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XRAYretired
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Tue Oct 15, 2019 8:11 pm

morrisond wrote:
rheinwaldner wrote:
morrisond wrote:
MCAS v 1.0 was not intended to be an Anti-stall - it was due to it's piss poor design that unfortunately it acted like one.

That is why MCAS v2.0 is not required to be one either.

A stick pusher would be an anti-stall system. It was not required for certification.

There is no anti-stall on the NG or MAX. All the systems were there to provide warnings for the pilots.

There is nothing on an 737 NG or MAX to keep the pilot from intentionally putting it into a stall. None of the other systems will prevent a stall. You can pull right through them.

MCAS was required to meet the FAR's for stall characteristics to help the pilot identify they were approaching a stall by not letting the stick force fall below a certain value.

I don't know how more plainly it can be said.

If you were flying the MAX in manual mode and were maintaining a certain angle of attack per the instruments or outside visual reference and MCAS fired once - you would feel the elevator getting a little heavier. You wouldn't let the nose drop by not counteracting that force unless you were being completely inattentive to what the aircraft was supposed to be doing - which is your job as you are flying an airplane in manual mode.

What else do you expect the pilot to be doing if they are trying to fly at way higher than normal AOA's? Going for a coffee or texting on there phone and not paying attention to what the aircraft is doing?

Why are you reversing the truth? Not many sentences in this huge post are correct. The red ones are wrong, the yellow ones are contradicting and the green ones are not relevant to judge whether MCAS is to prevent stalls.

You continue to provide some platitudes as answers but never reach the answer to the final "why is this?"...

E.g. (picking just some of your statements)
- Why is there a certification requirement that demands particular stick forces when approaching a stall? Final answer: to prevent stalls....
- Why are there systems to provide warnings to the pilots? Final answer: to help avoiding stalls.
- Why was the MAX required to meet certain stall characteristics? Final answer: to help avoiding stalls (<- if that is not a no brainer, then maybe questions about ones brain should be asked)
- Why pilots must identify that they are approaching a stall by not letting the stick force fall below a certain value? Final answer: to help avoiding stalls.


It seems like we are arguing about the English language. I'll admit some of what I type is pretty bad sometimes so I apologize if it's ever confusing.

I'll try once more.

The systems on the Max help to give the pilots clues to prevent inadvertently entering a stall - but none of them will actually cause the stall to not happen like a FBW design in Normal Law with all safeties working. They will not "prevent a stall" automatically. They still require the correct action from the pilot. They are helping the pilot to avoid a stall by giving them clues.

A properly functioning Stick Shaker, MCAS, or Audio alarm will not stop a stall from happening.

The probably only automatic thing on a non-FBW aircraft that would prevent(stop) a stall from happening would be a stick pusher that can't be countermanded by the pilot.

The MAX or NG do not have any anti-stall (meaning will automatically stop a stall from happening) systems. They just have systems to help avoid stalls by giving the pilot tactile and Audio clues - MCAS would be included in that category - it gives the pilots clues to help avoid stalls. it won't stop a stall from happening. MCAS gives tactile clues like a stick shaker would.

Ray - help!

Not sure I can help at all. It looks too much like a duck such that JATR did not make a determination. The one thing it isn't, is a pilot warning system.

You will need to accept that the primary concern is not for pilots pulling through into stall, but for stall being accelerated due to a combination of the tendency to nose up on its own or including atmospheric disturbance. Longitudinal stability linearity per se is looking to maintain elevator authority and discourage out of trim in the lead to stall such that recovery is assured. In this case in my view, MCAS only activates between stall warning and actual stall onset, which, if accelerated, could happen before the pilot has had time to feel the stick shaker in hand and it is already pushing the nose down in advance of pilot action. Both of which together, hopefully prevent/protect against/stop/discourage/deter stall occurring.

After all, the intention of stall warnings etc. is to avoid a stall actually occurring if possible.

The stability augmentation label applied by Boeing may be in the same ball park as the New MCAS system being just a minor extension to STS - smoke and mirrors.

NB. NG and MAX have a stall identification/protection/prevention function as part of the A/P also hidden behind the title of A/P STS. If it then relinquishes control to the pilot, I don't know.

Call it what you like, it does what it does and it exists to do it and is not just a nod in the direction of some unimportant regulation.

Ray
 
FlyBoeingAirbus
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Tue Oct 15, 2019 10:54 pm

For the less technically-minded on this thread (including myself), I found the following link which pretty well explains why MCAS was needed in the first-place....

https://www.vox.com/business-and-financ ... -explained
 
DenverTed
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Tue Oct 15, 2019 11:30 pm

If the pitch stability varies with the trim setting, then MCAS is there to move it to the nose down configuration that is stable. Having it activate beyond the range for which it is needed was a severe engineering oversight.
 
ODwyerPW
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Tue Oct 15, 2019 11:36 pm

rheinwaldner wrote:
morrisond wrote:
MCAS v 1.0 was not intended to be an Anti-stall - it was due to it's piss poor design that unfortunately it acted like one.

That is why MCAS v2.0 is not required to be one either.

A stick pusher would be an anti-stall system. It was not required for certification.

There is no anti-stall on the NG or MAX. All the systems were there to provide warnings for the pilots.

There is nothing on an 737 NG or MAX to keep the pilot from intentionally putting it into a stall. None of the other systems will prevent a stall. You can pull right through them.

MCAS was required to meet the FAR's for stall characteristics to help the pilot identify they were approaching a stall by not letting the stick force fall below a certain value.

I don't know how more plainly it can be said.

If you were flying the MAX in manual mode and were maintaining a certain angle of attack per the instruments or outside visual reference and MCAS fired once - you would feel the elevator getting a little heavier. You wouldn't let the nose drop by not counteracting that force unless you were being completely inattentive to what the aircraft was supposed to be doing - which is your job as you are flying an airplane in manual mode.

What else do you expect the pilot to be doing if they are trying to fly at way higher than normal AOA's? Going for a coffee or texting on there phone and not paying attention to what the aircraft is doing?


Why are you reversing the truth? Not many sentences in this huge post are correct. The red ones are wrong, the yellow ones are contradicting and the green ones are not relevant to judge whether MCAS is to prevent stalls.

etc... etc....


Wow, you all take arguing on the internet pretty serious.

What ever happens when and if the MAX returns to service, I just hope pilots are told everything they need to know about MCAS. That way we can get back to arguing about other stuff like if the MAX9ER will be more effective in sales campaigns against the A321 than the 900, 900ER, MAX9 or MAX10
learning never stops.
 
justloveplanes
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 12:55 am

Excuse these probably already answered questions (long thread)...
A) How necessary is MCAS in the first place?
B) If no MCAS, would a bigger rear stabilizer help?
 
Astronage
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 1:29 am

justloveplanes wrote:
Excuse these probably already answered questions (long thread)...
A) How necessary is MCAS in the first place?
B) If no MCAS, would a bigger rear stabilizer help?


A: It was necessary for grandfathering purposes. I certain flight regimes the lift from the engine placement makes the nose light rendering the plane more sensitive to pitch up commands. That is not a dangerous behavior per se but that's not how the old 737s fly and it could have been trained around. But the entire point of the Max was that transitioning to it from a NG is trivial(see infamous ipad course) so they made MCAS to compensate for the behavior.

B: Yes but that would be a major engineering change and that would have affected the certification since a larger rear stab would affect plane handling. If they were open to major engineering nchange they would have lengthened the gear which would have most likely prevented the issue MCAS was designed to assist with from happening in the 1st place.
 
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PixelFlight
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 1:37 am

justloveplanes wrote:
Excuse these probably already answered questions (long thread)...
A) How necessary is MCAS in the first place?

The most recent official information we have at this time about this is from https://www.faa.gov/news/media/attachments/Final_JATR_Submittal_to_FAA_Oct_2019.pdf

"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."

While the O3.4-A is presented only as a risk (and EASA asking for test flight without MCAS give an idea on how this risk in not actually well evaluated), the O3.4-B is presented as necessary "due to unacceptable stall characteristics with STS only".

justloveplanes wrote:
B) If no MCAS, would a bigger rear stabilizer help?

Don't know. It has been reported that Boeing has tried to use vortex generator to fix the CFR part 25 issue before giving up and go for the MCAS.
: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:
 
planecane
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 1:46 am

PixelFlight wrote:
justloveplanes wrote:
Excuse these probably already answered questions (long thread)...
A) How necessary is MCAS in the first place?

The most recent official information we have at this time about this is from https://www.faa.gov/news/media/attachments/Final_JATR_Submittal_to_FAA_Oct_2019.pdf

"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."

While the O3.4-A is presented only as a risk (and EASA asking for test flight without MCAS give an idea on how this risk in not actually well evaluated), the O3.4-B is presented as necessary "due to unacceptable stall characteristics with STS only".

justloveplanes wrote:
B) If no MCAS, would a bigger rear stabilizer help?

Don't know. It has been reported that Boeing has tried to use vortex generator to fix the CFR part 25 issue before giving up and go for the MCAS.

I can't picture how a larger stabilizer would solve the issue since the issue is non-linear. According to available information, the lift caused by the nacelles increases as AoA increases. I don't see how a larger surface would prevent the stick force reduction as AoA increases.
 
planecane
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 1:49 am

DenverTed wrote:
If the pitch stability varies with the trim setting, then MCAS is there to move it to the nose down configuration that is stable. Having it activate beyond the range for which it is needed was a severe engineering oversight.

Where have you seen that pitch stability varies with trim setting? What I've read, it varies with AoA. It activated because it thought it was in the range where it was needed due to the failed sensor.
 
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aerolimani
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 2:27 am

Astronage wrote:
justloveplanes wrote:
Excuse these probably already answered questions (long thread)...
A) How necessary is MCAS in the first place?
B) If no MCAS, would a bigger rear stabilizer help?


A: It was necessary for grandfathering purposes. I certain flight regimes the lift from the engine placement makes the nose light rendering the plane more sensitive to pitch up commands. That is not a dangerous behavior per se but that's not how the old 737s fly and it could have been trained around. But the entire point of the Max was that transitioning to it from a NG is trivial(see infamous ipad course) so they made MCAS to compensate for the behavior.

B: Yes but that would be a major engineering change and that would have affected the certification since a larger rear stab would affect plane handling. If they were open to major engineering nchange they would have lengthened the gear which would have most likely prevented the issue MCAS was designed to assist with from happening in the 1st place.

The answer for question A is wrong. The aircraft did not meet the FAR requirements regarding stall characteristics. As angle of attack increases, and the plane gets closer to stalling, the forces on the stick must not decrease at any point. The MAX engine nacelles generate lift and cause a lightening of the stick forces. For numerous reasons, grandfathering among them, MCAS was Boeing’s chosen solution to this problem, allowing the plane to be certified. The FAR can be downloaded and read here: https://www.govinfo.gov/app/details/CFR ... -sec25-203

Considering the number of other exceptions Boeing received from the FAA, especially as regards flight deck warning systems, the fact that Boeing did not get an exception from 14 CFR § 25.203 indicates to me that the aircraft has a serious issue, and that the plane is not safe without some means of meeting this regulation. The regulations exist to ensure safety.

Once again, all posters here should have a read through this page I link to below. I disagree with its initial description of MCAS, as I believe MCAS should be described as an anti-stall measure, but the rest of the information is good. http://www.b737.org.uk/mcas.htm
 
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par13del
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 3:05 am

Ok correct me if I am wrong, but I was under the impression that the JTAR group was put together to look at certification issues in general, it was not to study and make recommendations necessary to unground the MAX.
 
justloveplanes
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 3:08 am

planecane wrote:

justloveplanes wrote:
B) If no MCAS, would a bigger rear stabilizer help?

Don't know. It has been reported that Boeing has tried to use vortex generator to fix the CFR part 25 issue before giving up and go for the MCAS.

I can't picture how a larger stabilizer would solve the issue since the issue is non-linear. According to available information, the lift caused by the nacelles increases as AoA increases. I don't see how a larger surface would prevent the stick force reduction as AoA increases.[/quote]

I was thinking more (or further extended rearward) rear horizontal stabilizer would provide a longer lever arm rearward around the center of rotation to mitigate the pitchup forward of the COR. I see your point about non-linearity.... still maybe might be enough...
 
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BoeingVista
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 4:24 am

par13del wrote:
Ok correct me if I am wrong, but I was under the impression that the JTAR group was put together to look at certification issues in general, it was not to study and make recommendations necessary to unground the MAX.


I think that this is correct.

Thats the way they approached their report anyway, many recommendations about certification in general which we have to assume the individual authorities believe need enacting, so if FAA ignores them and ploughs on regardless these authorities seem very unlikely to sign off on FAA certifications in future. Obviously this is a major hazzard to 777x as none, zero are going to be flying exclusively in North America.
BV
 
oschkosch
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 5:41 am

Oh dear, looks like middle to late 1st quarter 2020 now....at least according to Southwest!

https://www.cnbc.com/2019/10/14/boeing- ... s-say.html

The Boeing 737 Max won’t return to service at Southwest Airlines until February at the earliest, the union that represents the airline’s pilots said Monday

Gesendet von meinem SM-G950F mit Tapatalk
:stirthepot: :airplane: "This airplane is designed by clowns, who in turn are supervised by monkeys" :airplane: :stirthepot:
 
uta999
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 7:11 am

Is it possible to add an extendable elevator to to the horizontal stabiliser, similar to a flap? This could greatly increase the HS wing area when needed close to a stall.

It would also be easy to upgrade the MAX, simply by replacing the HS.
Your computer just got better
 
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seahawk
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 7:28 am

The stab size is not the problem, the problem is that the engines create too much lift at certain angles of attack, imagine the wing leading edge and the engine cowling working like a slotted flap.

This additional lift means that the control forces on the stick are not linear and at that point the nose movement increases without any stick movement. This is against regulations.

MCAS counters this by trimming the plane nose down so that the stabilizer so that the stabilizer input is effectively reduced.
 
kalvado
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 7:55 am

seahawk wrote:
The stab size is not the problem, the problem is that the engines create too much lift at certain angles of attack, imagine the wing leading edge and the engine cowling working like a slotted flap.

This additional lift means that the control forces on the stick are not linear and at that point the nose movement increases without any stick movement. This is against regulations.

MCAS counters this by trimming the plane nose down so that the stabilizer so that the stabilizer input is effectively reduced.

Linearity is not an issue, local reversal of the gradient is. Larger stab could do the trick, adding more force.

HOWEVER, one must remember that forces on the frame are not the only thing to consider. There is a thing called elevator feel computer - force on 737 stick is not the force of airflow acting on the elevator, but an artificial parameter. Think about it in terms of ET crew facing extreme forces and unable to control as a result.

The 737 elevator feel computer is - drumbeats- an analog hydraulic computer. From my perspective of late 20th century kid, hydraulic computer is perversion akin to sleeping in the celling, born out of direst need with no proper tools to help. It is dead end, you probably have better chance of finding stone tool making expert than hydraulic computer expert. I, for one, successfully tried making stone tools, but memories of my only lab with analog computer - electronic, not hydraulic - makes my hair rise quarter century later.
Cleanest possible way to deal with engine forces would be to replace that monster with a chip. Probably would void legacy standing. Redesign of hydraulic computer... I bet nobody dared to touch it with 10 foot pole even after 7 digit salary was offered.
So, MCAS is it. Think about it as a curtain strapped to baby pants, which are normal pants on a right and a kilt on the left, and the problem is a kid who grew up - but school dress code require covered knees.
So... Happy flying!
 
Amiga500
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 9:13 am

kalvado wrote:
seahawk wrote:
The stab size is not the problem, the problem is that the engines create too much lift at certain angles of attack, imagine the wing leading edge and the engine cowling working like a slotted flap.

Linearity is not an issue, local reversal of the gradient is. Larger stab could do the trick, adding more force.


Your both talking about different linearities.

Seahawk is talking about the pitching moment of wing/body and you are talking about the load response on the elevator.


I'm pretty sure that increasing the stabilizer size won't fix the issue. A trimmed aircraft is a trimmed aircraft. If the wing/body pitching moment increases non-linearly with AoA, then you'd need to have the same non-linear response in your h-stab/elevator to compensate. A bigger h-stab will not produce that non-linearity.

I don't believe h-stab AoA will ever be large enough for LERX to work. Perhaps dorsal strakes somewhere near the empennage might work, but that could play havoc with lateral stability and rudder effectiveness.

[while both of those solutions would increase stick weight with AoA even outside the MCAS regime, that at least is acceptable for FARs]
 
asdf
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 9:21 am

istnt that pitch effect (and stick force) dependend on thrust?

why not automaticaly reduce the thrust in case of pitch up instead of re-trimming flight surfaces and making the overall handling problematic?
 
XRAYretired
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 9:23 am

Reports of shenanigans during the Lion Air investigation in relation to the installation of the AoA sensor. It pretty much has to either be incorrect calibration by the MRO (XTRA Aerospace) or incorrect installation that resulted in the ~22deg AoA offset and this might appear as an attempt to push focus on to the MRO but its a mightily confused write up.
https://theprint.in/world/fake-photos-t ... on/306372/

Ray
 
asdf
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 9:32 am

XRAYretired wrote:
Reports of shenanigans during the Lion Air investigation in relation to the installation of the AoA sensor. It pretty much has to either be incorrect calibration by the MRO (XTRA Aerospace) or incorrect installation that resulted in the ~22deg AoA offset and this might appear as an attempt to push focus on to the MRO but its a mightily confused write up.
https://theprint.in/world/fake-photos-t ... on/306372/
Ray


never says never again

but to install it wrong you would need to drill additional holes into the fuselage ..
into a brand new ship ...

that is not completely impossible but sounds pretty unlikely, doesent it?
 
Amiga500
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 9:45 am

asdf wrote:
istnt that pitch effect (and stick force) dependend on thrust?

why not automaticaly reduce the thrust in case of pitch up instead of re-trimming flight surfaces and making the overall handling problematic?


That may not be a good idea if you are at low altitude.
 
Amiga500
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 9:50 am

asdf wrote:
XRAYretired wrote:
Reports of shenanigans during the Lion Air investigation in relation to the installation of the AoA sensor. It pretty much has to either be incorrect calibration by the MRO (XTRA Aerospace) or incorrect installation that resulted in the ~22deg AoA offset and this might appear as an attempt to push focus on to the MRO but its a mightily confused write up.
https://theprint.in/world/fake-photos-t ... on/306372/
Ray


never says never again

but to install it wrong you would need to drill additional holes into the fuselage ..
into a brand new ship ...

that is not completely impossible but sounds pretty unlikely, doesent it?


Indeed. Designs are made foolproof with hole arrangement just-so to prevent this very thing from happening. If the holes for an AoA vane were at a constant PCD with constant circular pitch - does anyone really think that we'd never have heard of more incorrectly installed AoA vanes before now? Like... really?

Either way, its largely irrelevant to the problems with MCAS. If a bird hit the vane - then your in the same boat with MCAS.
 
art
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 10:03 am

Anyone got amy info regarding rthe ungrounding of the MAX?
 
ShamrockBoi330
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 10:18 am

art wrote:
Anyone got amy info regarding rthe ungrounding of the MAX?


yup... its not happening anytime soon!
Last edited by ShamrockBoi330 on Wed Oct 16, 2019 10:28 am, edited 1 time in total.
 
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PixelFlight
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 10:21 am

Amiga500 wrote:
asdf wrote:
XRAYretired wrote:
Reports of shenanigans during the Lion Air investigation in relation to the installation of the AoA sensor. It pretty much has to either be incorrect calibration by the MRO (XTRA Aerospace) or incorrect installation that resulted in the ~22deg AoA offset and this might appear as an attempt to push focus on to the MRO but its a mightily confused write up.
https://theprint.in/world/fake-photos-t ... on/306372/
Ray


never says never again

but to install it wrong you would need to drill additional holes into the fuselage ..
into a brand new ship ...

that is not completely impossible but sounds pretty unlikely, doesent it?


Indeed. Designs are made foolproof with hole arrangement just-so to prevent this very thing from happening. If the holes for an AoA vane were at a constant PCD with constant circular pitch - does anyone really think that we'd never have heard of more incorrectly installed AoA vanes before now? Like... really?

Either way, its largely irrelevant to the problems with MCAS. If a bird hit the vane - then your in the same boat with MCAS.

Very true !
If fact, bird hit is to date the most plausible scenario of ET302 AoA failure. Proving how irrelevant that AoA install issue is to return the 737-8/9 MAX into service.
That said, findings about the maintenance of JT610 must be part of the final report even if there are not conclusive. Improvement must be done everywhere to ensure safety, including tracing of maintenance procedures.
: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

Wed Oct 16, 2019 11:07 am

aerolimani wrote:
Considering the number of other exceptions Boeing received from the FAA, especially as regards flight deck warning systems, the fact that Boeing did not get an exception from 14 CFR § 25.203 indicates to me that the aircraft has a serious issue, and that the plane is not safe without some means of meeting this regulation. The regulations exist to ensure safety.

Once again, all posters here should have a read through this page I link to below. I disagree with its initial description of MCAS, as I believe MCAS should be described as an anti-stall measure, but the rest of the information is good. http://www.b737.org.uk/mcas.htm


Please provide some evidence of the MAX being aerodynamically unsafe. Yes MCAS does help prevent stalls. We have yet to actually hear of anything that is real however on unaugmented Aerodynamic instability vs just speculation.

From the JATR report

Observation O3.11-A: STS inoperative wind-up turns were completed to 1.6g as part of the B737 MAX certification. STS inoperative stalls were completed to stick shaker + 1 second (approach to stall). The JATR team’s assessment is that the limited envelope for evaluation of characteristics for this failure condition does not support the absence of an envelope limitation in the associated non- normal procedure.

This is a good point - however then the next one is:

o Observation O3.11-B: STS inoperative wind-up turns, flown by Boeing during the course of the JATR, did not show any unsafe characteristics to approximately 2g.

Followed by:

Observation O3.18-B: Within the limited scope of the E-Cab session conducted by the JATR team, no unsafe conditions were noted with MCAS inoperative for high-speed wind-up turns.


Yes - not a real life test flight (except for Boeing's test flight) - but with all the noise that EASA is making and JATR is making about flying the max without augmentation you would think that has already happened or will happen.

Would the FAA really ignore that simple test? I would be stunned if that test has not already been flown.

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.

One last try on Anti-stall.

Car A has classic Anti-Lock brakes - as you get close to locking up the wheels the ABS controller modulates the Hydraulic Pressure to keep the brakes from locking. The equivalent of an Anti-stall device would be a stick pusher.

Car B has normal brakes and only has a system that keeps the pedal pressure linear throughout the pedal stroke (as normally as you slow you may not need to exert as much force to get the same deceleration) but you can still lock up the brakes.

Does Car B have anti-lock brakes? No

The 737.org site is right - MCAS is not Anti-stall (at least when properly operating) - it will not stop a stall from happening.

If the 737 is shown to unsafe unaugmented aerodynamic qualities then that is another issue - but so far there is no evidence vs just speculation.
 
FluidFlow
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 11:45 am

morrisond wrote:

Car A has classic Anti-Lock brakes - as you get close to locking up the wheels the ABS controller modulates the Hydraulic Pressure to keep the brakes from locking. The equivalent of an Anti-stall device would be a stick pusher.

Car B has normal brakes and only has a system that keeps the pedal pressure linear throughout the pedal stroke (as normally as you slow you may not need to exert as much force to get the same deceleration) but you can still lock up the brakes.

Does Car B have anti-lock brakes? No

The 737.org site is right - MCAS is not Anti-stall (at least when properly operating) - it will not stop a stall from happening.

If the 737 is shown to unsafe unaugmented aerodynamic qualities then that is another issue - but so far there is no evidence vs just speculation.


The classic Anti-Lock brakes actually do not prevent the wheels from locking up, but the moment the wheels do lock up it senses that the rotation rate is 0 and reduces the pressure on the breaks to release the wheel.

It is therefore an anti-lock system because it unlocks the wheels and not an lock-prevention system that actually reduces hydraulic pressure before the wheels lock up.
 
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 11:55 am

oschkosch wrote:
Oh dear, looks like middle to late 1st quarter 2020 now....at least according to Southwest!

https://www.cnbc.com/2019/10/14/boeing- ... s-say.html

The Boeing 737 Max won’t return to service at Southwest Airlines until February at the earliest, the union that represents the airline’s pilots said Monday

You do understand that union reps do not speak for the company, right?

The union's job is to represent the pilot's point of view, not the company's.

The expression of glee at the losses the delays represent is noted.
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 12:06 pm

BoeingVista wrote:
par13del wrote:
Ok correct me if I am wrong, but I was under the impression that the JTAR group was put together to look at certification issues in general, it was not to study and make recommendations necessary to unground the MAX.

I think that this is correct.

Thats the way they approached their report anyway, many recommendations about certification in general which we have to assume the individual authorities believe need enacting, so if FAA ignores them and ploughs on regardless these authorities seem very unlikely to sign off on FAA certifications in future. Obviously this is a major hazzard to 777x as none, zero are going to be flying exclusively in North America.

Yes, as JATR was being set up FAA was focused on making the report focus on future certifications. If you prepare the ground you control the battle. Yet it never was realistic to charge the international regulators with such a mandate. They had the MAX crisis staring them in the face, it was impossible for them to not use MAX as an example of what not to do going forward. As a member who doesn't seem to post anymore was telling us, they were having separate meetings in Montreal to frame their response. As noted above the main weapon in their arsenal is the threat to not certify future designs, a potent weapon. It will be interesting to see how FAA navigates these rocky waters going forward.
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morrisond
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 12:37 pm

FluidFlow wrote:
morrisond wrote:

Car A has classic Anti-Lock brakes - as you get close to locking up the wheels the ABS controller modulates the Hydraulic Pressure to keep the brakes from locking. The equivalent of an Anti-stall device would be a stick pusher.

Car B has normal brakes and only has a system that keeps the pedal pressure linear throughout the pedal stroke (as normally as you slow you may not need to exert as much force to get the same deceleration) but you can still lock up the brakes.

Does Car B have anti-lock brakes? No

The 737.org site is right - MCAS is not Anti-stall (at least when properly operating) - it will not stop a stall from happening.

If the 737 is shown to unsafe unaugmented aerodynamic qualities then that is another issue - but so far there is no evidence vs just speculation.


The classic Anti-Lock brakes actually do not prevent the wheels from locking up, but the moment the wheels do lock up it senses that the rotation rate is 0 and reduces the pressure on the breaks to release the wheel.

It is therefore an anti-lock system because it unlocks the wheels and not an lock-prevention system that actually reduces hydraulic pressure before the wheels lock up.


Not that it matters as my point was Car B can't prevent the wheels from locking at all - but here is a technical description of how ABS works from Howstuffworks.com:

"The controller monitors the speed sensors at all times. It is looking for decelerations in the wheel that are out of the ordinary. Right before a wheel locks up, it will experience a rapid deceleration. If left unchecked, the wheel would stop much more quickly than any car could. It might take a car five seconds to stop from 60 mph (96.6 kph) under ideal conditions, but a wheel that locks up could stop spinning in less than a second.

The ABS controller knows that such a rapid deceleration is impossible, so it reduces the pressure to that brake until it sees an acceleration, then it increases the pressure until it sees the deceleration again. It can do this very quickly, before the tire can actually significantly change speed. The result is that the tire slows down at the same rate as the car, with the brakes keeping the tires very near the point at which they will start to lock up. This gives the system maximum braking power.

When the ABS system is in operation you will feel a pulsing in the brake pedal; this comes from the rapid opening and closing of the valves. Some ABS systems can cycle up to 15 times per second."
 
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 12:44 pm

ODwyerPW wrote:
rheinwaldner wrote:
morrisond wrote:
MCAS v 1.0 was not intended to be an Anti-stall - it was due to it's piss poor design that unfortunately it acted like one.

That is why MCAS v2.0 is not required to be one either.

A stick pusher would be an anti-stall system. It was not required for certification.

There is no anti-stall on the NG or MAX. All the systems were there to provide warnings for the pilots.

There is nothing on an 737 NG or MAX to keep the pilot from intentionally putting it into a stall. None of the other systems will prevent a stall. You can pull right through them.

MCAS was required to meet the FAR's for stall characteristics to help the pilot identify they were approaching a stall by not letting the stick force fall below a certain value.

I don't know how more plainly it can be said.

If you were flying the MAX in manual mode and were maintaining a certain angle of attack per the instruments or outside visual reference and MCAS fired once - you would feel the elevator getting a little heavier. You wouldn't let the nose drop by not counteracting that force unless you were being completely inattentive to what the aircraft was supposed to be doing - which is your job as you are flying an airplane in manual mode.

What else do you expect the pilot to be doing if they are trying to fly at way higher than normal AOA's? Going for a coffee or texting on there phone and not paying attention to what the aircraft is doing?


Why are you reversing the truth? Not many sentences in this huge post are correct. The red ones are wrong, the yellow ones are contradicting and the green ones are not relevant to judge whether MCAS is to prevent stalls.

etc... etc....


Wow, you all take arguing on the internet pretty serious.

What ever happens when and if the MAX returns to service, I just hope pilots are told everything they need to know about MCAS. That way we can get back to arguing about other stuff like if the MAX9ER will be more effective in sales campaigns against the A321 than the 900, 900ER, MAX9 or MAX10

No, I just don't have enough time to not describe very plausibly what I think. My statements on the other hand are 100% on topic, while the stuff you mention is 100% off topic in this thread.

And b.t.w. Boeings business case for the MAX depends on not having to tell the pilots a lot about MCAS. In other words, the business case breaks if the pilots do require extra training to handle MCAS.
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morrisond
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 1:06 pm

rheinwaldner wrote:
ODwyerPW wrote:
rheinwaldner wrote:

Why are you reversing the truth? Not many sentences in this huge post are correct. The red ones are wrong, the yellow ones are contradicting and the green ones are not relevant to judge whether MCAS is to prevent stalls.

etc... etc....


Wow, you all take arguing on the internet pretty serious.

What ever happens when and if the MAX returns to service, I just hope pilots are told everything they need to know about MCAS. That way we can get back to arguing about other stuff like if the MAX9ER will be more effective in sales campaigns against the A321 than the 900, 900ER, MAX9 or MAX10

No, I just don't have enough time to not describe very plausibly what I think. My statements on the other hand are 100% on topic, while the stuff you mention is 100% off topic in this thread.

And b.t.w. Boeings business case for the MAX depends on not having to tell the pilots a lot about MCAS. In other words, the business case breaks if the pilots do require extra training to handle MCAS.


You are implying that the MAX has some unknown dangerous aerodynamic instability that Boeing is trying to hide and that needs to be corrected before Return to Service and that they were trying to hide it with MCAS - how is that not relevant to the discussion if I refute that position?

You may be right - but so far we have not seen anything other than speculation - other than the info from the JATR report I quoted above which seems to say that there is no problem.
 
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 1:33 pm

planecane wrote:
DenverTed wrote:
If the pitch stability varies with the trim setting, then MCAS is there to move it to the nose down configuration that is stable. Having it activate beyond the range for which it is needed was a severe engineering oversight.

Where have you seen that pitch stability varies with trim setting? What I've read, it varies with AoA. It activated because it thought it was in the range where it was needed due to the failed sensor.


Every n-thousand posts, it's worth reminding everybody that we don't know what is really happening from an aerodynamic viewpoint. We have no wind tunnel test results, we have no CFD predictions, we have no MCAS-off flight test data. This type of information is a closely guarded secret in the best of times. If you go to aerospace technical conferences, at best you get normalized plots, with y-axis from 0 to 1 or no scales at all. For a controversial case like the MAX, we'll find even less. Some of this information can be reconstructed more or less easily if you have a MAX available to test fly, or at least to measure (for the CFD predictions and wind tunnel testing). So all discussions on linearity vs nonlinearity, stability vs instability, and so on, are at best informed guesses, but not much more for now.

Among the elephants in the room, there is the post-stall behavior, and we don't know if it a small toy elephant or a thousand pound beast. If the MAX stalls more or less like the NG, it's the former. If it stall very differently, it's the latter. The bits and pieces of information that we can reconstruct point to a complex nacelle/pylon/leading edge coupled aerodynamic interaction, different at low speed vs high-speed wind up turns (a NYT article talked about "transonic effects"). The danger is that, if the MAX does get into a stall, recovery could be much harder than for an NG.

We don't have to get into conspiracy theory territory -- an hour of MCAS-off flight testing can give a very good idea of the size of the elephant. On the other hand, to trust the simulator tests, one would have to assess the simulator fidelity, and specifically what's in the math model driving the simulator. If there is shock-induced boundary layer separation (is this what the NYT meant?) I'd love to know how they model it in the sim. I suspect they don't.
 
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 1:41 pm

art wrote:
Anyone got amy info regarding rthe ungrounding of the MAX?


At this point I’m actually wondering if “never” is the answer. This is taking an absurdly long time and we are receiving little concrete information. Lots of rumors and innuendo but few facts.
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 2:41 pm

saab2000 wrote:
art wrote:
Anyone got amy info regarding rthe ungrounding of the MAX?


At this point I’m actually wondering if “never” is the answer. This is taking an absurdly long time and we are receiving little concrete information. Lots of rumors and innuendo but few facts.

We have the WSJ report ( https://www.wsj.com/articles/friction-b ... 1570527001 ) saying EASA is requesting more test points to prove the new multi sensor comparison function, and Boeing saying EASA is not giving enough clarity on what they want. I suppose it falls into the rumour / innuendo category but WSJ is usually a reliable source of rumors and innuendo, and neither Boeing or EASA has issued a denial.
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 2:43 pm

Always look on the bright side of Life!
 
Amiga500
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 2:56 pm

AVENSAB727 wrote:
https://www.seattletimes.com/business/questions-raised-about-photos-used-as-evidence-of-repairs-in-lion-air-737-max-crash-investigation/

https://www.chicagotribune.com/business ... story.html

Interesting articles, I wonder if this could lead to something.


As I've pointed out elsewhere, its both misleading and irrelevant.

Misleading in that the bolt group arrangement means its impossible to install the vane in such a way as to provide an erroneous AoA - exception being failure of the electronics behind the vane.

Irrelevant in that a bird striking the vane would produce the same MCAS issues.
 
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par13del
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 3:01 pm

Revelation wrote:
BoeingVista wrote:
par13del wrote:
Ok correct me if I am wrong, but I was under the impression that the JTAR group was put together to look at certification issues in general, it was not to study and make recommendations necessary to unground the MAX.

I think that this is correct.

Thats the way they approached their report anyway, many recommendations about certification in general which we have to assume the individual authorities believe need enacting, so if FAA ignores them and ploughs on regardless these authorities seem very unlikely to sign off on FAA certifications in future. Obviously this is a major hazzard to 777x as none, zero are going to be flying exclusively in North America.

Yes, as JATR was being set up FAA was focused on making the report focus on future certifications. If you prepare the ground you control the battle. Yet it never was realistic to charge the international regulators with such a mandate. They had the MAX crisis staring them in the face, it was impossible for them to not use MAX as an example of what not to do going forward. As a member who doesn't seem to post anymore was telling us, they were having separate meetings in Montreal to frame their response. As noted above the main weapon in their arsenal is the threat to not certify future designs, a potent weapon. It will be interesting to see how FAA navigates these rocky waters going forward.

My concern here is that we have all our A.Net experts who see the time frame of 1 year for accident investigations to be acceptable, but here we have a group set up to focus on Certification and Regulation of OEM's who produce a/c and they have completed their report in just a couple months? How deep did they delve between the myriad of complex relationships that exist to provide solid or realistic solutions to actual and or perceived issues, were they barred from commenting on the role of politicians, how about the teaching environment in producing enough qualified individuals to allow the government and private sector to be properly staffed, or was their mandate just technical?.
I would have thought that this body was going to produce recommendations sometime next year.
 
DenverTed
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 3:16 pm

IADFCO wrote:
planecane wrote:
DenverTed wrote:
If the pitch stability varies with the trim setting, then MCAS is there to move it to the nose down configuration that is stable. Having it activate beyond the range for which it is needed was a severe engineering oversight.

Where have you seen that pitch stability varies with trim setting? What I've read, it varies with AoA. It activated because it thought it was in the range where it was needed due to the failed sensor.


Every n-thousand posts, it's worth reminding everybody that we don't know what is really happening from an aerodynamic viewpoint. We have no wind tunnel test results, we have no CFD predictions, we have no MCAS-off flight test data. This type of information is a closely guarded secret in the best of times. If you go to aerospace technical conferences, at best you get normalized plots, with y-axis from 0 to 1 or no scales at all. For a controversial case like the MAX, we'll find even less. Some of this information can be reconstructed more or less easily if you have a MAX available to test fly, or at least to measure (for the CFD predictions and wind tunnel testing). So all discussions on linearity vs nonlinearity, stability vs instability, and so on, are at best informed guesses, but not much more for now.

Among the elephants in the room, there is the post-stall behavior, and we don't know if it a small toy elephant or a thousand pound beast. If the MAX stalls more or less like the NG, it's the former. If it stall very differently, it's the latter. The bits and pieces of information that we can reconstruct point to a complex nacelle/pylon/leading edge coupled aerodynamic interaction, different at low speed vs high-speed wind up turns (a NYT article talked about "transonic effects"). The danger is that, if the MAX does get into a stall, recovery could be much harder than for an NG.

We don't have to get into conspiracy theory territory -- an hour of MCAS-off flight testing can give a very good idea of the size of the elephant. On the other hand, to trust the simulator tests, one would have to assess the simulator fidelity, and specifically what's in the math model driving the simulator. If there is shock-induced boundary layer separation (is this what the NYT meant?) I'd love to know how they model it in the sim. I suspect they don't.

What is the trim setting in the low speed case? I assume the trim is set at a high nose up angle. In the high speed turn case, maybe the trim is near level, but the elevator is nose up. So the stability graphs for these are two different configurations. Any configuration of elevator and trim before stall has to reach a stable configuration angle and not continue to rotate into stall. I guess my question in the high speed case is if MCAS needs to trim past level to nose down trim (which I think there is only about 3 degrees of) to offset the upward pitch of the elevators and engines?
 
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 3:18 pm

par13del wrote:
Revelation wrote:
BoeingVista wrote:
I think that this is correct.

Thats the way they approached their report anyway, many recommendations about certification in general which we have to assume the individual authorities believe need enacting, so if FAA ignores them and ploughs on regardless these authorities seem very unlikely to sign off on FAA certifications in future. Obviously this is a major hazzard to 777x as none, zero are going to be flying exclusively in North America.

Yes, as JATR was being set up FAA was focused on making the report focus on future certifications. If you prepare the ground you control the battle. Yet it never was realistic to charge the international regulators with such a mandate. They had the MAX crisis staring them in the face, it was impossible for them to not use MAX as an example of what not to do going forward. As a member who doesn't seem to post anymore was telling us, they were having separate meetings in Montreal to frame their response. As noted above the main weapon in their arsenal is the threat to not certify future designs, a potent weapon. It will be interesting to see how FAA navigates these rocky waters going forward.

My concern here is that we have all our A.Net experts who see the time frame of 1 year for accident investigations to be acceptable, but here we have a group set up to focus on Certification and Regulation of OEM's who produce a/c and they have completed their report in just a couple months? How deep did they delve between the myriad of complex relationships that exist to provide solid or realistic solutions to actual and or perceived issues, were they barred from commenting on the role of politicians, how about the teaching environment in producing enough qualified individuals to allow the government and private sector to be properly staffed, or was their mandate just technical?.
I would have thought that this body was going to produce recommendations sometime next year.

The JATR almost only worked on the basis of certification documents already available, to find how it could be improved, this is why there where able to provides a review in a relative small time frame.
This is completely different of the crash investigation that have to collect information, and that can be very hard, to find how likely each scenarios can explain the actual crash.
: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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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 3:20 pm

morrisond wrote:
Answer this one simple question - will MCAS stop a stall from happening? Yes or no. If no then it is not anti-stall. If yes then it is Anti-stall.

Properly working it is no different than a stick shaker. It will not stop a stall from happening.


The level of wilful ignorance is, honestly, reaching intolerable levels. MCAS v1 would, indeed, stop the aircraft from stalling by virtue of continually dialling in large amounts of ND trim via the horizontal stabiliser. Aircraft stall when they exceed a certain AoA value, depending on speed. MCAS made sure that never happened: It's an anti-stall system.

As for your second remark, that is so far off the charts it beggars belief. The stick shaker has absolutely zero impact on the movement of any flight controls, in stark contrast to MCAS v1 which, even working perfectly as intended, had full authority over the most powerful element of pitch control. If that's the same to you, taking this debate any further would be the ultimate exercise in futility.
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ubeema
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 3:22 pm

par13del wrote:
My concern here is that we have all our A.Net experts who see the time frame of 1 year for accident investigations to be acceptable, but here we have a group set up to focus on Certification and Regulation of OEM's who produce a/c and they have completed their report in just a couple months? How deep did they delve between the myriad of complex relationships that exist to provide solid or realistic solutions to actual and or perceived issues, were they barred from commenting on the role of politicians, how about the teaching environment in producing enough qualified individuals to allow the government and private sector to be properly staffed, or was their mandate just technical?.
I would have thought that this body was going to produce recommendations sometime next year.

12 - 18 months is the expected timeline for accident investigations.

Re:JATR review. FAA Chartered the group a pretty define scope. See below
Image
 
frmrCapCadet
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 3:22 pm

One last try on Anti-stall.

Car A has classic Anti-Lock brakes - as you get close to locking up the wheels the ABS controller modulates the Hydraulic Pressure to keep the brakes from locking. The equivalent of an Anti-stall device would be a stick pusher.

Car B has normal brakes and only has a system that keeps the pedal pressure linear throughout the pedal stroke (as normally as you slow you may not need to exert as much force to get the same deceleration) but you can still lock up the brakes.

Does Car B have anti-lock brakes? No


And a bit of a parallel to when automation works and when it does not. My 1995 era Subaru was AWD and ABS. Coming home involved a major 110 degree turn to the right into the driveway and prudently driving about 5mph. The drive way was positioned at the middle of the 50 mph highway turn to the left. (advisory to slow to 35 mph) There were several inches of snow on the steeply banked 50 mph road. car would not do it, even after 2 or 3 attempts, I had to back up and speed up a little. There was a button, as I remember by my knee which might have helped. The ABS would not power the slipping wheels. Now with traction control and ABS you can and need to turn it off at very slow speeds in the snow to do this sort of driveway turns and backing. Extended discussion of this not appropriate to this thread.
Last edited by frmrCapCadet on Wed Oct 16, 2019 3:29 pm, edited 1 time in total.
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Erebus
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 3:29 pm

Amiga500 wrote:
As I've pointed out elsewhere, its both misleading and irrelevant.

Misleading in that the bolt group arrangement means its impossible to install the vane in such a way as to provide an erroneous AoA - exception being failure of the electronics behind the vane.

Irrelevant in that a bird striking the vane would produce the same MCAS issues.


Aircraft were not "airworthy", well before any of them were delivered to airline customers. How: none of them are flying right now and await fixes to get back in the air. No reason to keep an "airworthy" aircraft from flying!
 
morrisond
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 3:37 pm

B777LRF wrote:
morrisond wrote:
Answer this one simple question - will MCAS stop a stall from happening? Yes or no. If no then it is not anti-stall. If yes then it is Anti-stall.

Properly working it is no different than a stick shaker. It will not stop a stall from happening.


The level of wilful ignorance is, honestly, reaching intolerable levels. MCAS v1 would, indeed, stop the aircraft from stalling by virtue of continually dialling in large amounts of ND trim via the horizontal stabiliser. Aircraft stall when they exceed a certain AoA value, depending on speed. MCAS made sure that never happened: It's an anti-stall system.

As for your second remark, that is so far off the charts it beggars belief. The stick shaker has absolutely zero impact on the movement of any flight controls, in stark contrast to MCAS v1 which, even working perfectly as intended, had full authority over the most powerful element of pitch control. If that's the same to you, taking this debate any further would be the ultimate exercise in futility.


That is why I said Properly working. V1 Should never had had that authority and it appears V2 does not at all.

Both were not intended to change the flight path - the intent was just to make the elevator heavier.

It's just what 737.org says - MCAS V.1 wasn't intended to be anti-stall but due to piss poor design it effectively was. Unintended consequences.
 
rheinwaldner
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 3:41 pm

morrisond wrote:
You are implying that the MAX has some unknown dangerous aerodynamic instability that Boeing is trying to hide and that needs to be corrected before Return to Service and that they were trying to hide it with MCAS - how is that not relevant to the discussion if I refute that position?

I have not said anything close to that IMO and this is also not my opinion. How did you come to this conclusion?

morrisond wrote:
Please provide some evidence of the MAX being aerodynamically unsafe. Yes MCAS does help prevent stalls. We have yet to actually hear of anything that is real however on unaugmented Aerodynamic instability vs just speculation.

Define aerodynamically unsafe.

The stick force issue is aerodynamically induced and requires MCAS in order that the MAX has compliant stall characteristics and becomes certifyable.


morrisond wrote:
One last try on Anti-stall.

Car A has classic Anti-Lock brakes - as you get close to locking up the wheels the ABS controller modulates the Hydraulic Pressure to keep the brakes from locking. The equivalent of an Anti-stall device would be a stick pusher.

Car B has normal brakes and only has a system that keeps the pedal pressure linear throughout the pedal stroke (as normally as you slow you may not need to exert as much force to get the same deceleration) but you can still lock up the brakes.

Does Car B have anti-lock brakes? No

The discussion is why MCAS was ultimately needed, isn't it?

So why are you no comparing two differently equiped cars, saying they are different? Sorry, I cant see any parallels to the discussion about why MCAS was needed. These two cars are simply built against two different sets of requirements, hence their capability is different.

morrisond wrote:
The 737.org site is right - MCAS is not Anti-stall (at least when properly operating) - it will not stop a stall from happening.

A anti stall system does not need to prevent a stall in all cases. How effective a system is in accomplishing its goals does not alter the reason why it exists.

b.t.w. in the brackets and in the detail descriptions 737.org absolutely says, that MCAS exists to comply with stall requirements.
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Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 3:45 pm

IADFCO wrote:
planecane wrote:
DenverTed wrote:
If the pitch stability varies with the trim setting, then MCAS is there to move it to the nose down configuration that is stable. Having it activate beyond the range for which it is needed was a severe engineering oversight.

Where have you seen that pitch stability varies with trim setting? What I've read, it varies with AoA. It activated because it thought it was in the range where it was needed due to the failed sensor.


Every n-thousand posts, it's worth reminding everybody that we don't know what is really happening from an aerodynamic viewpoint. We have no wind tunnel test results, we have no CFD predictions, we have no MCAS-off flight test data. This type of information is a closely guarded secret in the best of times. If you go to aerospace technical conferences, at best you get normalized plots, with y-axis from 0 to 1 or no scales at all. For a controversial case like the MAX, we'll find even less. Some of this information can be reconstructed more or less easily if you have a MAX available to test fly, or at least to measure (for the CFD predictions and wind tunnel testing). So all discussions on linearity vs nonlinearity, stability vs instability, and so on, are at best informed guesses, but not much more for now.

Among the elephants in the room, there is the post-stall behavior, and we don't know if it a small toy elephant or a thousand pound beast. If the MAX stalls more or less like the NG, it's the former. If it stall very differently, it's the latter. The bits and pieces of information that we can reconstruct point to a complex nacelle/pylon/leading edge coupled aerodynamic interaction, different at low speed vs high-speed wind up turns (a NYT article talked about "transonic effects"). The danger is that, if the MAX does get into a stall, recovery could be much harder than for an NG.

We don't have to get into conspiracy theory territory -- an hour of MCAS-off flight testing can give a very good idea of the size of the elephant. On the other hand, to trust the simulator tests, one would have to assess the simulator fidelity, and specifically what's in the math model driving the simulator. If there is shock-induced boundary layer separation (is this what the NYT meant?) I'd love to know how they model it in the sim. I suspect they don't.

And looks like Boeing is not very eager to create a precedent of technical data released into public domain, and even minimizes regulator access to data. While they may have some legitimate reasons behind such control, rebuild of trust is certainly not one of them.
And, as a reminder: this is not criminal process, it is up to manufacturer to prove things are safe - they are NOT assumed innocent until proven otherwise.
 
morrisond
Posts: 2663
Joined: Thu Jan 07, 2010 12:22 am

Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 3:53 pm

rheinwaldner wrote:
morrisond wrote:
You are implying that the MAX has some unknown dangerous aerodynamic instability that Boeing is trying to hide and that needs to be corrected before Return to Service and that they were trying to hide it with MCAS - how is that not relevant to the discussion if I refute that position?

I have not said anything close to that IMO and this is also not my opinion. How did you come to this conclusion?

morrisond wrote:
Please provide some evidence of the MAX being aerodynamically unsafe. Yes MCAS does help prevent stalls. We have yet to actually hear of anything that is real however on unaugmented Aerodynamic instability vs just speculation.

Define aerodynamically unsafe.

The stick force issue is aerodynamically induced and requires MCAS in order that the MAX has compliant stall characteristics and becomes certifyable.


morrisond wrote:
One last try on Anti-stall.

Car A has classic Anti-Lock brakes - as you get close to locking up the wheels the ABS controller modulates the Hydraulic Pressure to keep the brakes from locking. The equivalent of an Anti-stall device would be a stick pusher.

Car B has normal brakes and only has a system that keeps the pedal pressure linear throughout the pedal stroke (as normally as you slow you may not need to exert as much force to get the same deceleration) but you can still lock up the brakes.

Does Car B have anti-lock brakes? No

The discussion is why MCAS was ultimately needed, isn't it?

So why are you no comparing two differently equiped cars, saying they are different? Sorry, I cant see any parallels to the discussion about why MCAS was needed. These two cars are simply built against two different sets of requirements, hence their capability is different.

morrisond wrote:
The 737.org site is right - MCAS is not Anti-stall (at least when properly operating) - it will not stop a stall from happening.

A anti stall system does not need to prevent a stall in all cases. How effective a system is in accomplishing its goals does not alter the reason why it exists.

b.t.w. in the brackets and in the detail descriptions 737.org absolutely says, that MCAS exists to comply with stall requirements.


Sorry if I lumped you into the "What is Boeing hiding crowd".

Paradoxically - we have been arguing the same things - Yes MCAS was needed to meet the stick force requirements to meet the stall characteristics as defined by the regs. Totally agreed.

I've also been the one arguing that that combined with Stick Shaker, Stall warning horn and the frame buffeting MCAS should be all that's needed for a Pilot to know that a stall is approaching and that they should do something.

Others were arguing that the MAX needed a device beyond that as pilots would not be able to handle that situation (I was not - that should be enough for any pilot) and that the MAX shouldn't be allowed back into the air unless it had full protections of something like an full FBW design.

I'll stop now on this subject.
 
B777LRF
Posts: 2686
Joined: Sun Nov 02, 2008 4:23 am

Re: Boeing 737MAX Grounded Worldwide Q4 2019

Wed Oct 16, 2019 3:56 pm

par13del wrote:
My concern here is that we have all our A.Net experts who see the time frame of 1 year for accident investigations to be acceptable, but here we have a group set up to focus on Certification and Regulation of OEM's who produce a/c and they have completed their report in just a couple months? (.) I would have thought that this body was going to produce recommendations sometime next year.


Don't think your concern is directed at a valid point. There is a world of difference between investigation a fatal aircraft accident, which involves cooperation between multiple countries, OEMs, operators, ATM, etc, and doing what is essentially a very comprehensive audit of a know and well documented process.

In other words, the two doesn't compare.
Signature. You just read one.

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