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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 2nd May 2019, 12:13
  #4741 (permalink)  
 
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Originally Posted by Loose rivets View Post
737 Driver

Quote:
. . . On the NG, the left switch disables the main electric (pilot actuated) trim and the right switch disable all automatic inputs (Speed Trim/Mach Trim/Autopilot Trim). We used to try to identify the offending system and actuate these switches separately in the runaway stab trim procedure depending on the situation. Somewhere along the way, Boeing changed their philosophy on the procedure (probably part of a larger trend of moving away from “troubleshooting” type actions) and now we always use both switches when necessary. I have previously speculated that two switches were retained in the MAX for both redundancy against possible relay welding and to simply harmonize the procedural aspects of runaway trim between the NG and the MAX. That is, both aircraft have two switches (for different reasons) and you always use both switches at the same time.
This is a very revealing quote. I can see how the procedures evolve, or de-evolve. But I can also see how it could lead even attentive crews down a very dark garden path.
This could be a case of compounded unexamined assumptions along the way:

The initial 737NG safety analysis used the availability of separate cutouts (automation and all) to justify smaller wheel/harder to move under high loading since in most cases pilot electrical trim would still be available.
This may also have been a factor in dropping training on the 'unloading' technique.

Over time training was simplified, not by itself a bad thing, but did not take the above into account.

When MAX was designed the fact that training always used both switches was used to justify removing the seperate functions for whatever reason.

Some have suggested that the training was changed to accomodate the upcoming MAX, I highly doubt this was true since there was no technical need to change the functionality to add MCAS.

Last edited by MurphyWasRight; 2nd May 2019 at 12:25. Reason: 787 > 737
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Old 2nd May 2019, 12:16
  #4742 (permalink)  
 
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Originally Posted by MurphyWasRight View Post

Others have posted that the runaway trim procedure was changed from first using the right switch only to using both a few years ago for unknown reasons.
No one has posted a rational sounding reason why the switch functions were changed.
I did my 737-3/400 initial course in 1998 and have no recollection at all of ever using just one of STAB TRIM CUTOUT switches. They were always, unless seniity has completely overtaken me, used together. Seems rather more than 'a few years ago' to me.
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Old 2nd May 2019, 12:34
  #4743 (permalink)  
 
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Originally Posted by MurphyWasRight View Post
:



Alll 3 of the FDR traces clearly show MCAS kicking in ~5 seconds after the last manual electric trim.
It is not clear what the current published FDR traces are actually reporting... I am not saying that your interpretation is wrong but it is not absolutely certain. Does the thumb switch have absolute authority in all circumstances (save for when electric trim is disabled)? The wiring schematics available suggests otherwise and the detailed software logic is not publicly known. The FDR data is not clear whether it is reporting inputs or final outputs or something in between. I have read what is available in this thread and still have doubts that there is sufficient information to be sure. What is certain is that the MCAS system was not properly or adequately designed. It is inherently dangerous and should never have been approved. Whether the pilots should or could be expected to resolve the defective system is a secondary issue. It is simply unacceptable for a critical system to continue to rely on plainly unreliable sensor information. The common factor is unreliable AoA that is easily detected but the system ignores. Autopilot is disabled but why on earth is MCAS allowed to continue to operate?
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Old 2nd May 2019, 12:56
  #4744 (permalink)  
 
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Originally Posted by meleagertoo View Post
I did my 737-3/400 initial course in 1998 and have no recollection at all of ever using just one of STAB TRIM CUTOUT switches. They were always, unless seniity has completely overtaken me, used together. Seems rather more than 'a few years ago' to me.
No you are not going senile. Only a couple of year ago I was looking at training 737 pilots and they do what is says in the QRH - SWITCHES OFF. PLURAL. And they trained for multiple failures during loss of airspeed concurrent with stick shakers.
I had a discussion in that I suggested pulling the CB for the stick shakers once you knew it was a false warning but the answer was that "Boeing doesn't say that in the checklist". I would call that action airmanship though!
Cheers
Y
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Old 2nd May 2019, 13:09
  #4745 (permalink)  
 
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Originally Posted by meleagertoo View Post
I did my 737-3/400 initial course in 1998 and have no recollection at all of ever using just one of STAB TRIM CUTOUT switches. They were always, unless seniity has completely overtaken me, used together. Seems rather more than 'a few years ago' to me.
We always used both switches on the 707 and 727, circa 1964-83.

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Old 2nd May 2019, 13:19
  #4746 (permalink)  
 
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Originally Posted by yanrair View Post

Originally Posted by meleagertoo
I did my 737-3/400 initial course in 1998 and have no recollection at all of ever using just one of STAB TRIM CUTOUT switches. They were always, unless seniity has completely overtaken me, used together. Seems rather more than 'a few years ago' to me.
No you are not going senile. Only a couple of year ago I was looking at training 737 pilots and they do what is says in the QRH - SWITCHES OFF. PLURAL. And they trained for multiple failures during loss of airspeed concurrent with stick shakers.
I had a discussion in that I suggested pulling the CB for the stick shakers once you knew it was a false warning but the answer was that "Boeing doesn't say that in the checklist". I would call that action airmanship though!
Cheers
Thanks all, interesting that it has been that way for many years,

Would take a while to find the post I was referring too, doesn't really matter though; as the total number of years increases sense of elapsed time does seem to compress.

This does totally put to bed any idea that training was changed to accomodate MAX.
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Old 2nd May 2019, 14:02
  #4747 (permalink)  
 
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Originally Posted by PerPurumTonantes View Post
​​​​​​
[...]

Every time you say 'just fly the plane' or 'basic airmanship' or 'get another career' you're completely ignoring human factors. This is as dangerous as not knowing how to fly the aircraft. And this is why you're getting such a deservedly robust response from others on here.
Originally Posted by 737 Driver View Post
Not ignoring the human element at all.

[...]
With respect, I think there may be a breakdown in communication here that may be in large part responsible for the ongoing disagreement. When people say "human factors", they don't mean "the human element", they mean Human Factors*, i.e., the study of how the human mind and body interacts with designed systems.

The human mind does not, ironically, work in the ways most people think it does - it has well-documented limitations and sources of error plumbed into its design. A human factors expert can I believe pretty trivially design a scenario where most (if not all) humans will consistently fail to correctly solve even relatively trivial problems, regardless of their competence under normal conditions.

Thus, when asking "why didn't they just fly the plane?", one possible answer is undoubtedly some variant on "they were incompetent". But another possible answer is "they were put into a scenario in which any human being would consistently fail to solve the problem, regardless of competence". Probably the truth is somewhere between those two points.

*See Wikipedia article "Human factors and ergonomics"
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Old 2nd May 2019, 15:18
  #4748 (permalink)  
 
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Originally Posted by MurphyWasRight View Post
Thanks all, interesting that it has been that way for many years,

Would take a while to find the post I was referring too, doesn't really matter though; as the total number of years increases sense of elapsed time does seem to compress.

This does totally put to bed any idea that training was changed to accomodate MAX.
It was probably mine. At one time, my airline customized a number of procedures (in coordination with Boeing, mind you), so that may explain the difference. Im pretty sure that all of our non-normals are now straight out of the Boeing manual.
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Old 2nd May 2019, 15:42
  #4749 (permalink)  
 
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Yo gums,
‘… still looking for the aero explanation that is more relevant than basic control column feel.’
Ethiopian airliner down in Africa
Ethiopian airliner down in Africa

Nothing more specific to add; no detailed knowledge or reasoning in the public domain.
I suspect that the aerodynamic issue caught Boeing by surprise - late in flight testing; the existence or extent of change of pitching moment (stick force stability), its origin - engine nacelle, nacelle / wing interaction. Possibly a judgement that the handling characteristics would be ‘good enough’ - FAA association.

The need for modification - increased stick force to meet stability requirements at a few specific points in the flight envelope could be achieved with a range alternative approaches; hardware fixes - cf Mach trim, STS, feel shift. These progressively require ‘controlling’ parameters best achieved with software, thence use of ‘full’ software, but it wasn’t ‘full’ or comprehensively protected - faster, better, cheaper; NASA got that wrong; how we fail to learn, how quickly we forget.

The comparisons with modern FBY wire systems and the aerodynamics of those aircraft, adds little to this debate. The 737 airframe and systems design are very old, progressively enhanced, adapted to market demand - with the perception of new shiny technologies are better, at least cheaper.
A more suitable comparison would be with the 707 / 727; in my case the Comet. I recall that the Comet, or its derivatives had a ‘pitch gear change’, (not a manual shift), a smooth electrical repositioning of a mechanical cam which changed the ratio of stick to elevator (also used in the Sea Vixen to cope with transonic trim change). The need for Mach trim in commercial aircraft emerged as speeds increased (stability, stick force reversal), but due to its novelty, solutions were carefully thought through with reliable implementation.

The recent events will go down in history. History, as with war crimes, is written by the victors (lawyers, politicians).
The most important aspect for the industry is in what we learn, how this is to be learnt and implemented. The issues with certification processes may dominate - how to certificate modern systems, common standards, international approval, … trust.
The industry is transitioning from the generally knowable, to more uncertainty. How do we manage aircraft and people in an uncertain world.
https://www.farnamstreetblog.com/201...r-uncertainty/ (Three parts linked)

FAA / Boeing could reconsider their relationship with ICAO, aviation language, safety culture.
More Integration opposed to dominating Assimilation:- https://www.dropbox.com/s/7425e8yykg...20%2B.pdf?dl=0 (use website option)
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Old 2nd May 2019, 16:56
  #4750 (permalink)  
 
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The direction of this thread is difficult to understand. There seems to be a surprising focus on the cut-out switches but no rational explanation for the changes in the MAX series. If there are no circumstances that only one cut-out should be operated there, is clearly no point in having two cut-out switches. If two contacts are needed to be operated it could be mechanically interlocked into one lever. The current information suggest the two switches are a product of muddled thinking... hardly a confidence builder.

Purely speculating, the reason that MCAS is not automatically disabled in the event of conflicting sensor inputs may be because MCAS needed to be permanently active to comply with 14CFR 25.203(a) "Stall characteristics". However, it is difficult to believe that the designers could have considered it a better option to leave it to the pilots to disable MCAS rather than by the automatic system that would be immediately aware of AoA sensor malfunction. It seems to be possible that focus was on conforming to wording of regulations rather than designing an adequate system.

A critical system that is intended to work in all circumstance must be designed in a way that reduces risks of malfunction to an acceptable level. Reliance on a single sensor or system does not appear to satisfy this obvious requirement. In the event that a critical sensor is no longer reliable, the system must automatically fall back to an alternate. That could be an alternate duplicate system or the manual control of the pilot or a combination or several nested fall-back options. The evidence so far is quite clear that Boeing failed to properly consider these options and required pilot intervention on scant information. In my view, it was negligent design and I suspect that I am not alone.

Many of the comments on this thread focus on the failure of the pilots to resolve the situation. There is good evidence that if the captain had handed control to the right hand seat or used the cut-outs earlier that they would have been successful. However, it does not excuse the fundamental design defects. In actual fact, Boeing could have easily prevented any uncertainty created by unreliable AoA through additional training automation and notification. There is no excuse for the design defects.

Further, much has been made of additional pilot training or improved memory items, QRH etc. Unfortunately, it is trying to close the stable door after the horse has bolted. The existing MCAS system will never be used again and any training or manuals will be based on a substantially different systems. Really all the focus at this stage must be on correcting the design defects... any manuals and training will fall from the new systems and will hopefully learn from the inadequacy of the previous systems and training.

I look forward to learning exactly how the MCAS electric trim system worked and how the situation will be resolved. One of the issues that I would like to further understand is why the pilots only appeared to make shortly electric trim corrections when it seemed likely that they would be trying to make large corrections. The FDR trace combines MCAS and electric trim... it is therefore uncertain what the thumb switch position was in.

Would permanently holding the thumb switch for nose-up, override AND from MCAS? Does MCAS cyclically override the thumb switch input in the 10s 5s cycle that requires further release and activation of the thumb switch. ie is the Boeing Ops Manual Bulletin TBC-19 entirely accurate... namely:

In the event of erroneous AOA data, the pitch trim system can trim the stabilizer
nose down in increments lasting up to 10 seconds. The nose down stabilizer trim
movement can be stopped and reversed with the use of the electric stabilizer trim
switches
but may restart 5 seconds after the electric stabilizer trim switches are
released.


If this is true then it would be possible (not desirable) to use electric trim to override MCAS without using the cutout switches. MCAS could be interrupted and corrected every time it kicked in. I suspect it is not entirely accurate... I wonder if anyone has an authoritative answer? None of this excuses MCAS remaining active with unreliable AoA information.
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Old 2nd May 2019, 17:36
  #4751 (permalink)  
 
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Originally Posted by Snyggapa View Post
I would also be fascinated if a gap analysis has been done between the MAX and what would need to change, were it a new aircraft type being certified today - several people have commented that "it would never be certified today" and "it relies on grandfather certification" - so in what ways does the MAX come up short to today's expected regulations?
Fair questions. The relevant regulations are generally referred to as the "Changed Product Rule", and are documented in 14 CFR part 21.101 and 21.19. FAA Advisory Circular 21.101-18 provides guidance on how to interpret and apply the regulations, including how to perform a gap analysis to compare the previous regulation to the new regulation. https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_21.101-1B.pdf The general takeaway is the changed systems, and affected systems that are unchanged but impacted by change, must generally step-up and comply with the most recent regulations.

The certification basis of an aircraft is a list of which regulations it has been demonstrated to comply with, and at which amendment level of that particular regulation is being used to show compliance. The certification basis is agreed to by the manufacturer and the FAA at the beginning of the certification process. The manufacturer has 5 years to complete certification of the aircraft, and the manufacturer is not required to comply with regulations that are changed within that 5 year period.

The cert basis is documented in the Type Certificate Data Sheet. Here's the 737 TCDS, the MAX 8 is on page 71. http://www.airweb.faa.gov/Regulatory...6WE_Rev_64.pdf

For each regulation, the center column lists the amendment level that the airplane complies with. NA indicates "No Amendment."

Then, you can go to the CFR and compare the most current amendment level to the amendment level in the TCDS. https://www.govinfo.gov/content/pkg/...tle14-vol1.pdf

For example, the MAX complies with 25.107 amendment 135 for Takeoff Speed, and that is the current amendment level in the CFR.

Another example, go in the TCDS and look at 25.807 for emergency exits. For some of the doors, the MAX complies with the most current amendment level 114. For others, it complies with amt. 72. Additionally, they are compliant with 25.807(c)(3) at amt. 15, because this section was removed from newer versions of the regulation.
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Old 2nd May 2019, 17:49
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Originally Posted by wheelsright View Post
Would permanently holding the thumb switch for nose-up, override AND from MCAS?
Yes, but you certainly would not want to do that, as if you literally held the switch up "permanently" you'd end up at the maximum ANU trim configuration.

... would be possible (not desirable) to use electric trim to override MCAS without using the cutout switches. MCAS could be interrupted and corrected every time it kicked in. I suspect it is not entirely accurate... I wonder if anyone has an authoritative answer? None of this excuses MCAS remaining active with unreliable AoA information.
Yes this is entirely possible, and is what happened on the penultimate flight of the Lion Air accident aircraft.
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Old 2nd May 2019, 18:58
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From something Ive just read MCAS was to compensate for the fact that due to the new engine nacelles the pitch stablity was so poor that it would tighten up in a turn at low airspeed and that it actually required a push on the control column to defeat this which is quite unaceptable in an airliner, not so much in a Pitts.
Obviously this could not have been corrected by adjusting the elevator cct feel so it explains the why of why did they do it this way
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Old 2nd May 2019, 19:08
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Originally Posted by rodlittle View Post
From something Ive just read MCAS was to compensate for the fact that due to the new engine nacelles the pitch stablity was so poor that it would tighten up in a turn at low airspeed and that it actually required a push on the control column to defeat this which is quite unaceptable in an airliner, not so much in a Pitts.
Obviously this could not have been corrected by adjusting the elevator cct feel so it explains the why of why did they do it this way

Thats interesting Rod - what was is that you read?
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Old 2nd May 2019, 19:13
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a report in Pilot magazine by Bob Grimstead, cant comment on its accuracy but hes a reputable man
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Old 2nd May 2019, 19:20
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It remains an inescapable fact, meaning as in the sense of a reality, that the introduction of a software based modification became a necessary in order to get this plane certified. That must have been considered as the most optimal solution to achieve the commercial aims of introducing a plane that could be competitive to others on the market, namely the Airbus offerings. The B737 had to be kept alive to do that. But how could it be possible to keep a plane designed half a century ago may still be fit for today`s world of aviation. The Douglas DC10 was also an all time winner, but can you imagine kitting it out with the latest high ratio by pass turbo fans of today, installing some fancy computers and software in it and saying here is the answer to short haul commuter, so long as you can get your pax to don their oxy masks if we hit some bad wx. Not really all that much different to saying the B737 MAX is more than safe as is, but just to make sure no airline has sat a pair of morons up front, we have with our clever MCAS thingy tell the computer how to handle them. Now if that does not make sense as to why they put in this MCAS thingy majig, then why did they do it in the first place. That of course takes us back to where we started, which then means we got nowhere and that is the whole purpose of the whole exercise.
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Old 2nd May 2019, 19:48
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Originally Posted by Chronus View Post
The Douglas DC10 was also an all time winner, but can you imagine kitting it out with the latest high ratio by pass turbo fans of today, installing some fancy computers and software in it and saying here is the answer to short haul commuter,
So, a MD-11?

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Old 2nd May 2019, 20:04
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Originally Posted by SystemsNerd View Post
Thus, when asking "why didn't they just fly the plane?", one possible answer is undoubtedly some variant on "they were incompetent". But another possible answer is "they were put into a scenario in which any human being would consistently fail to solve the problem, regardless of competence". Probably the truth is somewhere between those two points.
​​​​​​Thank you so much for this This is why I cannot accept the analysis of those that pile with unwavering assertiveness on the pilots' performance. We have only a partial view of what they experienced. We simply cannot know what the average crew would do in their shoes, vs what some hypothetical post-hoc average response should be, as evident as it may seem. Even so, are they at fault for the training they received? That's why when someone can't come back to tell their version, I prefer unanswered questions to "sure" answers.
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Old 2nd May 2019, 20:05
  #4759 (permalink)  
 
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Originally Posted by rodlittle View Post
From something Ive just read MCAS was to compensate for the fact that due to the new engine nacelles the pitch stablity was so poor that it would tighten up in a turn at low airspeed and that it actually required a push on the control column to defeat this which is quite unaceptable in an airliner, not so much in a Pitts.
Obviously this could not have been corrected by adjusting the elevator cct feel so it explains the why of why did they do it this way
This is a part of what I've been working on- where did you read that information??

Everyone has been focusing on the failure modes of MCAS and related components, but there has been little discussion about how stupidly huge the whacks that MCAS takes at a relatively minor (so we have been told) control feel issue. MCAS is, no two ways about it, a control system, one that exerts immense authority over the most important control surface on the airplane. Such a system, that sits unmonitored and unapologetically inserting itself when required, is unlikely to have been created in such a way without there being an equally significant issue that needed to be dealt with. Quickly and with huge control inputs.

THanks for sourcing that information-
dce
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Old 2nd May 2019, 20:15
  #4760 (permalink)  
 
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Originally Posted by SystemsNerd View Post

Thus, when asking "why didn't they just fly the plane?", one possible answer is undoubtedly some variant on "they were incompetent". But another possible answer is "they were put into a scenario in which any human being would consistently fail to solve the problem, regardless of competence". Probably the truth is somewhere between those two points.

*See Wikipedia article "Human factors and ergonomics"
Thank you for breaking this down into such understandable terms. When I posted a number of days ago my own experience (extremely experienced pilot with proper training, well-rested and otherwise not prone to panic or loss of functionality) I was sharing this exact point: Despite the firm assurances of many here there are circumstances you can be placed into wherein you will cease to function effectively. No machismo or mantra is going to change your basic incapacitation and the time it takes for you to return to a quasi-functional human being. From the outcome of the two MAX flights it is abundantly clear that the crews were partially incapacitated and overwhelmed. Given that 6 out of 6 pilots who were in this situation (The earliest incident went on for six minutes until the GIB piped up and suggested the cutout the trim. That flight was also on the brink of total loss...) a 100 percent incapacitation rate argues fairly forcefully (and empirically) against the hero-pilot who will just FTFA.

Warm Regards,
dce
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