 'logical'?

Kyle,

My reasoning is based upon every other thumbwheel I have ever used either rolls forward or up to increase a value and backward or down to decrease a value or rolls in the direction you want to effect a change. My question was simple and Roar answered with a single sentence. I don't see the need for sarcasm.

 

Kevin Wilson

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28 minutes ago, kmw510 said:

I don't see the need for sarcasm.

Agreed. That's why there wasn't any in my earlier post. I was genuinely curious, given the earlier point that you made about human factors. You, yourself, brought up human factors, so I'd assumed that in your mind, you were considering the points I had raised (i.e. were using other examples of human-computer interfaces on the flight deck). With that in mind, I was curious as to what logic you were applying to the concept, regarding human factors in the flight deck. I'm not in your head, though, so I cannot assume what is going on inside of it. As such, I asked what thought process was going on in your head that justified the opposite directionality of what exists in reality (outside of your head).

Your answer here, though, seems to point less to aviation-related HF, and generic computer interfacing, so that answers my question.

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33 minutes ago, scandinavian13 said:

Agreed. That's why there wasn't any in my earlier post. I was genuinely curious, given the earlier point that you made about human factors. You, yourself, brought up human factors, so I'd assumed that in your mind, you were considering the points I had raised (i.e. were using other examples of human-computer interfaces on the flight deck). With that in mind, I was curious as to what logic you were applying to the concept, regarding human factors in the flight deck. I'm not in your head, though, so I cannot assume what is going on inside of it. As such, I asked what thought process was going on in your head that justified the opposite directionality of what exists in reality (outside of your head).

Your answer here, though, seems to point less to aviation-related HF, and generic computer interfacing, so that answers my question.

Kyle,

I brought up human factors versus aircraft operation based on the varying and conflicting views I read about the use of V/S on the MCP. If V/S is used solely for setting a definite vertical speed then why not a knob to set the displayed value just like almost every other method of setting a value in the cockpit. From what I have read no one rolls the thumbwheel to see how it affects the plane, they simply roll it to a specific value or until the green altitude arc is placed where it needs to be. I inferred sarcasm from your use of the single quote marks around the word logical in your question.

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16 minutes ago, kmw510 said:

From what I have read no one rolls the thumbwheel to see how it affects the plane, they simply roll it to a specific value or until the green altitude arc is placed where it needs to be.

Correct. They don't test (in theory) how it would affect the VS setting, and therefore the aircraft. They simply set it by following the logic of every other wheel in the plane.

17 minutes ago, kmw510 said:

I inferred sarcasm from your use of the single quote marks around the word logical in your question.

It was only intended to show that it was hypothetical/theoretical logic, as it didn't align with the logic of the actual methodology.

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54 minutes ago, kmw510 said:

If V/S is used solely for setting a definite vertical speed then why not a knob to set the displayed value just like almost every other method of setting a value in the cockpit. From what I have read no one rolls the thumbwheel to see how it affects the plane, they simply roll it to a specific value or until the green altitude arc is placed where it needs to be.

This is actually a fair point. If the same logic followed through to the MCP altitude select knob, it would presumably roll toward us to emulate a power setting decrease for a descent to a lower altitude, and vice versa, although I suppose it could sort of go the other way too if it was emulating a pitch down. I guess it all depends on how one relates to the aircraft controls, whether one sees the autopilot controls as their own thing, or as being related to manual control inputs.

Interesting to note that the selection knobs on an Airbus MCP forego all that stuff for V/S and instead function a bit more like a 'volume knob' on a stereo, i.e. clockwise to increase a value and anti-clockwise to reduce it, as is the case for some MCP controls on a Boeing. As far as I'm aware, that is intentional on the part of the Airbus designers in terms of haptics, whereby the newer generation of pilots are expecting things to work like the controls on everyday things they are familiar with. Although as we know, in different modes, that seemingly more commonplace switchology can still catch people out, as it did with the crew of Air Inter Flight 148, when they dialed in -33 for the descent rate, thinking they were dialing in -3.3 degrees for the Flight Path Angle, which made them come down into a mountain at 3,300 feet per minute instead of at a typical approach descent angle, because they forgot to select FPA. When one considers that particular accident, one might conclude the Boeing way is a bit smarter, since it would in that case at least, have prevented that confusion.

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19 minutes ago, Chock said:

This is actually a fair point. If the same logic followed through to the MCP altitude select knob, it would presumably roll toward us to emulate a power setting decrease for a descent to a lower altitude, and vice versa, although I suppose it could sort of go the other way too if it was emulating a pitch down. I guess it all depends on how one relates to the aircraft controls, whether one sees the autopilot controls as their own thing, or as being related to manual control inputs.

Not quite sure I follow this logic.

V/S is a pitch mode. It would follow that the wheel for the V/S setting would emulate the pitch trim wheel. Your logic forces a logical jump from pitch to pitch for speed, based on throttle motion, which is an entirely separate function and action.

I can see how you've linked them, but that's an additional layer of logic, where, when dealing with humans and interfaces, you really want to keep it as straightforward as possible.

Imagine explaining pushing the yoke forward to go up because pushing forward to go up requires more thrust to accomplish that action.

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I'm with Kyle.

Every plane I've ever flown has trim wheels or VS wheels (or even raw CWS autopilot functionality) that works in the same way. I.E. emulating the trim wheel direction.

the MCP is just a VS selector but it works in the natural way. I could get very confused if it didn't. 11,000 hours of flying will do that to an old man!

 

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2 hours ago, scandinavian13 said:

Not quite sure I follow this logic...

when dealing with humans and interfaces, you really want to keep it as straightforward as possible.

Well, there you said it youself, keep it straighforward; a rotating knob, with clockwise to increase and anti-clockwise to decrease is about as simple as you can get. It's intuitive too, since pretty much everything else in the world - from a gas cooker hob switch, a volume knob, a car ignition switch, watch winder, light switch dimmer etc, etc - moves in that way, which is presumably why Airbus did it that way.

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I'm going with Boeing on this one. Trim wheel, yoke movement, V/S all move in the same direction.

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