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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 5th Apr 2019, 09:34
  #3261 (permalink)  
PJ2
 
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Originally Posted by Freehills View Post
https://leehamnews.com/2019/04/05/bj...is/#more-29839

Thinks that the force when electric tirm/ MCAS was switched back on probably bounced the crew out of their seats, causing them to lose/ weaken grip on the controls
While the gee is slightly less than 0g, the arms may fly up momentarily, but the crew would be belted-in, perhaps with the shoulder-straps still on, (though they may have been removed for greater mobility). "Hitting the ceiling"? Hm.
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Old 5th Apr 2019, 09:44
  #3262 (permalink)  
 
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In the prelim. report is a clear statement by the FO that the manual trim attempt did not work as advertised in the AD.
There is also a subtle hint that probably shows why the pilots in a last desperate attempt did reengage the trim motors, and how the pilots were desperately trying to follow the AD and manually resetting the trim, which was most likely aerodynamically blocked:
After the cutout, there is a very slow, long, subtle nose-down movement of the fin according to the report. What do you do when the crank is blocked, instinctively? You're rattling it! And then in this phase it moves only a few hairs nose-down, but not a bit Nose-Up.
Then, in desperation, they probably switched on the electric motors again, only to find out now, with two very short trim-up switch attempts, that in the meantime, electric trim quit working too (speed has meanwhile increased further). A nightmare.

This last attempt to implement the AD has now reset MCAS. And then comes design-wise (but is not in the FCOM or the AD, was never mentioned in training), while they still think about what to do next, after 5 s the final death blow of MCAS ...

The plane systems (MCAS and Trim) and the AD procedure just did not give them a fair chance IMHO.

An excellent overview over these 60 year old speed issues with the 737 trim system can be found in many old manuals and here: https://www.satcom.guru/2019/04/stab...and-range.html
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Old 5th Apr 2019, 09:44
  #3263 (permalink)  
 
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Originally Posted by SLFstu View Post
(From an ex hardware/software tech writer) - a comment about software rather than aeronautics. If the timeline story (CVR derived) in comparison to the FDR traces is accurate, here is something weird from the preliminary report's data nobody has commented on.

The third MCAS activation lasting 9 or so seconds starting at 05:40:41 did not alter stab pitch trim because the FO had just cut power to the stabilizer jackscrew motor. The report glibly notes that fact. But why did MCAS even try to activate, as if sitting there fat, dumb and stupid? Exactly what type of coding allows the FCC to attempt to command AND trim when both STAB TRIM switches are already set to CUTOUT? Seems the designed use case never anticipated this sequence.

So it appears that this bolted on chunk of MAX-only software was not monitoring real-time trim motor electrics. Hell no, you cannot do that - a loom change might be required and that would disturb the production line and possibly delay certification! Or better yet, a few lines of more rigorous code were required.

Way up in the thread at least 2 incredulous posters suggested, sarcastically I think, that an intern might have programmed MCAS_1? Makes you wonder.
I agree, but this anomaly is only part of the story. There is also the question of why there are so few electric trim corrections considering the circumstances? MCAS has massive authority despite massive AoA disagreement. Surely, the obvious solution is for MCAS to be automatically disabled but not electric trim? Why would the engineers even contemplated MCAS continuing to operate with significant AoA disagree? What is the effect of a constant input on the pickle switch? Does it give continuous control authority or intermittent authority?

It is fairly obvious that the automated system should have disabled MCAS authority as soon as there was significant disagreement with the two AoA sensors. Blaming the pilots is not sufficient, the more fundamental defect is plainly a Boeing issue and seemingly inexcusable. I feel that the pilots needed to act within the first 15 or 20 seconds of stick shaker but failed to recognize the issue quickly enough. The question is how many crews would have acted quickly enough and why should they have to react at all? It is all so unnecessary.

It is suggested that Boeing provided the MCAS system to overcome approval considerations. However, it does not make sense to leave it to the pilots to disable MCAS when it could be handled automatically. Neither does it make any sense to disable electric trim completely in order to disable MCAS.

...Just touching the surface of the negligent design and certification issues...
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Old 5th Apr 2019, 09:51
  #3264 (permalink)  
 
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DaveReidUK
"The increased safety provided by the Boeing design limits on the thumb switches (for out-of-trim dive characteristics) provides a compensating factor for the inability to use the thumb switches throughout the entire flight envelope."
I assume from your post that you understand what this gobbledygook means? Can you explain it in English?
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Old 5th Apr 2019, 09:56
  #3265 (permalink)  
 
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Originally Posted by ecto1 View Post
...
Those are the official excuses. I don't buy them. It was honestly a very reasonable system when safety was important but not as important as today, data buses did not exist and pilots came from the military.
...
They're not "official excuses". The dual redundant system has been thoroughly analysed and its consequences known and calculated to a nicety.

What you're proposing is a hybrid system (disabling an input to a good system in case of a single failure on the other system) which will have its own consequences.

There is a solution, as has been implemented in FBW aircraft - if you are going to patch FBW onto a dinosaur, then its sensor suite must also be upgraded to meet those requirements and not rely on more patching to a grandfathered certification.
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Old 5th Apr 2019, 10:11
  #3266 (permalink)  
 
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From what I`ve read ,the MCAS operates when flaps are `UP`...What is the flap limiting speed,and does the system(MCAS) depend on the flap lever position only...?
I used to fly C-130,which had power controls,but power to the rudderboost was limited when the flaps were UP,but full hydraulic power beyond 20 deg,primarily to prevent overstressing the fin at `high speed`,but cover the lower speed asymmetric case requiring more rudder...
However,if one was doing `tactical/fighter affiliation/more aggressive flying,one could `cheat` by pulling a c/b for the FLAP hydraulics,and then select the flap lever to 20 deg.This then gave the rudder full hyd.,but the flaps were still `UP`..

I would have thought that the immediate actions drill would have also stated to have reduced speed to perhaps below 300 kts..
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Old 5th Apr 2019, 10:16
  #3267 (permalink)  
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Originally Posted by ManaAdaSystem View Post


Chesty, we discussed this earlier, and you said you have flown the 737 with manual trim and it was no problem.
I’ve only tried this a few times, but found the manual trim to be pretty hard. A friend of mine got «Stab out of trim» enroute and diverted because he thought he had a jammed stab. This after he tried manual trim and found it so hard he concluded he had a jammed stab.
It now looks like manual trim is nearly impossible at higher speeds.
It puzzels me a bit that the stab can be trimmed so far it will bring the aircraft out of the pilot’s control. And then you can’t manually bring it back under control because the trim forces are too high.

How Boeing will solve this is beyond me. MCAS is a killer and if they restrict it it will affect the certification. In order to get rid of MCAS they have to redesign the aircraft.
IMHO the MAX will stay on ground for a long time.
Yes but that's a function of aerodynamic load.

My point was that anyone can turn a wheel regardless of hours (obviously if it's not prevented by aerodynamic load) so to suggest that the FO couldn't turn it because he had only 200 hours was and is total nonsense (and I know you didn't make that point).
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Old 5th Apr 2019, 10:17
  #3268 (permalink)  
 
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Originally Posted by 42go View Post
DaveReidUK
"The increased safety provided by the Boeing design limits on the thumb switches (for out-of-trim dive characteristics) provides a compensating factor for the inability to use the thumb switches throughout the entire flight envelope."
I assume from your post that you understand what this gobbledygook means? Can you explain it in English?
Nope, sorry, you assume incorrectly - I don't speak gobbledygook either. You would need to ask EASA.

I think that a rough translation is "when electric trim runs out, pray you have enough time, strength and altitude left to start winding ..."
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Old 5th Apr 2019, 10:28
  #3269 (permalink)  
 
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Originally Posted by PJ2 View Post
Is that what it is?...250 turns of the trim wheel from stop to stop? That info wasn't available anywhere in the AMM, the FCOM or even the FCTM. Like some, I wondered how many turns it was, so thanks.

The full range (from the AMM) of the stab is 17°. This range is not available to all controls, (electric, manual, wheel), as noted in this thread, but let us assume the available range is -1 AND to 16 ANU using the big wheel.

Now we can calculate turns and degrees of trim, (remembering the comments on the difficulty of turning the wheel under some circumstances).

250 turns / 17 degrees = 14.7 turns per degree, or,
17 degrees / 250 turns = 0.07° per turn.

If the thinking and the math is correct, we can see that there is a lot of work and time to manually modify the stab trim using the wheel. In fact, those who fly/flew the B727/B737 will recall just how fast the wheel goes around when electrically-trimming in normal flight, flaps-up; the white mark on the wheel is almost a blur...

PJ2
having done manual trim on 707-737:-800 during sim training and air test over thirty years - a few points
1 stop wheel turning before you get way out of trim is the drill. But you have to notice. I note in the video posted here it took 10 seconds to disable STAB. Lion air struggled for 10 ?? minutes. In other words STAB is off so quickly that all these situations we speak of here don’t occur. And if they do, go to next step >>
2 old trick as mentioned earlier- off load stab by releasing back pressure for a few seconds allows you to trim ANU in any load situation . Both pilots both wheels with handles extended. Very quick. It’s the elevator loads against the STAB jackscrew that causes the high loads . But you have to know this and I think it’s not taught any more.
3 Stab is three times more powerful than elevators - they don’t ‘blow back’- just not designed to overcome STAB.
4 if you’ve turned off STAB ELECTRICS you can turn them on to enable ANU trim. Thumb switches. Then when back in green range - safe range- STAB OFF and trim manually.

5 But- and this all gets back to training- you have to know all this. Not look in manuals. It has to be in the core of your airplane skill base. Trained by the trainers. And if the trainers don’t have it ........
Summary. Are pilots new to 737 aware of the dangers posed by the stabiliser?
They do runaway stab, jammed stab and manual reversion during type rating training- at least did until recently! So they know how tough an animal the STAN can be but manageable.
MCAS
So. MCAS being sorted. Good thing. Does that leave us still with a much bigger problem? The elephant in the room! What’s going to happen next time an automated function badly misbehaves- and it will.
Y
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Old 5th Apr 2019, 10:48
  #3270 (permalink)  
 
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Originally Posted by PJ2 View Post
Is that what it is?...250 turns of the trim wheel from stop to stop? That info wasn't available anywhere in the AMM, the FCOM or even the FCTM. Like some, I wondered how many turns it was, so thanks.
Having been on the jumpiest of a classic or NG (never been in a MAX), those trim wheels seemed to turn quite a lot even for very short bursts of trim input, so 250 is quite credible.
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Old 5th Apr 2019, 10:48
  #3271 (permalink)  
 
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5 But- and this all gets back to training- you have to know all this. Not look in manuals. It has to be in the core of your airplane skill base. Trained by the trainers. And if the trainers don’t have it ........
Years and years of drift towards ‘lean operations’ where training gets faster and shallower and faster and shallower as the decades slide by.
Why keep 10 sim sessions for a type rating when you can get away with 9 and collect a $10,000 KPI bonus?
Two years later........ why keep 9 sim sessions for a type rating when you can get away with 8 and collect a $15,000 KPI bonus?
Two years later.........why do 8 full flight sim sessions for a type rating when you can get away with 6 + 2 cheaper ‘motion off’ sessions and collect a $20,000 KPI bonus?
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Old 5th Apr 2019, 10:56
  #3272 (permalink)  
 
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Aviate, navigate, communicate?
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Old 5th Apr 2019, 10:57
  #3273 (permalink)  
 
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Originally Posted by spornrad View Post
In the prelim. report is a clear statement by the FO that the manual trim attempt did not work as advertised in the AD.
There is also a subtle hint that probably shows why the pilots in a last desperate attempt did reengage the trim motors, and how the pilots were desperately trying to follow the AD and manually resetting the trim, which was most likely aerodynamically blocked:
After the cutout, there is a very slow, long, subtle nose-down movement of the fin according to the report. What do you do when the crank is blocked, instinctively? You're rattling it! And then in this phase it moves only a few hairs nose-down, but not a bit Nose-Up.
Then, in desperation, they probably switched on the electric motors again, only to find out now, with two very short trim-up switch attempts, that in the meantime, electric trim quit working too (speed has meanwhile increased further). A nightmare.

This last attempt to implement the AD has now reset MCAS. And then comes design-wise (but is not in the FCOM or the AD, was never mentioned in training), while they still think about what to do next, after 5 s the final death blow of MCAS ...

The plane systems (MCAS and Trim) and the AD procedure just did not give them a fair chance IMHO.

An excellent overview over these 60 year old speed issues with the 737 trim system can be found in many old manuals and here: https://www.satcom.guru/2019/04/stab...and-range.html
excellent article with diagrams- all thanks to Peter Lemme. It’s a pity that level of schematic is not easily available to lone pilots.
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Old 5th Apr 2019, 11:05
  #3274 (permalink)  
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Yanrair, all 5 points well-worth reading and memorizing. Thank you for a fellow aviator's recollections from those days - they remain as valuable and potentially life-saving as ever. I don't know what happened to them in the last two or three decades but there weren't too many wheels left that needed re-inventing, yet here we are. Another guy worth reading, just like Centaurus in Tech.

PJ2
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Old 5th Apr 2019, 11:07
  #3275 (permalink)  
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. . . so 250 is quite credible.
Thanks, Alpine Flyer, yes, that seemed reasonable to me too.
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Old 5th Apr 2019, 11:12
  #3276 (permalink)  
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Originally Posted by BluSdUp View Post
Let one thing be clear, we now have facts.
The crew was extremely inexperienced :
The FO had grand total 361hrs of wich 207 the last 3 months.
The captain was 29 years. Had an impressive career!
Had 8122hrs total

July 23 2010 he graduated
FO 737-800 31 jan 2011
Then FO 757/767 777 and 787.
BUT!
And here comes the problem: In 26 Okt 2017 he made Cpt 737-800 , SO less then 1.5 years Command.
There is a total of 1477hrs 738 and 103hrs Max.
Of which a lot is FO time!!
So, a low timer indeed!

This is a warning on so many levels!

BLU, do we stop using captains that have less than 1.5 years in command?
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Old 5th Apr 2019, 11:13
  #3277 (permalink)  
 
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Update

It looks like the FAA has decided to postpone the Certification of the Software update past April, according memo!
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Old 5th Apr 2019, 11:15
  #3278 (permalink)  
 
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Also

No Max for RYR this summer schedule!
Summer in Ireland is April to end of October!

Max
RIP
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Old 5th Apr 2019, 11:21
  #3279 (permalink)  
 
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That said do disagree with statements on manual trim, pretty strong evidence that at the speed and trim they were in it would be physically very hard or impossible to trim manually without unloading maneuvers that the did not have the altitude for and/or knowledge/training of.
MurphywasRight
If the column forces were too high, one option (if you hadn't worked out how to engage the manual trim, which these guys hadn't) is to turn the trim back on, correct it with the normal electric trim switches, and then turn it off again before MCAS kicks back in. You asked what I would do, that's what I would do.
PaperHanger

They decide to cut out the trim switches at 0540:35, 35 seconds after first MCAS activation.N1 remains at 94% throughout leading to loss of speed control. But If ANU manual trim had been ordered immediately following cutout of stab trim switches, or better still, PF had trimmed back to 5 units(which has a visual marking on the trim index) and then disabled the trim switches,can we calculate if the aerodynamic loads were already too much for manual trim to work.What was the speed at 0540:35?
Captain asks if trim is functional at 0541:46,so that's 71 seconds after trim cutout where no attempt is made to relieve control forces and speed is allowed to build.

Last edited by Rananim; 5th Apr 2019 at 11:32.
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Old 5th Apr 2019, 11:21
  #3280 (permalink)  
 
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Originally Posted by DaveReidUK View Post
Nope, sorry, you assume incorrectly - I don't speak gobbledygook either. You would need to ask EASA.

I think that a rough translation is "when electric trim runs out, pray you have enough time, strength and altitude left to start winding ..."
This is a master piece of an aviation agency output. Could be any, this is not sepcific to EASA: It is the result of lawyers writing tech statements or manuals. The 737MAX emergency AD is no better. It is contradictary, leaves open questions and is not the smart wording standard other industries have reached in the past 40 years, partially because of tough consumer laws.
The peak is the FAA "Continued Airworthiness Notification to the International Community" dated March 12, a document type that was non existant before this date, is not based on ICAO rules and had just one obvious purpose. CMA.

Too often I sit in front of aviation regulations, rulings and manuals and think: damn sh.., what is it they want to tell me? And the obvious questions that every semi-intelligent guy/gal would have from a paragraph are never raised in the document nor answered. Still in this modern world people are too often ashamed to ask the obvious. There is no shame if it can save lifes.
Commercial aviation is stuck in the late 60s.
It is the answer to thick pants mentality and low management quality; as long as knee-jerk reactions dictate it will never change.
I have been there. For more than 30 years and unsuccessful to change that.
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