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WPIAeroGuy
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 3:35 am

PixelFlight wrote:
Chemist wrote:
Contrary to the hyperbole we've read in these threads, there's never been any documented evidence that the MAX pitches up, or is unstable or uncontrollable.

The evidence is that MCAS commands nose down stabilizer to enhance pitch characteristics with flaps up during elevated angles of attack. (according to Boeing presentation to FAA).
Why do you think a nose down command is required, if this is not to fix a nose up pitch characteristics ?


I think the confusion is the difference between a "nose up pitching moment" (i.e., a torque applied about the CG in the direction that would raise the nose) and the aircraft actually pitching up. During normal trimmed flight, the nacelles and the horizontal stabilizer usually have a nose up pitching moment to balance the nose down pitching moments from the wing and the CG being forward of the neutral point, i.e, trimmed flight is a net zero pitching moment. Because the MAX nacelles contribute disproportionately to the nose up pitching moment at high AoA, the horizontal stabilizer compensates by reducing its AoA, which causes the pilots to have to deflect the elevator further to maintain a net zero pitching moment, thus generating the requisite stick force gradient . This is the key misconception. The stab doesn't move because it needs to point the nose down.
-WPIAeroGuy
 
Chemist
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 4:42 am

PixelFlight wrote:
Chemist wrote:
Contrary to the hyperbole we've read in these threads, there's never been any documented evidence that the MAX pitches up, or is unstable or uncontrollable.

The evidence is that MCAS commands nose down stabilizer to enhance pitch characteristics with flaps up during elevated angles of attack. (according to Boeing presentation to FAA).
Why do you think a nose down command is required, if this is not to fix a nose up pitch characteristics ?


I don't pretend to know for sure as I've not flown a max without MCAS near stall.

I can envision a behavior where if pulling back and approaching stall, the forces don't continue to increase, but get lighter. In that example, relaxing back pressure would still drop the nose. Therefore the aircraft is still stable in this axis, it just doesn't meet a goal of steadily increasing force as required by regulation. It's not unstable, and posters seem to confuse the two scenarios. However, this is a hypothetical behavior case and I don't remember seeing any factual data that says this is or is not the MAX's actual behavior.

If that hypothetical case were the actual MAX behavior, then the nose would not be "pitching up". It would just take less force to increase the pitch further. And if this were the behavior, the plane would not have abnormal "pitch up" tendencies.

We are all guessing unless somebody has evidence to finalize the answer. The citation in a previous post is from a professor of aeronautics, but is quoted as "he understands it". I'd like to know where he is getting his information? We are guessing unless we have the actual data. And posters saying the MAX is unstable have no evidence to support that statement. It appears to be a wish rather than anything supported by public data.
 
IADFCO
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 4:54 am

PixelFlight wrote:
JayinKitsap wrote:
SomebodyInTLS wrote:

The short answer is because we *don't* have the computational power... and never will.

All simulation is based on human interpretation of what actually tends to happen in nature in real life. Unless you can build a computer model 100% accurately describing every interaction of every atom within the aircraft and all the airspace it interacts with you will always find that some assumption about how things behave or how humans behave or how manufacturing processes work in real life, etc. was not quite the same as in the real world.

Science is only as accurate as humans can make it by testing theories against the real world. And those tests bring changes... Newton becomes Einstein, the flat Earth becomes a globe, witchcraft becomes medicine. And the same with technology... the MCAS debacle is a result of assumptions not matching the real world - hence tests can never completely be replaced by simulation. QED.


Yes, never will have the computational power. Each litre of air contains 2.15×10^22 molecules, each molecule has 6 freedoms of movement, just in the airplane's path it passes thru billions of litres every second at mach .75. Flat not possible to do. So each element in a finite element model uses classical physics.

And air is only gas: low density and relative uniformity. Now try to simulate fatigue of something as dense as the metal alloy at the atom level to take in account each phase grain boundary, with each possible force vectors, temperatures, imperfections, contamination, current flow, radiation, etc. Then try to do the same with even more complex composite materials...


Weeeellll... in reality it's not nearly that messy. For a real-time, pilot-in-the-loop simulator you can get away with fairly simple equations of motion (the linearized small perturbation equations) for most of the flight envelope -- generally not stall, though, because it's too nonlinear for that. Fully replacing flight testing, or even just wind tunnel testing, with computers, has been the Holy Grail of aeronautical engineering for decades. Simulation accuracy has increased dramatically, even just in the last decade, but we are not yet at the point where we can do without wind tunnel/flight testing.

Speaking specifically of the MAX, I wouldn't be surprised at all if the nonreal-time simulation of a stall entry in a high speed windup turn, followed by recovery, was well beyond the state-of-the-art even for Boeing, at least without extensive flight test calibration.
 
XRAYretired
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 11:02 am

Natalie Kitroeff (NYT) is carrying the latest SWAPA 'MAX Update' to pilots. (Cant find a clean link).
https://twitter.com/Nataliekitro/status ... aster.html

The takeaways are that they are clearly still miffed with Boeing -

“Boeing will never, and should not ever, be given the benefit of the doubt again. The combination of arrogance, ignorance, and greed should and will haunt Boeing for eternity.”

and the view is expressed that commonality of FCC software between NG and MAX can no longer be maintained.

Ray
 
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PixelFlight
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 11:10 am

par13del wrote:
PixelFlight wrote:
Why do you think a nose down command is required, if this is not to fix a nose up pitch characteristics ?

So in level flight with flaps up the autopilot is required to keep the aircraft level, so what happens if the AP is disengaged, will the pilots be able to use the electric trim or will MCAS kick in to keep the aircraft level?
How is it that so many MAX a/c were flying around and no one else encountered MCAS other than the two fatal crashes, I have to believe that there were times when pilots flew the a/c manually, if it is unstable, surely other pilots would have come forward after the crashes. Indeed a lot of the American pilots were angry that they did not know anything about MCAS. Is it taking liberties saying the MAX is unstable and MCAS is required, or the instability is only evident in certain sections of the flight envelope?

The Boeing presentation to the FAA document provides some answers to you questions:

* MCAS is a pitch augmentation flight control law implemented into the 737 MAX that commands nose down stabilizer to enhances pitch characteristics with flaps up during elevated angle of attack.

* MCAS is activated without pilot input and only operate when the autopilot is disengaged.

* MCAS control law becomes active and applies automatic nose down stabilizer in increments based on a table schedule as a function of AOA and Mach.

There no indication that the autopilot need special law similar to MCAS in level flight with flaps up. The autopilot is by definition a closed loop system so it automatically compensate any tendencies (up to design limits). If AP is disengaged then 737 pilots controls an open loop system and this is where the pitch characteristics need to comply with the safety regulation. The MCAS introduce a bit of closed loop to enhance pitch characteristics in what is presented to the pilots as an open loop.

It's clear that MCAS only activate in unusual high angle of attack, flaps up, and in manual flight only. I understand that there is debate between two basics choices: relaxing the pitch characteristics regulation in unusual high angle of attack to avoid the MCAS entirely, or keeping the pitch regulation characteristics regulation in unusual high angle of attack as is and fix the MCAS. Fact is that Boeing and the safety agencies have followed the second basic choice, and given the massive crisis context it's unlikely to be without solid reasons. The available documents all point to a failure to design a safe enough MCAS, not to a failure of the MCAS to comply with the pitch characteristics regulation.
:stirthepot: 737-8 MAX: "For all speeds higher than 220 Kts and trim set at a value of 2.5 units, the difficulity level of turning the manual trim wheel was level A (trim wheel not movable)." :stirthepot:
 
LondonAero
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 11:13 am

From the above SWAPA MAX post it is pretty clear that Boeing has not come up with the final software solution. I cannot believe how much confidence they have expressed without actually finishing this.
 
planecane
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 11:19 am

XRAYretired wrote:
Natalie Kitroeff (NYT) is carrying the latest SWAPA 'MAX Update' to pilots. (Cant find a clean link).
https://twitter.com/Nataliekitro/status ... aster.html

The takeaways are that they are clearly still miffed with Boeing -

“Boeing will never, and should not ever, be given the benefit of the doubt again. The combination of arrogance, ignorance, and greed should and will haunt Boeing for eternity.”

and the view is expressed that commonality of FCC software between NG and MAX can no longer be maintained.

Ray


The ending paragraph reads to me like the union wanting a payoff from Boeing to regain their trust.

The FCC software commonality issue is just mentioned as an aside along with other remote risks. If it is true as stated that the MAX and NG FCCs are from different manufactures, they weren't "common" to start with. That doesn't mean the behavior isn't common from the pilot's perspective. The two cockpits have different displays and that is perfectly ok. Different displays is far less "common" than "black box" FCC hardware/software.
 
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par13del
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 11:36 am

PixelFlight wrote:
It's clear that MCAS only activate in unusual high angle of attack, flaps up, and in manual flight only.

So the posters who are saying the MAX is unstable without including your "unusual high angle of attack" caveat are incorrect?
 
morrisond
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 12:04 pm

par13del wrote:
PixelFlight wrote:
It's clear that MCAS only activate in unusual high angle of attack, flaps up, and in manual flight only.

So the posters who are saying the MAX is unstable without including your "unusual high angle of attack" caveat are incorrect?


Yes - based on the evidence we have it is not unstable - and may not be unstable close to stall with flaps up - it's just the stick force gets lighter than it is allowed - for example instead of taking 20 lbs of force to hold it it goes to say 18 lbs whereas by reg it should go to 22 - it does not go negative and the controls reverse.

At close to stall if you let go of the control column the nose will come down and it will return to its previous in trim aingle of attack and airspeed as far as we know.

The EASA test flights (where they have said they will test it without MCAS)should put an end to this argument if they allow RTS without aerodynamic changes.

It's not an ideal situation (lesser stick force) but in reality it should never lead to a stall (which all pilots should be able to recover from) and a fatal outcome due to all the other protection systems and warnings going off.
 
Noshow
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 12:05 pm

Will the FAA require Boeing to actually demo some real MAX flight with MCAS disabled at MCAS triggering conditions? Any system can fail so it the flight behavior without it should be known shouldn't it?
 
flipdewaf
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 12:31 pm

My understanding is as follows below
Image
The Orange line represents the Minimum force per G required for the regs
Curves 1 and 2 show acceptable levels as the stick force increases linearly above the line or increase more with higher G loading.
Curve 5 is linear but not enough loading so is not acceptable.
Curve 3 has enough force per g loading but the increase is not linear (or greater so is not acceptable) This could be Pre MCAS type curve.
Curve4 could also be the Pre MCAS type curve and would fail for the same reason plus it drops below the minimum regulation leve
Curve 6 shows a faily whereby the curve goes negative, this would be incredibly dangerous and I don't believe this would be the pre MCAS one as this would probably require aero/control system change bigger.

My understanding is that MCAS is required to make curve 3 or 4 (not 5 or 6) look more like curve 1 or 2.

morrisond wrote:

Yes - based on the evidence we have it is not unstable - and may not be unstable close to stall with flaps up - it's just the stick force gets lighter than it is allowed - for example instead of taking 20 lbs of force to hold it it goes to say 18 lbs whereas by reg it should go to 22 - it does not go negative and the controls reverse.

Effectively:
Control force can go negative but needs to produce less than 1g.
First derivative of control force with respect to G loading must not be below a certain value
Second derivative of control force with respect to G loading must not be negative.

Fred
Last edited by flipdewaf on Thu Nov 14, 2019 12:50 pm, edited 3 times in total.
Image
 
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PixelFlight
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 12:34 pm

WPIAeroGuy wrote:
PixelFlight wrote:
Chemist wrote:
Contrary to the hyperbole we've read in these threads, there's never been any documented evidence that the MAX pitches up, or is unstable or uncontrollable.

The evidence is that MCAS commands nose down stabilizer to enhance pitch characteristics with flaps up during elevated angles of attack. (according to Boeing presentation to FAA).
Why do you think a nose down command is required, if this is not to fix a nose up pitch characteristics ?


I think the confusion is the difference between a "nose up pitching moment" (i.e., a torque applied about the CG in the direction that would raise the nose) and the aircraft actually pitching up. During normal trimmed flight, the nacelles and the horizontal stabilizer usually have a nose up pitching moment to balance the nose down pitching moments from the wing and the CG being forward of the neutral point, i.e, trimmed flight is a net zero pitching moment. Because the MAX nacelles contribute disproportionately to the nose up pitching moment at high AoA, the horizontal stabilizer compensates by reducing its AoA, which causes the pilots to have to deflect the elevator further to maintain a net zero pitching moment, thus generating the requisite stick force gradient . This is the key misconception. The stab doesn't move because it needs to point the nose down.

MCAS is generating a nose down input command to the horizontal stabilizer actuator, all available documents are pretty clear about that point. Boeing could have choose an other design that would command a node down action to the elevator, or some vortex generators that would make an appropriate node down action in the required conditions, or any appropriate designs that might exists to make a nose down action in the required conditions. Fact is that in a open loop design like the 737 in manual flight you can't split the stick force apart of the elevator, horizontal stabilizer, angle of attack. speed, and pitch characteristics. It kind of absurd to analyse the pitch characteristics regulation out of the full context of that open loop system. The only real other alternative to date is a closed loop manual flight system like provided by full-authority fly by wire system.
:stirthepot: 737-8 MAX: "For all speeds higher than 220 Kts and trim set at a value of 2.5 units, the difficulity level of turning the manual trim wheel was level A (trim wheel not movable)." :stirthepot:
 
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PixelFlight
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 12:49 pm

XRAYretired wrote:
Natalie Kitroeff (NYT) is carrying the latest SWAPA 'MAX Update' to pilots. (Cant find a clean link).
https://twitter.com/Nataliekitro/status ... aster.html

The takeaways are that they are clearly still miffed with Boeing -

“Boeing will never, and should not ever, be given the benefit of the doubt again. The combination of arrogance, ignorance, and greed should and will haunt Boeing for eternity.”

and the view is expressed that commonality of FCC software between NG and MAX can no longer be maintained.

Ray
:thumbsup: Thanks.
Interesting part:

"However, the above-mentioned FCC changes are not interchangeable between the NG and the MAX FCCs (there are made by different manufacturers)."

So the Rockwell Collins FCC might have a entirely different processing architecture that the old Sperry / Honeywell original design.
Do anyone have more info about this ?
:stirthepot: 737-8 MAX: "For all speeds higher than 220 Kts and trim set at a value of 2.5 units, the difficulity level of turning the manual trim wheel was level A (trim wheel not movable)." :stirthepot:
 
morrisond
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 1:55 pm

PixelFlight wrote:
WPIAeroGuy wrote:
PixelFlight wrote:
The evidence is that MCAS commands nose down stabilizer to enhance pitch characteristics with flaps up during elevated angles of attack. (according to Boeing presentation to FAA).
Why do you think a nose down command is required, if this is not to fix a nose up pitch characteristics ?


I think the confusion is the difference between a "nose up pitching moment" (i.e., a torque applied about the CG in the direction that would raise the nose) and the aircraft actually pitching up. During normal trimmed flight, the nacelles and the horizontal stabilizer usually have a nose up pitching moment to balance the nose down pitching moments from the wing and the CG being forward of the neutral point, i.e, trimmed flight is a net zero pitching moment. Because the MAX nacelles contribute disproportionately to the nose up pitching moment at high AoA, the horizontal stabilizer compensates by reducing its AoA, which causes the pilots to have to deflect the elevator further to maintain a net zero pitching moment, thus generating the requisite stick force gradient . This is the key misconception. The stab doesn't move because it needs to point the nose down.

MCAS is generating a nose down input command to the horizontal stabilizer actuator, all available documents are pretty clear about that point. Boeing could have choose an other design that would command a node down action to the elevator, or some vortex generators that would make an appropriate node down action in the required conditions, or any appropriate designs that might exists to make a nose down action in the required conditions. Fact is that in a open loop design like the 737 in manual flight you can't split the stick force apart of the elevator, horizontal stabilizer, angle of attack. speed, and pitch characteristics. It kind of absurd to analyse the pitch characteristics regulation out of the full context of that open loop system. The only real other alternative to date is a closed loop manual flight system like provided by full-authority fly by wire system.


We went over this a few weeks ago - the intent of MCAS was not to produce a nose down pitching movement - the stabilizer moves - but it's intended effect (with one activation ) was to make the controls heavier by placing the plane out of trim - not point the nose down. If you are actually flying the airplane like you are supposed to you would instinctively counteract the stabilizer with the Elevator for in manual flight you would be trying to maintain a certain attitude or climb angle based on you instruments or outside visual reference. Your controls would get heavier but you would maintain the same flight path.

If they actually wanted to automatically point the nose down like an anti-stall device they would have used an Stick pusher acting on the elevator.
 
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seahawk
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 1:59 pm

Chicken and egg problem.
The stabilizer moves to counteract the additional pitch up movement created by the engines, as without that movement the same stick position (and force) would suddenly create a stronger pitch up movement.
 
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Revelation
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 2:50 pm

XRAYretired wrote:
Natalie Kitroeff (NYT) is carrying the latest SWAPA 'MAX Update' to pilots. (Cant find a clean link).
https://twitter.com/Nataliekitro/status ... aster.html

The takeaways are that they are clearly still miffed with Boeing -

“Boeing will never, and should not ever, be given the benefit of the doubt again. The combination of arrogance, ignorance, and greed should and will haunt Boeing for eternity.”

and the view is expressed that commonality of FCC software between NG and MAX can no longer be maintained.

The paragraph of interest with respect to FCC says:

We believe these issues are the source for speculation about requiring simulator training for the Return to Service (RTS) and the discussion of a split fleet requirement. We do not think, at this time, simulator training for the RTS will be required, nor will NG or MAX fleets be split based on the information we have presently. However, the above-mentioned FCC changes are not interchangeable between the NG and MAX FCCs (they are made by different manufacturers). Since these changes are not finalized, the simulator training and split fleet requirement issues remain open, however remote.

So, sure, by definition if we have two different makes FCC computers the software is not going to be interchangeable, but that does NOT mean there will be split fleets, in fact he says the current thinking is there will NOT be split fleets.

In theory at some level of the software stack it really could be common software, because there are ways to emulate the older FCC computer and/or translate its machine language from its original format to the new machine's format, or some mix of both. For instance, Java source code gets translated to bytecode which is an intermediate machine level language that then gets run on a "virtual machine" that implements the bytecode in the machine's native language. In some cases the Java VM will translate bytecode to native code and cache the result. All these techniques are well understood, but some may not be appropriate for this environment.

I think some may find the more significant part of the letter is that the SWAPA union chief is saying he thinks at this time simulator training prior to RTS will NOT be required, along with the thinking that split fleets will NOT be required, and the chance that this thinking changes is "remote".

Of course the pilots are miffed, Boeing produced a terrible feature that their design and testing process never evaluated correctly. When push comes to shove, though, pilots don't make fleet decisions. There's nothing in that letter that suggests they are going to do anything about their state of miffdom.
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frmrCapCadet
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 4:03 pm

SomebodyInTLS wrote:
hivue wrote:
benbeny wrote:
Why do we need to test fly a plane when we have immense computational power to simulate it?


This way of thinking has more similarities to the process by which Boeing got into its present mess than may at first be apparent. It's a unique malady of our times that the distinction between the real world and virtual worlds starts to get confused.


Yeah, I tried to touch on that in my reply as well. Quite ironic that the response to fixing a system based on bad assumptions would be to prove the fix using a system based on more assumptions...

It is true that there are a number of people out there who believe that just because simulations exist that somehow makes them equal to nature. It really really doesn't!

And fluid dynamics (at the root of the MCAS issue, after all) remains one of the toughest things to simulate accurately. (I've mentioned it on the forum before, but one of the newer F1 teams reckoned it could do without windtunnel tests a few years ago "because of simulation"... that car tanked BADLY!)

I've just thought of a great point: literally the most powerful simulations on Earth outside of the military are employed to predict the weather... can they tell me exactly when it will start and stop raining in a month's time? Or next week Tuesday? Or even tomorrow?


This all was useful information, but a philosophical aside: The problem is even more difficult in any number of realms. (1) There is the outside world and whatever reality it has, (2) there is each individual's perception of that reality, (3) there may be an infinity of other perceptions of reality by other persons, by software constructs, by social constructs - and in this case regulatory constructs.

The interaction of the three of these: the plane and its new characteristics, Boeing management and engineers, FAA and EASA failed. Each of the three were perceiving things as safe (or safe enough) and that they would work together. Tragically they did not. We live in a world where increasingly software and its multitudes of realities are in fact the world we have to deal with.
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AABusDrvr
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 4:13 pm

Revelation wrote:
XRAYretired wrote:
Natalie Kitroeff (NYT) is carrying the latest SWAPA 'MAX Update' to pilots. (Cant find a clean link).
https://twitter.com/Nataliekitro/status ... aster.html

The takeaways are that they are clearly still miffed with Boeing -

“Boeing will never, and should not ever, be given the benefit of the doubt again. The combination of arrogance, ignorance, and greed should and will haunt Boeing for eternity.”

and the view is expressed that commonality of FCC software between NG and MAX can no longer be maintained.

The paragraph of interest with respect to FCC says:

We believe these issues are the source for speculation about requiring simulator training for the Return to Service (RTS) and the discussion of a split fleet requirement. We do not think, at this time, simulator training for the RTS will be required, nor will NG or MAX fleets be split based on the information we have presently. However, the above-mentioned FCC changes are not interchangeable between the NG and MAX FCCs (they are made by different manufacturers). Since these changes are not finalized, the simulator training and split fleet requirement issues remain open, however remote.

So, sure, by definition if we have two different makes FCC computers the software is not going to be interchangeable, but that does NOT mean there will be split fleets, in fact he says the current thinking is there will NOT be split fleets.

In theory at some level of the software stack it really could be common software, because there are ways to emulate the older FCC computer and/or translate its machine language from its original format to the new machine's format, or some mix of both. For instance, Java source code gets translated to bytecode which is an intermediate machine level language that then gets run on a "virtual machine" that implements the bytecode in the machine's native language. In some cases the Java VM will translate bytecode to native code and cache the result. All these techniques are well understood, but some may not be appropriate for this environment.

I think some may find the more significant part of the letter is that the SWAPA union chief is saying he thinks at this time simulator training prior to RTS will NOT be required, along with the thinking that split fleets will NOT be required, and the chance that this thinking changes is "[b]remote".[/b]

Of course the pilots are miffed, Boeing produced a terrible feature that their design and testing process never evaluated correctly. When push comes to shove, though, pilots don't make fleet decisions. There's nothing in that letter that suggests they are going to do anything about their state of miffdom.



My money is on this. There will be no simulator training required. Probably a few hours of online training, going over the systems/differences, and new procedures/check lists, followed by a short pass/fail test.
 
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PixelFlight
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 4:19 pm

morrisond wrote:
PixelFlight wrote:
WPIAeroGuy wrote:

I think the confusion is the difference between a "nose up pitching moment" (i.e., a torque applied about the CG in the direction that would raise the nose) and the aircraft actually pitching up. During normal trimmed flight, the nacelles and the horizontal stabilizer usually have a nose up pitching moment to balance the nose down pitching moments from the wing and the CG being forward of the neutral point, i.e, trimmed flight is a net zero pitching moment. Because the MAX nacelles contribute disproportionately to the nose up pitching moment at high AoA, the horizontal stabilizer compensates by reducing its AoA, which causes the pilots to have to deflect the elevator further to maintain a net zero pitching moment, thus generating the requisite stick force gradient . This is the key misconception. The stab doesn't move because it needs to point the nose down.

MCAS is generating a nose down input command to the horizontal stabilizer actuator, all available documents are pretty clear about that point. Boeing could have choose an other design that would command a node down action to the elevator, or some vortex generators that would make an appropriate node down action in the required conditions, or any appropriate designs that might exists to make a nose down action in the required conditions. Fact is that in a open loop design like the 737 in manual flight you can't split the stick force apart of the elevator, horizontal stabilizer, angle of attack. speed, and pitch characteristics. It kind of absurd to analyse the pitch characteristics regulation out of the full context of that open loop system. The only real other alternative to date is a closed loop manual flight system like provided by full-authority fly by wire system.


We went over this a few weeks ago - the intent of MCAS was not to produce a nose down pitching movement - the stabilizer moves - but it's intended effect (with one activation ) was to make the controls heavier by placing the plane out of trim - not point the nose down. If you are actually flying the airplane like you are supposed to you would instinctively counteract the stabilizer with the Elevator for in manual flight you would be trying to maintain a certain attitude or climb angle based on you instruments or outside visual reference. Your controls would get heavier but you would maintain the same flight path.

If they actually wanted to automatically point the nose down like an anti-stall device they would have used an Stick pusher acting on the elevator.

As I said, it's absurd to try to split some parts of the open loop out of the full context. The MCAS use a table schedule as a function of AOA and Mach (according to Boeing) and generate nose down stabilizer trim. It's then very clear that the only closed loop part of the system use AoA input and speed input. Then Boeing indicate that:
"If elevated AOA conditions persist and increase, MCAS commands additional incremental stabilizer in accordance with the table schedule referenced above"
The only possible conclusion is that the closed loop part of the system is designed to lower the measured AoA (if speed remain about the same) compared to the same situation if the MCAS did not exists. This is only possible with a nose down command. The way the nose down command is implemented (actually the stab trim) is an implementation detail. And the interpretation of the expected pilots consequences on the open loop part alone, without all the context, just absurd.
Last edited by PixelFlight on Thu Nov 14, 2019 4:25 pm, edited 1 time in total.
:stirthepot: 737-8 MAX: "For all speeds higher than 220 Kts and trim set at a value of 2.5 units, the difficulity level of turning the manual trim wheel was level A (trim wheel not movable)." :stirthepot:
 
DenverTed
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 4:25 pm

Revelation wrote:
There's nothing in that letter that suggests they are going to do anything about their state of miffdom.

They want some compensation for loss of wages. I wonder if Boeing will have to address that to some degree for all the airlines MAX aircraft crews to get a little more cooperation with RTS?
 
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sassiciai
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 4:29 pm

Revelation wrote:
par13del wrote:


TFA says:

Replacing Mills is Conrad Chun, who was vice president of communications for Boeing Global Services, the business unit formerly led by Deal.

Chun will continue to report to Deal and Anne Toulouse, Boeing's senior vice president of communications.


Anyone else find the name of the Boeing SVP Communications slightly ironic?? :boggled:
 
phollingsworth
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 4:34 pm

morrisond wrote:
par13del wrote:
PixelFlight wrote:
It's clear that MCAS only activate in unusual high angle of attack, flaps up, and in manual flight only.

So the posters who are saying the MAX is unstable without including your "unusual high angle of attack" caveat are incorrect?


Yes - based on the evidence we have it is not unstable - and may not be unstable close to stall with flaps up - it's just the stick force gets lighter than it is allowed - for example instead of taking 20 lbs of force to hold it it goes to say 18 lbs whereas by reg it should go to 22 - it does not go negative and the controls reverse.

At close to stall if you let go of the control column the nose will come down and it will return to its previous in trim aingle of attack and airspeed as far as we know.

The EASA test flights (where they have said they will test it without MCAS)should put an end to this argument if they allow RTS without aerodynamic changes.

It's not an ideal situation (lesser stick force) but in reality it should never lead to a stall (which all pilots should be able to recover from) and a fatal outcome due to all the other protection systems and warnings going off.


Stick force lightening, or more appropriately reduced static margin/increased control effectiveness is an inherent feature of all unadulterated aft swept wing aircraft as the AoA increases to near stall. This is due to spanwise flow. The tips unload first, this moves the effective mean aerodynamic cord inboard and further forward. This moves the neutral point of the aircraft forward. The result is the elevator inherently becomes more effective. Some aircraft have solved this with aerodynamic augmentation, e.g. vortex generators on the outboard wing, ventral strakes, etc. In other aircraft it isn't meaningful enough over the range of effective c.g. to matter, finally other aircraft have implemented active augmentation systems to solve this. In the case of the A330-600/A310 and the 767-2C, this involves stab trim driven by the FCC based on 3 AoA sensors. In the case of FBW aircraft it will be in the flight control software and generally opaque to the user. For some aircraft, particularly tailless designs, it is possible that the aircraft will become statically unstable. Keep in mind static stability and control effectiveness are slightly different, but highly related phenomena. Longitudinal pitch control effectiveness is highest when the aircraft is neutrally stable and decreases as the static margin increases or decreases from 0.

The simple way to check (though actually much harder than it sounds) static stability is to put the aircraft in trim and give a small pitch perturbation. If the aircraft returns to the original condition, or oscillates about the original point it is statically stable. This is true even if dynamically it eventually diverges or reaches a limit cycle. If it remains where it is or oscillates about the upset point it is neutral, if it moves further away or oscillates about a diverging point it is negatively stable. As long as you have to keep pulling back to get more pitch up your aircraft remains statically stable. If you have to push forward to stop it from pitching up you have a big problem. If as the angle of attack increases you have to push more and more forward to prevent it from diverging you have a really massive problem.

The fact is that the 737 exhibits classic reduced static stability at higher angles of attack. It does not, as far as any evidence I have seen, exhibit neutral or negative static stability. In fact given the way MCAS works if it were statically unstable by more than 1% or so, it is highly likely that the aircraft would have diverged, there just isn't enough bandwidth in MCAS to counter it. The reason we care about stick lightening, is that if it happens too rapidly it makes it much more likely, especially in high workload situations that the pilot might pull back just a bit too much and actually stall the aircraft.

One other thing, looking at the FDR traces on the two accidents it looks like a trim speed actually exists for full electronic nose down stabiliser. However, there was no way the aircraft would be able to have flown that fast.
 
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aerolimani
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 4:54 pm

morrisond wrote:
Yes - based on the evidence we have it is not unstable - and may not be unstable close to stall with flaps up - it's just the stick force gets lighter than it is allowed - for example instead of taking 20 lbs of force to hold it it goes to say 18 lbs whereas by reg it should go to 22 - it does not go negative and the controls reverse.

I believe you misunderstand the regulation, and the behaviour of the controls. What happens on the MAX, a lessening of pressure, IS what is referred to as going negative. It’s not that the stick starts moving itself towards the pilot. Also, it’s the not a reversal of longitudinal control that will happen. It’s a reversal of the rudder and aileron controls, as the plane wants to roll as it approaches stall. It’s that roll tendency which must be controllable. The pitch is not what will reverse.
 
DenverTed
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 4:54 pm

sassiciai wrote:
Revelation wrote:
par13del wrote:


TFA says:

Replacing Mills is Conrad Chun, who was vice president of communications for Boeing Global Services, the business unit formerly led by Deal.

Chun will continue to report to Deal and Anne Toulouse, Boeing's senior vice president of communications.


Anyone else find the name of the Boeing SVP Communications slightly ironic?? :boggled:


If someone is leaking Boeing secrets, who might that be? Toulouse... hello.
 
flipdewaf
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 4:55 pm

phollingsworth wrote:
One other thing, looking at the FDR traces on the two accidents it looks like a trim speed actually exists for full electronic nose down stabiliser. However, there was no way the aircraft would be able to have flown that fast.
Are you saying that at the full extent of nose down trim there could still be a downward force acting on the tail without elevator input that allows, albeit at high speed, a zero net moment applied to the aircraft? The moment before the dive could be characterised as the top of the phugoid and not necessarily a dive.

Excellent post BTW.

Fred
Image
 
DenverTed
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 4:58 pm

flipdewaf wrote:
My understanding is as follows below
Image
The Orange line represents the Minimum force per G required for the regs
Curves 1 and 2 show acceptable levels as the stick force increases linearly above the line or increase more with higher G loading.
Curve 5 is linear but not enough loading so is not acceptable.
Curve 3 has enough force per g loading but the increase is not linear (or greater so is not acceptable) This could be Pre MCAS type curve.
Curve4 could also be the Pre MCAS type curve and would fail for the same reason plus it drops below the minimum regulation leve
Curve 6 shows a faily whereby the curve goes negative, this would be incredibly dangerous and I don't believe this would be the pre MCAS one as this would probably require aero/control system change bigger.

My understanding is that MCAS is required to make curve 3 or 4 (not 5 or 6) look more like curve 1 or 2.

morrisond wrote:

Yes - based on the evidence we have it is not unstable - and may not be unstable close to stall with flaps up - it's just the stick force gets lighter than it is allowed - for example instead of taking 20 lbs of force to hold it it goes to say 18 lbs whereas by reg it should go to 22 - it does not go negative and the controls reverse.

Effectively:
Control force can go negative but needs to produce less than 1g.
First derivative of control force with respect to G loading must not be below a certain value
Second derivative of control force with respect to G loading must not be negative.

Fred

Yes, looking at the graph, it does not look like the stick force is the determining factor, it is positive everywhere on the graph. The determining factor is slope, at no point can the slope on any curve be less than the orange slope. Slope is increase in force per increase in G load.
 
kalvado
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 5:15 pm

DenverTed wrote:
flipdewaf wrote:
My understanding is as follows below
Image
The Orange line represents the Minimum force per G required for the regs
Curves 1 and 2 show acceptable levels as the stick force increases linearly above the line or increase more with higher G loading.
Curve 5 is linear but not enough loading so is not acceptable.
Curve 3 has enough force per g loading but the increase is not linear (or greater so is not acceptable) This could be Pre MCAS type curve.
Curve4 could also be the Pre MCAS type curve and would fail for the same reason plus it drops below the minimum regulation leve
Curve 6 shows a faily whereby the curve goes negative, this would be incredibly dangerous and I don't believe this would be the pre MCAS one as this would probably require aero/control system change bigger.

My understanding is that MCAS is required to make curve 3 or 4 (not 5 or 6) look more like curve 1 or 2.

morrisond wrote:

Yes - based on the evidence we have it is not unstable - and may not be unstable close to stall with flaps up - it's just the stick force gets lighter than it is allowed - for example instead of taking 20 lbs of force to hold it it goes to say 18 lbs whereas by reg it should go to 22 - it does not go negative and the controls reverse.

Effectively:
Control force can go negative but needs to produce less than 1g.
First derivative of control force with respect to G loading must not be below a certain value
Second derivative of control force with respect to G loading must not be negative.

Fred

Yes, looking at the graph, it does not look like the stick force is the determining factor, it is positive everywhere on the graph. The determining factor is slope, at no point can the slope on any curve be less than the orange slope. Slope is increase in force per increase in G load.

FAA is actually OK with 3 and 4, as long as curves don't go beyond flat at the edge of the window.
BUt the way I prefer to look at it is a flipped graph - not force as a function of G, but G as a function of control input. then it becomes clear what "stick lightening" really means
 
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PW100
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 5:20 pm

morrisond wrote:
par13del wrote:
PixelFlight wrote:
It's clear that MCAS only activate in unusual high angle of attack, flaps up, and in manual flight only.

So the posters who are saying the MAX is unstable without including your "unusual high angle of attack" caveat are incorrect?


**Yes - based on the evidence we have it is not unstable - and may not be unstable close to stall with flaps up - it's just the stick force gets lighter than it is allowed - for example instead of taking 20 lbs of force to hold it it goes to say 18 lbs whereas by reg it should go to 22 - it does not go negative and the controls reverse.

At close to stall if you let go of the control column the nose will come down and it will return to its previous in trim aingle of attack and airspeed as far as we know.**


The EASA test flights (where they have said they will test it without MCAS) should put an end to this argument if they allow RTS without aerodynamic changes.


So until that test flight, there is no evidence of your claim (bolded by me) either . . . .

One could also claim that based on the evidence we have it may very well be unstable (in some part of the operating flight envelope), given the significant authority delegated to MCAS (in terms of pitch change amplitude and rate)

Noteworthy, that was also a finding in the JATR report:
JATR Report wrote:
Recommendation R3.4: The FAA should review the natural (bare airframe) stalling
characteristics of the B737 MAX to determine if unsafe characteristics exist. If unsafe
characteristics exist, the design of the speed trim system (STS)/MCAS/elevator feel shift
(EFS) should be reviewed for acceptability.


This suggests that the natural (unaugmented) stall characteristics had not been fully explored for the full operational flight envelope, during the initial certification campaign.

As a point of order, I'm not in the camp that claims it is unstable, I do believe that it is lacking stability margin (in some parts of the operational flight envelope).
I'm just pointing out that you use the absence of evidence to prove the opposite thing. Which is not correct of course.
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 5:41 pm

flipdewaf wrote:
My understanding of the Airbus implementation of the control systems is that it effectively works in reverse and the required output (by virtue of the spring loaded joystick) is always a linear response because its filtered through the computers to achieve this.

AFAIK the trick is, that the Airbus stick controls the G-Load. As long as the stick is centered, the aircraft keeps the current flight path. Deflections of the stick simply load or unload the effective G on the aircraft. That way simply the flight path is adjusted and as soon as the stick is released, the aircraft will continue to fly again in 1G condition. Bank angle similarly: stick deflections simply change the lateral acceleration. That means as long as the stick is deflected x degrees to the left, acceleration to the left (by banking) is increased with a rate that matches the stick deflection. Once released, lateral acceleration is kept constant again (e.g. during the turn).
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jollo
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 6:25 pm

PW100 wrote:
So until that test flight, there is no evidence of your claim (bolded by me) either . . . .

Do you mean that the “natural” (aka unaugmented, bare airframe, no-MCAS) stall test requested by EASA and recommended by JATR has not been flown yet?
 
asdf
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 6:43 pm

jollo wrote:
PW100 wrote:
So until that test flight, there is no evidence of your claim (bolded by me) either . . . .

Do you mean that the “natural” (aka unaugmented, bare airframe, no-MCAS) stall test requested by EASA and recommended by JATR has not been flown yet?


there are only reports that authorities WANT to get those testflights since more than half a year

as far as we know they have not happend till now
 
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flybynight
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 7:21 pm

The news just isn't getting better for Boeing.
Even loyal partners are potentially looking elsewhere (or it is a negotiation tactic) -https://www.king5.com/article/tech/science/aerospace/boeing/leader-of-pilots-union-blasts-boeing-over-grounded-737-max/281-288a339e-5d1e-4bcd-9211-f9a37786d7d5
Heia Norge!
 
747megatop
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 8:38 pm

flybynight wrote:
The news just isn't getting better for Boeing.
Even loyal partners are potentially looking elsewhere (or it is a negotiation tactic) -https://www.king5.com/article/tech/science/aerospace/boeing/leader-of-pilots-union-blasts-boeing-over-grounded-737-max/281-288a339e-5d1e-4bcd-9211-f9a37786d7d5

350+ lost lives later, nothing that anybody says can be a "negotiating tactic" IMHO unless some folks have come to admit that 350+ lives lost is just "a cost of doing business". Boeing & FAA should give it their best now and put the safest possible product back in the sky; not some product with known short comings that puts lives at stake (which lead to the grounding in the 1st place).
 
2175301
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 8:48 pm

asdf wrote:
jollo wrote:
PW100 wrote:
So until that test flight, there is no evidence of your claim (bolded by me) either . . . .

Do you mean that the “natural” (aka unaugmented, bare airframe, no-MCAS) stall test requested by EASA and recommended by JATR has not been flown yet?


there are only reports that authorities WANT to get those testflights since more than half a year

as far as we know they have not happend till now


We have no information that they have not happened already either.

We do have a recent statement from EASA that they foresee FAA recertification in December and their rectification in January. I take that as an indication that EASA is already satisfied on this issue and that the test flights were most likely already done.

Have a great day,
 
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 8:52 pm

747megatop wrote:
flybynight wrote:
The news just isn't getting better for Boeing.
Even loyal partners are potentially looking elsewhere (or it is a negotiation tactic) -https://www.king5.com/article/tech/science/aerospace/boeing/leader-of-pilots-union-blasts-boeing-over-grounded-737-max/281-288a339e-5d1e-4bcd-9211-f9a37786d7d5

350+ lost lives later, nothing that anybody says can be a "negotiating tactic" IMHO unless some folks have come to admit that 350+ lives lost is just "a cost of doing business". Boeing & FAA should give it their best now and put the safest possible product back in the sky; not some product with known short comings that puts lives at stake (which lead to the grounding in the 1st place).


It take me back when the press found out in the late 70's when Ford was calculating the cost of a human life related to the Pinto. I feel the same arrogance has crept in at Boeing. I am struggling with respecting Boeing. Not the men and women working hard to put together the planes, but people at the management level.
Heia Norge!
 
dtw2hyd
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 8:57 pm

jollo wrote:
PW100 wrote:
So until that test flight, there is no evidence of your claim (bolded by me) either . . . .

Do you mean that the “natural” (aka unaugmented, bare airframe, no-MCAS) stall test requested by EASA and recommended by JATR has not been flown yet?


I bet the air show flights were with MCAS off, otherwise, MCAS would go crazy with that climb.
All posts are just opinions.
 
XRAYretired
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 8:59 pm

2175301 wrote:
asdf wrote:
jollo wrote:
Do you mean that the “natural” (aka unaugmented, bare airframe, no-MCAS) stall test requested by EASA and recommended by JATR has not been flown yet?


there are only reports that authorities WANT to get those testflights since more than half a year

as far as we know they have not happend till now


We have no information that they have not happened already either.

We do have a recent statement from EASA that they foresee FAA recertification in December and their rectification in January. I take that as an indication that EASA is already satisfied on this issue and that the test flights were most likely already done.

Have a great day,

EASA flight program (~1 week/4 flights) will be with the certification standard software and was last reported, by EASA, to be slated for mid December.

Ray
 
flipdewaf
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 8:59 pm

dtw2hyd wrote:
jollo wrote:
PW100 wrote:
So until that test flight, there is no evidence of your claim (bolded by me) either . . . .

Do you mean that the “natural” (aka unaugmented, bare airframe, no-MCAS) stall test requested by EASA and recommended by JATR has not been flown yet?


I bet the air show flights were with MCAS off, otherwise, MCAS would go crazy with that climb.

It’s quite a high deck angle but probably not all that high AoA.

Fred


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747megatop
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 9:26 pm

flybynight wrote:
747megatop wrote:
flybynight wrote:
The news just isn't getting better for Boeing.
Even loyal partners are potentially looking elsewhere (or it is a negotiation tactic) -https://www.king5.com/article/tech/science/aerospace/boeing/leader-of-pilots-union-blasts-boeing-over-grounded-737-max/281-288a339e-5d1e-4bcd-9211-f9a37786d7d5

350+ lost lives later, nothing that anybody says can be a "negotiating tactic" IMHO unless some folks have come to admit that 350+ lives lost is just "a cost of doing business". Boeing & FAA should give it their best now and put the safest possible product back in the sky; not some product with known short comings that puts lives at stake (which lead to the grounding in the 1st place).


It take me back when the press found out in the late 70's when Ford was calculating the cost of a human life related to the Pinto. I feel the same arrogance has crept in at Boeing. I am struggling with respecting Boeing. Not the men and women working hard to put together the planes, but people at the management level.

The fact that Muilenberg keeps his job says a lot about the management. For far lesser disasters foot soldiers are expendable and let go. The 1st thing that Boeing should have done is shown the door to both Kevin McAllister and Muilenberg as soon as it became public that the 2 crashes were as a result of MAX design flaws. I think it is time to bring Mullaly out of retirement maybe? That is if he is willing to take on the job to right the ship, bring Boeing out of this mess and then search for the correct replacement.
 
Sooner787
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 9:47 pm

747megatop wrote:
flybynight wrote:
747megatop wrote:
350+ lost lives later, nothing that anybody says can be a "negotiating tactic" IMHO unless some folks have come to admit that 350+ lives lost is just "a cost of doing business". Boeing & FAA should give it their best now and put the safest possible product back in the sky; not some product with known short comings that puts lives at stake (which lead to the grounding in the 1st place).


It take me back when the press found out in the late 70's when Ford was calculating the cost of a human life related to the Pinto. I feel the same arrogance has crept in at Boeing. I am struggling with respecting Boeing. Not the men and women working hard to put together the planes, but people at the management level.

The fact that Muilenberg keeps his job says a lot about the management. For far lesser disasters foot soldiers are expendable and let go. The 1st thing that Boeing should have done is shown the door to both Kevin McAllister and Muilenberg as soon as it became public that the 2 crashes were as a result of MAX design flaws. I think it is time to bring Mullaly out of retirement maybe? That is if he is willing to take on the job to right the ship, bring Boeing out of this mess and then search for the correct replacement.



I think Alan would be the perfect person to restore confidence in Boeing.

Bring him in for as long as he wants to stay. :)
 
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Revelation
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 9:53 pm

flybynight wrote:
The news just isn't getting better for Boeing.
Even loyal partners are potentially looking elsewhere (or it is a negotiation tactic) -https://www.king5.com/article/tech/science/aerospace/boeing/leader-of-pilots-union-blasts-boeing-over-grounded-737-max/281-288a339e-5d1e-4bcd-9211-f9a37786d7d5

Boeing's partner is Southwest management, the Southwest pilot's union does not make fleet decisions.
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Wake now, discover that you are the song that the morning brings
The heart has its seasons, its evenings and songs of its own
 
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Seabear
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 11:27 pm

Broward County (FL) mayor wants to ban 737MAX from FLL...and wants to enlist fellow mayors across the country to join the boycott. Our tax dollars at work. Hmmmm, wonder who would benefit....?

https://www.google.com/amp/s/www.nbcmia ... ml%3famp=y
 
MSPNWA
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 11:39 pm

flybynight wrote:
The news just isn't getting better for Boeing.
Even loyal partners are potentially looking elsewhere (or it is a negotiation tactic) -https://www.king5.com/article/tech/science/aerospace/boeing/leader-of-pilots-union-blasts-boeing-over-grounded-737-max/281-288a339e-5d1e-4bcd-9211-f9a37786d7d5


The "news" won't get better until the "news" decides it's better. I'll put all my money down on it being a negotiation tactic. They've already filed a lawsuit. Public complaining is part of that game. Personally I'm disappointed that the WN pilot union has decided to go down this path. It displays a horrible image of profiteering off of tragedy.

As stated already, WN pilots aren't Boeing's business partner.

747megatop wrote:
The fact that Muilenberg keeps his job says a lot about the management. For far lesser disasters foot soldiers are expendable and let go. The 1st thing that Boeing should have done is shown the door to both Kevin McAllister and Muilenberg as soon as it became public that the 2 crashes were as a result of MAX design flaws. I think it is time to bring Mullaly out of retirement maybe? That is if he is willing to take on the job to right the ship, bring Boeing out of this mess and then search for the correct replacement.


Not many decisions are more foolish than ceremonial firings. you'd think in the 21st century we'd be past such nonsense. If he keeps his job, it speaks highly of the board and management, as it tell us they're not in the business of making foolish, rash decisions based on public pressure.
 
747megatop
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 11:45 pm

MSPNWA wrote:
flybynight wrote:
The news just isn't getting better for Boeing.
Even loyal partners are potentially looking elsewhere (or it is a negotiation tactic) -https://www.king5.com/article/tech/science/aerospace/boeing/leader-of-pilots-union-blasts-boeing-over-grounded-737-max/281-288a339e-5d1e-4bcd-9211-f9a37786d7d5


The "news" won't get better until the "news" decides it's better. I'll put all my money down on it being a negotiation tactic. They've already filed a lawsuit. Public complaining is part of that game. Personally I'm disappointed that the WN pilot union has decided to go down this path. It displays a horrible image of profiteering off of tragedy.

As stated already, WN pilots aren't Boeing's business partner.

747megatop wrote:
The fact that Muilenberg keeps his job says a lot about the management. For far lesser disasters foot soldiers are expendable and let go. The 1st thing that Boeing should have done is shown the door to both Kevin McAllister and Muilenberg as soon as it became public that the 2 crashes were as a result of MAX design flaws. I think it is time to bring Mullaly out of retirement maybe? That is if he is willing to take on the job to right the ship, bring Boeing out of this mess and then search for the correct replacement.


Not many decisions are more foolish than ceremonial firings. you'd think in the 21st century we'd be past such nonsense. If he keeps his job, it speaks highly of the board and management, as it tell us they're not in the business of making foolish, rash decisions based on public pressure.

Well, they (the management) already made foolish and rash decisions. And, BTW, we are not talking about the ceremonial firings that happen yearly or quarterly in most companies not making the financial goals promised to wall street.
 
bob75013
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 11:45 pm

Revelation wrote:
flybynight wrote:
The news just isn't getting better for Boeing.
Even loyal partners are potentially looking elsewhere (or it is a negotiation tactic) -https://www.king5.com/article/tech/science/aerospace/boeing/leader-of-pilots-union-blasts-boeing-over-grounded-737-max/281-288a339e-5d1e-4bcd-9211-f9a37786d7d5

Boeing's partner is Southwest management, the Southwest pilot's union does not make fleet decisions.


You mean the same pilots union that after the first crash, but before the second professed supreme confidence in the safety of the MAX, and the head of the union told the world that he had no reservations about putting his family on the plane?

Is that the union you mean???

:rotfl: :rotfl: :rotfl: :rotfl:
 
bob75013
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Nov 14, 2019 11:50 pm

Seabear wrote:
Broward County (FL) mayor wants to ban 737MAX from FLL...and wants to enlist fellow mayors across the country to join the boycott. Our tax dollars at work. Hmmmm, wonder who would benefit....?

https://www.google.com/amp/s/www.nbcmia ... ml%3famp=y



Many elected officials are idiots -- take the Broward County Mayor for instance.

From the linked article:

""Under Federal law, the safety of aircraft, including their certification and operation is preempted by federal law," the statement read. "If an airport restricts certain aircraft or operations when the Federal Aviation Administration (FAA) has determined those to be safe, that action would violate federal law."
 
MSPNWA
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Nov 15, 2019 12:04 am

747megatop wrote:
Well, they (the management) already made foolish and rash decisions. And, BTW, we are not talking about the ceremonial firings that happen yearly or quarterly in most companies not making the financial goals promised to wall street.


I'm assuming you're serious. You really have things backwards. Firing someone because they didn't deliver on Wall Street isn't a ceremonial firing. It's a rational, merit-based decision. Firing someone who had nothing to do with the MAX because it will "satisfy" the public is a prime example of a ceremonial firing, and that's precisely what you're calling for. If the best argument is you have is that making mistakes in the past mean they should be made again, then you're showing that Muilenburg and company should stay.
 
kalvado
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Nov 15, 2019 12:18 am

MSPNWA wrote:
747megatop wrote:
Well, they (the management) already made foolish and rash decisions. And, BTW, we are not talking about the ceremonial firings that happen yearly or quarterly in most companies not making the financial goals promised to wall street.


I'm assuming you're serious. You really have things backwards. Firing someone because they didn't deliver on Wall Street isn't a ceremonial firing. It's a rational, merit-based decision. Firing someone who had nothing to do with the MAX because it will "satisfy" the public is a prime example of a ceremonial firing, and that's precisely what you're calling for. If the best argument is you have is that making mistakes in the past mean they should be made again, then you're showing that Muilenburg and company should stay.

DM was in charge at time of both crashes, and anemic response to Lion crash is on him. I don't believe that (not) firing DM solves any problems, but he is not an innocent bystander in this case.
Unlike MCAS development flow and decisions, crash is an event CEO should be aware of. Moreso for the crash of a brand new product.
 
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flybynight
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Nov 15, 2019 12:25 am

MSPNWA wrote:
flybynight wrote:
The news just isn't getting better for Boeing.
Even loyal partners are potentially looking elsewhere (or it is a negotiation tactic) -https://www.king5.com/article/tech/science/aerospace/boeing/leader-of-pilots-union-blasts-boeing-over-grounded-737-max/281-288a339e-5d1e-4bcd-9211-f9a37786d7d5


The "news" won't get better until the "news" decides it's better. I'll put all my money down on it being a negotiation tactic. They've already filed a lawsuit. Public complaining is part of that game. Personally I'm disappointed that the WN pilot union has decided to go down this path. It displays a horrible image of profiteering off of tragedy.

As stated already, WN pilots aren't Boeing's business partner.

747megatop wrote:
The fact that Muilenberg keeps his job says a lot about the management. For far lesser disasters foot soldiers are expendable and let go. The 1st thing that Boeing should have done is shown the door to both Kevin McAllister and Muilenberg as soon as it became public that the 2 crashes were as a result of MAX design flaws. I think it is time to bring Mullaly out of retirement maybe? That is if he is willing to take on the job to right the ship, bring Boeing out of this mess and then search for the correct replacement.


Not many decisions are more foolish than ceremonial firings. you'd think in the 21st century we'd be past such nonsense. If he keeps his job, it speaks highly of the board and management, as it tell us they're not in the business of making foolish, rash decisions based on public pressure.


Uhhh, isn't that exactly what Boeing did with the 737 MAX? It is why they are exactly at this point. I think he should be shown the door. I still have the taste of you-know-what when he contacted Trump whining to keep the MAX in the air. To me I makes everything he's said about safety and being humble seem extremely disingenuous.
Heia Norge!
 
WPIAeroGuy
Posts: 323
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Nov 15, 2019 1:16 am

phollingsworth wrote:
morrisond wrote:
par13del wrote:
So the posters who are saying the MAX is unstable without including your "unusual high angle of attack" caveat are incorrect?


Yes - based on the evidence we have it is not unstable - and may not be unstable close to stall with flaps up - it's just the stick force gets lighter than it is allowed - for example instead of taking 20 lbs of force to hold it it goes to say 18 lbs whereas by reg it should go to 22 - it does not go negative and the controls reverse.

At close to stall if you let go of the control column the nose will come down and it will return to its previous in trim aingle of attack and airspeed as far as we know.

The EASA test flights (where they have said they will test it without MCAS)should put an end to this argument if they allow RTS without aerodynamic changes.

It's not an ideal situation (lesser stick force) but in reality it should never lead to a stall (which all pilots should be able to recover from) and a fatal outcome due to all the other protection systems and warnings going off.


Stick force lightening, or more appropriately reduced static margin/increased control effectiveness is an inherent feature of all unadulterated aft swept wing aircraft as the AoA increases to near stall. This is due to spanwise flow. The tips unload first, this moves the effective mean aerodynamic cord inboard and further forward. This moves the neutral point of the aircraft forward. The result is the elevator inherently becomes more effective. Some aircraft have solved this with aerodynamic augmentation, e.g. vortex generators on the outboard wing, ventral strakes, etc. In other aircraft it isn't meaningful enough over the range of effective c.g. to matter, finally other aircraft have implemented active augmentation systems to solve this. In the case of the A330-600/A310 and the 767-2C, this involves stab trim driven by the FCC based on 3 AoA sensors. In the case of FBW aircraft it will be in the flight control software and generally opaque to the user. For some aircraft, particularly tailless designs, it is possible that the aircraft will become statically unstable. Keep in mind static stability and control effectiveness are slightly different, but highly related phenomena. Longitudinal pitch control effectiveness is highest when the aircraft is neutrally stable and decreases as the static margin increases or decreases from 0.

The simple way to check (though actually much harder than it sounds) static stability is to put the aircraft in trim and give a small pitch perturbation. If the aircraft returns to the original condition, or oscillates about the original point it is statically stable. This is true even if dynamically it eventually diverges or reaches a limit cycle. If it remains where it is or oscillates about the upset point it is neutral, if it moves further away or oscillates about a diverging point it is negatively stable. As long as you have to keep pulling back to get more pitch up your aircraft remains statically stable. If you have to push forward to stop it from pitching up you have a big problem. If as the angle of attack increases you have to push more and more forward to prevent it from diverging you have a really massive problem.

The fact is that the 737 exhibits classic reduced static stability at higher angles of attack. It does not, as far as any evidence I have seen, exhibit neutral or negative static stability. In fact given the way MCAS works if it were statically unstable by more than 1% or so, it is highly likely that the aircraft would have diverged, there just isn't enough bandwidth in MCAS to counter it. The reason we care about stick lightening, is that if it happens too rapidly it makes it much more likely, especially in high workload situations that the pilot might pull back just a bit too much and actually stall the aircraft.

One other thing, looking at the FDR traces on the two accidents it looks like a trim speed actually exists for full electronic nose down stabiliser. However, there was no way the aircraft would be able to have flown that fast.


Excellent description. I suspected that all airliners exhibit this to some extent but I don’t have data on hand. Interesting note though, it in the link I posted about stick forces it stated that the A330 and A350 had 0% static margin,I.e. neutral stability. I would suspect that isn’t quite true, however it’s probably close as any trim drag is going to result in increased fuel burn.
-WPIAeroGuy

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