Boeing admits flaw in 737 Max flight simulator
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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.
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.
[...]
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.
Last edited by MemberBerry; 19th May 2019 at 19:52. Reason: Additional NY Times quote added.
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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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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".
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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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".
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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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.
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.
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?
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.”
‘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.”
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.....
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.....
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...
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.
The regulations were written with the intent of preventing a stall
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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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...
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...
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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.
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.
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...
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...
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...
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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Copy your recipe
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...
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...
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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.
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.
Mind you, if that didn’t work the old man got out too...
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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.
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.
N4790P
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.
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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to accept MCAS is there only to increase back stick force, we need to accept that Boeing engineers decided it was a good idea to repeatedly move the stab, probably one of the most critical control surfaces, just in oder to simulate increased stick force.
We need to accept that noone asked if this might by any chance be a bad idea. Like, you know, trimming all the way nose down in close proximity to the mother Earth. Noone remembered AF447 where pilot error resulted in full up trim, making stall unrecoverable - so nobody said "uhm guys, if something goes wrong and this system fails, it could mean trouble".
Again - all with the goal to produce some back stick force? I mean, for sure there must be better solutions for that alone?
What if there is another explanation? Perhaps the nacelles are so far out that it's a serious problem? Perhaps they act to some degree as canards when approaching stall? Imagine the wing stalls but the nacelles still produce lift... you'd be in big, big trouble.
Now this big big trouble would be something to justify MCAS. But due to competition and regulation requirements Boeing could not be open about it, or it would have meant entierly new certification. That's why it's half baked, hidden and relies on a single AoA.
Test flight data should show if this is indeed the case. Requirement for 2.5 units trim every 5s surely does seem like a smoking gun. Testimony from test pilot would be interesting. I'm sure we will hear about it in the coming years.
Then another question is, why were the cutout switches changed to prevent manual electric trim along with MCAS. There must be a reason. Without a reason it makes no sense. Did Boeing by any chance estimated that keeping the electric trim on without MCAS could easily put the airplane in the high AoA situation as described above? That could be another smoking gun. If that is not the reason to change the switches, then what was it? Any reasonably ideas?
Gums et al, Boeing admits flaw in 737 Max flight simulator
Re ‘like other 737’, stability ‘enhancement’, or anti stall.
First point, this discussion is probably in the wrong thread. Second, there is very little definitive information on these aspects (see Boeing refs), thus supposition reigns. Third, using what is known about an aircraft to build a simulator is not the same as taking a simulator and inferring what the actual aircraft characteristics are, but there ominous indications in this instance.
‘Like other 737’, is more of a marketing or commercial argument; as such it could be managed by other means (even if not saving $1M per a/c).
‘Stability vs stall’; the critical points are when and where. Any problems with stall ident - the point of stall, or characteristics at that point, or recovery capability, requires quick and forceful action, loud and positive, thus stick push or similar.
‘Anti stall’, not a good term, is more associated with stability, usually prior to stall warning - stick shake; awareness, but not always with action.
I conclude that MCAS is a requirement of stability certification, quiet and subtle background enhancement, ‘dressed-up’ to placate customers. Note the use of AoA vs speed input, flaps up only, and Mach input to manage what appears to be a complex problem in a small part of the flight envelope - wt, cg.
The trim input was intended to be small, incremental, and unobtrusive. The design theory appears to be OK, the engineering implementation, checking, and certification a disaster.
MCAS should not be compared with STS, or even Mach trim; nor its implementation as FBY.
I agree with gums # 36 …
Stability involves ‘feel’, measured as stick force in certification.
As an explanatory description only: consider trimmed flight at constant speed, constant thrust. Enter a turn without changing trim position or thrust (aircraft will descend). The ‘feel’ increases as a pull force; this can be assessed at various bank angles - different AoA.
Repeating these tests for a range of speeds (different trim speed) there should be a consistent relationship between bank angle and pull force. Inconsistent force - reduced pull force with bank angle, or with speed decrease at constant bank angle, could add workload in manual flight.
In extreme, slowing down in a turn or level flight at constant trim should always require more pull force, if not the aircraft feel is an unnatural ‘push to turn’. In some cases reducing forces could tend to oscillation or pitchup. There could be similar interactions with thrust - altitude.
MCAS “will not be a significant issue after modification”, nor require hands-on training except if the handling in the failed state is significantly degraded - cruise flight only. [opinion]
The important issues arising from the simulator mistake are in the processes of checking and certification of training simulators, and the possibly of a shortfall in knowledge about the aircraft, particularly the effect of trim failure.
Gums, [engineering or aerodynamic fix] Instead of lengthening the undercarriage, Boeing should have put the engines on top of the wing [/ fix]
Re ‘like other 737’, stability ‘enhancement’, or anti stall.
First point, this discussion is probably in the wrong thread. Second, there is very little definitive information on these aspects (see Boeing refs), thus supposition reigns. Third, using what is known about an aircraft to build a simulator is not the same as taking a simulator and inferring what the actual aircraft characteristics are, but there ominous indications in this instance.
‘Like other 737’, is more of a marketing or commercial argument; as such it could be managed by other means (even if not saving $1M per a/c).
‘Stability vs stall’; the critical points are when and where. Any problems with stall ident - the point of stall, or characteristics at that point, or recovery capability, requires quick and forceful action, loud and positive, thus stick push or similar.
‘Anti stall’, not a good term, is more associated with stability, usually prior to stall warning - stick shake; awareness, but not always with action.
I conclude that MCAS is a requirement of stability certification, quiet and subtle background enhancement, ‘dressed-up’ to placate customers. Note the use of AoA vs speed input, flaps up only, and Mach input to manage what appears to be a complex problem in a small part of the flight envelope - wt, cg.
The trim input was intended to be small, incremental, and unobtrusive. The design theory appears to be OK, the engineering implementation, checking, and certification a disaster.
MCAS should not be compared with STS, or even Mach trim; nor its implementation as FBY.
I agree with gums # 36 …
Stability involves ‘feel’, measured as stick force in certification.
As an explanatory description only: consider trimmed flight at constant speed, constant thrust. Enter a turn without changing trim position or thrust (aircraft will descend). The ‘feel’ increases as a pull force; this can be assessed at various bank angles - different AoA.
Repeating these tests for a range of speeds (different trim speed) there should be a consistent relationship between bank angle and pull force. Inconsistent force - reduced pull force with bank angle, or with speed decrease at constant bank angle, could add workload in manual flight.
In extreme, slowing down in a turn or level flight at constant trim should always require more pull force, if not the aircraft feel is an unnatural ‘push to turn’. In some cases reducing forces could tend to oscillation or pitchup. There could be similar interactions with thrust - altitude.
MCAS “will not be a significant issue after modification”, nor require hands-on training except if the handling in the failed state is significantly degraded - cruise flight only. [opinion]
The important issues arising from the simulator mistake are in the processes of checking and certification of training simulators, and the possibly of a shortfall in knowledge about the aircraft, particularly the effect of trim failure.
Gums, [engineering or aerodynamic fix] Instead of lengthening the undercarriage, Boeing should have put the engines on top of the wing [/ fix]
