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PixelFlight
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 4:58 pm

morrisond wrote:
PixelFlight wrote:
If Boeing was so happy with the simulation of the 737-8/9 MAX without MCAS, why did there add the MCAS ?


Because the stick got just a little too light close to stall. They needed MCAS to meet the new regs. That is it. According to PW100 that reg did not exist when the NG was certified. The NG may have had the same issue and I don't think many of those fell out of the sky due to Pilot's stalling them.

If true, this can allow a scenario similar to the #2 in my post #719 list: an exception from the regulation and the MCAS can be removed.
But if it was so simple, It would not have taken so long, and Boeing would not have designed a MCAS v2, nor a MCAS v0 in the first place...
The medication look strangely too massive to cure only a small imperfection well accepted before.
: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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PW100
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 5:00 pm

morrisond wrote:
PixelFlight wrote:
If Boeing was so happy with the simulation of the 737-8/9 MAX without MCAS, why did there add the MCAS ?


Because the stick got just a little too light close to stall. They needed MCAS to meet the new regs. That is it. According to PW100 that reg did not exist when the NG was certified. The NG may have had the same issue and I don't think many of those fell out of the sky due to Pilot's stalling them.


Did I state that? Boy, these threads are way to long (as is the grounding . . .)

Why couldn't Boeing adjust the Elevator Feel System? One would expect that to be the preferred way to adjust feel force, that is why that system is in the 737 in the first place?
Immigration officer: "What's the purpose of your visit to the USA?" Spotter: "Shooting airliners with my Canon!"
 
morrisond
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 5:09 pm

PW100 wrote:
morrisond wrote:
PixelFlight wrote:
If Boeing was so happy with the simulation of the 737-8/9 MAX without MCAS, why did there add the MCAS ?


Because the stick got just a little too light close to stall. They needed MCAS to meet the new regs. That is it. According to PW100 that reg did not exist when the NG was certified. The NG may have had the same issue and I don't think many of those fell out of the sky due to Pilot's stalling them.


Did I state that? Boy, these threads are way to long (as is the grounding . . .)

Why couldn't Boeing adjust the Elevator Feel System? One would expect that to be the preferred way to adjust feel force, that is why that system is in the 737 in the first place?


You did back months ago - I don't know when exactly but it was part of the rant from Aerolami yesterday where he quoted the same thing from me about 20 times and in there I had quoted you from previously.

I don't think the elevator feel system is that smart - that's the problem. It is not FBW where you can easily iron out any control issue quirks and make an A380 feel like an A320
 
morrisond
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 5:10 pm

PixelFlight wrote:
morrisond wrote:
PixelFlight wrote:
If Boeing was so happy with the simulation of the 737-8/9 MAX without MCAS, why did there add the MCAS ?


Because the stick got just a little too light close to stall. They needed MCAS to meet the new regs. That is it. According to PW100 that reg did not exist when the NG was certified. The NG may have had the same issue and I don't think many of those fell out of the sky due to Pilot's stalling them.

If true, this can allow a scenario similar to the #2 in my post #719 list: an exception from the regulation and the MCAS can be removed.
But if it was so simple, It would not have taken so long, and Boeing would not have designed a MCAS v2, nor a MCAS v0 in the first place...
The medication look strangely too massive to cure only a small imperfection well accepted before.


No clue - I don't know what the FAA will allow exceptions on.
 
morrisond
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 5:13 pm

DenverTed wrote:
morrisond wrote:
PixelFlight wrote:
If Boeing was so happy with the simulation of the 737-8/9 MAX without MCAS, why did there add the MCAS ?


Because the stick got just a little too light close to stall. They needed MCAS to meet the new regs. That is it. According to PW100 that reg did not exist when the NG was certified. The NG may have had the same issue and I don't think many of those fell out of the sky due to Pilot's stalling them.

Because the stick got light? Or because at a set configuration of trim and elevator before stall, instead of coming to equilibrium of pitch at a certain angle, the aircraft continued to rotate backwards? If that was the case, which I don't know, it seems to fix that required some artificial movement of either the elevator or trim to move the aircraft out of the tailplane configuration where it was unstable and applying too much downward force.


It's because it got too light. You still had to pull the controls - just not with as much force - if you let go the plane would return to equilibrium at a lower AOA.

If it went negative then it could possibly to continue to rotate up.
 
mzlin
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 5:27 pm

Finally some real news:

"A select group of US and international airline pilots are expected to participate in the final round of simulator testing of Boeing's new flight control system software for the 737 MAX as soon as early November...
Once these crucial simulator tests conclude, which could take roughly a week, the FAA's certification flight will occur. The simulator tests and the FAA's certification flight are the last two major steps before the FAA can decide whether the plane is safe to fly passengers again."

My guess is Boeing will have to announce a rightward shift in its previous RTS estimate soon.

https://www-m.cnn.com/2019/10/17/politi ... index.html
 
DenverTed
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 5:28 pm

PW100 wrote:
morrisond wrote:
PixelFlight wrote:
If Boeing was so happy with the simulation of the 737-8/9 MAX without MCAS, why did there add the MCAS ?


Because the stick got just a little too light close to stall. They needed MCAS to meet the new regs. That is it. According to PW100 that reg did not exist when the NG was certified. The NG may have had the same issue and I don't think many of those fell out of the sky due to Pilot's stalling them.


Did I state that? Boy, these threads are way to long (as is the grounding . . .)

Why couldn't Boeing adjust the Elevator Feel System? One would expect that to be the preferred way to adjust feel force, that is why that system is in the 737 in the first place?

I would imagine that an elevator feel system works as long as their is a reasonable downward slope on the righting moment versus AOA curve. The feel system could increase the force required to configure from 11 degrees to 12 or whatever. On the other hand, if the graph is flat once the aircraft gets to 11 degrees, even with the same force it would continue to rotate nose up from 11 degrees to 14 degrees with no movement of the stick, or the control surfaces, which seems like a big problem. That can only be solved by an outside system that either moves the elevator or the trim to reduce the AOA a degree or two away from the unstable range.
 
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ExperimentalFTE
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 5:35 pm

mzlin wrote:
Finally some real news:

"A select group of US and international airline pilots are expected to participate in the final round of simulator testing of Boeing's new flight control system software for the 737 MAX as soon as early November...
Once these crucial simulator tests conclude, which could take roughly a week, the FAA's certification flight will occur. The simulator tests and the FAA's certification flight are the last two major steps before the FAA can decide whether the plane is safe to fly passengers again."

My guess is Boeing will have to announce a rightward shift in its previous RTS estimate soon.

https://www-m.cnn.com/2019/10/17/politi ... index.html


Solid as fartness at wind! How about using some Qualified Engineering Test Pilots (pool of them) to assess deficiencies of the aircraft and issue clear recommendations for fixing it?!?!

If FAA takes opinion of "pool of international airline pilots" regarding serious flight control and system architecture flaw and certifies aircraft based on it, it would certainly mark major milestone and shift into dark abyss of the whole aerospace industry in the USA...
 
ikramerica
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 6:17 pm

Revelation wrote:
jollo wrote:
morrisond wrote:
In regards to Flight deck warning systems creating a startle effect - please remember that the NTSB says this is not specific to the MAX - other designs such as the A330 are susceptible to the same issues(AF447). Assuming most Airbuses are designed around the same common cockpit this could be an issue with those as well. I suspect the Boeing 777/787 cockpit would have the same issues. Cockpits are just too complex and too many interconnected systems to keep track of in an emergency.


Sorry for the late reply, but I find this attempt to draw a parallel with AF447 (trying to peddle the "hey, it's more of the same, nothing to see here" narrative) too far fetched to be left alone.

So let's analyze the similarities between AF447 and JT610-ET302:

The problem with AF447 was: a double sensor failure caused unreliable airspeed indications, stall warnings and loss of flight envelope protections. The pilot actions that - in hindsight - could have saved AF447 were: fly pitch and thrust per memory items as trained in sim, or even simply do nothing - just leave the stick alone until the pitots unfreeze.

The problem with JT610-ET302 was: a single sensor failure caused unreliable airspeed indications, stall warnings and aggressive, repeated, uncommanded AND control inputs up to maximum nose-down stab trim. The pilot actions that - in hindsight - could have saved JT610-ET302 were (strictly in this order):
  • 1 - counteract MCAS with ANU electric trim inputs within 3 seconds per Boeing assumptions - but this only buys you 5 seconds of respite before next MCAS cycle
  • 2 - bleed off with elevator inputs any speed buildup caused by MCAS's nose down trim inputs
  • 3 - return to neutral stab trim with ANU electric trim inputs - those inputs need to last longer than MCAS's AND inputs, because MCAS has greater trim authority than manual electric trim inputs; e.g. it would have taken close to 4 seconds of continuous ANU manual electric trim input to neutralize 3 seconds of MCAS control inputs (that is, if you managed to enact item #1 within the assumed 3 seconds, otherwise it's gonna take longer)
  • 4 - recognize the problem as a runaway stabilizer, run the corresponding NNC (despite the checklist being prefixed with the misleading condition "Uncommanded stabilizer trim movement occurs continuously", whereas with item #1 the trim has temporarily stopped moving) and only after returning the stabilizer to neutral trim (that's not described in the NNC but, c'mon, it's basic airmanship) proceed to cut out electric stab trim
  • 5 - did you manage to perform 2-3-4 in less than 5 seconds? If not, then start over, because in the meanwhile MCAS has kicked in again
  • 6 - did you cut out electric trim before correcting any mis-trim and overspeed (meaning anywhere near Vmo, not necessarily above)? Then - unless you're also a professional weight lifter - you're dead anyway, because you'll find that the manual trim wheel is too heavy to operate as mandated by the runaway stabilizer NNC
  • 7 - all of the above without any specific training (and especially no sim training), nor any mention of MCAS in either FCOM or EADs.

Was startle factor caused by multiple simultaneous cockpit warnings a factor in why the crews failed to save their flights? Probably. However the complexity of the tasks that were expected from the crews were so many orders of magnitude apart that any comparison is simply absurd.

The fact is (sadly for the victims, happily for all passengers flying every day on other types, both A and B), MAX's predicament is simply without precedent.

Impressive post, would be even more impressive if the time line started with one stick shaker going off at take off rather than a couple minutes later when MCAS kicked in, how flight before JT610 saved the same airplane, etc. Without these considerations it seems more one sided than it should be, but would still reach the same conclusion, workload was too great.

But part of the reason workload was so great was that crew had no idea what was happening. In a vacuum that’s one thing. But as you point out, the timeline should begin the previous day, and explore why this aircraft was dispatched at all on the fateful flight, and why the crew seemed to be taken by surprise by the failure mode.
Of all the things to worry about... the Wookie has no pants.
 
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aerolimani
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 6:29 pm

PW100 wrote:
morrisond wrote:
PixelFlight wrote:
If Boeing was so happy with the simulation of the 737-8/9 MAX without MCAS, why did there add the MCAS ?


Because the stick got just a little too light close to stall. They needed MCAS to meet the new regs. That is it. According to PW100 that reg did not exist when the NG was certified. The NG may have had the same issue and I don't think many of those fell out of the sky due to Pilot's stalling them.


Did I state that? Boy, these threads are way to long (as is the grounding . . .)

Why couldn't Boeing adjust the Elevator Feel System? One would expect that to be the preferred way to adjust feel force, that is why that system is in the 737 in the first place?

I would question the suggestion that this regulation was not in place when the NG was certified. At the end of section 25.203, it says that it is from Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25–84, 60 FR 30750, June 9, 1995. This also seems like something very obviously desired in a non-FBW aircraft, and I would be surprised if it was not included in the 1964 version. What is interesting to note is that the amendment occurred in 1995, while the NG certification was applied for in 1993, but the certificate was granted in 1997. This regulation only applies to non-FBW designs, so it seems strange that this would be added in 1995, when FBW had already become standard for most clean-sheet designs.
 
XRAYretired
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 6:30 pm

Firstly, I think all should remind themselves that we are here because of the loss of 346 lives in two crashes with a common causal factor of incompetent design and safety assessment of a new system fitted to 737 Max. The discussions around the reason for the fit of that system are merely a distraction, or perhaps worse, has some nefarious intent.

Secondly, I think all should ignore the made up stories, more than one by Boeing and including 'just a slight lightening of the yoke that does not meet some new and un-important regulation', and remind themselves what the JATR - Experts with Access - determined:-

'Observation O3.4-A: The original implementation of MCAS was driven primarily by its ability to provide the B737 MAX with FAA-compliant flight characteristics at high speed. An unaugmented design would have been at risk of not meeting 14 CFR part 25 maneuvering characteristics requirements due to aerodynamics.

Observation O3.4-B: Extension of MCAS to the low-speed and 1g environment during the flight program was due to unacceptable stall characteristics with STS only. The possibility of a pitch-up tendency during approach to stall was identified for the flaps-up configuration prior to the implementation of MCAS.'


'Stall Characteristics' requirement 25.203 was new in 1964 and last revised very recently in 1995. Associated Out Of Trim' requirement 25.255 is a lot newer issued 1978.

Thirdly, we should remind ourselves that the perceived need to extend MCAS to cover the 1g environment was reported, by Boeing staff quotation, and as JATR above, during flight testing, not CAB simulator testing. This reminds us of the integrity we can give to such, in that simulator testing (as described above) did not identify the problem and cannot be used to demonstrate compliance for certification. Flight test in a properly configured aircraft is required. The primary concern was acceleration of stall due to atmospheric disturbance not pilot pull through (and constantly ignored for story telling purposes).

On a final point, the Regulations have been developed, and commonalised around the globe, with the primary objective of improving the safety of commercial aircraft and their operation for the benefit of all. This has been a decades long effort and continues. And it has worked pretty well.

The challenge of these recent posts has been escalated from show MCAS was required, to show MCAS improves safety, to prove MCAS would prevent a fatal event. This is to miss-represent what safe flight is about and achieved. Failure to comply with the requirements will increase the propensity for events to occur and potentially the severity of them, which in turn will increase the propensity for injury to persons/damage to property and increase the likelihood of catastrophic event.

Dismissal of requirements is a retrograde and reprehensible approach.

Ray
 
XRAYretired
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 6:45 pm

ExperimentalFTE wrote:
mzlin wrote:
Finally some real news:

"A select group of US and international airline pilots are expected to participate in the final round of simulator testing of Boeing's new flight control system software for the 737 MAX as soon as early November...
Once these crucial simulator tests conclude, which could take roughly a week, the FAA's certification flight will occur. The simulator tests and the FAA's certification flight are the last two major steps before the FAA can decide whether the plane is safe to fly passengers again."

My guess is Boeing will have to announce a rightward shift in its previous RTS estimate soon.

https://www-m.cnn.com/2019/10/17/politi ... index.html


Solid as fartness at wind! How about using some Qualified Engineering Test Pilots (pool of them) to assess deficiencies of the aircraft and issue clear recommendations for fixing it?!?!

If FAA takes opinion of "pool of international airline pilots" regarding serious flight control and system architecture flaw and certifies aircraft based on it, it would certainly mark major milestone and shift into dark abyss of the whole aerospace industry in the USA...

Did you read the article?You may have the smelly end of the stick. The objective is to evaluate if modified procedures are adequate and assess training requirements. FAA has specifically requested pilots with low experience to achieve this, as you would hope.

Ray
 
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aerolimani
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 6:50 pm

morrisond wrote:
Here is a great article from Aviation Week that I think we should all familiarize ourselves with again as I think this would help the discussion.

It emphasizes the need to keep to under 250 knots when the plane is degraded and also talks about changes Boeing made to the MAX aero to help deal with MAX specific issues to give it - in Boeing's words "the same benign stall Characteristics of the NG". They don't make those changes unless they have tested it at stall.

From the article "During design of the MAX, Boeing added two more leading-edge vortilons [generating vortices over the top of the wing at high AOA] in 2018, for a total of six per side and also lengthened and raised the inboard leading-edge stall strips to assure stall behavior would be as docile as that of the NG."


These demonstrations were done in the engineering cab. Yes it is possible that Boeing intentionally hid poor handling of the MAX by manipulating the Engineering Simulator - but I would have to guess we would have heard that by now.

From the article: https://aviationweek.com/commercial-avi ... lator-demo

"A full aerodynamic stall with the MCAS inoperative is another exercise pilots experience in the MAX engineering cab simulator. “We reduced thrust at 5,000 ft. and slowed the aircraft at about 1 kt. per sec. We were at a midrange cg [center of gravity] with gear, slats and flats up. We trimmed until we reached 30% above stall speed and then just continued to ease back on the control wheel,” one of the pilots says.

“Pitch feel was natural, progressively increasing as airspeed decayed. Somewhere between the audible low airspeed warning and stickshaker, I felt the slightest lightening on control pressure in my fingertips. Quite candidly, if I had not been watching for it, I don’t think I would have noticed any difference between the MAX and the Next Gen [NG] models. I kept pulling back through stickshaker, then buffet, then elevator feel shift [a function that doubles the artificial control feel forces near stall] and finally until the yoke was buried in my lap. The nose just flopped down gently at the stall, and I initiated recovery as I would in most other airplanes I’ve flown,” he adds.

During design of the MAX, Boeing added two more leading-edge vortilons [generating vortices over the top of the wing at high AOA] in 2018, for a total of six per side and also lengthened and raised the inboard leading-edge stall strips to assure stall behavior would be as docile as that of the NG."


So I'll ask again - does MCAS really improve safety? It's not a bad thing to have but will it save any actual stalls from happening by it's inclusion on the MAX - probably not. The elevator feel shift (which we all forget about) seems to be much stronger than MCAS will impart and much more critical to safety.

If you don't agree with my statement above - please describe a scenario where MCAS would be the difference between saving the plane or not.

This article (from April 2019) is the one where the author’s second paragraph is later contradicted by a pilot he quotes. So, we have anonymous pilot quotes, contradicting the author’s statement in the same article. I very much call into question the journalistic quality of the entire article.

Fred George (the author): “ However, the system [called MCAS] is only needed to enhance stability with slats and flaps retracted at very light weights and full aft center of gravity (CG).

Anonymous pilot:We were at a midrange cg [center of gravity] with gear, slats and flats up. We trimmed until we reached 30% above stall speed and then just continued to ease back on the control wheel,” one of the pilots says.“Pitch feel was natural, progressively increasing as airspeed decayed. Somewhere between the audible low airspeed warning and stickshaker, I felt the slightest lightening on control pressure in my fingertips.

Author says full aft CG only, but pilot says problem occurred at midrange CG. So, one or the other of them does not know what they are talking about.

I believe the author’s confusion comes from the fact that the FAA-required test, to prove compliance with 25.203, must be conducted at light weight and full aft CG. Of course, the FAA test is for worst case scenario, but it does not preclude the problem happening in other circumstances.

In any case, I expect better journalism than this.
 
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ExperimentalFTE
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 6:54 pm

XRAYretired wrote:
ExperimentalFTE wrote:
mzlin wrote:
Finally some real news:

"A select group of US and international airline pilots are expected to participate in the final round of simulator testing of Boeing's new flight control system software for the 737 MAX as soon as early November...
Once these crucial simulator tests conclude, which could take roughly a week, the FAA's certification flight will occur. The simulator tests and the FAA's certification flight are the last two major steps before the FAA can decide whether the plane is safe to fly passengers again."

My guess is Boeing will have to announce a rightward shift in its previous RTS estimate soon.

https://www-m.cnn.com/2019/10/17/politi ... index.html


Solid as fartness at wind! How about using some Qualified Engineering Test Pilots (pool of them) to assess deficiencies of the aircraft and issue clear recommendations for fixing it?!?!

If FAA takes opinion of "pool of international airline pilots" regarding serious flight control and system architecture flaw and certifies aircraft based on it, it would certainly mark major milestone and shift into dark abyss of the whole aerospace industry in the USA...

Did you read the article?You may have the smelly end of the stick. The objective is to evaluate if modified procedures are adequate and assess training requirements. FAA has specifically requested pilots with low experience to achieve this, as you would hope.

Ray


Yeah, good luck.... So QTP who is trained and all his life puts himself in the role of the "average pilot" carefully assessing for potentially required "exceptional piloting skill" is not good and we will get opinion of airline pilots....hmmmm

I can maybe just maybe see assessment of appropriateness of training package...everything else as far as HQ, MCAS FLT CTRL is something they are very very incompetent in....

Also there is a question of representatives of the simulator Boeing is using....

Regards,
 
morrisond
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 6:55 pm

aerolimani wrote:
morrisond wrote:
Here is a great article from Aviation Week that I think we should all familiarize ourselves with again as I think this would help the discussion.

It emphasizes the need to keep to under 250 knots when the plane is degraded and also talks about changes Boeing made to the MAX aero to help deal with MAX specific issues to give it - in Boeing's words "the same benign stall Characteristics of the NG". They don't make those changes unless they have tested it at stall.

From the article "During design of the MAX, Boeing added two more leading-edge vortilons [generating vortices over the top of the wing at high AOA] in 2018, for a total of six per side and also lengthened and raised the inboard leading-edge stall strips to assure stall behavior would be as docile as that of the NG."


These demonstrations were done in the engineering cab. Yes it is possible that Boeing intentionally hid poor handling of the MAX by manipulating the Engineering Simulator - but I would have to guess we would have heard that by now.

From the article: https://aviationweek.com/commercial-avi ... lator-demo

"A full aerodynamic stall with the MCAS inoperative is another exercise pilots experience in the MAX engineering cab simulator. “We reduced thrust at 5,000 ft. and slowed the aircraft at about 1 kt. per sec. We were at a midrange cg [center of gravity] with gear, slats and flats up. We trimmed until we reached 30% above stall speed and then just continued to ease back on the control wheel,” one of the pilots says.

“Pitch feel was natural, progressively increasing as airspeed decayed. Somewhere between the audible low airspeed warning and stickshaker, I felt the slightest lightening on control pressure in my fingertips. Quite candidly, if I had not been watching for it, I don’t think I would have noticed any difference between the MAX and the Next Gen [NG] models. I kept pulling back through stickshaker, then buffet, then elevator feel shift [a function that doubles the artificial control feel forces near stall] and finally until the yoke was buried in my lap. The nose just flopped down gently at the stall, and I initiated recovery as I would in most other airplanes I’ve flown,” he adds.

During design of the MAX, Boeing added two more leading-edge vortilons [generating vortices over the top of the wing at high AOA] in 2018, for a total of six per side and also lengthened and raised the inboard leading-edge stall strips to assure stall behavior would be as docile as that of the NG."


So I'll ask again - does MCAS really improve safety? It's not a bad thing to have but will it save any actual stalls from happening by it's inclusion on the MAX - probably not. The elevator feel shift (which we all forget about) seems to be much stronger than MCAS will impart and much more critical to safety.

If you don't agree with my statement above - please describe a scenario where MCAS would be the difference between saving the plane or not.

This article (from April 2019) is the one where the author’s second paragraph is later contradicted by a pilot he quotes. So, we have anonymous pilot quotes, contradicting the author’s statement in the same article. I very much call into question the journalistic quality of the entire article.

Fred George (the author): “ However, the system [called MCAS] is only needed to enhance stability with slats and flaps retracted at very light weights and full aft center of gravity (CG).

Anonymous pilot:We were at a midrange cg [center of gravity] with gear, slats and flats up. We trimmed until we reached 30% above stall speed and then just continued to ease back on the control wheel,” one of the pilots says.“Pitch feel was natural, progressively increasing as airspeed decayed. Somewhere between the audible low airspeed warning and stickshaker, I felt the slightest lightening on control pressure in my fingertips.

Author says full aft CG only, but pilot says problem occurred at midrange CG. So, one or the other of them does not know what they are talking about.

I believe the author’s confusion comes from the fact that the FAA-required test, to prove compliance with 25.203, must be conducted at light weight and full aft CG. Of course, the FAA test is for worst case scenario, but it does not preclude the problem happening in other circumstances.

In any case, I expect better journalism than this.


The other mistake in the article says the Aero changes were made in 2018 - kind of hard to do as it was certificated in 2017 - they must have meant 2016 and it was a typo.

Who knows on COG - usually Aviation Week is pretty good.
 
morrisond
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Joined: Thu Jan 07, 2010 12:22 am

Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 7:16 pm

XRAYretired wrote:
Firstly, I think all should remind themselves that we are here because of the loss of 346 lives in two crashes with a common causal factor of incompetent design and safety assessment of a new system fitted to 737 Max. The discussions around the reason for the fit of that system are merely a distraction, or perhaps worse, has some nefarious intent.

Secondly, I think all should ignore the made up stories, more than one by Boeing and including 'just a slight lightening of the yoke that does not meet some new and un-important regulation', and remind themselves what the JATR - Experts with Access - determined:-

'Observation O3.4-A: The original implementation of MCAS was driven primarily by its ability to provide the B737 MAX with FAA-compliant flight characteristics at high speed. An unaugmented design would have been at risk of not meeting 14 CFR part 25 maneuvering characteristics requirements due to aerodynamics.

Observation O3.4-B: Extension of MCAS to the low-speed and 1g environment during the flight program was due to unacceptable stall characteristics with STS only. The possibility of a pitch-up tendency during approach to stall was identified for the flaps-up configuration prior to the implementation of MCAS.'


'Stall Characteristics' requirement 25.203 was new in 1964 and last revised very recently in 1995. Associated Out Of Trim' requirement 25.255 is a lot newer issued 1978.

Thirdly, we should remind ourselves that the perceived need to extend MCAS to cover the 1g environment was reported, by Boeing staff quotation, and as JATR above, during flight testing, not CAB simulator testing. This reminds us of the integrity we can give to such, in that simulator testing (as described above) did not identify the problem and cannot be used to demonstrate compliance for certification. Flight test in a properly configured aircraft is required. The primary concern was acceleration of stall due to atmospheric disturbance not pilot pull through (and constantly ignored for story telling purposes).

On a final point, the Regulations have been developed, and commonalised around the globe, with the primary objective of improving the safety of commercial aircraft and their operation for the benefit of all. This has been a decades long effort and continues. And it has worked pretty well.

The challenge of these recent posts has been escalated from show MCAS was required, to show MCAS improves safety, to prove MCAS would prevent a fatal event. This is to miss-represent what safe flight is about and achieved. Failure to comply with the requirements will increase the propensity for events to occur and potentially the severity of them, which in turn will increase the propensity for injury to persons/damage to property and increase the likelihood of catastrophic event.

Dismissal of requirements is a retrograde and reprehensible approach.

Ray


I don't disagree that the idea of having a linear control feel is a good idea. But at some point sometimes somebody should say stop - this is getting too complex and not overall improving safety.

In retrospect that should have been the point when they pulled the plug on the MAX vs adding just another patch or gave an exception to the rule if that was even possible. The FAA shouldn't have allowed Boeing to do what it did.

I doubt we will ever know what flights are flown but based on today's articles it doesn't sound like there will be any except for the MCAS 2.0 certification flights.
 
hivue
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 7:25 pm

XRAYretired wrote:
The challenge of these recent posts has been escalated from show MCAS was required, to show MCAS improves safety, to prove MCAS would prevent a fatal event. This is to miss-represent what safe flight is about and achieved. Failure to comply with the requirements will increase the propensity for events to occur and potentially the severity of them, which in turn will increase the propensity for injury to persons/damage to property and increase the likelihood of catastrophic event.


MCAS 1.0 helped the MAX meet the requirements that it was designed to help the MAX meet. The problem was that it was badly engineered, rushed and not thought through, so when the unexpected (unplanned-for and untested) happened it produced situations with which the accident crews were unable to cope.
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rheinwaldner
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 7:36 pm

morrisond wrote:
If you don't agree with my statement above - please describe a scenario where MCAS would be the difference between saving the plane or not.

Simple: manual recovery of a high altitude upset. Somewhere close to the coffin corner. Flying manually at high speed and starting just a turn could bring the aircraft at the edge of a stall. You can expect that the worst undesired effects from the MAX aerodynamics happen at high speeds.

The described simulator session in the article is not representative for a high altitude upset because the speed is totally different.
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morrisond
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 7:44 pm

rheinwaldner wrote:
morrisond wrote:
If you don't agree with my statement above - please describe a scenario where MCAS would be the difference between saving the plane or not.

Simple: manual recovery of a high altitude upset. Somewhere close to the coffin corner. Flying manually at high speed and starting just a turn could bring the aircraft at the edge of a stall. You can expect that the worst undesired effects from the MAX aerodynamics happen at high speeds.

The described simulator session in the article is not representative for a high altitude upset because the speed is totally different.


Where the Stick Shaker, Alarms and Elevator Feel Difference Computer would not be going off as well? Or are you guessing the MAX stalls before you get to those systems?
 
art
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 8:09 pm

FluidFlow wrote:
I drive ABS equipped cars since 1987 and I tell you it does not work the way it should when you need it most: If you hit the breaks with full force the wheels lock up straight away, there is no time to react initially it just blocks, then it starts to balance out the pressure to keep it rolling.

I guess you have a car: go on a gravel road and hit the breaks with as much force as you can. You will feel the initial lock up of your wheels.

But way more important: If you ABS does not work on the front right wheel because the sensor is broke but you did not buy the ABS warning light upgrade (so your car actually knows that one sensor failed bu you do not get this information on the dashboard of your car, but the car dealer told you that it works fine) and therefore the moment you break with your car the one wheel will lock up and the following inbalance will lead to a spin. Now the manual for your car actually does not include a procedure how to handle this situation correctly and neither does your "training" (Driving license course). Now if you make an accident, is it the fault of the driver or the manufacturer?


Valid parallel to me and a sensible question to finish. I think that reasoning non-partisan people will almost all agree on the answer.
 
jplatts
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 8:17 pm

There is an article on CNBC that said that lawyers representing Boeing 737 MAX crash victims are planning on issuing subpoenas to WN and AA, and that article can be found at https://www.cnbc.com/2019/10/17/boeing-737-max-crash-victims-lawyers-to-subpoena-southwest-american-airlines.html.
 
planecane
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 8:20 pm

mzlin wrote:
Finally some real news:

"A select group of US and international airline pilots are expected to participate in the final round of simulator testing of Boeing's new flight control system software for the 737 MAX as soon as early November...
Once these crucial simulator tests conclude, which could take roughly a week, the FAA's certification flight will occur. The simulator tests and the FAA's certification flight are the last two major steps before the FAA can decide whether the plane is safe to fly passengers again."

My guess is Boeing will have to announce a rightward shift in its previous RTS estimate soon.

https://www-m.cnn.com/2019/10/17/politi ... index.html


Certainly early Q4 is out since the simulator and certification flights won't have occurred yet until mid Q4.
 
rheinwaldner
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 8:23 pm

morrisond wrote:
rheinwaldner wrote:
morrisond wrote:
If you don't agree with my statement above - please describe a scenario where MCAS would be the difference between saving the plane or not.

Simple: manual recovery of a high altitude upset. Somewhere close to the coffin corner. Flying manually at high speed and starting just a turn could bring the aircraft at the edge of a stall. You can expect that the worst undesired effects from the MAX aerodynamics happen at high speeds.

The described simulator session in the article is not representative for a high altitude upset because the speed is totally different.


Where the Stick Shaker, Alarms and Elevator Feel Difference Computer would not be going off as well? Or are you guessing the MAX stalls before you get to those systems?

All these things cover different aspects of stall prevention. Some of the things you mention, exist to create awareness. MCAS exists to create compliant stick forces. All these things work in a symbiosis to accomplish one goal: help the crew to prevent a stall.

Note: there should be no debate that the stick force requirements while nearing a stall are warranted. Very likely somewhere blood was shed, before requirements like these were added.
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planecane
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 8:25 pm

DenverTed wrote:
PW100 wrote:
morrisond wrote:

Because the stick got just a little too light close to stall. They needed MCAS to meet the new regs. That is it. According to PW100 that reg did not exist when the NG was certified. The NG may have had the same issue and I don't think many of those fell out of the sky due to Pilot's stalling them.


Did I state that? Boy, these threads are way to long (as is the grounding . . .)

Why couldn't Boeing adjust the Elevator Feel System? One would expect that to be the preferred way to adjust feel force, that is why that system is in the 737 in the first place?

I would imagine that an elevator feel system works as long as their is a reasonable downward slope on the righting moment versus AOA curve. The feel system could increase the force required to configure from 11 degrees to 12 or whatever. On the other hand, if the graph is flat once the aircraft gets to 11 degrees, even with the same force it would continue to rotate nose up from 11 degrees to 14 degrees with no movement of the stick, or the control surfaces, which seems like a big problem. That can only be solved by an outside system that either moves the elevator or the trim to reduce the AOA a degree or two away from the unstable range.

The elevator feel system does not know what the AoA is. This is the primary reason it couldn't be easily used to provide the necessary stick force increase.

The elevator feel computer provides simulated aerodynamic forces using airspeed (from the elevator pitot system) and stabilizer position.
 
jollo
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 8:37 pm

Revelation wrote:
jollo wrote:
morrisond wrote:
In regards to Flight deck warning systems creating a startle effect - please remember that the NTSB says this is not specific to the MAX - other designs such as the A330 are susceptible to the same issues(AF447). Assuming most Airbuses are designed around the same common cockpit this could be an issue with those as well. I suspect the Boeing 777/787 cockpit would have the same issues. Cockpits are just too complex and too many interconnected systems to keep track of in an emergency.


Sorry for the late reply, but I find this attempt to draw a parallel with AF447 (trying to peddle the "hey, it's more of the same, nothing to see here" narrative) too far fetched to be left alone.

So let's analyze the similarities between AF447 and JT610-ET302:

The problem with AF447 was: a double sensor failure caused unreliable airspeed indications, stall warnings and loss of flight envelope protections. The pilot actions that - in hindsight - could have saved AF447 were: fly pitch and thrust per memory items as trained in sim, or even simply do nothing - just leave the stick alone until the pitots unfreeze.

The problem with JT610-ET302 was: a single sensor failure caused unreliable airspeed indications, stall warnings and aggressive, repeated, uncommanded AND control inputs up to maximum nose-down stab trim. The pilot actions that - in hindsight - could have saved JT610-ET302 were (strictly in this order):
  • 1 - counteract MCAS with ANU electric trim inputs within 3 seconds per Boeing assumptions - but this only buys you 5 seconds of respite before next MCAS cycle
  • 2 - bleed off with elevator inputs any speed buildup caused by MCAS's nose down trim inputs
  • 3 - return to neutral stab trim with ANU electric trim inputs - those inputs need to last longer than MCAS's AND inputs, because MCAS has greater trim authority than manual electric trim inputs; e.g. it would have taken close to 4 seconds of continuous ANU manual electric trim input to neutralize 3 seconds of MCAS control inputs (that is, if you managed to enact item #1 within the assumed 3 seconds, otherwise it's gonna take longer)
  • 4 - recognize the problem as a runaway stabilizer, run the corresponding NNC (despite the checklist being prefixed with the misleading condition "Uncommanded stabilizer trim movement occurs continuously", whereas with item #1 the trim has temporarily stopped moving) and only after returning the stabilizer to neutral trim (that's not described in the NNC but, c'mon, it's basic airmanship) proceed to cut out electric stab trim
  • 5 - did you manage to perform 2-3-4 in less than 5 seconds? If not, then start over, because in the meanwhile MCAS has kicked in again
  • 6 - did you cut out electric trim before correcting any mis-trim and overspeed (meaning anywhere near Vmo, not necessarily above)? Then - unless you're also a professional weight lifter - you're dead anyway, because you'll find that the manual trim wheel is too heavy to operate as mandated by the runaway stabilizer NNC
  • 7 - all of the above without any specific training (and especially no sim training), nor any mention of MCAS in either FCOM or EADs.

Was startle factor caused by multiple simultaneous cockpit warnings a factor in why the crews failed to save their flights? Probably. However the complexity of the tasks that were expected from the crews were so many orders of magnitude apart that any comparison is simply absurd.

The fact is (sadly for the victims, happily for all passengers flying every day on other types, both A and B), MAX's predicament is simply without precedent.

Impressive post, would be even more impressive if the time line started with one stick shaker going off at take off rather than a couple minutes later when MCAS kicked in, how flight before JT610 saved the same airplane, etc. Without these considerations it seems more one sided than it should be, but would still reach the same conclusion, workload was too great.


My aim was obviously not to present an accurate timeline, but to highlight that "workload was too great" is still a vague and possibly biased understatement. The only possible conclusion, IMO, is that the MAX was working against them. Call me one-sided if you will: my side is with the pilots that were fighting an aircraft actively trying to kill them, even if those pilots didn't put up the best - or even a good enough - fight, and ultimately failed.
 
jollo
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 9:08 pm

morrisond wrote:
jollo wrote:
morrisond wrote:
In regards to Flight deck warning systems creating a startle effect - please remember that the NTSB says this is not specific to the MAX - other designs such as the A330 are susceptible to the same issues(AF447). Assuming most Airbuses are designed around the same common cockpit this could be an issue with those as well. I suspect the Boeing 777/787 cockpit would have the same issues. Cockpits are just too complex and too many interconnected systems to keep track of in an emergency.


Sorry for the late reply, but I find this attempt to draw a parallel with AF447 (trying to peddle the "hey, it's more of the same, nothing to see here" narrative) too far fetched to be left alone.

So let's analyze the similarities between AF447 and JT610-ET302:

The problem with AF447 was: a double sensor failure caused unreliable airspeed indications, stall warnings and loss of flight envelope protections. The pilot actions that - in hindsight - could have saved AF447 were: fly pitch and thrust per memory items as trained in sim, or even simply do nothing - just leave the stick alone until the pitots unfreeze.

The problem with JT610-ET302 was: a single sensor failure caused unreliable airspeed indications, stall warnings and aggressive, repeated, uncommanded AND control inputs up to maximum nose-down stab trim. The pilot actions that - in hindsight - could have saved JT610-ET302 were (strictly in this order):
  • 1 - counteract MCAS with ANU electric trim inputs within 3 seconds per Boeing assumptions - but this only buys you 5 seconds of respite before next MCAS cycle
  • 2 - bleed off with elevator inputs any speed buildup caused by MCAS's nose down trim inputs
  • 3 - return to neutral stab trim with ANU electric trim inputs - those inputs need to last longer than MCAS's AND inputs, because MCAS has greater trim authority than manual electric trim inputs; e.g. it would have taken close to 4 seconds of continuous ANU manual electric trim input to neutralize 3 seconds of MCAS control inputs (that is, if you managed to enact item #1 within the assumed 3 seconds, otherwise it's gonna take longer)
  • 4 - recognize the problem as a runaway stabilizer, run the corresponding NNC (despite the checklist being prefixed with the misleading condition "Uncommanded stabilizer trim movement occurs continuously", whereas with item #1 the trim has temporarily stopped moving) and only after returning the stabilizer to neutral trim (that's not described in the NNC but, c'mon, it's basic airmanship) proceed to cut out electric stab trim
  • 5 - did you manage to perform 2-3-4 in less than 5 seconds? If not, then start over, because in the meanwhile MCAS has kicked in again
  • 6 - did you cut out electric trim before correcting any mis-trim and overspeed (meaning anywhere near Vmo, not necessarily above)? Then - unless you're also a professional weight lifter - you're dead anyway, because you'll find that the manual trim wheel is too heavy to operate as mandated by the runaway stabilizer NNC
  • 7 - all of the above without any specific training (and especially no sim training), nor any mention of MCAS in either FCOM or EADs.

Was startle factor caused by multiple simultaneous cockpit warnings a factor in why the crews failed to save their flights? Probably. However the complexity of the tasks that were expected from the crews were so many orders of magnitude apart that any comparison is simply absurd.

The fact is (sadly for the victims, happily for all passengers flying every day on other types, both A and B), MAX's predicament is simply without precedent.


Tell it to the NTSB - they specifically mentioned AF447 in the MAX report as subject to the same startle issues as the MAX.

BTW if ET302 had flown pitch and power they would have a greatly increased possibly of still being here.


I would gladly tell NTSB too, if they mucked around in these forums. Besides, their mission statement is to find out and document every aspect of the flight that could be a contributing factor, and multiple erroneous and distracting warnings for sure didn't help. Reducing the potential for startle factor is an overall Good Thing (tm) that everyone can agree with, along with enhancing manual flying skills and training. However, startle factor is NOT the reason why the MAX is grounded - nor pilot training is.

Re ET302: flying pitch and power could probably have helped - mainly through not making things worse - but would NOT have solved their MCAS-induced problems.
 
morrisond
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 9:11 pm

rheinwaldner wrote:
morrisond wrote:
rheinwaldner wrote:
Simple: manual recovery of a high altitude upset. Somewhere close to the coffin corner. Flying manually at high speed and starting just a turn could bring the aircraft at the edge of a stall. You can expect that the worst undesired effects from the MAX aerodynamics happen at high speeds.

The described simulator session in the article is not representative for a high altitude upset because the speed is totally different.


Where the Stick Shaker, Alarms and Elevator Feel Difference Computer would not be going off as well? Or are you guessing the MAX stalls before you get to those systems?

All these things cover different aspects of stall prevention. Some of the things you mention, exist to create awareness. MCAS exists to create compliant stick forces. All these things work in a symbiosis to accomplish one goal: help the crew to prevent a stall.

Note: there should be no debate that the stick force requirements while nearing a stall are warranted. Very likely somewhere blood was shed, before requirements like these were added.


There is no debate it's a good thing but with the elevator feel controller doubling forces after warning horn, mcas, stick shaker and frame buffeting does it add anything meaningful to safety?

Can't you do a probability calculation on this?
 
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Revelation
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 9:51 pm

jollo wrote:
My aim was obviously not to present an accurate timeline, but to highlight that "workload was too great" is still a vague and possibly biased understatement. The only possible conclusion, IMO, is that the MAX was working against them. Call me one-sided if you will: my side is with the pilots that were fighting an aircraft actively trying to kill them, even if those pilots didn't put up the best - or even a good enough - fight, and ultimately failed.

By a.net standards, "workload was too great" and "pilots that were fighting an aircraft actively trying to kill them" represents rough consensus! :biggrin:

Presuming we are seeking common ground, maybe "workload was too great because the result of a terrible design, implementation and testing regime was actively trying to kill them" goes some way to bridge the gap.
Last edited by Revelation on Thu Oct 17, 2019 9:56 pm, edited 1 time in total.
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jollo
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 9:52 pm

PixelFlight wrote:
jollo wrote:
[*]3 - return to neutral stab trim with ANU electric trim inputs - those inputs need to last longer than MCAS's AND inputs, because MCAS has greater trim authority than manual electric trim inputs; e.g. it would have taken close to 4 seconds of continuous ANU manual electric trim input to neutralize 3 seconds of MCAS control inputs (that is, if you managed to enact item #1 within the assumed 3 seconds, otherwise it's gonna take longer)

I didn't realize the stab trim rate difference before. This could explain why the JT610 and ET302 pilots finally lost the fight against MCAS. In the stress there could have perceived that a manual electric stab trim up of the same duration of the MCAS stab trim down was enough, not knowing that it's not the case.

I have already asked before if the simultaneous pitch up actions of both the pilots on the columns could have also biased the perception of the neutral stab trim position for the pilot that activate the manual electric stab trim. Still no hint at the possible response, but if true, this combined with the stab trim rate difference are yet another tricks that increase the difficulty of a recovery in high workload and high stress.


I remember your question from a few (dozens of) pages back, and I think it's an interesting observation: if I understood correctly, you're saying that one pilot steadily pulling back on his yoke could trick the other pilot into thinking that pitch feedback is back to neutral (and therefore it's time to stop trimming ANU) too early. This is probably true (and a very good reason why only the PF should have his hands on the controls), but IMO it's probably not the reason why ET302 pilots apparently stopped their trim inputs always at the same non-zero position for the simple reason that, in the mayhem of that cockpit, it's very unlikely that one pilot continued to pull up with exactly the same force through multiple attempts by the other pilot to electrically trim back to neutral.

However, it's an interesting counter-argument for Boeing's design philosophy fans, claiming the superiority of connected controls where "the PM can feel the PF's control inputs". True if the PM's touch is light, but what if the PM puts some force offset on the controls (without informing the PF)?
 
DenverTed
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Thu Oct 17, 2019 10:30 pm

Was there something different aerodynamically on the 767-2C that required MCAS, or did they just miss it in 1982 on the 767-200?
 
prebennorholm
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Oct 18, 2019 1:34 am

DenverTed wrote:
Was there something different aerodynamically on the 767-2C that required MCAS, or did they just miss it in 1982 on the 767-200?

We will hardly ever know everything about MCAS on 767-2C simply because it is a military plane. We may, however, assume some qualified or semi qualified guesses.

But what we know is that 767-MCAS is an entirely different animal, since it is triggered by combined elevated G force and AoA sensing. While MAX-MCAS is not connected to G force and can be activated in a straight and level 1G environment.

767-MCAS may explain the somewhat strange name - "Maneuvering Characteristic - ", as it unlike MAX-MCAS only activates to "Augment" certain maneuvering. 767-MCAS provides some sort of primitive envelope protection much like FBW planes. It can avoid that during excessive pitch maneuvering you break off the wings. Maybe there is a slightly different "peacetime software" to preserve fatigue life. No doubt the USAF expects the 767-2C to last at least the same 60-70 years as its predecessor KC-135.

The 767-2C competed against the KC-45A project (A330 based) which was so equipped as a natural part of its control system. At one time in the competition the KC-45 was the winner, There can be little doubt that its envelope protection was judged as a positive asset, and that the 767 would position itself better in the competition by emulating that protection.

I think we can rule out that 767-MCAS was made due to aerodynamic differences between 767-200 an 767-2C. If that had been the case, then 767-MCAS would have been just as needed to activate at low G and even 1G load as at elevated G force.

As I see it MCAS is a software which automatically manipulates stab trim to avoid unwanted elevator characteristics. Unwanted elevator characteristics may be of any type. MAX-MCAS was made as a subset of 767-MCAS which excludes the G force input and serves an entirely different purpose. But it kept its name MCAS even if it is totally non-descriptive for the MAX version.
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maint123
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Oct 18, 2019 2:46 am

So 12 months after the Max accidents, with all the hindsight and analysis, the experts and analysts here are still unable to concur on -
1. The correct actions to be taken incase of a similar MCAS caused emergency.
2. The airworthiness of the MAX after all the changes.

The crew in the case of lion air had less than 5km altitude during take off and maybe a minute to react to a new system they had no idea was pitching the nose down continously.
Why I am pointing this out is, reading the initial comments in the max crash thread, most of the "experts" were convinced of a crew fault.
 
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Oct 18, 2019 3:31 am

maint123 wrote:
So 12 months after the Max accidents, with all the hindsight and analysis, the experts and analysts here are still unable to concur on -
1. The correct actions to be taken incase of a similar MCAS caused emergency.

I'm not sure that matters, since there will never be another MCAS 1.0 commercial flight.

maint123 wrote:
2. The airworthiness of the MAX after all the changes.

I'm sure that does matter, but it seems people prefer to discuss (1) more than (2).
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planecane
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Oct 18, 2019 4:08 am

prebennorholm wrote:
DenverTed wrote:
Was there something different aerodynamically on the 767-2C that required MCAS, or did they just miss it in 1982 on the 767-200?

We will hardly ever know everything about MCAS on 767-2C simply because it is a military plane. We may, however, assume some qualified or semi qualified guesses.

But what we know is that 767-MCAS is an entirely different animal, since it is triggered by combined elevated G force and AoA sensing. While MAX-MCAS is not connected to G force and can be activated in a straight and level 1G environment.

767-MCAS may explain the somewhat strange name - "Maneuvering Characteristic - ", as it unlike MAX-MCAS only activates to "Augment" certain maneuvering. 767-MCAS provides some sort of primitive envelope protection much like FBW planes. It can avoid that during excessive pitch maneuvering you break off the wings. Maybe there is a slightly different "peacetime software" to preserve fatigue life. No doubt the USAF expects the 767-2C to last at least the same 60-70 years as its predecessor KC-135.

The 767-2C competed against the KC-45A project (A330 based) which was so equipped as a natural part of its control system. At one time in the competition the KC-45 was the winner, There can be little doubt that its envelope protection was judged as a positive asset, and that the 767 would position itself better in the competition by emulating that protection.

I think we can rule out that 767-MCAS was made due to aerodynamic differences between 767-200 an 767-2C. If that had been the case, then 767-MCAS would have been just as needed to activate at low G and even 1G load as at elevated G force.

As I see it MCAS is a software which automatically manipulates stab trim to avoid unwanted elevator characteristics. Unwanted elevator characteristics may be of any type. MAX-MCAS was made as a subset of 767-MCAS which excludes the G force input and serves an entirely different purpose. But it kept its name MCAS even if it is totally non-descriptive for the MAX version.

I'm pretty sure there were reports which stated that the MCAS on the 767 tanker is only for refueling operations. I'm pretty sure the same report said that vortex generators took care of a similar to MAX issue early in the 767 program.
 
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aerolimani
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Oct 18, 2019 5:09 am

prebennorholm wrote:
767-MCAS may explain the somewhat strange name - "Maneuvering Characteristic - ", as it unlike MAX-MCAS only activates to "Augment" certain maneuvering...
…But it kept its name MCAS even if it is totally non-descriptive for the MAX version.

In the earlier days of its development, didn’t Boeing have a different name/acronym for MCAS as found in the MAX? I seem to remember something like that in the early days of these threads. Does anyone else recall this?
 
rheinwaldner
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Oct 18, 2019 6:45 am

morrisond wrote:
Can't you do a probability calculation on this?

Very hard. For that we would have to find samples (= incidents) in aviation history, where non linear stick forces main factors.
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Oct 18, 2019 8:24 am

jollo wrote:
PixelFlight wrote:
jollo wrote:
[*]3 - return to neutral stab trim with ANU electric trim inputs - those inputs need to last longer than MCAS's AND inputs, because MCAS has greater trim authority than manual electric trim inputs; e.g. it would have taken close to 4 seconds of continuous ANU manual electric trim input to neutralize 3 seconds of MCAS control inputs (that is, if you managed to enact item #1 within the assumed 3 seconds, otherwise it's gonna take longer)

I didn't realize the stab trim rate difference before. This could explain why the JT610 and ET302 pilots finally lost the fight against MCAS. In the stress there could have perceived that a manual electric stab trim up of the same duration of the MCAS stab trim down was enough, not knowing that it's not the case.

I have already asked before if the simultaneous pitch up actions of both the pilots on the columns could have also biased the perception of the neutral stab trim position for the pilot that activate the manual electric stab trim. Still no hint at the possible response, but if true, this combined with the stab trim rate difference are yet another tricks that increase the difficulty of a recovery in high workload and high stress.


I remember your question from a few (dozens of) pages back, and I think it's an interesting observation: if I understood correctly, you're saying that one pilot steadily pulling back on his yoke could trick the other pilot into thinking that pitch feedback is back to neutral (and therefore it's time to stop trimming ANU) too early. This is probably true (and a very good reason why only the PF should have his hands on the controls), but IMO it's probably not the reason why ET302 pilots apparently stopped their trim inputs always at the same non-zero position for the simple reason that, in the mayhem of that cockpit, it's very unlikely that one pilot continued to pull up with exactly the same force through multiple attempts by the other pilot to electrically trim back to neutral.

However, it's an interesting counter-argument for Boeing's design philosophy fans, claiming the superiority of connected controls where "the PM can feel the PF's control inputs". True if the PM's touch is light, but what if the PM puts some force offset on the controls (without informing the PF)?

Glade to read that you perfectly understand the arguments. :thumbsup:

According to ET302 FDR published graph of the traces, the pilots make 4 manual electrical stab trims after MCAS activation, but 1 was short, 1 was long, and the 2 last was very short. A single one was long enough to significantly revert the pitch trim position. It that time the recorded control column position left and right deceased from about +14 deg for the left and +9 deg for the right to about +6 for both left and right. That is, the delta between the left and right was about +5 deg at the start of the manual electrical stab trim, and about 0 deg at the end. As there are positions measurement, the delta between left and right can certainly be translated in torque on the columns central pitch axis. If true, then the ET302 pilot stopped the only long manual electrical stab trim when the torque was neutral on the columns central pitch axis instead than when the position was neutral on the columns central pitch axis. This resulted in a remaining +6 deg on the columns pitch position that translate in 2.3 units in the stab trim position (due to too early abort of the manual electrical stab trim) instead of the 4.6 units required to fully neutralize the column pitch (as before the first MCAS activation). From the ET302 CVR published transcript it's very plausible that both the pilots applied aft force to both columns simultaneously just before that long manual electrical stab trim (after the second MCAS activation):

"At 05:40:20, approximately five seconds after the end of the ANU stabilizer motion, a second
instance of automatic AND stabilizer trim occurred and the stabilizer moved down and reached 0.4
units."

"At 05:40:27, the Captain advised the First-Officer to trim up with him."

"At 05:40:28 Manual electric trim in the ANU direction was recorded and the stabilizer reversed
moving in the ANU direction and then the trim reached 2.3 units."

This was also the case when there tried to re-enable the manual electrical stab trim:

"At 05:40:44, the Captain called out three times “Pull-up” and the First-Officer acknowledged."

"From 05:40:42 to 05:43:11 [...] The data indicates that aft force was applied to both columns simultaneously several times
throughout the remainder of the recording."

"At 05:41:30, the Captain requested the First-Officer to pitch up with him and the First-Officer
acknowledged."

"At 05:43:04, the Captain asked the First Officer to pitch up together and said that pitch is not
enough."

"At 05:43:11, about 32 seconds before the end of the recording, at approximately 13,400 2 ft, two
momentary manual electric trim inputs are recorded in the ANU direction. The stabilizer moved in
the ANU direction from 2.1 units to 2.3 units."


I would love to see a video of the simulation of a manual electrical stab trim neutralization by one pilot when the both pilots apply aft force to columns simultaneously.
: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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Spiderguy252
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Oct 18, 2019 8:45 am

This thread can go on and on.

Is there a set date for re-entry yet, or is it all still up in the air?
Vahroone
 
jollo
Posts: 396
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Oct 18, 2019 10:34 am

Revelation wrote:
maint123 wrote:
So 12 months after the Max accidents, with all the hindsight and analysis, the experts and analysts here are still unable to concur on -
1. The correct actions to be taken incase of a similar MCAS caused emergency.

I'm not sure that matters, since there will never be another MCAS 1.0 commercial flight.

maint123 wrote:
2. The airworthiness of the MAX after all the changes.

I'm sure that does matter, but it seems people prefer to discuss (1) more than (2).


I for one would very much like to be having a discussion about the airworthiness of the MAX “candidate for RTS” if we knew anything specific about “all the changes”. What’s been disclosed by Boeing so far amounts to a statement of intents in my book. Would be glad to be corrected.
 
ShamrockBoi330
Posts: 353
Joined: Fri Sep 21, 2018 3:28 am

Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Oct 18, 2019 4:47 pm

Shares currently falling today, the bad news keeps coming! Will it get to a point whereby the FAA will look to fully recertify the Max and not just the updates?

Boeing shares slipped Friday after a Reuters report said instant messages from 2016 suggest that employees misled the FAA about a key safety system on the 737 Max, the plane that has been grounded since mid-March after two fatal crashes.

The FAA turned over the instant messages to U.S. lawmakers and the Department of Transportation Inspector General, the FAA said in a statement. The FAA says Boeing discovered the messages "some months ago" and the flight regulatory agency finds the document "concerning."


https://www.cnbc.com/2019/10/18/boeing- ... 7-max.html
 
User avatar
aerolimani
Posts: 1321
Joined: Tue Jun 18, 2013 5:46 pm

Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Oct 18, 2019 4:56 pm

ShamrockBoi330 wrote:
Shares currently falling today, the bad news keeps coming! Will it get to a point whereby the FAA will look to fully recertify the Max and not just the updates?

Boeing shares slipped Friday after a Reuters report said instant messages from 2016 suggest that employees misled the FAA about a key safety system on the 737 Max, the plane that has been grounded since mid-March after two fatal crashes.

The FAA turned over the instant messages to U.S. lawmakers and the Department of Transportation Inspector General, the FAA said in a statement. The FAA says Boeing discovered the messages "some months ago" and the flight regulatory agency finds the document "concerning."


https://www.cnbc.com/2019/10/18/boeing- ... 7-max.html


Yikes. Some potentially really bad news for Boeing. Certainly, the market is afraid.

Here’s the Reuter’s report mentioned in the article: https://www.reuters.com/article/ethiopi ... SL2N27310U

Sources told Reuters the Boeing internal messages raised questions about the performance of the so-called MCAS anti-stall system that has been tied to the two fatal crashes in five months. Boeing declined to immediately comment.

The messages are between the MAX’s then-chief technical pilot and another Boeing pilot, the sources said, and raised questions about the MCAS’s performance in the simulator.
 
mrbots
Posts: 46
Joined: Tue Mar 12, 2019 5:31 pm

Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Oct 18, 2019 5:00 pm

ShamrockBoi330 wrote:
Shares currently falling today, the bad news keeps coming! Will it get to a point whereby the FAA will look to fully recertify the Max and not just the updates?

Boeing shares slipped Friday after a Reuters report said instant messages from 2016 suggest that employees misled the FAA about a key safety system on the 737 Max, the plane that has been grounded since mid-March after two fatal crashes.

The FAA turned over the instant messages to U.S. lawmakers and the Department of Transportation Inspector General, the FAA said in a statement. The FAA says Boeing discovered the messages "some months ago" and the flight regulatory agency finds the document "concerning."


https://www.cnbc.com/2019/10/18/boeing- ... 7-max.html


I saw that! I'm curious what exactly those IM's contained? I'd like to see the detail. I've been giving Boeing the benefit of the doubt on this all being gross incompetence until more evidence came to light. Assuming this isn't just an exaggeration by the news, this could turn into criminal negligence or fraud and if so people should be indicted if that's the case whether or not they're still at BA. Also, why weren't these turned over "some months ago" when they were discovered? Any idea what the FBI has discovered so far in their investigation? Time for a raid in Everett and Chicago?
 
justloveplanes
Posts: 1014
Joined: Thu Jul 08, 2004 5:38 am

Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Oct 18, 2019 5:02 pm

morrisond wrote:
rheinwaldner wrote:
morrisond wrote:

Where the Stick Shaker, Alarms and Elevator Feel Difference Computer would not be going off as well? Or are you guessing the MAX stalls before you get to those systems?

All these things cover different aspects of stall prevention. Some of the things you mention, exist to create awareness. MCAS exists to create compliant stick forces. All these things work in a symbiosis to accomplish one goal: help the crew to prevent a stall.

Note: there should be no debate that the stick force requirements while nearing a stall are warranted. Very likely somewhere blood was shed, before requirements like these were added.


There is no debate it's a good thing but with the elevator feel controller doubling forces after warning horn, mcas, stick shaker and frame buffeting does it add anything meaningful to safety?

Can't you do a probability calculation on this?


Earlier in this thread there was a statement that the current stick force was created with a hydraulic (analog) computer. It seems it would be a simple thing to put in a multi-redundant fail safe non linearity valve with a pressure reserve to increase the stick force (pressure in the hydraulic line and leave it at that. Like an electronically adjustable shock absorber on a car. I guess it would need a pressure input if the stick was getting light. MCAS was much simpler and totally feasible IMHO, but since they got that wrong.....
 
planecane
Posts: 1568
Joined: Thu Feb 09, 2017 4:58 pm

Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Oct 18, 2019 5:04 pm

prebennorholm wrote:
But it kept its name MCAS even if it is totally non-descriptive for the MAX version.


Isn't the wind up turn test referred to in the regulations or test regimen as "maneuvering characteristics?" If so, the name is perfectly descriptive.
 
asdf
Posts: 696
Joined: Tue Mar 18, 2014 12:03 am

Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Oct 18, 2019 5:30 pm

justloveplanes wrote:
Earlier in this thread there was a statement that the current stick force was created with a hydraulic (analog) computer. It seems it would be a simple thing to put in a multi-redundant fail safe non linearity valve with a pressure reserve to increase the stick force (pressure in the hydraulic line and leave it at that. Like an electronically adjustable shock absorber on a car. I guess it would need a pressure input if the stick was getting light. MCAS was much simpler and totally feasible IMHO, but since they got that wrong.....


Linear stick force is essential to be able to fly the plane safely manually.
Based on the resistance of the stick, the pilot senses which aerodynamic situation the aircraft is in and how it reacts to its inputs.

If this feedback about the stick is augmented then it is very difficult for the pilot to detect how his plane reacts
whether and to what extent this has played an additional role in the two crashes is unclear.

With fly-by-wire aircraft, there is generally no such feedback from the stick. You have to learn that and that gives a distinctly different control feeling for the pilot, but that is not uncertain.

what is uncertain and hardly realizable, is a feedback on the stick, but sometimes it is not the real but a fake
whether by influencing the elevators or by using a non-linear valve
 
Chemist
Posts: 746
Joined: Tue Oct 20, 2015 4:46 am

Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Oct 18, 2019 5:58 pm

asdf wrote:
justloveplanes wrote:
Earlier in this thread there was a statement that the current stick force was created with a hydraulic (analog) computer. It seems it would be a simple thing to put in a multi-redundant fail safe non linearity valve with a pressure reserve to increase the stick force (pressure in the hydraulic line and leave it at that. Like an electronically adjustable shock absorber on a car. I guess it would need a pressure input if the stick was getting light. MCAS was much simpler and totally feasible IMHO, but since they got that wrong.....


Linear stick force is essential to be able to fly the plane safely manually.
Based on the resistance of the stick, the pilot senses which aerodynamic situation the aircraft is in and how it reacts to its inputs.

If this feedback about the stick is augmented then it is very difficult for the pilot to detect how his plane reacts
whether and to what extent this has played an additional role in the two crashes is unclear.

With fly-by-wire aircraft, there is generally no such feedback from the stick. You have to learn that and that gives a distinctly different control feeling for the pilot, but that is not uncertain.

what is uncertain and hardly realizable, is a feedback on the stick, but sometimes it is not the real but a fake
whether by influencing the elevators or by using a non-linear valve


Not intending to be argumentative, but on the one hand you say linear stick force is essential to fly safely manually, but then don't some FBW aircraft such as the A32x not have that, and yet you can fly them manually, is that not correct? Feels like a contradiction.
 
User avatar
aerolimani
Posts: 1321
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Oct 18, 2019 6:14 pm

Chemist wrote:
asdf wrote:
justloveplanes wrote:
Earlier in this thread there was a statement that the current stick force was created with a hydraulic (analog) computer. It seems it would be a simple thing to put in a multi-redundant fail safe non linearity valve with a pressure reserve to increase the stick force (pressure in the hydraulic line and leave it at that. Like an electronically adjustable shock absorber on a car. I guess it would need a pressure input if the stick was getting light. MCAS was much simpler and totally feasible IMHO, but since they got that wrong.....


Linear stick force is essential to be able to fly the plane safely manually.
Based on the resistance of the stick, the pilot senses which aerodynamic situation the aircraft is in and how it reacts to its inputs.

If this feedback about the stick is augmented then it is very difficult for the pilot to detect how his plane reacts
whether and to what extent this has played an additional role in the two crashes is unclear.

With fly-by-wire aircraft, there is generally no such feedback from the stick. You have to learn that and that gives a distinctly different control feeling for the pilot, but that is not uncertain.

what is uncertain and hardly realizable, is a feedback on the stick, but sometimes it is not the real but a fake
whether by influencing the elevators or by using a non-linear valve


Not intending to be argumentative, but on the one hand you say linear stick force is essential to fly safely manually, but then don't some FBW aircraft such as the A32x not have that, and yet you can fly them manually, is that not correct? Feels like a contradiction.

I think what you’re missing in asdf’s statement is that linear stick force is essential to fly a non-FBW aircraft safely, manually. There is no point at which one is ever flying a FBW airplane truly manually. It is always assisted by some amount of computer, even in its most degraded state. So, the same standards are not applicable to both.
 
kalvado
Posts: 2817
Joined: Wed Mar 01, 2006 4:29 am

Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Oct 18, 2019 6:24 pm

Chemist wrote:
asdf wrote:
justloveplanes wrote:
Earlier in this thread there was a statement that the current stick force was created with a hydraulic (analog) computer. It seems it would be a simple thing to put in a multi-redundant fail safe non linearity valve with a pressure reserve to increase the stick force (pressure in the hydraulic line and leave it at that. Like an electronically adjustable shock absorber on a car. I guess it would need a pressure input if the stick was getting light. MCAS was much simpler and totally feasible IMHO, but since they got that wrong.....


Linear stick force is essential to be able to fly the plane safely manually.
Based on the resistance of the stick, the pilot senses which aerodynamic situation the aircraft is in and how it reacts to its inputs.

If this feedback about the stick is augmented then it is very difficult for the pilot to detect how his plane reacts
whether and to what extent this has played an additional role in the two crashes is unclear.

With fly-by-wire aircraft, there is generally no such feedback from the stick. You have to learn that and that gives a distinctly different control feeling for the pilot, but that is not uncertain.

what is uncertain and hardly realizable, is a feedback on the stick, but sometimes it is not the real but a fake
whether by influencing the elevators or by using a non-linear valve


Not intending to be argumentative, but on the one hand you say linear stick force is essential to fly safely manually, but then don't some FBW aircraft such as the A32x not have that, and yet you can fly them manually, is that not correct? Feels like a contradiction.

Spring loaded side stick provides nice force feedback depending on deflection, no lightening no reversals. Position of sidestick is interpreted by computer to do things right.
I believe some fighters use just force, no deflection of rigid sidestick, to control things.
FBW unloads all linearity problems from the pilot into computer logic...
 
User avatar
aerolimani
Posts: 1321
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Oct 18, 2019 6:25 pm

mrbots wrote:
ShamrockBoi330 wrote:
Shares currently falling today, the bad news keeps coming! Will it get to a point whereby the FAA will look to fully recertify the Max and not just the updates?

Boeing shares slipped Friday after a Reuters report said instant messages from 2016 suggest that employees misled the FAA about a key safety system on the 737 Max, the plane that has been grounded since mid-March after two fatal crashes.

The FAA turned over the instant messages to U.S. lawmakers and the Department of Transportation Inspector General, the FAA said in a statement. The FAA says Boeing discovered the messages "some months ago" and the flight regulatory agency finds the document "concerning."


https://www.cnbc.com/2019/10/18/boeing- ... 7-max.html


I saw that! I'm curious what exactly those IM's contained? I'd like to see the detail. I've been giving Boeing the benefit of the doubt on this all being gross incompetence until more evidence came to light. Assuming this isn't just an exaggeration by the news, this could turn into criminal negligence or fraud and if so people should be indicted if that's the case whether or not they're still at BA. Also, why weren't these turned over "some months ago" when they were discovered? Any idea what the FBI has discovered so far in their investigation? Time for a raid in Everett and Chicago?

There’s some more detail here: https://www.nytimes.com/2019/10/18/busi ... 69ing-news

Especially, there’s some very PO’d comments from the FAA’s Stephen Dickson. He has sent Muilenburg a letter saying “I expect your explanation immediately regarding the content of this document and Boeing’s delay in disclosing the document to its safety regulator.”
 
sharpley
Posts: 25
Joined: Mon Jul 29, 2019 10:28 pm

Re: Boeing 737MAX Grounded Worldwide Q4 2019

Fri Oct 18, 2019 6:31 pm

aerolimani wrote:
mrbots wrote:
ShamrockBoi330 wrote:
Shares currently falling today, the bad news keeps coming! Will it get to a point whereby the FAA will look to fully recertify the Max and not just the updates?

Boeing shares slipped Friday after a Reuters report said instant messages from 2016 suggest that employees misled the FAA about a key safety system on the 737 Max, the plane that has been grounded since mid-March after two fatal crashes.

The FAA turned over the instant messages to U.S. lawmakers and the Department of Transportation Inspector General, the FAA said in a statement. The FAA says Boeing discovered the messages "some months ago" and the flight regulatory agency finds the document "concerning."


https://www.cnbc.com/2019/10/18/boeing- ... 7-max.html


I saw that! I'm curious what exactly those IM's contained? I'd like to see the detail. I've been giving Boeing the benefit of the doubt on this all being gross incompetence until more evidence came to light. Assuming this isn't just an exaggeration by the news, this could turn into criminal negligence or fraud and if so people should be indicted if that's the case whether or not they're still at BA. Also, why weren't these turned over "some months ago" when they were discovered? Any idea what the FBI has discovered so far in their investigation? Time for a raid in Everett and Chicago?

There’s some more detail here: https://www.nytimes.com/2019/10/18/busi ... 69ing-news

Especially, there’s some very PO’d comments from the FAA’s Stephen Dickson. He has sent Muilenburg a letter saying “I expect your explanation immediately regarding the content of this document and Boeing’s delay in disclosing the document to its safety regulator.”

The letter in question can be seen on Jon Ostrower's twitter
https://twitter.com/jonostrower/status/ ... 7008973826
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