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Boeing admits flaw in 737 Max flight simulator

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Boeing admits flaw in 737 Max flight simulator

Old 19th May 2019, 19:37
  #21 (permalink)  
 
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Originally Posted by fgrieu View Post
What substantiates too easy ? The only source I know is Boeing's statement "changes will improve the simulation of force loads on the manual trim wheel". I have yet to find any authoritative source on if the change makes turning the wheel of the simulator easier or harder, and in which part of the flight envelope / position of the ailerons.
From what I read Boeing's Saturday statement is in response to a New York Times article from Friday (later edit: actually, upon further reading, Boeing's statement is from Friday as well):

https://www.nytimes.com/2019/05/17/b...imulators.html

From the article:

The simulators did not reflect the immense force that it would take for pilots to regain control of the aircraft once the system activated on a plane traveling at a high speed.
[...]
On the Ethiopian flight, the pilots struggled to turn the wheel while the plane was moving at a high speed, when there is immense pressure on the tail. The simulators did not properly match those conditions, and Boeing pilots found that the wheel was far easier to turn than it should have been.
If the article was inaccurate, I doubt Boeing's wouldn't have pointed it out in their statement.

Last edited by MemberBerry; 19th May 2019 at 19:52. Reason: Additional NY Times quote added.
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Old 19th May 2019, 19:50
  #22 (permalink)  
 
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There are several things a simulator won’t replicate. In some cases fidelity is no way comparable to the aircraft - for example, a manual reversion. I find it pretty unimaginable that the way a simulator characterises MCAS would mirror that of the aircraft. Certainly not in it’s present form.
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Old 19th May 2019, 20:07
  #23 (permalink)  
 
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It's not about MCAS, it's about using the manual trim wheels at high speed, while pulling on the control column, with the aircraft severely out of trim nose down. And it's not just MCAS that can bring the aircraft in that situation.

And from what I've seen in Mentour's YouTube video, where he attempts to replicate that condition in a level D simulator for the 737 NG, the old simulator replicated the condition quite well.

So it seems the issue is specific to the MAX simulators. One requirement for a level D simulator is that it should accurately provide force feedback for the pilot's flight controls through a system called "control loading".
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Old 19th May 2019, 20:42
  #24 (permalink)  
 
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Why is MCAS referred to as an "anti stall" feature?

From my understanding it's purpose is to make the airplane behave like previous generation of 737 to share the common type rating due to the engines being mounted further forward and higher, this creates more lift and pitches the nose up more than older generations of aircraft so MCAS was designed to keep the characteristics similar to the older models thus not needing pilots to be retrained

There seems to be a common misconception that MCAS was put on the airplane because it was not safe to fly without this "protection" for a stall but I don't believe that is the case it is purely there to share the common type rating

Can someone correct me if I am wrong?
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Old 19th May 2019, 20:47
  #25 (permalink)  
 
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Originally Posted by Takwis View Post
What could happen if the nose pitches up too high? Other than the fact that it wouldn't be just like the other airplanes?
Isn't that the pilots job to counteract a too high nose tendency if approaching a stall not MCAS?
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Old 19th May 2019, 20:55
  #26 (permalink)  
 
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Originally Posted by Takwis View Post
Yes it is. But if he is used to the pitch stability of an NG, and pulls the same way on a MAX (in a small part of the envelope,we are told), he might very unexpectedly pull the nose up too high, and possibly get into a stall. So MCAS is in the airplane to prevent THAT. So, it's one degree of Kevin Bacon away from being stall prevention.
It seems to be a stall prevention system without actually being designed for that purpose originally? Also would that be why pilots were not told about it as the thinking was "there should be no difference in handling with the previous versions of 737"?
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Old 19th May 2019, 21:19
  #27 (permalink)  
 
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Originally Posted by MemberBerry View Post
It's not about MCAS, it's about using the manual trim wheels at high speed, while pulling on the control column, with the aircraft severely out of trim nose down. And it's not just MCAS that can bring the aircraft in that situation.

And from what I've seen in Mentour's YouTube video, where he attempts to replicate that condition in a level D simulator for the 737 NG, the old simulator replicated the condition quite well.

So it seems the issue is specific to the MAX simulators. One requirement for a level D simulator is that it should accurately provide force feedback for the pilot's flight controls through a system called "control loading".
I'm wondering if downsizing the trim wheel on the Max was overlooked in the sim.

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Old 19th May 2019, 21:24
  #28 (permalink)  
 
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MCAS: Stick-force corrector or anti-stall device?

We are constantly reminded that MCAS is not an anti-stall device. It was introduced solely to cause the forces pilots experience from the yoke are more intuitive. So we are told.

But, is it possible that MCAS really is, and really is required, as an anti-stall device? I have not heard of anyone flying the MAX right up to stall other than Boeing test pilots, so all the information about what happens near that cliff has passed through Boeing management. Perhaps passing off MCAS as a minor change was intended to divert attention away from a more serious problem.
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Old 19th May 2019, 21:32
  #29 (permalink)  
 
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Didn’t Boeing put several pilots through the sim to show them how good the “fix” is? Perhaps I have that wrong. But if so, how could the pilots make a reasonable judgement?
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Old 19th May 2019, 21:37
  #30 (permalink)  
 
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From #91 , 737 Stuck Manual Trim Technique (RVF750)

I can confirm that Mechatronix NG simulator we have does not have loading to the trim wheels. Very disconcerting when you try the scenario and the F/O can wind in full Nose down on you.
And no, it's not recoverable in that state. Very sobering.’

Huummm. Mix that in with some earlier speculative assessment at #8, #11, #16.

Re MCAS purpose; from Boeing original statement, definitions.
Maneuvering Characteristics Augmentation System (MCAS) – flight controlaw implemented on the 737 MAX to improve aircraft handling characteristics and decrease pitch-up tendency at elevated angles of attack.”
https://www.boeing.com/commercial/73...e-updates.page

Also; “The Maneuvering Characteristics Augmentation System (MCAS) flight control law was designed and certified for the 737 MAX to enhance the pitch stability of the airplane – so that it feels and flies like other 737s.”

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Old 19th May 2019, 21:47
  #31 (permalink)  
 
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Salute!

Good friggin' grief!!

The damned thing is not "anti-stall" or "stall prevention". It had to be added to the other kludges to keep "control" forces higher at higher AoA. Stall AoA is higher than MCAS activation, but if the plane requires less and less "control" force to increase AoA, then it will not satisfy the FAR requirements.
I am not sure where "they" are measuring "control" forces, so maybe FCeng or "racer" could add to the discussion versus all the "fly the plane" folks. Using control column force is not a valid test because Boeing already has sfwe and hdwe in the way between the elevator and yoke connections. Maybe PEI could also contribute, as he has some commercial plane test experience.
If we are talking about what the pilot feels, then all bets are off, because the plane has crapola gettin in the way already. If we are talking about the 737block 1, mod 0 then we have actual cables and such to measure the tension and so forth.
If we are measuring the tension back at the elevator hinge ( see diagrams we had from back in November), I would be more comfortable. In other words, we are seeing a changed pitch moment resulting from the new engine mounts and who knows what else compared to the grandfather plane so many claim is easy to fly and any "competent" pilot could have avoided the crashes.

Back to the BBQ now.

Gums.....
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Old 19th May 2019, 22:37
  #32 (permalink)  
 
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Salute!

Before back to the seafood gumbo on the stove......
the FAR requirements were written to keep the airplane from getting too close to a stall.
My examination of the FAR requirements do not reference stall prevention, just a requirement to have increased back stick force or actual elevator force as AoA increases. They could have done the trim kludge at a much lower AoA.
The regulations were written with the intent of preventing a stall
Somehow, I cannot find "intent" on the applicable requirement sections. But on a personal level, I would always like for the plane to be harder to increase AoA the closer I got to the stall AoA. Maybe it's just me.

If you want to "prevent" a stall it is not easy for the engineers working with a 60 year old plane that has many changes in aerodynamic configuration and avionics. A FBW inmplementation that had AoA as a prime input might have made it thru the FAR process, but I doubt it. Even the 'bus had good longitudinal stability and such that the FBW laws could use. That was not the case with the Max. The thing did not meet the requirements and Boeing had to use the stab trim in a way most of us would not have anticipated.

Gums...
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Old 19th May 2019, 23:02
  #33 (permalink)  
 
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Originally Posted by gums View Post
Salute!

Before back to the seafood gumbo on the stove......


My examination of the FAR requirements do not reference stall prevention, just a requirement to have increased back stick force or actual elevator force as AoA increases. They could have done the trim kludge at a much lower AoA.

Somehow, I cannot find "intent" on the applicable requirement sections. But on a personal level, I would always like for the plane to be harder to increase AoA the closer I got to the stall AoA. Maybe it's just me.

If you want to "prevent" a stall it is not easy for the engineers working with a 60 year old plane that has many changes in aerodynamic configuration and avionics. A FBW inmplementation that had AoA as a prime input might have made it thru the FAR process, but I doubt it. Even the 'bus had good longitudinal stability and such that the FBW laws could use. That was not the case with the Max. The thing did not meet the requirements and Boeing had to use the stab trim in a way most of us would not have anticipated.

Gums...
And so the layers of deceit are peeling off boeings 'story' . . . the closer one looks into these things the worse it tends to get . . . sadly (for all the people that got killed) . . .
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Old 19th May 2019, 23:14
  #34 (permalink)  
 
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Originally Posted by gums View Post
Salute!

Good friggin' grief!!

Back to the BBQ now.

Gums.....
Gums I always read your posts with great interest because you are far more knowledgeable than I, and many others here, about airplanes. I’m just a lowly Commercial SEL/IR with a thousand hours who quit flying myself around in 1993.

On the the other hand, I know a lot about marketing, risk assessment, and the lengths to which management will go to sell a buyer on the reliability of a system, while at the same time the engineers are telling them their expectations are impossible to meet. The world is full of examples of this phenomenon. Challenger, Columbia, and the FIU bridge collapse being just a few.

The MBAs are rarely able assess risk and come up with all sorts of clever vocabulary to hide it. I’m a Boeing shareholder and have faith in the long term future of the company. Short-term they have blown it big time. Their reluctance to ground the fleet even after it had essentially self-grounded worldwide is clear evidence of management in denial. I suspect that internally the engineers were waving red flags for a long time.

None of us know what was discussed at Boeing, but we do know that control forces became increasingly light as AoA increased, possibly to the point of needing an augmentation system to help the pilot push the nose down.

To me, MCAS was designed to prevent situations which might lead to a stall. As such public perception is going to stay “stall prevention”. A plane requiring a stall prevention system will scare the public. A system augmenting pilot control is an easy sell, like power steering.
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Old 20th May 2019, 00:29
  #35 (permalink)  
 
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Originally Posted by gums View Post
Salute!

Before back to the seafood gumbo on the stove......


My examination of the FAR requirements do not reference stall prevention, just a requirement to have increased back stick force or actual elevator force as AoA increases. They could have done the trim kludge at a much lower AoA.

Somehow, I cannot find "intent" on the applicable requirement sections. But on a personal level, I would always like for the plane to be harder to increase AoA the closer I got to the stall AoA. Maybe it's just me.

If you want to "prevent" a stall it is not easy for the engineers working with a 60 year old plane that has many changes in aerodynamic configuration and avionics. A FBW inmplementation that had AoA as a prime input might have made it thru the FAR process, but I doubt it. Even the 'bus had good longitudinal stability and such that the FBW laws could use. That was not the case with the Max. The thing did not meet the requirements and Boeing had to use the stab trim in a way most of us would not have anticipated.

Gums...
What is also puzzling is why, having used something as powerful as stab trim to increase the stick force, they had to go from an initial expectation of a much smaller 0.6 degrees max movement to a significanlty larger 2.5 degrees.

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Old 20th May 2019, 00:45
  #36 (permalink)  
 
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Salute!

First of all, this is serious!!! @ Tak
I may not know as much about aerodynamics as some, but I had natural "touch" and survived........ Grew up on the Gulf coast and I enjoy nature's bounty while I can still move about and cook, ingest, digest and excrete.
- Use a blue crab or two that your break up and simmer in a quart of water for an hour
- make your own roux with flour and oil, or use one of the Louisiana blends. Many seafood spice packages here, so just watch the heat index if you are serving a wimp! Add this after the broth is nice
- veggie mix should be okra, sauteed celery and onion. Bell peppers are good, but not essential
- dump veggies in and simmer a long time or until the celery is tender.
- Then add a lotta popcorn shrimp and some fish fillet chunks.
- Simmer for maybe 30 minutes and dine!
++++++++++++++++++++++++++++++++++++++
BTW, I flew two jets with actual AoA/Gee limiters, and another one with a rudder shaker when getting high AoA.
I prefer the actual limiter as the 'bus has and maybe some kinda vibrator if getting too close to the corner of the envelope.
The Voodoo pusher yanked the stick outta your hand, and since it was connected to the elevator the AoA decreased for a second or two. You could still defeat it, but had to overcome about 28 pounds of force and then another 60 pounds for the limiter ( manual command signal limiter, if you had it on). If you tried that hard to pitch-up, then explain it to your boss and the accident board.
Remember that all this was back in the mid 60's with an airframe designed in late 50's.

Gums sends...
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Old 20th May 2019, 00:59
  #37 (permalink)  
 
Join Date: Jun 2008
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Copy your recipe

Originally Posted by gums View Post
Salute!

First of all, this is serious!!! @ Tak
I may not know as much about aerodynamics as some, but I had natural "touch" and survived........ Grew up on the Gulf coast and I enjoy nature's bounty while I can still move about and cook, ingest, digest and excrete.
- Use a blue crab or two that your break up and simmer in a quart of water for an hour
- make your own roux with flour and oil, or use one of the Louisiana blends. Many seafood spice packages here, so just watch the heat index if you are serving a wimp! Add this after the broth is nice
- veggie mix should be okra, sauteed celery and onion. Bell peppers are good, but not essential
- dump veggies in and simmer a long time or until the celery is tender.
- Then add a lotta popcorn shrimp and some fish fillet chunks.
- Simmer for maybe 30 minutes and dine!
++++++++++++++++++++++++++++++++++++++
Gums sends...
This sounds good! Any recipe with the instructions “dump” in it has to be on par with a Clemenza Spaghetti.
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Old 20th May 2019, 01:08
  #38 (permalink)  
 
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Gums, I'll bet you know more about aerodynamics than most.


But I copied your gumbo recipe, anyway.

I had to explain a few things to my boss. Mid-air collision with an F-117, for one... I wish I had some AoA stories, but I always managed to keep that pretty sane. Vmo...well, that's another story.
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Old 20th May 2019, 04:43
  #39 (permalink)  
 
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Originally Posted by Takwis View Post
...
Fun fact about stall prevention/recovery: "Apparently in the Gloster Javelin (a two seat delta with a T tail) if the aircraft got into a deep stall, the recovery technique was for the navigator to eject (thus shifting the CG forwards
Which proves that aeroplanes are more important than navigators.
Mind you, if that didn’t work the old man got out too...
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Old 20th May 2019, 05:08
  #40 (permalink)  
 
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And the hits keep coming. Did nobody test this thing before releasing it to the public?

This is rather concerning, because the simulator designers are going to be using the same engineering calculations used to inform the designers of the hardware. If the maximum forces involved in this system are much larger than calculated then that calls into question all of the engineering that went into it, from bolt sizes to the number of strands in the cable. This is at least the second indication that the engineering projections related to relocating the engines did not match reality.
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