FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

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FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby 3WE » Sun Apr 07, 2019 4:37 pm

Yes, I know, you get an aeroplanie that likes to help with relentless pull ups...

Yes, I know, then it doesn't feel the same as other 737s (which is the major BUSINESS problem)...you can't play card that we are like Airbus where A320+/- are all the same.

But so what...just redo all the 737-MinLav training I-pads and say, "Remember, on the 'MinLav you ever royally screw up and get into a stall, this plane needs a real HARD shove over

...and maybe you can add one item to the takeoff? checklist of ALL 737s: Even though we want to never ever ever ever ever get close to stalling, you normally recover in this 737 by a:

[Legacy 737s]

deliberate-but-reserved nose over shove

[737-MinLav]

relatively vigorous shove over


(Evan can revel in type specific checklists).

Not only that, but then you can put AOA indicators and tell the pilots to look at them as part of the stall recovery...but not to focus TOO hard cuz the dang things go bonkers sometimes, so you may have to figure out that the plane is actually flying in a healthy manner.
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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby 3WE » Mon Apr 15, 2019 1:22 pm

Gabieee: This was a fairly serious post for the purpose of a little discussion.

Given that MCAS has an arguably dark side, what would happen if it was removed?

Does A the plane simply require more nose-over input in stall situation, or B does the stall behavior become nasty and somewhat unrecoverable?

I know that situation A brings about a bunch of certification effort AND makes the plane a significantly different type vs. the other 737 line...and that means $ are involved.

But beyond that: Is there other stuff wired in- and undoing MCAS will cause a cascade of engineering and massive recertification efforts?

Or do we send the whole fleet to the scrap yard and bring back the 757?
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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby Gabriel » Mon Apr 15, 2019 6:11 pm

Gabieee: This was a fairly serious post for the purpose of a little discussion.

Given that MCAS has an arguably dark side, what would happen if it was removed?

Does A the plane simply require more nose-over input in stall situation, or B does the stall behavior become nasty and somewhat unrecoverable?

I know that situation A brings about a bunch of certification effort AND makes the plane a significantly different type vs. the other 737 line...and that means $ are involved.

But beyond that: Is there other stuff wired in- and undoing MCAS will cause a cascade of engineering and massive recertification efforts?

Or do we send the whole fleet to the scrap yard and bring back the 757?
Well, the problem is that I don't know if it's A or B. And, anyway, define "the stall behavior become nasty and somewhat unrecoverable". We might be already there even before the MAX.

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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby 3WE » Mon Apr 15, 2019 10:06 pm

3BSIEEE:

Gabieee: This was a fairly serious post for the purpose of a little discussion.

Given that MCAS has an arguably dark side, what would happen if it was removed?

Does A the plane simply require more nose-over input in stall situation, or B does the stall behavior become nasty and somewhat unrecoverable?

I know that situation A brings about a bunch of certification effort AND makes the plane a significantly different type vs. the other 737 line...and that means $ are involved.

But beyond that: Is there other stuff wired in- and undoing MCAS will cause a cascade of engineering and massive recertification efforts?

Or do we send the whole fleet to the scrap yard and bring back the 757?
Gabieee:

Well, the problem is that I don't know if it's A or B.
Noted and Indeed (I have the same question).
Gabieee:

And, anyway, define "the stall behavior become nasty and somewhat unrecoverable". We might be already there even before the MAX.
Are you Evan? That is not_a black and white statement question- you can list examples of "nasty and somewhat unrecoverable".

I know the exact definition may affect the aircraft certification.

For the sake of this discussion- perhaps "Nasty and somewhat recoverable" might be somewhere in the neighborhood of where the stall warning is kicking in...that maybe there's a lift component to the engine cowling that significantly compromises your ability to nose over even though you haven't stalled yet.

ALL OF this is uber ass-hat unsubstantiated babbling, and perhaps that makes it impossible to discuss.

Still, I think the questions are valid...Is the 'MinLav totally stuck with requiring some sort of MCAS?

And what are the fixes- (besides a second, third, or 13th AOA sensor)?

Thanks.
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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby Gabriel » Mon Apr 15, 2019 10:56 pm

Sorry, black and white was not my intent. Perhaps the correct question, rather than a definition, would be "what do you have in mind when you say nasty and somehow unrecoverable stall"? Let me explain...

There were at least 1 incident with a 737 in approach that started Turkish-style, were the throttle levers were accidentally left at idle (or the AT left them at idle), the plane was on AP so as it slowed down the AP was pulling up and at the same time it was applying nose-up trim to cancel the pull-out force. Eventually, the pilots realized of the situation and called go-around and the stickshaker started simultaneously. Full power, flaps 15, positive climb, gear up but wait, we are pitching up too much, push down... more... more What? You are already pushing to the stop? Then why does the nose keep going up? And the speed going down even with (or should I say thanks to) the full throttles... Full stall, the nose drops, down we go, we start to gain speed and the nose starts to go up again, push down, push down more... ok, with the speed gained in the fall now the elevator has enough authority to keep the nose from going uncontrollably up, stickshaker stopped shaking, but we need to keep pushing hard on the yoke to keep the plane from pitching up by itself. Time to put some nose-down trim perhaps? Duh? If we had put some nose-down trim from the beginning, we would have not lost pitch control in the first place.

Some may say that in this real incident "the stall behavior became nasty and somewhat unrecoverable". (I instead would say pilots should have it as natural and automatic that trim stabilizer is an integral part of pitch control and MUST be used, and would be used without even thinking, to control pitch, especially if elevator alone is not enough, which by the way would have applied to Lion Air and Ethiopian too).

And this incident was not in a MAX.

Is that not-black-and-white enough?

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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby Gabriel » Mon Apr 15, 2019 11:03 pm

The fixes are:
- MCAS will be based on averaging 2 AoA readings/sensors.
- Triple filter to discard spikes or transient spurious AoA values.
- There will be a triple check, any of these conditions not met will render the MCAS inhibited:
==> Difference between the 2 readings do not exceed 5 degrees or so.
==> Sanity check for the averaged value compared with other variables (like airspeed and load factor)
==> Detection of unrealistic sudden changes in the readings.
- The MCAS will not restart 5 seconds later (or ever) if nose-up trim thumb switch is actuated. during/after the operation of the MCAS.
- The FCC will compute a max nose-down MCAS input that will ensure that the pilot retain an authority of at least 1.2 Gs on the yoke.
- AoA disagree indication in the PFD will be standard (AoA indicator itself will still be optional).
- The MCAS will be described in the FCOM and AFM and specific training will be required.

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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby Not_Karl » Tue Apr 16, 2019 12:36 am

And what are the fixes- (besides a second, third, or 13th AOA sensor)?

Thanks.
Put bigger, heavier lavs up front, to counteract the undesired nose-up tendency.

You're welcome.
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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby 3WE » Tue Apr 16, 2019 1:09 am

*** specific training will be required. ***
Oh no! Curtains for Boeing (or at least curtains for minimal training).

Good idea on the lavs Not_Karlieee
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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby 3WE » Tue Apr 16, 2019 2:07 am

Sorry, black and white was not my intent.
Cool story & appreciate the variations.

My context was the 737-MinLav...and just how much nose over help it needs...does it really need the DCAS (Dive Causing Augmentation System) to ‘assure’ recovery, or is it ‘only’ “nice to have” and ‘only’ to make it FEEL like the 737-TraditionalLav?
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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby Gabriel » Tue Apr 16, 2019 8:53 am

My context was the 737-MinLav...and just how much nose over help it needs...does it really need the DCAS (Dive Causing Augmentation System) to ‘assure’ recovery, or is it ‘only’ “nice to have” and ‘only’ to make it FEEL like the 737-TraditionalLav?
The example that I gave shows how, at very low speeds and high nose-up trim setting and high AoA, changing from very low power setting to very high power setting may render the elevator (alone) unable to control pitch and prevent an uncontrollable pitch-up that can end in a full stall crash burn did died. In the MAX this effect is likely stronger due to the more more forward location of the engines. Likely, too, in both cases using trim thumb switch to trim down and hence augment the effect of the nose down elevator would be enough to control the situation, as also would pulling back a but on the thrust. But how much more violent would the effect be in the MAX? It's just a handling feel difference or it makes the condition not compatible with airworthiness?

So, again, the answer is I don't know if the MAX would be certifiable without the MCAS or if it is just a matter of having both airplanes feel more similar so you can have pilots flying both types alternatively and under the same type rating. Educated gossip in youtube and forums seem to point to the later.

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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby elaw » Tue Apr 16, 2019 12:25 pm

I wonder if a partial solution to this sort of thing would be a revamp of how type ratings work.

It appears now it's "all or nothing"... if you're rated on the old-school 737 and they decide you need a new one for the 737-CrashMatic, you have to go through an entire new training program. This of course involves time and expense which nobody wants because training people doesn't generate income and thus is to be avoided at all cost.

But how about some sort of "endorsement" system where to fly the new damn-similar-to-the-old plane, you spend maybe 2 hours in a classroom and 1/2 hour in a sim, being instructed on what's different about this plane vs. the one you were previously rated on?

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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby flyboy2548m » Tue Apr 16, 2019 1:34 pm


But how about some sort of "endorsement" system where to fly the new damn-similar-to-the-old plane, you spend maybe 2 hours in a classroom and 1/2 hour in a sim, being instructed on what's different about this plane vs. the one you were previously rated on?
"We" do that already, but thanks for the suggestion.
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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby 3WE » Tue Apr 16, 2019 1:57 pm

Gabieee:

So, again, the answer is I don't know if the MAX would be certifiable without the MCAS or if it is just a matter of having both airplanes feel more similar so you can have pilots flying both types alternatively and under the same type rating. Educated gossip in youtube and forums seem to point to the later.
Yes, I don't think any of us will every know the TOTAL answer- that's probably somewhere inside of Boeing and they won't be saying one way or the other.

If DCAS really is 'only' a "nice to have", I'd say unplug the dang thing...the old version is just so darn creepy that I can't bring myself to like the new one...

...and yes, do whatever certification / training you need to do (as Elaw describes and Flyboy confirms is currently done).

However, I am guessing that unplugging/deactivating/removing/whatever is an over simplification.

And then the issue of "nice to have" vs. "need to have"...a gray area.

PS: Flyboy, your rare, somewhat biting and harshly realistic, yet light and humourous input to our all-important discussions is always appreciated.
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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby elaw » Tue Apr 16, 2019 2:10 pm


But how about some sort of "endorsement" system where to fly the new damn-similar-to-the-old plane, you spend maybe 2 hours in a classroom and 1/2 hour in a sim, being instructed on what's different about this plane vs. the one you were previously rated on?
"We" do that already, but thanks for the suggestion.
Then why go to such great lengths to make planes flyable by people with the same type ratings as others?
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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby 3WE » Tue Apr 16, 2019 2:56 pm


But how about some sort of "endorsement" system where to fly the new damn-similar-to-the-old plane, you spend maybe 2 hours in a classroom and 1/2 hour in a sim, being instructed on what's different about this plane vs. the one you were previously rated on?
"We" do that already, but thanks for the suggestion.
Then why go to such great lengths to make planes flyable by people with the same type ratings as others?
I think you are debating a no-win-purely-gray concept...You wanted to not_do type ratings, but instead a fuzzy, gray, in-between-but- short compare contrast...

To which Flyboy said, ""We" already do that".

How different a plane is ideally determines how much compare/contrast training you need.

At some point, when the differences become great (and perhaps conflicting) you draw a line...different type and the "cross-certified" thing doesn't really work.

Ironingly- I guess I can claim that I am rated in BOTH the 172M AND the 172XP (The XP required a logbook endorsement). To be honest, I never felt comfortable in the XP, it was very nose heavy and required rather relentless pull ups just to flare the thing. I should ask Bobby if he knows what it's like to turn final with three hundred and sixty injected cubic inches of power, constant-speed prop and 2300 lbs and a 2500 ft airstrip?
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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby Gabriel » Tue Apr 16, 2019 3:55 pm


But how about some sort of "endorsement" system where to fly the new damn-similar-to-the-old plane, you spend maybe 2 hours in a classroom and 1/2 hour in a sim, being instructed on what's different about this plane vs. the one you were previously rated on?
"We" do that already, but thanks for the suggestion.
Then why go to such great lengths to make planes flyable by people with the same type ratings as others?
Because 2 hours of classroom and 1/2 hour of simulator is way much more expensive and time-consuming than 45 minutes of self home training in an iPad. Pus, you need to have simulators available, of which there were somewhere between very few to none when the MAX was introduced.

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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby Gabriel » Tue Apr 16, 2019 4:09 pm

I should ask Bobby if he knows what it's like to turn final with three hundred and sixty injected cubic inches of power, constant-speed prop and 2300 lbs and a 2500 ft airstrip?
He owns and flies a J3, so... I think we will laugh at you at both ends of the spectrum.

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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby 3WE » Tue Apr 16, 2019 4:34 pm

I should ask Bobby if he knows what it's like to turn final with three hundred and sixty injected cubic inches of power, constant-speed prop and 2300 lbs and a 2500 ft airstrip?
He owns and flies a J3, so... I think we will laugh at you at both ends of the spectrum.
IMMATERIAL....wimpy ass 75 horse carbureted fixed pitch stick-controlled tail dragger, 1700 lbs and much lower stall speed and ridiculous short-field performance.

Cub vs. Hawk XP are very different types...type rating not_required, but there better be a couple hours of classroom, a good I-Pad class and "simulator" time before you hope from one to the other. (Yes, there is a tail-dragger set of requirements and endorsements).

(Please read all of this with a little bit of blue shading AND a little bit of technical accuracy, and trim your sense of humor control significantly up).
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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby ocelot » Mon Apr 22, 2019 8:11 am

So I have a stupid question... if the purpose of the thing is to adjust the elevator feel for type commonality, why attach it to the trim and not to, say, the elevator feel system?

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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby Gabriel » Mon Apr 22, 2019 9:12 am

So I have a stupid question... if the purpose of the thing is to adjust the elevator feel for type commonality, why attach it to the trim and not to, say, the elevator feel system?
I do't know. I don't know the design of the artificial feel in the 737. I suspect that it is similar in the MAX as it was in the -200, which must be an electormechanicalhydraulicgravityspringpitotptressure analog thing, into which incorporating a feature that works with "logic" may be complex. The trim on the other hand is already controlled by the FCC (which is an electronic computer) on behalf of the autopilot and the speed trim. Adding the MCAS is a matter of adding some lines of code.

But it's just a guess.

Not to mention that in the incident-just-by-luck-not-a-total-air-disaster case that I mentioned some slots above, the elevator deflected all the way down was not enough to prevent the plane from pitching uncontrollably up and fully stall. Having the MCAS command more nose-down elevator would not have helped since there was no more nose-down elevator available.

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Evanie wants to power back...

Postby 3WE » Wed Apr 24, 2019 8:20 am

Gabe:

While thinking about the great closed-minded pontificator who always has the right answer for the stupid cowboy pilots, I had an uber-BS, purely-theoretical thought.

IF you had plenty of altitude...and MCAS is making you nose over relentlessly...

Could someone "just" go inverted, and maintain not_excessive airspeeds and unload the aerodynamic stresses and regain manual trim?

It's a purely theoretical question of zero practical value- I would think that there would STILL be problems with high airspeeds (just not a death dive) and maybe very similar loads on surfaces that bind up the manual trim...(and the engines are probably going to shut down).

This has zero relevance to Ethiopian...and probably doesn't even make sense for Lion Air...I just go back to the Alaska guys who faced extreme nose-down "trim" and bought themselves a couple of minutes :(
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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby Gabriel » Wed Apr 24, 2019 1:11 pm

From an aerodynamic point of view, yes, it would have been possible. Proof of that is that the plane achieved -3Gs in the final dive. You only need -1G to fly inverted. And yes, it is very possible that doing that would have "freed" the trim wheel. If the plane is trimmed to more negative than -1, the plane would tend to pitch up (meaning the nose pointing higher to the sky even if inverted) if you let go on the elevator, and it that condition the trim wheel would be very likely easy to move, with the plus that the plane would start to slow down and gain altitude.

From a practical point of view, oh boy... Would the structure resist? FAR 25 requires just -0,5G limit load and -0.75G ultimate load. Now, since flexion structural response tends to be more or less symmetrical and the plane is rated to resist 2.5 / 3.5 in the positive direction (limit / ultimate), it will probably resist quite more than -0.75 or even than -1G (Ethiopian sustained up to -3 but I don't know what damage if any the structure sustained at that point). And then the engines... Hopefully fuel starvation will shut them down in the first few seconds, because if not oil starvation will destroy them in the next few seconds. And we still didn't discuss the maneuver to enter in the inverted flight.

Finally, if you are going to admit negative Gs and inverted flight, why not pitch up first , then let go on the elevator at least partially (say to achieve close to zero but still positive G) and while the nose is going down, spin the trim wheel like crazy?

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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby flyboy2548m » Thu Apr 25, 2019 6:19 pm


PS: Flyboy, your rare, somewhat biting and harshly realistic, yet light and humourous input to our all-important discussions is always appreciated.
I'm sure.
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Do [i]we[/i] think there is a broken culture?

Postby 3WE » Tue Apr 30, 2019 6:41 pm

Rant, rant, rant, rant on DCAS...

And, yes, many of us don't like the way it's designed.

Do we really think that Boeing heartlessly ramrodded this through?

Are there NUMEROUS silenced voices who said, "this is really bad and potentially deadly"?

Were those voices silenced by a broken culture of Kool-Aide-drinking middle managers? (who are probably better brown nosers than engineers?)

OR

One more case of Mister Murphy and his nasty, insidious law of reality? (And that the sad fact that competitive deadlines and pressure to deliver can result in oversights).

OR somewhere in between- but you have to lean one way or the other...
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Re: FAO: Gabriel; Why don't [i]we[/i] just unplug MCAS?

Postby ocelot » Mon May 20, 2019 4:55 am

So I have a stupid question... if the purpose of the thing is to adjust the elevator feel for type commonality, why attach it to the trim and not to, say, the elevator feel system?
I do't know. I don't know the design of the artificial feel in the 737. I suspect that it is similar in the MAX as it was in the -200, which must be an electormechanicalhydraulicgravityspringpitotptressure analog thing, into which incorporating a feature that works with "logic" may be complex. The trim on the other hand is already controlled by the FCC (which is an electronic computer) on behalf of the autopilot and the speed trim. Adding the MCAS is a matter of adding some lines of code.
It's a lot cheaper to tweak an electromechanicalhydrograviticelastopitot thing than add some lines of code, though...

Anyway, this gets back to one of the core questions, which is whether MCAS is really supposed to be a feel adjustment or a stick pusher.

I suspect, having seen a fair number of software projects go wahooni-shaped, that the reason nobody seems to be able to figure this is that Boeing never really figured it either -- it is one thing to management, another thing to engineering, a third thing to the group responsible for it, and maybe a fourth thing to the group doing the certification work, and they never all managed to get on the same page
Not to mention that in the incident-just-by-luck-not-a-total-air-disaster case that I mentioned some slots above, the elevator deflected all the way down was not enough to prevent the plane from pitching uncontrollably up and fully stall. Having the MCAS command more nose-down elevator would not have helped since there was no more nose-down elevator available.
True.


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