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Indonesian aircraft missing off Jakarta

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Indonesian aircraft missing off Jakarta

Old 15th Nov 2018, 18:07
  #1281 (permalink)  
 
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Originally Posted by CONSO View Post
Challenger issue is off topic- and NOT applicable here- It was a management/PR decision which overrode the engineers concerns on challenger . .
Why is that off-topic? Could have been the same issue that led to here.
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Old 15th Nov 2018, 18:16
  #1282 (permalink)  
 
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Originally Posted by Hi_Tech View Post
For all those questions about WHY this MCAS on B737 MAX fleet, the following link has a very nice easy to follow explanation with clear graphics written by a test pilot Bjorn Fehrm.
When you apply a lot of lipstick to an old lady like B737, something else goes wrong. Boeing had to do this change as the large engines made the aircraft stability to go wrong. Thanks Bjorn. I think it will clear up several questions about MCAS, STS, etc. in this forum.

https://leehamnews.com/2018/11/14/bo...to-the-pilots/
Have been wondering what effect larger engine nacelles might have on MAC and/or CoG, when moved further forward on the airframe.....!
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Old 15th Nov 2018, 18:28
  #1283 (permalink)  
 
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Red face

Originally Posted by Organfreak View Post
Why is that off-topic? Could have been the same issue that led to here.
Suggest you read the two reports on Challenger and pay attention to Dr Richard Feynman comments

https://spaceflight.nasa.gov/outreac...ion_report.pdf

https://www.gpo.gov/fdsys/pkg/GPO-CR...99hrpt1016.pdf
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Old 15th Nov 2018, 19:39
  #1284 (permalink)  
 
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Originally Posted by sAx_R54 View Post
Have been wondering what effect larger engine nacelles might have on MAC and/or CoG, when moved further forward on the airframe.....!
Another problem with these larger engines, is that they are more powerful, and I presume their center of thrust is lower on the airframe (because of the larger N1 fan diameter). Both of which result in a greater nose up moment when at full power, and therefore a greater risk of overpowering the elevator and leading to an uncontrolled pitch up. And therefore requiring a MCAS system to prevent this. Which was not fully thought through, and led to unforseen secondary failure modes.

Silver
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Old 15th Nov 2018, 19:57
  #1285 (permalink)  
 
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If the nose of the airplane starts to move towards the ground wouldn't you automatically pull the control column AND move the stabilizer trim switches to the nose up position which would stop this MCAS trimming nose down?
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Old 15th Nov 2018, 20:30
  #1286 (permalink)  
 
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You might, and you might think you had everything resolved once you had restored roughly level flight. But if the fault is still there, then as soon as you think you are safely trimmed in level flight and move on to addressing something else, it comes back into operation and does it to you again.
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Old 15th Nov 2018, 20:44
  #1287 (permalink)  
 
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Originally Posted by 747-8driver View Post
If the nose of the airplane starts to move towards the ground wouldn't you automatically pull the control column AND move the stabilizer trim switches to the nose up position which would stop this MCAS trimming nose down?
From day one of flight school we are taught to fly the stick, and only use trim to take out stick-loads. And never to fly the trimmer. (And that slides across to the 737, even though its stab-trimmer is more powerful than the stick-elevator.). Ok, in the 737 you get used to stopping the STS auto trimmer with opposite trim - but only if you regularly fly the departure beyond 5,000 ft.

If you are a company man-woman who engages the autopilot at 1,000 ft on every departure, you are not going to be familiar with that reaction. So if the autopilot hands back control at 1,500 ft, you might be left in unfamiliar territory.

Silver
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Old 15th Nov 2018, 20:46
  #1288 (permalink)  
 
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The stick shake was going all the while, wasn't it?

irrespective of the mantra to adopt a sensible pitch/power setting, it is quite a leap of faith to pull hard on the yoke while the stick shake is going. Horrible scenario.

The flight international report also mentioned that the trim brake is inhibited when the MCAS is running due to high AOA.
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Old 15th Nov 2018, 21:05
  #1289 (permalink)  
 
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The STS starts way before 5000 ft. The moment you start to accelerate, it will trim nose up. And that can happen from 800 ft.
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Old 15th Nov 2018, 21:26
  #1290 (permalink)  
 
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Originally Posted by 747-8driver View Post
If the nose of the airplane starts to move towards the ground wouldn't you automatically pull the control column AND move the stabilizer trim switches to the nose up position which would stop this MCAS trimming nose down?
If i understood the description correctly just pulling would not stop the trim in the case of MCAS.
The stab trim switch would stop it and it would start again after 5 seconds.

They had been flying more or less stable at around 5000 ft for quite a while (7 minutes) before they plummeted so the sudden pitch down is a puzzle.

It's hard to speculate any further without additional info but anyway:
Maybe the fault was intermittent?
Maybe they believed the stick shaker that they were stalled when they started the last pitch down?
Then when trying to pull up they could not because of the trim?
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Old 15th Nov 2018, 21:27
  #1291 (permalink)  
 
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Originally Posted by 747-8driver View Post
If the nose of the airplane starts to move towards the ground wouldn't you automatically pull the control column AND move the stabilizer trim switches to the nose up position which would stop this MCAS trimming nose down?
I wondered that as well, but the answer is YES (trimming) and NO(pulling).
From the Leehamnews article:
It can be stopped by the Pilot counter-trimming on the Yoke or by him hitting the CUTOUT switches on the center pedestal. It’s not stopped by the Pilot pulling the Yoke, which for normal trim from the autopilot or runaway manual trim triggers trim hold sensors.
Reasons are explained, interesting reading!
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Old 15th Nov 2018, 21:28
  #1292 (permalink)  
 
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Originally Posted by ManaAdaSystem View Post
The STS starts way before 5000 ft. The moment you start to accelerate, it will trim nose up. And that can happen from 800 ft.
No one is talking STS anymore. Everyone is talking about MCAS.

The aggressive trim down due to AoA failure occurs only after the flaps are retracted. (MCAS)
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Old 15th Nov 2018, 23:07
  #1293 (permalink)  
 
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First of many Law suits

Lion Air crash: Boeing sued by victim's family over aircraft design

Image copyright Reuters Image caption Investigators examine one of the engines from the doomed Lion Air flight JT 610

The family of a passenger killed when a Lion Air flight crashed into the sea near Indonesia are suing Boeing over an alleged fault with the jet's design.

The lawsuit accuses the US aircraft manufacturer of failing to inform pilots and airlines of a feature with its new 737 Max plane system that could "push the nose down unexpectedly".

Investigators have been looking into reported technical issues.

Boeing maintains that it is "confident in the safety of the 737 Max".

Lion Air flight JT 610 was carrying 189 people when it crashed on 29 October.



It plummeted into the Java Sea following a request from the pilot for permission to turn back to the airport just moments after taking off from Jakarta.

It was later established that the aircraft had had an airspeed indicator problem on its final four flights.What does the lawsuit say?

On Thursday, a complaint was filed by a Florida-based law firm on behalf of the parents of Rio Nanda Pratama, who was on board the ill-fated flight JT 610.

The lawsuit focuses on the 737 Max's new automated flight control system, which it says was designed to help prevent pilots from raising the aircraft's nose "dangerously high".

However, the lawsuit adds: "Under certain conditions [the system] can push the nose down unexpectedly and so strongly that the pilot cannot pull it back up in time to avoid a crash.

"This automated feature can be triggered even if pilots are manually flying the aircraft and don't expect flight-control computers to kick in.

"It is particularly surprising to hear from safety experts and the heads of pilots' unions that Boeing failed to warn its customers and the pilots of its new 737 Max aircraft about this significant change in the flight-control systems."

Boeing, meanwhile, has said that it is not able to "discuss specifics of an ongoing investigation".
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Old 16th Nov 2018, 01:45
  #1294 (permalink)  
 
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"Boeing’s automatic trim for the 737 MAX was not disclosed to the Pilots"

https://leehamnews.com/2018/11/14/bo...to-the-pilots/
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Old 16th Nov 2018, 04:46
  #1295 (permalink)  
 
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Originally Posted by AndyJS View Post
"Boeing’s automatic trim for the 737 MAX was not disclosed to the Pilots" (Link to Leeham News article)
The Leeham News article is quite informative of why the MCAS is required on the MAX, and fills in some blanks. I originally thought heavier engines further forward should if anything bring COG forward (unless balanced by other modifications), creating a more longitudinally stable MAX. However the idea that at high AoA the nacelles become aerodynamic surfaces sufficient to longitudinally destabilise the aircraft is interesting. It's a big aside, but a similar problem was noted on the WWII Supermarine Spitfire. As development to more powerful engines dictated more and more propeller blade area, the non obvious effect of this as an aerodynamic surface way forward of the aerodynamic center caused degraded longitudinal stability margin.

So when you are at high AoA, your MAX may become pitch divergent (without MCAS). At the same time you are likely to be slow but with high thrust beneath the wings, pitching you upward into the stall.

One thing that keeps coming up considering how much importance the AoA signal now has in the MAX, is whether there is redundancy in the two vanes. I think the answer is not really, as many conditions (rolling, yawing!) will lead to expected AoA disagree between the two sides of the nose. A warning (i.e. stick shaker) based on a single high alpha vane is reasonable, but any kind of consensus signal from two vanes only with severe consequence for faulty data is quite problematic.

So the current two vanes are really only one sensor for the purposes of redundancy. I wonder whether to have such a high degree of reliance on a AoA signal you should incorporate three vanes on each side.

Last edited by LEOCh; 16th Nov 2018 at 04:53. Reason: spelling
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Old 16th Nov 2018, 04:56
  #1296 (permalink)  
 
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Originally Posted by LEOCh View Post
The Leeham News article is quite informative of why the MCAS is required on the MAX, and fills in some blanks. I originally thought heavier engines further forward should if anything bring COG forward (unless balanced by other modifications), creating a more longitudinally stable MAX. However the idea that at high AoA the nacelles become aerodynamic surfaces sufficient to longitudinally destabilise the aircraft is interesting. It's a big aside, but a similar problem was noted on the WWII Supermarine Spitfire. As development to more powerfull engines dictated more and more propeller blade area, the non obvious effect of this as an aerodynamic surface way forward of the aerodynamic center caused degraded longitudinal stability margin.

So when you are at high AoA, your MAX may become pitch divergent (without MCAS). At the same time you are likely to be slow but with high thrust beneath the wings, pitching you upward into the stall.

One thing that keeps coming up considering how much importance the AoA signal now has in the MAX, is whether there is redundency in the two vanes. I think the answer is not really, as many conditions (rolling, yawing!) will lead to expected AoA disagree between the two sides of the nose. A warning (i.e. stick shaker) based on a single high alpha vane is reasonable, but any kind of consensus signal from two vanes only with severe consequence for faulty data is quite problematic.

So the current two vanes are really only one sensor for the purposes of redundancy. I wonder whether to have such a high degree of reliance on a AoA signal you should incorporate three vanes on each side.
That’s changes to Pitch done and dusted. If the manual did not include something as tricky as sole source AoA data FAIL, what else is missing? Are there new issues as regards OEI? Roll problems? Does Max need bigger ailerons? Is the Rudder effective in OEI? ETOPS? Will I fly to Hawaii on MAX? Yaw damping? What manner of control issues are different? MCAS is not so much about erroneous data recovery as it is about the whole picture. How do we trust that MAX is just the same as NG? Because with the fit of MCAS, Boeing admits it int the same aircraft....then disguises that finding by casually excluding the mitigation to show “it isn’t that important...” Who says?

Slow rolling the aircraft’s Test program with pax? Testing potential failures that demonstrably don’t meet statistical proofs with manufacturers prior “approval”?



What else is new and exciting? What other issues are too complex in failure to overwhelm the “average pilot” such that they need not to know and train for them?

Iceberg. Tip of....?

Last edited by Concours77; 16th Nov 2018 at 05:16.
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Old 16th Nov 2018, 05:11
  #1297 (permalink)  
 
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Originally Posted by Concours77 View Post


That’s changes to Pitch done and dusted. If the manual did not include something as tricky as sole source AoA data FAIL, what else is missing? Are there new issues as regards OEI? Roll problems? ETOPS? Will I fly to Hawaii on MAX? Yaw damping? What manner of control issues are different? MCAS is not so much about erroneous data recovery as it is about the whole picture.

What else is new and exciting? What other issues are too complex in failure to overwhelm the average pilot such that they need not to know and train for them?

Iceberg. Tip of....?
The regulatory approval process is interesting. A threshold of differences are permitted before a new type (and associated cost) is 'badged'
Thus it is in the interest of the manufacturer, the airlines and the regulator to keep the changes to a minimum.
So it may be the case that this was 'forgotten' or considered sufficiently similar not to warrant inclusion or simply part of the permitted differences.

What ought be readily apparent now, is that this system is substantially different and it would appear increasingly the case that it changes handling characteristics. That the pilot ought never see it in normal operation, it is of concern that when 'it does make itself known' that the pilots may have not even been aware what 'it did'

It is approaching the time where the FAA may be forced to require operators to train the pilots.
Clearly to date the intent of the manufacturer, airline customers and the regulator has to not impact the commercial return.
Are we approaching a point whereby pilots refuse to operate the aircraft until a differences course inclusive of this (be it simulator or ground modules) is completed.
Will it be the pilots and their organised labour representatives that do what the regulator ought conceivably do?
This ought concern all aviation professionals.
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Old 16th Nov 2018, 06:23
  #1298 (permalink)  
 
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Willow #1287, and previous MFS, and td, #1255 1257.
A very good assessment of the certification issues.

The certification considers the aircraft and the situation together, the context; it does not judge or rate pilots.
This is a very difficult process, particularly nowadays with rapidly advancing and varied technologies.
Additionally there is range of design philosophies, even within one manufacturer; and challenges of grandfather rights spanning 40+ years. Although not required to meet all of the latest regulations, ask if this system would be approved on a new aircraft, a useful thought for guidance. (Special conditons sheet)
Is the situation beyond reasonable human capability; can any training ensure correct recall and actions in these situations.

Also in this period, levels of experience have changed, operations more varied, and surprising events more surprising due to higher levels of safety

Certification assessment is even more difficult when considering what appears to be an undeclared system, a failure, complex consequential implications, and without any published drill.


SLF, #1284. See # 1282. Why. Random, depending on a ‘by chance’ change of squat switch.

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Old 16th Nov 2018, 06:38
  #1299 (permalink)  
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Does MCAS explain fr24 data

If MCAS is a key contributor to this crash, how does it fit with the fr24 data for the flight ?

For MCAS to be implicated, the pilots have disengaged AP or it has disengaged itself, right ?
When did that happen? At the two minute mark ?
There is then an ascent to 5000 feet which is untidily maintained for six minutes before the final dive. If MCAS is aggressively STAB trimming the nose down during those six minutes, the pilots must have been aware of that fact and compensating / counteracting it. Otherwise, the plane would have crashed much earlier, correct ?

The pilots would also have read the previous crew's report about STS running reverse, and hence stab trim would have been at the forefront of their mind in the event of flight control difficulties.

Two questions emerge :
1. Knowing the stabiliser was pitching the nose down, why didn't they activate the CUTOUT switch ?
2. Knowing the stabiliser was pitching the nose down, and having counteracted it successfully for six minutes, how did they eventually lose control of the aircraft ?
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Old 16th Nov 2018, 07:00
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Originally Posted by WillowRun 6-3 View Post
Mad (Flt) Scientist - likely you were addressing (1256) a couple posts I set out (1198, 1203).
SNIP

But when the public sees "average", the meaning includes some items that are above that level or value, some that are below. And while of course there always will be variations among any quite large population, the implication in the phrasing was too easily that some aviators have to have nominal information sets dumbed-down.

SNIP

WillowRun 6-3
Personally, I read "average" in that context to mean pilots going about their normal transport work (which may include emergencies of course), but not engaged in testing or developing systems or procedures. But I can see that others may have read it differently!
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