Boeing 737 Max MCAS System

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I agree with that. I just prefer to see them in a thread that is not linked to a recent accident.
I understand your sentiment. Let's keep in mind that while the incidents raise these concerns and inquiries, they are not closed cases, and while there is some compelling initial evidence that implies there is something wrong with the plane, it's definitely not conclusive. Whether the aircraft is at fault or not, no one should be prematurely assigning any culpability.
 
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All 737 Max grounded !!

Looks like something nasty has shown up in the flight data...

Truly, advances in safety are too-often bought in blood...
To clarify, I don't think it was the data from the FDR. It seems unclear whether the FAA did this from public pressure and optics or it is in fact from the same data Canada received about the plane altitude during the flight via satellite. The odd thing to me is that I saw the graphs for the erratic rate of decent and climb almost immediately after the crash, which would show the similarity to Lion Air. Perhaps the satellite data confirmed this previous early data or perhaps indeed it was more about optics.
 
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Is that under computer control or is that the pilot or a mixture?
On the F-14 that would be pilot control. The F-14 never got any kind of fly-by-wire. They're all out of service now; I believe the F/A-18, which is the Navy's main jet aircraft now, does have some fly-by-wire controls with computer software involved.
 
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It seems here that there is no clear way to clear way to disable the MCAS in the event of a failure. Am I reading this right?
Not as far as I know. As I understand it, the "master trim cutout switch" referred to disables all automatic trim control, including MCAS. What the pilot is saying is that, now that pilots know about the risks involved with MCAS, at the first sign of any anomaly, instead of going through the steps Boeing says, which they don't trust to actually be effective, they're just going to disable automatic trim control entirely and adjust it by hand, since that way they know what they're dealing with.
 
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All 737 Max grounded !!

Looks like something nasty has shown up in the flight data...

Truly, advances in safety are too-often bought in blood...
It looks like indeed the early information was radar / land based. The new information that lead to Canada and then the FAA grounding the plane was from satellite data from Aireon. Not sure why the early radar data wasn't enough when other authorities felt it was, probably multiple factors involved, but it's safe to say it doesn't look good on Canada or the FAA to not lead on this.

 
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t does seem MCAS is closely related to protecting the plane from entering a stall scenario.
Only in the sense that it is giving the pilots the feedback, through the stick force, about how close the plane is to a stall, that the pilots are used to from previous 737 models. The point of MCAS is that without it, the stick force feedback as a function of angle of attack would be different from what the pilots were used to, so they might misjudge how close to a stall they were.
 
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Only in the sense that it is giving the pilot the feedfback
Is it not also adjusting the pitch in addition to providing feedback?
 
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Is it not also adjusting the pitch in addition to providing feedback?
They aren't two separate things. Giving the feedback means adding more nose down trim, which, if the pilot does not compensate by increasing the force he uses on the yoke, will pitch the nose down. Any adjustment of trim does the same thing: it changes the force the pilot needs to exert on the yoke to maintain a particular pitch attitude.
 
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Not as far as I know. As I understand it, the "master trim cutout switch" referred to disables all automatic trim control, including MCAS. What the pilot is saying is that, now that pilots know about the risks involved with MCAS, at the first sign of any anomaly, instead of going through the steps Boeing says, which they don't trust to actually be effective, they're just going to disable automatic trim control entirely and adjust it by hand, since that way they know what they're dealing with.
This is somewhat confusing. The pilot commenting also says:

Second, for obvious reasons, the control column cutout switches do not disable MCAS, which is different from a runaway stabilizer. In that case, simply opposing the control column force kills the trim motor. There wouldn’t be much point in having the MCAS if the control column switches could disable it.
Is he not implying that MCAS is not effected by the bypass cutouts? When he says "trim motor" is he saying that if the pilot opposes the force by pulling on the yoke it disables MCAS? This seems like it couldn't of been the case looking at what we know from the flight data available. It's pretty clear the pilots were fighting against the pitch down maneuvering by the computer. And we see MCAS continuing to pitch down in spite of continued pilot input.
 
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They aren't two separate things. Giving the feedback means adding more nose down trim, which, if the pilot does not compensate by increasing the force he uses on the yoke, will pitch the nose down. Any adjustment of trim does the same thing: it changes the force the pilot needs to exert on the yoke to maintain a particular pitch attitude.
Wait but then are they not indeed completely correlated and not separate? MCAS adding more nose down trim provides the feedback and also literally is pitching the nose down. It provides feedback, but it also effects the actual pitch / attitude of the plane.
 
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Is he not implying that MCAS is not effected by the bypass cutouts?
Hm, you're right, that is confusing. I think we probably would need to have the specifications of the trim control and adjustment system to know for sure.
 
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MCAS adding more nose down trim provides the feedback regardless of whether the pilot changes the force he's exerting on the yoke or not and also literally is pitching the nose down if the pilot does not change the force he's exerting on the yoke.
See the bolded statements I added. (And note that they apply for any method of adjusting the trim, not just MCAS. The same things would be true if the pilot manually added nose down trim using the trim wheel, or whatever manual trim adjustment system the aircraft has.)
 
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See the bolded statements I added. (And note that they apply for any method of adjusting the trim, not just MCAS. The same things would be true if the pilot manually added nose down trim using the trim wheel, or whatever manual trim adjustment system the aircraft has.)
OK, but isn't it safe to say that in these cases, the pilot would see the plane pitching down and indeed, exerted force on the yoke to correct it? In which case the MCAS should of disabled / trim motor. And perhaps it did, but the faulty sensor or perhaps some other error may have allowed the system to execute the pitch down trim again and again?
 
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isn't it safe to say that in these cases, the pilot would see the plane pitching down and indeed, exerted force on the yoke to correct it?
Not under normal conditions. Under normal conditions, the pilot would feel the feedback and increase the force he exerts on the yoke before there was time for the plane to pitch down. The feedback is a continuous process; it's not a series of discrete events. Under normal conditions, the pilot expects the feedback force to increase as angle of attack increases, so if he wants to pitch the plane up, he will be automatically adjusting the force he exerts on the yoke based on the feedback he expects to receive. The increase in the feedback force as the plane gets near a stall is what he would expect; the fact that it's the MCAS causing it, because he's flying a 737 MAX, instead of the natural pitch moment of an older 737, doesn't make a difference in what he feels or what he does, under normal operation.

This assumes, though, that the system is working properly and has accurate sensor data. The difference with MCAS is what failure modes the system has: if MCAS goes wrong because of faulty sensor data, it could suddenly dial in a large nose down trim while the plane is flying level, or climbing at a constant rate at a stable pitch attitude, when the pilot does not expect any sharp change in the feedback force. Under those conditions, yes, the plane would pitch down, because the pilot would not be expecting the change and wouldn't be adjusting the force he exerts on the yoke to compensate. And "adjusting the feedback force" isn't really a good description of what the MCAS is doing under this failure condition, because the plane's pitch attitude is not actually changing, so the feedback force should not be changing either.
 

berkeman

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or a mixture?
Fly-by-wire plus some enhancement by the computer probably.

For example, as I understand it, in launch mode off a carrier, fighter jets are put into an automatic launch mode, where the computer flys the jet for the first few seconds. That's because the g-forces from the launch can possibly compromise the pilot's ability to control the takeoff well. In-cockpit videos often show the pilot grabbing onto handles near the baseline of the canopy for the launches.

So in general, fly-by-wire computers take the pilots' inputs and process them to best control the aircraft. Some advanced aircraft are too unstable to control with just human control (not commercial aircraft).
 
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Is this helpful?
This says "Using electric pitch trim will only pause MCAS, to deactivate it you need to switch off the STAB TRIM SUTOUT switches." This seems to indicate that the cutout switch the pilot comment we were discussing referred to does disable MCAS.
 

berkeman

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This says "Using electric pitch trim will only pause MCAS, to deactivate it you need to switch off the STAB TRIM SUTOUT switches." This seems to indicate that the cutout switch the pilot comment we were discussing referred to does disable MCAS.
Right, it also has a note underneath that that says, "High control forces may be needed to correct any stabilizer nose down trim already applied." Then it says to use electronic trim control to correct it first, then cutout, then manual can be used after.

This sounds ridiculously cumbersome in the event of the MCAS operating in error, where the plane can literally be in a dive at fast airspeed. Really I think what we're going to see is a complete revamp of the MCAS system if it can even be redesigned effectively.

In fact this is alluded to in the March 11, Continued Airworthiness Notification to the International Community (CANIC):
Reviewed Boeing’s production processes related to the AOA vane and Maneuvering Characteristics Augmentation System (MCAS)

Ongoing oversight activities by the FAA include:

- Boeing’s completion of the flight control system enhancements, which provide reduced reliance on procedures associated with required pilot memory items. The FAA anticipates mandating these design changes by AD no later than April 2019.

- Design changes include:

 MCAS Activation Enhancements
 MCAS AOA Signal Enhancements
 MCAS Maximum Command Limit
The last design change is something I suggested along with the minimum altitude threshold, basically that if the pilot is continually pitching upward and MCAS keeps sending a pitch down command it should be smart enough to know something is wrong. Hence "MCAS Maximum Command Limit"

It may be the design of the MAX 8 was so aggressive to save on fuel that software or MCAS can't reliably create safe dependable flight controls in all scenarios. For Boeing sake, hopefully that's not the case. But given their revenue yearly, it's a cost they could afford and recover from.
 
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"See" it how? What if they are climbing out through clouds, and there is no visible horizon? What do pilots use to keep their situational awareness (SA or Sierra Alpha) with no visible horizon? :smile:

https://upload.wikimedia.org/wikipedia/commons/thumb/c/c5/VMS_Artificial_Horizon.jpg/184px-VMS_Artificial_Horizon.jpg

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Right, that's the wrong verbiage. A better term would be "determine".

Yes, I imagine that is a very mission critical instrument to a pilot. Not many failure modes for that sucker I imagine.
 

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