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Indonesian aircraft missing off Jakarta

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Indonesian aircraft missing off Jakarta

Old 24th Nov 2018, 18:33
  #1621 (permalink)  
 
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Originally Posted by wiedehopf View Post
As far as i understand moving the trim wheel moves a drum with steel cable on it. That steel cable runs all the way back to the tail and turns the jackscrew.
So when the electric trim is used the trim wheel is backdriven via the steel cable.
The electric trim motor is located at the jackscrew.
Correct, except that there is also a gearbox in the loop, which takes the mechanical inputs from the cable drum and the electric actuator and produces rotation of the jackscrew:

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Old 24th Nov 2018, 18:51
  #1622 (permalink)  
 
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Salute Dave!

Wow. It is obvious Dave has more than the FCOM at his disposal. e.g. How many foot-pounds torque do we need to tighten those bolts?

As some suspected, the manual cable drum does not have its own connection to the jackscrew. So a failed gearbox could be a player. The manual drum could just be spinning and not turning the big screw. Or it could be jammed.

Gums...
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Old 24th Nov 2018, 19:11
  #1623 (permalink)  
 
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Originally Posted by gums View Post
So a failed gearbox could be a player. The manual drum could just be spinning and not turning the big screw. Or it could be jammed.
Or (and my money is still on this one), it was perfectly serviceable and working as intended (in the sense of responding correctly to the inputs from the STS/MCAS).

Occam's Razor
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Old 24th Nov 2018, 19:25
  #1624 (permalink)  
 
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Yeah DaveReidUK, and the famous case of the Alaska MD-80 that took The Dive because of a broken jackscrew was older and the screw had been improperly serviced, whereas this plane was almost new.

Sincerely,
Master of the Obvious
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Old 24th Nov 2018, 19:54
  #1625 (permalink)  
 
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Originally Posted by FCeng84 View Post
- MCAS has an authority limit of at most 2.5 degrees of stabilizer (less as speed/Mach increase).
- MCAS will not move the stabilizer an increment more than its authority unless it has been reset by either pilot manual stabilizer trim command or engagement followed by disengagement of the autopilot.
- MCAS would not be reset as a result of mechanical manual stabilizer trim (i.e., pilot physically turning the trim wheel by hand)
The way I (and others, see e.g. https://www.satcom.guru/2018/11/737-...is-option.html ) have interpreted the published/leaked MCAS descriptions is that it will limit movement to 2.5degrees in one increment, the assumption is that multiple increments are possible.

In the description:
The function is reset once angle of attack falls below the Angle of Attack threshold or if manual stabilizer commands are provided by the flight crew. If the original elevated AOA condition persists, the MCAS function commands another incremental stabilizer nose down command according to current aircraft Mach number at actuation.
the reset conditions are mentioned in one sentence and then the next sentence covers if "AOA condition persists" - it isn't clear that one is conditional on the other, or how long the condition has to persist for. Consensus seems to be that STS, from which MCAS appears to derive, has a restart timer.

If it is in fact the way that you describe, then all the concerns expressed publicly (from various pilots) that MCAS doesn't honour the column cutouts would be wrong - if you are correct, then if you fight MCAS with stick back you'll face at most 2.5deg adverse trim, whereas if you fight it with trim it'll fight you all the way to the stops
[ The DFDR trace doesn't help tell us which way it is, because AFAICS every down trim is countered by manual up, just not enough to keep them flying ]

And of course if you are right then Boeing thought it wasn't important to tell the pilots which way was best to counter incorrect MCAS...
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Old 24th Nov 2018, 20:11
  #1626 (permalink)  
 
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Salute!

No , infrequent.

Many pilots are not saying MCAS does not honor pilot trim cmds from the wheel. And further....

The data traces clearly show all the pilot trim cmds and they are correlated one for one with Hal stopping and waiting 5 seconds and re-applying nose down trim. The AoA rules the MCAS, not STS system.

Something different happened about 30 seconds before the dive. Power application, diversion of control forces, 4+ degrees of stab position. Would be nice to see gee and best of all, the cvr. Maybe the trim wheel has been recorded, and that could explain a few things, as well.

Gums sends...


Last edited by gums; 24th Nov 2018 at 23:55. Reason: typo for cvr
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Old 24th Nov 2018, 20:48
  #1627 (permalink)  
 
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RE GUMS # 1630 and "PULLEY

.
"Thanks for the explanation, as I was sure someone else had mentioned the wheel-to- cable- to- drum-to-jackscrew implementation versus a pulley-to-stab connection
See my post 1500 21 Nov time 18;14 for that comment plus a youtube video on actual operation o 737 NG ballscrew ( jackscrew)
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Old 24th Nov 2018, 21:03
  #1628 (permalink)  
 
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Originally Posted by gums View Post
Salute!

No , infrequent.

Many pilots are not saying MCAS does not honor pilot trim cmds from the wheel. And further....
Sorry, I may not have been clear, the comments I was to were about MCAS not honoring the aft column cutout switch - if you pull the yoke back far enough STS will stop trimming forward, MCAS won't. See e.g. last few paragraphs of this link: https://leehamnews.com/2018/11/14/bo...to-the-pilots/ (I know that's not from a pilot but I'm sure I've seen similar from pilots).

Something different happened about 30 seconds before the dive.
I've seen some speculation that the traces indicate a handover of control, I don't know if that is so, but I agree - something happened.
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Old 24th Nov 2018, 21:23
  #1629 (permalink)  
 
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Salute infrequent!

O.K., I get it. No offense, and the big beef from pilots is the system doing something that you have not commanded when not in A/P. Fer chrissakes, "manual" should be as much "manual" as possible so you don't have to remember all the sub-modes and special procedures. See the AF447 endless posts.

The shaker is one example of "warning", but it doesn't move a damned thing. The "pusher" on some planes is same-o, same-o. Both are telling you to pay attention to something. I flew with both types of "alerts", and they helped if I was having a bad hair day. I also flew with two planes that had actual aoa/gee limiters, and you could pull all you wanted, but the FLCS ( flight control system) would not let you command more than it wanted, heh heh.

The STS thread over on Tech Log is very interesting, and discusses STS much more than MCAS. So Vess and Concourse are over there contributing on a new thread that goes more toward total pitch trim system(s).

Gums sends...
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Old 24th Nov 2018, 21:38
  #1630 (permalink)  
 
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Dave #1625, but that reply doesn’t answer my question (#1622) whether an AoA display is removed from EFIS with an AOA DISAGREE alert. Lion does not have the mod.

If the AoA display is not removed, then the crew will face further conflicting indications, stick shake, low speed awareness, and an erroneous EFIS AoA display; the latter being of particularly concern given all of the AoA enthusiasts in this forum - ‘AoA is the answer to stalling’. Except in this instance the indication is inaccurate - nose high, requiring a nose down pitch which could be the most unwanted action for the situation.
Yet another weak design feature (there is no third system to compare), and an aspect which again could limit the effectiveness of the abnormal drill.



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Old 24th Nov 2018, 21:54
  #1631 (permalink)  
 
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Originally Posted by PEI_3721 View Post
Dave #1625, but that reply doesn’t answer my question (#1622) whether an AoA display is removed from EFIS with an AOA DISAGREE alert. Lion does not have the mod.
Ah, OK. I'd assumed it was a question specifically about the Lion Air aircraft rather than a general one.

If the latter, I don't know the answer - you might be better asking in the Tech Log forum rather than here, where it doesn't apply.
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Old 24th Nov 2018, 22:16
  #1632 (permalink)  
 
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For those who missed this re stab trim and how much and how long

https://theaircurrent.com/aviation-s...em-mcas-jt610/
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Old 24th Nov 2018, 22:34
  #1633 (permalink)  
 
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threemiles: "seems much comes down to training, organization, leadership, documentation, culture in the airline, the FAA and Boeing."

No objection to observations that the looming lawsuit or multiple lawsuits will be big legal jam-sessions - unfortunately including unsavory as well as diligent attorneys, probably.

But some lawyers involved with aviation aren't principally interested in crash litigation, as important as that practice area may well be. Instead their legal acumen focus is on advancing the national and international legal frameworks within which aviation is conducted....which includes advocating for, and helping "the complex" create and implement, reforms ("complex" here meaning, for example, manufacturers plus regulators plus pilots and their unions plus other safety experts; one leading figure in international civil aviation yesterday referred to the "aviation ecosystem", same thing).

Yet when one sits back, unrelaxed, and contemplates what reforms might be needed and might be effective to rectify the faults in five realms listed by threemiles, in three key components of "the complex".....this is going to require a lot of very focused non-cynical (non-greed-driven) expertise. And the NTSC report (eventually) and any other official reports may well prove to escalate the....complexity here.
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Old 25th Nov 2018, 05:42
  #1634 (permalink)  
 
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A simple solution maybe for regulators to start forcing manufacturers to actually design new aircraft and not keep recylcing old type certificates.

The whole A320/737 situation especially the 737 is bordering on farcical. You wouldn't build a car or boat like that but in aviation somehow its a good idea.
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Old 25th Nov 2018, 05:58
  #1635 (permalink)  
 
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Have to keep the grandfathers in business...
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Old 25th Nov 2018, 07:56
  #1636 (permalink)  
 
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#1644: Except that MCAS does not have any ‘grandparents’. The ideas behind this ‘single-failure prone system’ may have its origins in modern aircraft with their high integrity stability enhancements based redundant architecture. Perhaps this is the shadow of grandfather designing, test and certification, and dated regulatory practice. Time to dust off James Reason’s views on organisational accidents.

Irrespective of what the Indonesian authorities identify in their investigations, the deficiencies in disseminating knowledge and crew checklists must be investigated.
I doubt that Indonesia alone would be able to pursue an investigation involving the FAA and Boeing in the US; according to Annex 13 they should, but …

The NTSB should be sufficiently independent to look at the FAA and delegated regulatory process, minimising any of criticism of an internal coverup.
An investigation would be in everyone’s interest worldwide. Without understanding where the design and certification process failed the confidence in aviation safety remains open to question, particularly for Boeing and all their aircraft types.
A separate investigation might also enhance the need for other regulators to review the integrity of their certification processes, and consider the effectiveness of the oversight of joint international approvals.
“Trust, but verify.”

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Old 25th Nov 2018, 09:52
  #1637 (permalink)  
 
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The reason for development of MAX was purely commercial. Their biggest customer the south west airline wasn't prepared to wait for completely new aircraft and was thinking of buying the AB neo. The 737 with low engines clearance we're not in position to accommodate a larger fan so it appears they juggled with attachment positions which in turn made the aircraft unstable so had to design untried concept of MCAS and installed it through the back door. So far it was fine but now what?
https://www.google.co.in/amp/s/amp.ft.com/content/c9ebe8c4-24d7-11e0-a919-00144feab49a
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Old 25th Nov 2018, 09:54
  #1638 (permalink)  
 
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A very simple question from a very old aviator. As AoA is so important to so many automated systems in modern aircraft, why are there not three AoA vanes with a simple voting system when one gives a wrong indication? Most autoland systems work this way.
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Old 25th Nov 2018, 10:03
  #1639 (permalink)  
 
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why are there not three AoA vanes with a simple voting system when one gives a wrong indication?
It's better that way but is not cure all. Airbus has three but in Parpignan crash two rougues voted out the third only good guy.
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Old 25th Nov 2018, 10:13
  #1640 (permalink)  
 
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vilas,

Agreed, but the Perpignan case with two failures is very much less likely than only one failure
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