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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 7th Apr 2019, 07:27
  #3521 (permalink)  
 
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Originally Posted by Derfred View Post


The EASA document is being mis-interpreted by many.

It notes that once you get to a certain point of AND trim (somewhere between 3 and 4 units from memory, varying by model), you cannot trim further AND with the yoke switches (flaps up). If you ever needed to, for an unusual reason (eg jammed flight controls), you would need to use manual trim. In normal ops, you would never need to.

This point is irrelevant to this discussion because it doesn’t prevent the yoke switches from trimming ANU, even if the aircraft has been trimmed full AND. It is a one directional limit switch only. It doesn’t prevent trim in the other direction.

Note: I’m referring to the limit switch in the forward trim range above. There is another limit switch aft which works similarly in reverse.



I hope this clears it up.
No. I take an aviation document as literal and binding. What you say may be from some private working papers, which is not an official numbered published document. So can be anything, including fake.
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Old 7th Apr 2019, 07:27
  #3522 (permalink)  
 
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Originally Posted by Flt.Lt Zed View Post
Why does Boeing not delete MCAS from their new B73 8/9s?. They have thousands flying around successfully without it.
Your comment (and my response) probably deserve to be deleted, but here goes:
- Thousands of fighter jets fly every week without the election seats being used. Why not delete them, and save all that weight and complexity?
- The inflight entertainment system poses a hazard due to the risk of fire in the cabin. Why not delete it, and save all that weight and complexity?

My points are intentional hyperbole, but highlight the fact that nothing is ever added to an aircraft unless there is a purpose for it, and nothing is ever deleted from an aircraft if there is a safety aspect involved.

Passenger aircraft still carry liferafts for over water flights, its a requirement, no matter how archaic. End of rant.
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Old 7th Apr 2019, 07:40
  #3523 (permalink)  
 
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Originally Posted by bill fly View Post


That post from Under Duress is unfortunately typical of what can get postulated after an accident / incident and reminds me of the criticism directed at Sullenberger and crew because it was demonstrated that a pre briefed crew, after some practice attempts could react within seconds and land the aircraft on a runway (see the documentary “Sully”). This without any time for recognition, analysis or decision. They were trained dogs performing in the sim and just about hacking it.
We should remember that lots of folk look in here - you can be sure that Boeing does too - engineers and legal team.
Any sensible suggestions will at least be taken on board - any condemnation of crew actions seen as vindication of their insistence on the suitability of the stab runaway drill for a different and complex failure.
Valid points, but I just read an equally convincing argument stating exactly the opposite. It was posted in a thread which is somehow in the Tech Log forum, but IMO worth cross posting (with due acknowledgement).
Originally Posted by Water pilot
I doubt there is going to be much in the way of legal arguments on this one, Boeing does not want to be anywhere near a jury. You can talk about the pilot's actions all that you want to, but ultimately you have two aircraft that were pointed to the ground at low altitude by a flight control system that was not disclosed to the pilots and that was (according to media reports) significantly different than the certification documentation described. Add in the cosy relationship with the FAA along with the whistleblower report and this is not something that goes to trial if Boeing has any competent lawyers left.

I am not a lawyer, but I don't think you ever want to be in a civil trial where the jury is wondering why the executives are not in jail yet.
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Old 7th Apr 2019, 07:48
  #3524 (permalink)  
 
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Originally Posted by Derfred View Post


The earlier trim durations you refer to happened with flaps extended. The trim wheel moves faster with flaps extended. That explains the difference.

Nope. Look at the FO trim up input (long one) that stops MCAS. First 3 s of that input moves the stab appr. 1 U up. Even at the lousy resolution of the plot you can see the difference. I copy/pasted all 4 events together:


Or, for more precision: The FO input lasts 10 s and brings the stab up appr. 2.3 U 1.9 U. That is appr. 0.7 0.6 U / 3 s. The third blue arrow from the left does not show that much movement. Flaps up applies to both rightmost events.
And, again, as you raised: Why does PF ask FO to help with the trim (switch)? [Edited because Derfred gave more correct numbers in a later post]

Last edited by spornrad; 7th Apr 2019 at 09:00.
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Old 7th Apr 2019, 08:06
  #3525 (permalink)  
 
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Originally Posted by FrequentSLF View Post
A simple question from an engineer, why a designer should put a pilot in such situation, why the designer cannot prevent and design a solid system?
They can design a solid system, although never perfect. In this case, sadly, they failed to design a solid system. That is not in question. Even Boeing have effectively admitted this.

The question now is, “how and why did this happen?”, especially in such a tightly regulated, conservative and safety-conscious industry, with one of the world’s most respected organisations. The answer to that is now under extensive inquiry.

We may or may not ever discover the truth, but typically when this many people die unnecessarily, the difficult questions finally get asked, and those with the answers are forced to actually answer.

Of course, it will fundamentally point to one thing: MONEY.

But we aren’t going to get rid of money, so it’s the movement of money, to whom and how much, and how much those in charge of money get to influence those in charge of solid design, that will come into question.


[And why if he is not able to do so the blame is on the operator? A wrong design is a wrong design, no matter how much you train the operators
Well, if by operator, you mean the airline, well they are in charge of employing sufficiently skilled pilots and providing them sufficient training to get their passengers from A to B safely. The airline is also in charge of purchasing sufficiently safe equipment to do so, and maintain it to a sufficient standard.

If they fail to do this, they must accept some liability for the failure. Whether they failed to do this is not yet ascertained - some think the pilots should have saved the passengers from the design fault, some think that’s an unreasonable ask, and some think it was impossible.


If, on the other hand, by “operator” you mean the particular pilots involved, well, in my opinion, pilots have a personal obligation to maintain a standard on top of that required by their employer and their regulator. They can also be held personally liable for the failure, and depending on the global jurisdiction may be supported and/or indemnified by their employer, or, not.

Aviation safety is a rich tapestry, that normally results in a high level of safety, but many argue that it is gradually being eroded in standards of design, training, and skills, generally by one thing: MONEY.

Think about that next time you buy the cheapest ticket available, because that MONEY only comes from one place: you. The less you pay, the less MONEY available to pay someone to design a solid system, or to pay or train the pilot to save you from the less-than-solid system.
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Old 7th Apr 2019, 08:09
  #3526 (permalink)  
 
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Has anyone tried trimming with the stick shaker going? Honest question. Is it difficult or no problem?
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Old 7th Apr 2019, 08:28
  #3527 (permalink)  
 
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Originally Posted by AerocatS2A View Post
Has anyone tried trimming with the stick shaker going? Honest question. Is it difficult or no problem?
In the Sim, yes.

We have done exercises pulling the aircraft into deep stall from initial stick shaker, while trimming back continuously (otherwise it’s hard to get deep stall due to increased elevator feel force - B737NG not MAX). Then having to be trimming forward again during recovery. I’ve never noticed a difficulty with this.

But not saying for one moment that the Captain in this event was not having a problem (I was the one who raised the possibility!). My stick shaker was happening at stall speed (150-ish kt), not 325 kt, and it was a Sim.
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Old 7th Apr 2019, 08:44
  #3528 (permalink)  
 
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Originally Posted by Derfred View Post
But not saying for one moment that the Captain in this event was not having a problem (I was the one who raised the possibility!).
Thanks for your explanations. Since it would be another lottery win the thumb switch going south at that exact instance (besides why less, not no stab movement): Is there any remote possibility that software reduces the thumb switch authority on the left, not right, in those conditions (AOA disagree/MCAS activation) ?
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Old 7th Apr 2019, 08:47
  #3529 (permalink)  
 
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Bill Fly,
Under Duress gave a pretty accurate description of what SHOULD have happened. Airline Pilots ARE “trained dogs” in certain circumstances. Few emergencies require immediate and appropriate action but stick-shaker on rotation and/or Unreliable Airspeed are definitely two of them. The metaphorical Swiss cheese started lining up from rotation and errors compounded from that point. It was badly mis-handled. Was MCAS the ultimate contributing factor? Absolutely. Was it the sole cause? Absolutely not. Most professional Pilots reading this thread with experience on the B737 would expect to do much better. By following published procedures. And exercising good Airmanship. Maybe that sounds like arrogance but that’s the nature of the beast.
Boeing and the families of victims are in a world of pain right now and comments should be worded accordingly.
But there is much more to this than MCAS.
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Old 7th Apr 2019, 08:48
  #3530 (permalink)  
 
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Originally Posted by threemiles View Post
No. I take an aviation document as literal and binding. What you say may be from some private working papers, which is not an official numbered published document. So can be anything, including fake.
???

I’m explaining how the 737 stab trim works, from the manuals. Not some ‘private working papers”. I know it works that way because I’ve been flying the thing most of my life.

I even know it works that way because I’ve used it that way on the ground. Actual aircraft, not Sim. You can use yoke trim to just forward of 4 units, then it stops. You can wind it forward to 0 units manually, then you can use yoke trim to electrically wind it back. That’s how it was designed, and that’s how it performs.

EASA brought it up because it was at odds with some certification criteria, and then allowed it because it made sense from a safety perspective.

Now whether it works at 365 knots with sufficient aft control column for level flight is an entirely different question. That question is currently under congecture. My point is that the EASA document is irrelevant to that congecture because that was not the subject of the EASA document, and the word “authority” is being mis-interpreted by some here. I doubt it was mis-interpreted by the actual audience it was intended for.

We know it works at 325-330 knots, because it did. It’s on the FDR trace. Yoke trim from 0.4-2.3 units.

I hope that helps.
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Old 7th Apr 2019, 09:12
  #3531 (permalink)  
 
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Originally Posted by George Glass View Post
Bill Fly,
Under Duress gave a pretty accurate description of what SHOULD have happened. Airline Pilots ARE “trained dogs” in certain circumstances. Few emergencies require immediate and appropriate action but stick-shaker on rotation and/or Unreliable Airspeed are definitely two of them. The metaphorical Swiss cheese started lining up from rotation and errors compounded from that point. It was badly mis-handled. Was MCAS the ultimate contributing factor? Absolutely. Was it the sole cause? Absolutely not. Most professional Pilots reading this thread with experience on the B737 would expect to do much better. By following published procedures. And exercising good Airmanship. Maybe that sounds like arrogance but that’s the nature of the beast.
Boeing and the families of victims are in a world of pain right now and comments should be worded accordingly.
But there is much more to this than MCAS.
Spot on, it's is also the view of every colleague I have spoken to.


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Old 7th Apr 2019, 09:15
  #3532 (permalink)  
 
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That post from Under Duress is unfortunately typical of what can get postulated after an accident / incident and reminds me of the criticism directed at Sullenberger and crew because it was demonstrated that a pre briefed crew, after some practice attempts could react within seconds and land the aircraft on a runway (see the documentary “Sully”). This without any time for recognition, analysis or decision.
Very much in agreement.

The Human Factors are, IMO, the most important/interesting part of these accidents.

To recap: There are many situations which require some sort of action from pilots, be it promptly or after consideration. The more time-critical an event is, the less time/capacity there is to figure out what to do, so responses to predictable events are based more on rules than extended cognition, hence “memory” or “recall” items are used. They need to have a simple, unambiguous trigger, e.g. an engine fails below V1, perform an RTO or GPWS says “PULL UP!”, perform the GPWS pull up manoeuvre.

When the situation is more complex and there is normally time for diagnosis, we have reference checklists which may contain decision trees, often leading to different actions and outcomes, dependent on further data. If no checklist really fits the bill completely, maybe due to multiple failures or unusual circumstances, then you need to use your general aviation understanding, backed up by specific type knowledge and all the resources you have access to in order to formulate and execute a plan of action. This is something you would generally do *after* you had determined there were no published normal or non-normal produces that were applicable, or you had applied the procedures and they had not helped or made the situation worse. Boeing specifically caution against “troubleshooting” unless all other possibilities have been exhausted but they also provide a useful “Situations Beyond the Scope of Non-Normal Checklists” guide in their training manuals.

Now, it is good aviation practice to have some kind of action associated with a single, predictable failure which affects the safe operation of the airframe, be it recall items or a reference checklist, or even just a note for crew awareness. In the case we are discussing, an AoA probe failure (which is singular, predictable and measurable) has caused a cascade of issues and warnings that are difficult to assimilate and don’t immediately point to any particular checklist, except maybe the Airspeed Unreliable one, which doesn’t include deactivating the trim. Remember we are looking at these accidents with hindsight and the warnings that occurred can be triggered by many different events that require different responses - we only know which was the correct path to take because we have most of the data in front of us to peruse at leisure.

There have been quite a few posts highlighting the startle effect plus the saturation of input channels by excess information of questionable usefulness, e.g. stick shaker, GPWS, fault messages, high control loadings, etc. It is quite easy to see how some things were missed, in fact most of the above is taught in basic HF modules but this seems have passed some manufacturers by.

It’s easy to say that you’d have disconnected the trim as soon as you got a stick shake in the climb out because the flaps are correct and power is set. Well done. But supposing that was a *real* stall warning because you put the wrong weights in the FMC so have rotated 20kts early? Not so well done now, eh? This has happened before and will happen again and is just one example of why it is so important NOT to rush to conclusions if you can absolutely help it.
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Old 7th Apr 2019, 09:44
  #3533 (permalink)  
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Originally Posted by threemiles View Post
I read it that this must be shown only for speeds between minimum for steady, unstalled flight and VLO/VFE. MCAS operates when flaps are retracted. The rubber word "appropriate" may be the secret.
But... 25.173 is for static longitudinal stability, the item of note is mis trim case which comes under 25.255 and that has a further set of criteria which if anything are inadequate for this case, or the underlying potential to get out of trim that exists on the B737 in general. The MCAS is covered in 25.672 and either will be determined to meet the requirement or be inadequate to show compliance with that. The out of trim case that resulted from the characteristics of MCAS is the major concern IMHO, which raises the matters of unloading the stab etc, which has it's own set of questions. That nexus is going to take lawyers to sort out, and that is not good for the operational outcome. That an aircraft can get out of trim excessively is not purely a Boeing matter, the Max just happens to be the current headline. A few years back it was A320's like the Perpignan event, a departure or two out of Reagan, and before that, it was A310s galore in-dispersed with A300-600's. Some of those ended up in smoking holes, some missed the ground on a number of occasions in the same event. If the conditions can occur that the pilot is at odds with the plane, it deserves more than a passing comment in the FCTM or a note in the FCOM.
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Old 7th Apr 2019, 09:49
  #3534 (permalink)  
 
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The Condensed ET-AVJ flight data from the Preliminary Accident Report
Omitted Parameters: Engine RPM, AOA, AOA Heat, Master Caution.
..
..

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Old 7th Apr 2019, 10:13
  #3535 (permalink)  
 
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Originally Posted by meleagertoo View Post
You must know by now that MCAS didn't (couldn't) start it's tricks until flap was retracted...er...don't you?
Always worth remembering that the MCAS functionality is a new, non-DAL A software routine, programmed into the FCC as an unmonitored open-loop system. Its function has already been drawn into doubt, as has its certification, safety analysis and technical documentation. Again, MCAS is a virtual system only - the FCC is the actual system that has control of the stab.

It is supremely unwise to state definitively as to what the FCC can or cannot do beyond stating that this software routine has full authority of the most powerful flight control installed on the aircraft.

It is also of note that the FCC commanded the stab aircraft nose down 3 times with the flaps still set.
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Old 7th Apr 2019, 10:13
  #3536 (permalink)  
 
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Is it possible that the electric trim was also unable to retrim the stab with a lot of control load?
Good point,why only a few blips at this point?..
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Old 7th Apr 2019, 10:50
  #3537 (permalink)  
 
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Originally Posted by Just This Once... View Post
It is also of note that the FCC commanded the stab aircraft nose down 3 times with the flaps still set.
Why is it of note? This is normal STS action.

- GY
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Old 7th Apr 2019, 11:11
  #3538 (permalink)  
 
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Originally Posted by GarageYears View Post
Why is it of note? This is normal STS action.

- GY
The STS functionality is also a software routine programmed into the FCC, it is a virtual system only.

The aviation community (outside of the test community) has become all-too-comfortable in accepting and using simplistic discrete 'system' descriptions for different functions that are actually hosted by a common system running a common code.

I readily accept and acknowledge that a number, or even the majority, of professional pilots will have their 'pedant' caption flashing when they read my words, but these distinctions matter. If and when Boeing produces an acceptable software-only fix for the current issues the only thing that will change will be the software version running in the FCCs.
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Old 7th Apr 2019, 11:23
  #3539 (permalink)  
 
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Originally Posted by Just This Once... View Post
It is also of note that the FCC commanded the stab aircraft nose down 3 times with the flaps still set.
No, it isn't of note.

That's autopilot trim.

It is the autopilot keeping the aircraft in trim while it accelerates to the selected bug speed of 238 knots while engaged in LVL CHG mode. What would you have it do... fly out of trim?

(It isn't speed trim - if the pilot was flying manually, then speed trim would have activated, but it would have been nose up instead of nose down.)

If and when Boeing produces an acceptable software-only fix for the current issues the only thing that will change will be the software version running in the FCCs.
And your point is?

The current problem appears to be a poorly designed piece of software known as "MCAS".

The proposed solution is a better designed piece of software to replace it.

If it works, what are you getting agitated about?
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Old 7th Apr 2019, 11:26
  #3540 (permalink)  
 
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Originally Posted by AerocatS2A View Post

The AD does in fact say to trim the forces out before using the cutout. https://theaircurrent.com/wp-content...AX-AD-1107.pdf
As far as I understand english, it does not. It says electric trim CAN be used to neutralise column forces before cutout (nobody would think it cannot, anyway). It says also Manual trim can be used before and after cutout. It never say electric trim MUST be used to neutralise column forces before cutout
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