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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 30th Apr 2019, 18:54
  #4641 (permalink)  
 
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Does anyone on this topic know about Boeings system design ? and if so can they please explain to this simple pilot why mcas was designed in the waay it was, If I understand correctly MCAS is a sub-system designsd solely to counteract the lift generated by the engine nacelles at higher than normal AOT. It does this by trimming the stab nose down meaning that if the MCAS system fails due to incorrect AOA info, unless corrected by the PF its heading for disaster.
Why did they not simply alter the elevator feel circuit so that higher force was required to pull back on the stick, sorry column if the AOT was too high and the stick forces were reducing due to the nacelle lift
This could surely have been done so that forward ie nose down column movement was not affected.
This would mean that what ever happened the aircraft would not be left with a nose down trim and would not therefore be trying to fly into the ground.
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Old 30th Apr 2019, 19:20
  #4642 (permalink)  
 
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Originally Posted by rodlittle View Post
Does anyone on this topic know about Boeings system design ? and if so can they please explain to this simple pilot why mcas was designed in the waay it was, If I understand correctly MCAS is a sub-system designsd solely to counteract the lift generated by the engine nacelles at higher than normal AOT. It does this by trimming the stab nose down meaning that if the MCAS system fails due to incorrect AOA info, unless corrected by the PF its heading for disaster.
Why did they not simply alter the elevator feel circuit so that higher force was required to pull back on the stick, sorry column if the AOT was too high and the stick forces were reducing due to the nacelle lift
This could surely have been done so that forward ie nose down column movement was not affected.
This would mean that what ever happened the aircraft would not be left with a nose down trim and would not therefore be trying to fly into the ground.
Rod,
There are about four of us on this thread who think that. So you are in good company.
Boeing has a history of faffing with stab trim to compensate feel inputs and to them I guess it came naturally.
However, a fail mode in the control feel or a separate dedicated feel box would only cause a harder pull - once - and could be trimmed out.
That is what should have been installed (says I) and even if retrofitted may well be:
- cheaper than losing public trust
- easier to explain to the world and the pilots
- a much less critical system than MCAS can become.
B
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Old 30th Apr 2019, 19:29
  #4643 (permalink)  
 
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Originally Posted by slacktide View Post
How did you arrive at that interpretation of the press release? Because I arrived at the exact opposite conclusion. Boeing has admitted that they screwed up by tying the activation of the AOA Disagree alert to the the selection of the AOA indicator customer option.

I don't see any language in the release that insinuates that this was in any way the customer's fault or that it is to a lack of the customer's understanding.
Regardless of the presence of a AOA disagree alert, the system had the data with which to disarm MCAS. Boeing’s recent statements that nothing was wrong with the design has already twice been disproven. And it’s wrong for at least two reasons, use of a single AOA sensor, the second, that when AOA sensors disagree, the MCAS is not disarmed.
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Old 30th Apr 2019, 20:19
  #4644 (permalink)  
 
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Originally Posted by bill fly View Post
There are about four of us on this thread who think that.


Count me in on that!

Nothing that some year dot bicycle technology (much like the rest of the flight control system) couldn't have resolved with simplicity, redundancy & no additional training requirements - it's considering this that make me wonder far more broadly about MCAS.
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Old 30th Apr 2019, 20:40
  #4645 (permalink)  
 
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Originally Posted by GlobalNav View Post


Regardless of the presence of a AOA disagree alert, the system had the data with which to disarm MCAS. Boeing’s recent statements that nothing was wrong with the design has already twice been disproven. And it’s wrong for at least two reasons, use of a single AOA sensor, the second, that when AOA sensors disagree, the MCAS is not disarmed.
The wiring diagram of the MCAS/STS is very eloquent. The pilots have no way to disarm the MCAS/STS. Is either both ON or CUT OFF, which means also thumb switches are disabled if in CUT OFF position. NG wiring diagram shows that STS could have been disarmed by one of the switches, keeping operative the thumb switches.
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Old 30th Apr 2019, 21:01
  #4646 (permalink)  
 
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Originally Posted by Cows getting bigger View Post
Dare I say it, but the differences between A & B philosophy really show here. In the early days of A, I was like many pilots - dubious and wary of automation. Over a generation of flying later we seem to have got our head around they fact that HAL(A) has matured, is now rather good at his job and, generally speaking, our side of the house only gets into trouble when we ignore HAL(A). Meanwhile, HAL(B) appears to still be at school and capable of having hissy-fits, just like my teenage daughter.
I think that is unfair to Boeing - B has had a proper grown up HAL since 777 and many think it is superior to the A model (certainly it came after and learned from it). From an engineering point of view (I accept that pilots may have a preference) there isn't much to choose between C* and C*U, sidesticks or yokes - both systems work and are well proven now.

What was clear to this engineer was the difference in philosophy between A & B Hals - HAL(A) will protect the pilot from him/herself overriding control inputs because HAL(A) knows best, while HAL(B) will warn pilots and make difficult what it considers as "incorrect" control inputs it will always allow the pilot to stuff it up if they really want because the pilot knows best.

The hissy-fit system HAL(MAX) seems to me to overturn the old B philosophy and head much more towards A, but worse, it decides it knows best (where best is mistrim AND to the stops at high speed and low alt) based on a single AOA sensor rather than the multiply redundant sensor sets of HAL(A) (or B).

That to me is the really sad thing - Boeing knows (or knew) how to do this stuff properly, but for some reason they decided not to for MAX. It's not just doing FBW properly 777-style, it's MCAS itself - it's looking like they ripped MCAS straight off the KC-46, except that there it uses 2 AOA inputs, so at some point in copying the system they reduced the number of AOA inputs to the MCAS system. Why on earth would anyone do that?
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Old 30th Apr 2019, 21:34
  #4647 (permalink)  
 
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Originally Posted by weemonkey View Post
No, just show us the evidence.
Please define what you mean by "evidence."

BTW, does that definition also apply to all the other players in the chain of causation, or just the aircrew?
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Old 30th Apr 2019, 21:47
  #4648 (permalink)  
 
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Salute!
From Bill
If I understand correctly MCAS is a sub-system designsd solely to counteract the lift generated by the engine nacelles at higher than normal AOT........
=======
Why did they not simply alter the elevator feel circuit so that higher force was required to pull back on the stick, sorry column if the AOT was too high and the stick forces were reducing due to the nacelle lift
The problem, Bill, et al, is that the plane required an aerodynamic fix for pitch moments approaching the stall AoA. Sure, in noirmal, non-FBW systems you would expect increasing back force to increase AoA. The new motor mount and such resulted in less back force per each increase in AoA - aero force, not the artificial feel sustem they already had. A pure cable system with no "help" would have made that very obvious for most of us here, especially those with lottsa light plane time. So Boeing figured they would just crank the stab to generate more nose down pitch moment, and the existing feel and such would take care of everything else, huh?
.
- Make the sucker nose heavy and use a single AoA vane to trigger it. Don't sweat a FUBAR vane, as the stick shaker would prolly be going off and provide a clue that something wasn't right
- Let her rip for almost ten seconds and 2.x units nose down, then wait 5 seconds and do it again.
- Don't look at airspeed, just flaps and autopilot settings besides the AoA vane
- To disable the doofer, simply turn off all the electric trim to the stab. Neat, huh? Oh, you lose the yoke trim Gums! No biggie, we can crank that little wheel 50 times. Just don't get fast.
- Yeah that's it. And let's increase the authority of MCAS a bit to be on the "safe" side and don't advertise this, as it might require a sim ride or something.
================
And finally today's comment: @ driver. The first crew call I can see about AoA vane is about 4 minutes from WoW. It could be that at that point they turned the electric trim back on.. at 43:11 we see manual trim from yoke, and sure enuf, 5 seconds later we see MCAS crank the trim down to 1.0 from 2.3 units and they were doomed.

Gums sends...
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Old 30th Apr 2019, 21:48
  #4649 (permalink)  
 
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infrequentflyer789

Far more eloquently presented than my effort. I wholeheartedly agree.
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Old 30th Apr 2019, 22:04
  #4650 (permalink)  
 
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Originally Posted by weemonkey
No, just show us the evidence.
Please define what you mean by "evidence."
Originally Posted by 737 Driver View Post
Please define what you mean by "evidence."

BTW, does that definition also apply to all the other players in the chain of causation, or just the aircrew?
At this point (for either accident) "evidence" in a formal sense is not available to the general public.

What is available are a precious few facts and (sometimes strongly held) opinions and theories based on individuals backgrounds.

While some (my self included) may disagree with 737 drivers analysis on some points he has presented detailed explanations and insight that clearly provide an experienced pilots view of things.

In that context it would be equally (not) usefull to say "show me the evidence it was -not- primarily pilot error".

If you have not read his longer posts they are well worth reading, even if you do not end up agreeing with all the points.





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Old 30th Apr 2019, 22:07
  #4651 (permalink)  
 
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Originally Posted by gums View Post
And finally today's comment: @ driver. The first crew call I can see about AoA vane is about 4 minutes from WoW.

Gums sends...
From the preliminary accident report:
At 05:38:44, shortly after liftoff, the left and right recorded AOA values deviated. Left AOA decreased to 11.1° then increased to 35.7° while value of right AOA indicated 14.94°. Then after, the left AOA value reached 74.5° in 3⁄4 seconds while the right AOA reached a maximum value of 15.3°. At this time, the left stick shaker activated and remained active until near the end of the recording. Also, the airspeed, altitude and flight director pitch bar values from the left side noted deviating from the corresponding right side values. The left side values were lower than the right side values until near the end of the recording.

At 05:38:43 and about 50 ft radio altitude, the flight director roll mode changed to LNAV.

At 05:38:46 and about 200 ft radio altitude, the Master Caution parameter changed state. The First Officer called out Master Caution Anti-Ice on CVR. Four seconds later, the recorded Left AOA Heat parameter changed state.

<snip>

At 05:42:51, the First-Officer mentioned Master Caution Anti-Ice. The Master Caution is recorded on DFDR.

At 05:42:54, both pilots called out “left alpha vane”.


​​​​​​
From the data provided, it appears that the Left Alpha Vane warning was triggered within 10 seconds after liftoff. The First Officer called out "Master Caution, Anti-Ice" as would have been procedure. Normally, that call should have been followed up with a verbalization of what particular malfunction triggered the Master Caution light. The crew did not actually get around to doing this until a little more than four minutes after the light first illuminated.

Further examination of the DFDR output indicates that the first Master Caution alert was reset. This is normal procedure to allow for additional alerts, but it also extinguished the "Anti-Ice" annunciator. It appears that the crew simply forgot to look for the actual malfunction annunciated on the overhead panel. For reasons, that are not entirely clear from the data, the Master Caution light came on again at around the 5:42:50 mark, re-illuminating the "Anti-Ice" annunciator. The Master Caution light was reset again. It is at this point, four minutes after the original alert, that the pilots looked up and confirmed the "L ALPHA VANE" annunciation.

737 Driver sends.....

Last edited by 737 Driver; 30th Apr 2019 at 22:43. Reason: added comment
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Old 30th Apr 2019, 22:16
  #4652 (permalink)  
 
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737Driver and his cohorts seem intent on diverting attention towards alleged deficiencies in the airmanship of the crews of the two 737 max aircaft that crashed rather than dealing with the real villains of the piece, namely, the FAA and Boeing. I hope that EASA and other foreign regulators hold the FAA's and Boeing's feet to the fire and refuse to lift their grounding of the MAX until a proper SAFE fix has been implemented.

MCAS needs to be removed completely from the 737 Max as it is a far too powerful and dangerous solution to the issue of stick force gradient at high angles of attack. EASA et al should demand that a stick-pusher system should be provided to meet the certification requirements, or else the MAX will not fly passengers in Europe.

Personally, I hold the FAA most culpable for the crashes that have occurred due to MCAS. Whilst aircraft manufacturers such as Boeing, or Airbus, may be tempted to cut corners in pursuit of profit, the regulators are supposed to prevent unsafe commercial aircraft from receiving certification.
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Old 30th Apr 2019, 22:43
  #4653 (permalink)  
 
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Originally Posted by rodlittle View Post
Does anyone on this topic know about Boeings system design ? and if so can they please explain to this simple pilot why mcas was designed in the waay it was, If I understand correctly MCAS is a sub-system designsd solely to counteract the lift generated by the engine nacelles at higher than normal AOT. It does this by trimming the stab nose down meaning that if the MCAS system fails due to incorrect AOA info, unless corrected by the PF its heading for disaster.
Why did they not simply alter the elevator feel circuit so that higher force was required to pull back on the stick, sorry column if the AOT was too high and the stick forces were reducing due to the nacelle lift
This could surely have been done so that forward ie nose down column movement was not affected.
This would mean that what ever happened the aircraft would not be left with a nose down trim and would not therefore be trying to fly into the ground.
This was discussed somewhere in the thousands of preceding posts. I think we've reached the point (probably long past it really) where there's nothing more to really be said until new information is released from the investigating authorities.

Basically (if I recall correctly) the elevator feel doesn't operate in a continuously variable fashion relative to AoA. Also the elevator feel system does not have enough authority to maintain the linear stick force called for by certification reqirements. Finally, EFS operates during the stall, stick shaker active, etc. while MCAS (or its effect on stick feel) is needed prior to the stall.

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Old 30th Apr 2019, 22:45
  #4654 (permalink)  
 
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Speaking for me and just about all of my colleagues of a quite big IT company having its main location in germany: I'll never ever fly a boeing again unless the 737 MAX Issue is resolved including a full analysis *what* went wrong certifying this aircraft.

From an engineers point of view it is quite incredible what has happened in this specific case. May the pilots have partial guilt or not, at least the following facts remain:
* no redundancy for a safety-critical subsystems' sensor
* no sanity-check of input-values of a safety-critical subsystem (e.g. not checking differential of movement, not checking absolute values, not comparing against other available sensors, not checking against absolute - i.e. measureable - orientation against groun(
* no coaching of pilots
* cross-linking of MCAS with assisted trim

In our company boeing is being called as "Boing", which in german means "Crash!". Anyone having to fly who determines to have been booked on a boing 737-MAX (i.e. crash 737-MAX) may refuse to fly, requiring the company to re-book. Do you even grasp what this means?

The longer boeing refuses to admit the obvious, glaring deficits in the MCAS implementation the longer it will permanently lose trust. Whatever 737driver or anyone else says will not rectify this, quite the opposite. Even if it is true to a certain degree.
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Old 30th Apr 2019, 22:52
  #4655 (permalink)  
 
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Salute!

Excuse me, Driver, but your post about all the warning lights you say in last sentence the crew called out “left vane”. And I do not see this right after WoW for several minutes. Sure, many alarms and such went off right away, and looks to me that somewhere along the way they turned off the electric trim. Can post timeline later.
EDIT WITH COCKPIT STUFF:
Takeoff at 5: 38 +/1 a second or two
At 05:39:45, Captain requested flaps up and First-Officer acknowledged. One second later, flap handle moved from 5 to 0 degrees and flaps retraction began.
[that is almost two minutes after WoW)

At 05:39:50, the selected heading started to change from 072 to 197 degrees and at the same time the Captain asked the First-Officer to request to maintain runway heading.
[no discussion of AoA vanes yet almost two minutes after WoW]

At 05:39:55, Autopilot disengaged,

At 05:39:57, the Captain advised again the First-Officer to request to maintain runway heading and that they are having flight control problems.

At 05:40:00 shortly after the autopilot disengaged, the FDR recorded an automatic aircraft nose down (AND) activated for 9.0 seconds and pitch trim moved from 4.60 to 2.1 units. The climb was arrested and the aircraft descended slightly.

[The MCAS activates and the real circus begins]

Gums....

Last edited by gums; 30th Apr 2019 at 23:09.
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Old 30th Apr 2019, 23:09
  #4656 (permalink)  
 
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Originally Posted by gums View Post
Salute!

Excuse me, Driver, but your post about all the warning lights you say in last sentence the crew called out “left vane”. And I do not see this right after WoW for several minutes. Sure, many alarms and such went off right away, and looks to me that somewhere along the way they turned off the electric trim. Can post timeline later.

Gums....
They had 2 master 'anti ice' cautions, the crew only announced cause after second one, not surprising since they had a lot going on and anti ice would not be of much concern given the conditions until they reached altitude.

My post below has a timeline for when they turned off electric trim including quotes from prelim report.

https://www.pprune.org/rumours-news/619272-ethiopian-airliner-down-africa-post10459320.html
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Old 30th Apr 2019, 23:51
  #4657 (permalink)  
 
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Salute1

Thanks, Murph

My point is that they did not call out AoA vane for 3 or more minutes, even tho they had the ice light and so forth.

Gums sends....
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Old 1st May 2019, 00:08
  #4658 (permalink)  
 
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Originally Posted by alexandersparry View Post
Speaking for me and just about all of my colleagues of a quite big IT company having its main location in germany: I'll never ever fly a boeing again unless the 737 MAX Issue is resolved including a full analysis *what* went wrong certifying this aircraft.
Oh man, here goes the Boeing stock. Oh wait, they don't care.

Boeing sells aircraft to airlines. Yes, in this particular case, it seems that something went wrong that should not have gone wrong. It will be fixed, and the company will bleed a lot of cash for it.

I could also announce that I will never buy a Volkswagen again because of the diesel scandal. However, the same thing applies: something went wrong that should not have gone wrong. It will be fixed, and the company will bleed a lot of cash for it.

In fact, when this is fixed, I'll be more than happy to fly the MAX because I'm pretty sure that with all that media attention if anything is going to be fixed properly, it will be MCAS. With a blank check from Boeing's beancounters.
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Old 1st May 2019, 00:30
  #4659 (permalink)  
 
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Originally Posted by Avionista View Post
737Driver and his cohorts seem intent on diverting attention towards alleged deficiencies in the airmanship of the crews of the two 737 max aircaft that crashed rather than dealing with the real villains of the piece, namely, the FAA and Boeing.
This is unfair, bordering on the slanderous. Are 737 pilots who happen to agree with him about airmanship really his "cohorts"? You make it sound like a plot.
Mr. Driver has, time and again, acknowledged the glaring "other factors" and has bent over backwards to be fair.

Speaking as an informed passenger, try to see my POV: If there is something wrong with the airplane you're riding, wouldn't you want the very best piloting skills possible sitting up there in the pointy end??? I sure would! I am shocked that there's so much sentiment against "Just fly the damned plane!"
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Old 1st May 2019, 00:45
  #4660 (permalink)  
 
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Stick force reduces as AoA increases under particular flight conditions on, and only on, the 737 MAX. This is not certifiable under FAA rules.

I don't know who originally stated the first part to be the case but it is apparently at the foundation of all that we have talked about and whose chosen "correction" is in whole or in part the cause of the loss of almost 400 lives.

What mentality uses uncommanded movement of the horizontal stab (MCAS) to correct for a decrease in stick force?

Perhaps a mentality that knows that if the 737 MAX were to actually stall under those particular conditions it would be game over?
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