DenverTed
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 4:20 pm

Is the problem specific to the MAX, or does it affect the NG as well? If it affects both, and safety comes first for the FAA, either this is problem is not a big deal for the MAX, or the NG should be grounded.
 
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BoeingVista
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 4:22 pm

planecane wrote:
BoeingVista wrote:
Revelation wrote:
It could be that the cost of accessing the 2nd AOA sensor is the straw breaking the camel's back. It may be that tuning the access rate of that and other sensors could be a fix. None of us know enough to say.



Its more likely that the issue is having only 2 rather than 3 sensors Boeing have had to add a whole bunch of processing logic to determine which one is good / bad (are they both bad?) and are doing this by comparing with other instruments / processes. This iterative process has to run often and is highest priority & time critical that needs to produce a data point as part of the control loop before trim is actioned. This data is also only good for a limited period of time so programmers face the problem of what to do if you don't get an answer in a prescribed time, do you wait, drop the data point, guess, use last data point etc, all of those choices have inferences. Late delivery, where data comes after the condition has changed could be worse than inaction i.e no trim change which is what we seem to have here.

The system designers have not budgeted any hardware resources for this additional high level process so chip could be crashing / shedding processes / locking up / lagging. If they are lucky its just sloppy coding but I doubt it, this is a can or worms.


Nothing in Boeing's official statements on the software update indicate that they are trying to figure out which sensor is the good one. Everything they said indicates that when the two sensors disagree by more than 5 degrees MCAS is disabled.


So one sensor reads 57 degrees and the other 60, we are all good here right? lets jack on some MCAS!!

Nah. You have to make more checks.
BV
 
planecane
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 4:30 pm

PW100 wrote:
OldAeroGuy wrote:
Interested wrote:
There was a report last week that Boeing safety analysis for Max relied on pilots being able to deal with MCAS within 3 seconds

Which at the time seemed incredibly ambitious and optimistic and risky to me for them to expect and plan for that?

Your post above is written in a way that kind of suggests that not being able to deal with stuff in seconds might not be considered a risk?


Both the FAA and EASA use 3 seconds as a standard pilot recognition time for a changing situation. See AC25-7C, pages 151 - 154. https://www.faa.gov/documentLibrary/med ... -7C%20.pdf

Boeing safety analyses use of 3 seconds is consistent with regulatory agency practice used for all Part 25 airplanes.


Is 3 seconds sufficient to recognize a runaway trim in a stand-alone failure scenario (leaving aside that usually other issues be present at the same time)?
If we look at MCAS, it has a 9 second cycle. Should pilots be expected to disable MCAS after only 3 seconds, or should they allow at least a full MCAS cyce, and take action at the next cycle (after 3 seconds)?
Leaving aside the question whether the intermittent behaviour of MCAS would be recognizable as runaway trim (prior to the accidents).


The expectation is/was that the pilots were expected to recognize a runaway stabilizer (caused by MCAS or otherwise) within 3 seconds and begin the NNC. That's why, to me, it has always been completely irrelevant that MCAS was intermittent. The big failure that was missed is that the same thing that would cause MCAS cause a runaway stabilizer ALSO caused other issues simultaneously. This factor is the reason that I believe the lack of documentation of MCAS and specific training played a huge factor. The training could have been part of the iPad course. Simple instructions that if there was uncommanded nose down trim that the runaway stabilizer NNC should be performed first, regardless of other issues would have gone a long way. The information should have been provided that other alerts (single side stick shaker, unreliable airspeed, etc.) would likely occur simultaneously but that responding to the runaway stabilizer should take priority. This should have been part of the training and the QRH.
 
planecane
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 4:36 pm

BoeingVista wrote:
planecane wrote:
BoeingVista wrote:

Its more likely that the issue is having only 2 rather than 3 sensors Boeing have had to add a whole bunch of processing logic to determine which one is good / bad (are they both bad?) and are doing this by comparing with other instruments / processes. This iterative process has to run often and is highest priority & time critical that needs to produce a data point as part of the control loop before trim is actioned. This data is also only good for a limited period of time so programmers face the problem of what to do if you don't get an answer in a prescribed time, do you wait, drop the data point, guess, use last data point etc, all of those choices have inferences. Late delivery, where data comes after the condition has changed could be worse than inaction i.e no trim change which is what we seem to have here.

The system designers have not budgeted any hardware resources for this additional high level process so chip could be crashing / shedding processes / locking up / lagging. If they are lucky its just sloppy coding but I doubt it, this is a can or worms.


Nothing in Boeing's official statements on the software update indicate that they are trying to figure out which sensor is the good one. Everything they said indicates that when the two sensors disagree by more than 5 degrees MCAS is disabled.


So one sensor reads 57 degrees and the other 60, we are all good here right? lets jack on some MCAS!!

Nah. You have to make more checks.


First, I can only assume that they have added limits so that if both sensors (which it would take now) read an impossible AoA, MCAS will not activate. But yes, hypothetically, if one reads 20 degrees and the other reads 17 degrees but the real AoA is 3 degrees, MCAS will activate. That's why they are adding limits to how much nose down trim it can command at a maximum and limiting it to only activating once per "event." They are also adding limits so that at any given airspeed the trim will not exceed a point where the pilots can counteract the nose down pitch with the control column.

But, no, they are not making any attempt to figure out which sensor is correct.
 
Agrajag
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 4:47 pm

Is the simulator they use different to the Max sims that have been bought by various airlines (but not necessarily delivered)? I thought they didnt replicate MCAS or the manual trip properly?
The plural of anecdote is anecdotes, not data.
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OldAeroGuy
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 4:59 pm

BoeingVista wrote:
So one sensor reads 57 degrees and the other 60, we are all good here right? lets jack on some MCAS!!

Nah. You have to make more checks.


I believe MCASv2.0 handles this by having only one cycle per event. If your case was present, MCASv2.0 would cycle once only as both vanes would be above the MCAS trigger AoA. The single MCAS nose down trim event would be handled via elevator and manual electric trim.

If both vanes stayed at your condition of 57 deg and 60 deg, MCASv2.0 would not re-arm and would be done for the flight. If one vane dropped below the MCASv2.0 trigger pointing the other stayed high, then the vane disagree would happen and MCASv2.0 would not re-arm for the flight.

Logic above is independent of the newly revised microprocessor issue.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
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BoeingVista
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 5:02 pm

planecane wrote:
BoeingVista wrote:
planecane wrote:

Nothing in Boeing's official statements on the software update indicate that they are trying to figure out which sensor is the good one. Everything they said indicates that when the two sensors disagree by more than 5 degrees MCAS is disabled.


So one sensor reads 57 degrees and the other 60, we are all good here right? lets jack on some MCAS!!

Nah. You have to make more checks.


First, I can only assume that they have added limits so that if both sensors (which it would take now) read an impossible AoA, MCAS will not activate. But yes, hypothetically, if one reads 20 degrees and the other reads 17 degrees but the real AoA is 3 degrees, MCAS will activate. That's why they are adding limits to how much nose down trim it can command at a maximum and limiting it to only activating once per "event." They are also adding limits so that at any given airspeed the trim will not exceed a point where the pilots can counteract the nose down pitch with the control column.

But, no, they are not making any attempt to figure out which sensor is correct.


I thought Boeing were going back to the original idea of sanity testing MCAS inputs, I don't see how Boeing can hope to pass certification standards if MCAS gets shut off with a disagree of 5.5 degrees and has less authority. Why was is it there in the first place if it can just be disregarded so easily?
BV
 
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BoeingVista
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 5:05 pm

Agrajag wrote:
Is the simulator they use different to the Max sims that have been bought by various airlines (but not necessarily delivered)? I thought they didnt replicate MCAS or the manual trip properly?


Yes. They are using an engineering validation tool rather than a simulator, it contains all the same computer hardware that a MAX does rather than it being simulated.
BV
 
OldAeroGuy
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 5:05 pm

Exeiowa wrote:
3 seconds might be how long it takes you to say "what the hell" when suddenly the plane does something you do not expect, let alone figure out which systems is the cause, and then turn it off.


Are you saying the certification agencies need to change their Part 25 flight test guidance material that underlies their certification requirements?

If so, it would call into question of all Part 25 airplanes in production currently.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
OldAeroGuy
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 5:16 pm

BoeingVista wrote:
I thought Boeing were going back to the original idea of sanity testing MCAS inputs, I don't see how Boeing can hope to pass certification standards if MCAS gets shut off with a disagree of 5.5 degrees and has less authority. Why was is it there in the first place if it can just be disregarded so easily?


There are many single failures that will result in a degraded airplane configuration that would not pass basic airplane certification requirements. These single failures are acceptable as long as continued safe flight and landing is possible.

For instance, failure of a leading edge slat actuator would prevent the airplane from achieving the certified flaps down handling characteristics and stall speeds. Use of NNC's for this failure allows continued safe flight and landing.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
planecane
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 5:37 pm

OldAeroGuy wrote:
BoeingVista wrote:
I thought Boeing were going back to the original idea of sanity testing MCAS inputs, I don't see how Boeing can hope to pass certification standards if MCAS gets shut off with a disagree of 5.5 degrees and has less authority. Why was is it there in the first place if it can just be disregarded so easily?


There are many single failures that will result in a degraded airplane configuration that would not pass basic airplane certification requirements. These single failures are acceptable as long as continued safe flight and landing is possible.

For instance, failure of a leading edge slat actuator would prevent the airplane from achieving the certified flaps down handling characteristics and stall speeds. Use of NNC's for this failure allows continued safe flight and landing.


Just to add to your response, MCAS is needed to ensure the required stick force gradient during certain extreme maneuvers in normal operation. When there is an AoA disagree, that becomes a non-normal situation and there will be a non-normal checklist to follow. That checklist will advise what part of the flight envelope to avoid and will likely inform the pilot what they will experience (reduced stick force gradient) if they enter the restricted part of the envelope.

Executing the NNC will allow for continued safe flight and landing in a non-normal condition. A 737 can't be certified with only one engine. That doesn't mean that it can't continue to fly and land safely with degraded performance on one engine. It's the same concept.
 
Exeiowa
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 5:43 pm

OldAeroGuy wrote:
Exeiowa wrote:
3 seconds might be how long it takes you to say "what the hell" when suddenly the plane does something you do not expect, let alone figure out which systems is the cause, and then turn it off.


Are you saying the certification agencies need to change their Part 25 flight test guidance material that underlies their certification requirements?

If so, it would call into question of all Part 25 airplanes in production currently.



3 seconds might be long enough to recognize and counteract something you have been specifically taught how to recognize and react to. Maybe not something which can be caused by multiple different types of failures or caused by something unknown. (to you).
 
planecane
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 5:47 pm

Exeiowa wrote:
OldAeroGuy wrote:
Exeiowa wrote:
3 seconds might be how long it takes you to say "what the hell" when suddenly the plane does something you do not expect, let alone figure out which systems is the cause, and then turn it off.


Are you saying the certification agencies need to change their Part 25 flight test guidance material that underlies their certification requirements?

If so, it would call into question of all Part 25 airplanes in production currently.



3 seconds might be long enough to recognize and counteract something you have been specifically taught how to recognize and react to. Maybe not something which can be caused by multiple different types of failures or caused by something unknown. (to you).


It doesn't matter what the cause is. The training is to recognize and react to the symptom of the failure. If there is a runaway stabilizer it doesn't matter if it was caused by MCAS or a flying unicorn landing on the horizontal stabilizer.

No pilot would ever be able to quickly respond to anything if they needed to know what caused the failure.
 
Vladex
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 5:50 pm

AeroplaneFreak wrote:
oschkosch wrote:
I wonder how much of the max backlog will actually ever be produced and/or delivered?


In my opinion which of course is meaningless I would guess around 80% of the backlog will be produced plus of course there will be many more orders in the coming years.

The people who think that MAX won't fly commercially again or that only a couple of hundred will ever be produced or that people will refuse to fly on them, they are living on another planet.

People have to accept that these issues will be fixed and the MAX will return to service. To say that the MAX is a failure or flop at this moment in time is completely irrational. We are less than three years after EIS and in my opinion judgement on aircraft success shouldn't be made until at least 10 years after EIS.

Yes there will plenty of media coverage of people refusing to fly it when it returns to service but this is nothing new. We saw it with the A380 and B787 when they had their respective incidents all be it those incidents didn't reach the level of the MAX but they came close.

Like it or not the flying public forgets very quickly and over 90% of the public barely know what type of plane they are flying and I would wager 99% of the public couldn't tell the difference between a NG and MAX 737.

Also let's not forget that Boeing will be offering some pretty amazing deals to airlines over the coming years on MAX frames so don't expect the line to shut down anytime soon.

I am not defending what Boeing did in anyway, I am just pointing out the most likely outcome.


Airplanes are not smartphones where they can come out with a new one after a few month or a year. Consider Samsung Note 7 which was a considerable loss for Samsung but they came better next year like nothing happened. That's not at all case with airplanes. Today, people can look up an airplane so airplane types can hardly be hidden.

Boeing was offering very sweet deals which is the only reason why MAX sold anything considering that NEO is better in every way possible. And that is the problem, deal making works only for so long before the value goes to negative which is where MAX is now.
 
XRAYretired
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 5:52 pm

PW100 wrote:
OldAeroGuy wrote:
Interested wrote:
There was a report last week that Boeing safety analysis for Max relied on pilots being able to deal with MCAS within 3 seconds

Which at the time seemed incredibly ambitious and optimistic and risky to me for them to expect and plan for that?

Your post above is written in a way that kind of suggests that not being able to deal with stuff in seconds might not be considered a risk?


Both the FAA and EASA use 3 seconds as a standard pilot recognition time for a changing situation. See AC25-7C, pages 151 - 154. https://www.faa.gov/documentLibrary/med ... -7C%20.pdf

Boeing safety analyses use of 3 seconds is consistent with regulatory agency practice used for all Part 25 airplanes.


Is 3 seconds sufficient to recognize a runaway trim in a stand-alone failure scenario (leaving aside that usually other issues be present at the same time)?
If we look at MCAS, it has a 9 second cycle. Should pilots be expected to disable MCAS after only 3 seconds, or should they allow at least a full MCAS cyce, and take action at the next cycle (after 3 seconds)?
Leaving aside the question whether the intermittent behaviour of MCAS would be recognizable as runaway trim (prior to the accidents).

As I read it, the 3 seconds is about control response to an upset, e.g. pulling the stick back and getting a relevant response when the nose drops unexpectedly, within 3 seconds. It has nothing to do or say about identifying an airframe or system cause of the upset in the first place or doing something about it.

I think the report, assuming correct, just tends to confirm that the safety analysis did not adequately identify AOA Sensor Failed High and/or the potential effects of single AOA sensor failed high and therefore demonstrate that the design solution was not acceptable. Consequently, any testing, validation and certification would have tested it either. QED.

Ray
 
XRAYretired
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 6:06 pm

planecane wrote:
PW100 wrote:
OldAeroGuy wrote:

Both the FAA and EASA use 3 seconds as a standard pilot recognition time for a changing situation. See AC25-7C, pages 151 - 154. https://www.faa.gov/documentLibrary/med ... -7C%20.pdf

Boeing safety analyses use of 3 seconds is consistent with regulatory agency practice used for all Part 25 airplanes.


Is 3 seconds sufficient to recognize a runaway trim in a stand-alone failure scenario (leaving aside that usually other issues be present at the same time)?
If we look at MCAS, it has a 9 second cycle. Should pilots be expected to disable MCAS after only 3 seconds, or should they allow at least a full MCAS cyce, and take action at the next cycle (after 3 seconds)?
Leaving aside the question whether the intermittent behaviour of MCAS would be recognizable as runaway trim (prior to the accidents).


The expectation is/was that the pilots were expected to recognize a runaway stabilizer (caused by MCAS or otherwise) within 3 seconds and begin the NNC. That's why, to me, it has always been completely irrelevant that MCAS was intermittent. The big failure that was missed is that the same thing that would cause MCAS cause a runaway stabilizer ALSO caused other issues simultaneously. This factor is the reason that I believe the lack of documentation of MCAS and specific training played a huge factor. The training could have been part of the iPad course. Simple instructions that if there was uncommanded nose down trim that the runaway stabilizer NNC should be performed first, regardless of other issues would have gone a long way. The information should have been provided that other alerts (single side stick shaker, unreliable airspeed, etc.) would likely occur simultaneously but that responding to the runaway stabilizer should take priority. This should have been part of the training and the QRH.

I know you are desparte to latch on to anything to justify your oft stated position, but this not it either. 3 seconds is the time for control repsponse not identification of runaway stabliser. Knocks the rest into a cocked hat again I'm afraid.

Just imagine for a moment spending a few seconds finding the QRH which then tells you to repond within 3 seconds. No it doesnt, nor does the EID because it is ludicrous.

Ray
 
OldAeroGuy
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 6:07 pm

XRAYretired wrote:
As I read it, the 3 seconds is about control response to an upset, e.g. pulling the stick back and getting a relevant response when the nose drops unexpectedly, within 3 seconds. It has nothing to do or say about identifying an airframe or system cause of the upset in the first place or doing something about it.
Ray


An upset is an upset, independent of being caused by a gust or a stab trim runaway.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
XRAYretired
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 6:12 pm

BoeingVista wrote:
planecane wrote:
BoeingVista wrote:

Its more likely that the issue is having only 2 rather than 3 sensors Boeing have had to add a whole bunch of processing logic to determine which one is good / bad (are they both bad?) and are doing this by comparing with other instruments / processes. This iterative process has to run often and is highest priority & time critical that needs to produce a data point as part of the control loop before trim is actioned. This data is also only good for a limited period of time so programmers face the problem of what to do if you don't get an answer in a prescribed time, do you wait, drop the data point, guess, use last data point etc, all of those choices have inferences. Late delivery, where data comes after the condition has changed could be worse than inaction i.e no trim change which is what we seem to have here.

The system designers have not budgeted any hardware resources for this additional high level process so chip could be crashing / shedding processes / locking up / lagging. If they are lucky its just sloppy coding but I doubt it, this is a can or worms.


Nothing in Boeing's official statements on the software update indicate that they are trying to figure out which sensor is the good one. Everything they said indicates that when the two sensors disagree by more than 5 degrees MCAS is disabled.


So one sensor reads 57 degrees and the other 60, we are all good here right? lets jack on some MCAS!!

Nah. You have to make more checks.

Try reading the statements on the V2.0 changes you will find that if both sensors fail high simultaneously within 5.5 degrees of each other, MCAS will initiate for one cycle only etc. This is deemed acceptable by just about everyone.


Ray
 
OldAeroGuy
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 6:13 pm

XRAYretired wrote:
Just imagine for a moment spending a few seconds finding the QRH which then tells you to repond within 3 seconds. No it doesnt, nor does the EID because it is ludicrous.

Ray


No need to find the QRH as the response to a Stab Trim Runaway is a memory item, as stated many times on this thread..
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
LDRA
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 6:19 pm

OldAeroGuy wrote:
XRAYretired wrote:
As I read it, the 3 seconds is about control response to an upset, e.g. pulling the stick back and getting a relevant response when the nose drops unexpectedly, within 3 seconds. It has nothing to do or say about identifying an airframe or system cause of the upset in the first place or doing something about it.
Ray


An upset is an upset, independent of being caused by a gust or a stab trim runaway.

Difference is gust requires no NNC, whereas trim runaway requires action to be executed within short time frame
 
XRAYretired
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 6:20 pm

OldAeroGuy wrote:
XRAYretired wrote:
As I read it, the 3 seconds is about control response to an upset, e.g. pulling the stick back and getting a relevant response when the nose drops unexpectedly, within 3 seconds. It has nothing to do or say about identifying an airframe or system cause of the upset in the first place or doing something about it.
Ray


An upset is an upset, independent of being caused by a gust or a stab trim runaway.

I don't disagree, just providing a 'for instance' relevant to the subject.

Ray
 
XRAYretired
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 6:23 pm

OldAeroGuy wrote:
XRAYretired wrote:
Just imagine for a moment spending a few seconds finding the QRH which then tells you to repond within 3 seconds. No it doesnt, nor does the EID because it is ludicrous.

Ray


No need to find the QRH as the response to a Stab Trim Runaway is a memory item, as stated many times on this thread..

Just a 'for instance' to stress the point. Sorry it upset you.

Ray
 
Cdydatzigs
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 6:36 pm

Does WN use the MAX between SAN and EWR? I have a trip planned the second weekend of October and am curious if it might be on the chopping block if the grounding continues further.
 
OldAeroGuy
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 6:45 pm

XRAYretired wrote:
OldAeroGuy wrote:
XRAYretired wrote:
Just imagine for a moment spending a few seconds finding the QRH which then tells you to repond within 3 seconds. No it doesnt, nor does the EID because it is ludicrous.

Ray


No need to find the QRH as the response to a Stab Trim Runaway is a memory item, as stated many times on this thread..

Just a 'for instance' to stress the point. Sorry it upset you.

Ray


Just making an effort to see that the statements made here are accurate. Inaccurate ones don't help the discussion.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
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aerolimani
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 6:46 pm

XRAYretired wrote:
PW100 wrote:
OldAeroGuy wrote:

Both the FAA and EASA use 3 seconds as a standard pilot recognition time for a changing situation. See AC25-7C, pages 151 - 154. https://www.faa.gov/documentLibrary/med ... -7C%20.pdf

Boeing safety analyses use of 3 seconds is consistent with regulatory agency practice used for all Part 25 airplanes.


Is 3 seconds sufficient to recognize a runaway trim in a stand-alone failure scenario (leaving aside that usually other issues be present at the same time)?
If we look at MCAS, it has a 9 second cycle. Should pilots be expected to disable MCAS after only 3 seconds, or should they allow at least a full MCAS cyce, and take action at the next cycle (after 3 seconds)?
Leaving aside the question whether the intermittent behaviour of MCAS would be recognizable as runaway trim (prior to the accidents).

As I read it, the 3 seconds is about control response to an upset, e.g. pulling the stick back and getting a relevant response when the nose drops unexpectedly, within 3 seconds. It has nothing to do or say about identifying an airframe or system cause of the upset in the first place or doing something about it.

I think the report, assuming correct, just tends to confirm that the safety analysis did not adequately identify AOA Sensor Failed High and/or the potential effects of single AOA sensor failed high and therefore demonstrate that the design solution was not acceptable. Consequently, any testing, validation and certification would have tested it either. QED.

Ray

While reading technical documents is not my forté, I also did not find where this document suggests anything about requiring a 3-second reaction time from pilots. As far as I can tell, the 3-second references in this Part 25 document are merely about defining how tests ought to be conducted.

Searching around a bit, there is some FAA documentation around the TCAS system where pilots response is expected to be around three seconds. That, however, is a totally different situation. TCAS gives a specific aural and visual instruction; no analysis required. On the other hand, detecting a runaway stabilizer is is an analytical task. For a system that normally (and frequently) moves autonomously, three seconds is a pretty small window, especially when many other distracting events are occurring simultaneously.

I'd like to know where this three second concept comes from, in relation to recognizing a runaway stab situation. The sentence from the article is "Boeing concluded there would be little risk in the event of an MCAS failure — in part because of an FAA-approved assumption that pilots would respond to an unexpected activation in a mere three seconds." This could be interpreted as the assumption being Boeing's, and the FAA merely approved it. And, with the FAA/manufacturer self-approval system in place, I think it's more than possible that the 3-second assumption was never mentioned to the actual FAA, and not just Boeing's self-appointed FAA rep. As to where the 3-second idea might come from, perhaps some misguided person at Boeing read the 3-second assumption in the TCAS documentation and mis-applied it to the MCAS situation.

So, from my reading… no, we do not need to re-certify every Part 25 aircraft, as I don't believe that a 3-second reaction time is specified in the Part 25 document. However, it still leaves open the question of how and where this 3-second idea came about, in responding to a runaway stabilizer situation. Would anybody else like to chime in on where this 3-second idea comes from?

Just in case someone wants to review that article again: https://www.seattletimes.com/seattle-ne ... afeguards/
 
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aerolimani
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 6:58 pm

OldAeroGuy wrote:
XRAYretired wrote:
Just imagine for a moment spending a few seconds finding the QRH which then tells you to repond within 3 seconds. No it doesnt, nor does the EID because it is ludicrous.

Ray


No need to find the QRH as the response to a Stab Trim Runaway is a memory item, as stated many times on this thread..

Except that we have a pilot telling us that their airline has no memory items. Instead, they have the NNC's on flashcards. I'll refer you to post 2716: viewtopic.php?f=3&t=1421471&p=21426351#p21426351
 
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enilria
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 7:20 pm

I posted this way upthread, and I stopped reading. Did anything happen with this?

There was an article about how it required something like 150 pounds of force to fight the yoke after the autopilot was turned off and the pilots eventually turned the autopilot back on because they gave up fighting the 150 pounds of force and hoped the autopilot which was not impacted by the yoke force requirement could be used to somehow overcome to force it had originally created.

SO, why not just have a switch to turn the force actuator off? This is a virtual force. There are no real cables. It's fly-by-wire. Why not be able to turn off the force actuator? I guess the risk is it damages the elevator to have the pilots ignoring the forces, but at some point that is the smaller risk. Even if it tore it off it might have made the plane more flyable than it was.
 
OldAeroGuy
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 7:20 pm

aerolimani wrote:
While reading technical documents is not my forté, I also did not find where this document suggests anything about requiring a 3-second reaction time from pilots. As far as I can tell, the 3-second references in this Part 25 document are merely about defining how tests ought to be conducted.

Searching around a bit, there is some FAA documentation around the TCAS system where pilots response is expected to be around three seconds. That, however, is a totally different situation. TCAS gives a specific aural and visual instruction; no analysis required. On the other hand, detecting a runaway stabilizer is is an analytical task. For a system that normally (and frequently) moves autonomously, three seconds is a pretty small window, especially when many other distracting events are occurring simultaneously.

I'd like to know where this three second concept comes from, in relation to recognizing a runaway stab situation. The sentence from the article is "Boeing concluded there would be little risk in the event of an MCAS failure — in part because of an FAA-approved assumption that pilots would respond to an unexpected activation in a mere three seconds." This could be interpreted as the assumption being Boeing's, and the FAA merely approved it. And, with the FAA/manufacturer self-approval system in place, I think it's more than possible that the 3-second assumption was never mentioned to the actual FAA, and not just Boeing's self-appointed FAA rep. As to where the 3-second idea might come from, perhaps some misguided person at Boeing read the 3-second assumption in the TCAS documentation and mis-applied it to the MCAS situation.

So, from my reading… no, we do not need to re-certify every Part 25 aircraft, as I don't believe that a 3-second reaction time is specified in the Part 25 document. However, it still leaves open the question of how and where this 3-second idea came about, in responding to a runaway stabilizer situation. Would anybody else like to chime in on where this 3-second idea comes from?

Just in case someone wants to review that article again: https://www.seattletimes.com/seattle-ne ... afeguards/


Here's an excerpt using the direct language from AC25-7C:

QUOTE
33. Out-Of-Trim Characteristics - § 25.255.
a. Explanation. Certain early, trimmable stabilizer equipped jet transports experienced “jet
upsets” that resulted in high speed dives. When the airplane was mistrimmed in the nose-down
direction and allowed to accelerate to a high airspeed, it was found that there was insufficient
elevator power to recover. Also, the stabilizer could not be trimmed in the nose-up direction,
because the stabilizer motor stalled due to excessive airloads imposed on the horizontal
stabilizer. As a result, a special condition was developed and applied to most part 25 airplanes
with trimmable stabilizers. With certain substantive changes, it was adopted as § 25.255,
effective with Amendment 25-2. While these earlier problems seem to be generally associated
with airplanes having trimmable stabilizers, it is clear from the preamble discussions to
Amendment 25-42 that § 25.255 applies “regardless of the type of trim system used in the
airplane.” Section 25.255 is structured to give protection against the following unsatisfactory
characteristics during mistrimmed flight in the higher speed regimes:

(1) Changes in maneuvering stability leading to overcontrolling in pitch.
(2) Inability to achieve at least l.5 g for recovery from upset due to excessive control
forces.
(3) Inability of the flightcrew to apply the control forces necessary to achieve recovery.
(4) Inability of the pitch-trim system to provide necessary control force relief when
high control force inputs are present.
b. Reference Regulation. Section 25.255.
c. Discussion of the Regulation.
(1) Section 25.255(a) is the general statement of purpose. Maneuvering stability may
be shown by a plot of applied control force versus normal acceleration at the airplane c.g..
Mistrim must be set to the greater of the following:
(a) Section 25.255(a)(l). A 3-second movement of the longitudinal trim system at
its normal rate for the particular flight condition with no aerodynamic load.
Since many modern
trim systems are variable rate systems, this subsection requires that the maneuver condition be
defined and that the no-load trim rate for that condition be used to set the degree of mistrim
required. For airplanes that do not have power-operated trim systems, experience has shown a
suitable amount of longitudinal mistrim to be applied is that necessary to produce a 30 pound
control force, or reach the trim limit, whichever occurs first.
UNQUOTE

Note the bold, italic text above. This describes how the airplane is put into a condition that it must be shown the the airplane is recoverable. The stabilizer is assumed to run nose up (airplane nose down) before pilot recovery is attempted. In real world service, the 3 sec corresponds to a pilot recognition and reaction time.

The 3 sec time bears no relationship to TCAS except for a general assumption as to pilot reaction time but is written directly into the mis-trim stabilizer condition.
Last edited by OldAeroGuy on Thu Jun 27, 2019 7:24 pm, edited 1 time in total.
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art
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 7:23 pm

planecane wrote:

If the MAX was never allowed to fly again, airlines that need aircraft would be foreced to fly older, less efficient, aircraft longer. They would need something between now and 2030 to replace retired aircraft and grow. Even if Airbus could produce enough A320 series to cover the need, the A320NEO is only silghtly more efficient than the 737MAX in certain missions. What would also happen is that Boeing would be forced to restart production of the NG and give huge discounts to keep customers. They can't have no narrowbody to sell for a decade and remain in the commercial aviation business.


After NEO was launched and Boeing realised the difficulty they were facing with fitting a bigger fan on the 737, they should bitten the lost profitable sales bullet and should have gone for NSA in my opinion (as you say with big financial incentives to keep NG sales going). That, however, would rhave required taking a longer term view which I don't think is part of their DNA.

Anyone want to hazard how much longer it would have taken to get NSA rolling off the line rather than MAX?
 
XRAYretired
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 7:25 pm

aerolimani wrote:
XRAYretired wrote:
PW100 wrote:

Is 3 seconds sufficient to recognize a runaway trim in a stand-alone failure scenario (leaving aside that usually other issues be present at the same time)?
If we look at MCAS, it has a 9 second cycle. Should pilots be expected to disable MCAS after only 3 seconds, or should they allow at least a full MCAS cyce, and take action at the next cycle (after 3 seconds)?
Leaving aside the question whether the intermittent behaviour of MCAS would be recognizable as runaway trim (prior to the accidents).

As I read it, the 3 seconds is about control response to an upset, e.g. pulling the stick back and getting a relevant response when the nose drops unexpectedly, within 3 seconds. It has nothing to do or say about identifying an airframe or system cause of the upset in the first place or doing something about it.

I think the report, assuming correct, just tends to confirm that the safety analysis did not adequately identify AOA Sensor Failed High and/or the potential effects of single AOA sensor failed high and therefore demonstrate that the design solution was not acceptable. Consequently, any testing, validation and certification would have tested it either. QED.

Ray

While reading technical documents is not my forté, I also did not find where this document suggests anything about requiring a 3-second reaction time from pilots. As far as I can tell, the 3-second references in this Part 25 document are merely about defining how tests ought to be conducted.

Searching around a bit, there is some FAA documentation around the TCAS system where pilots response is expected to be around three seconds. That, however, is a totally different situation. TCAS gives a specific aural and visual instruction; no analysis required. On the other hand, detecting a runaway stabilizer is is an analytical task. For a system that normally (and frequently) moves autonomously, three seconds is a pretty small window, especially when many other distracting events are occurring simultaneously.

I'd like to know where this three second concept comes from, in relation to recognizing a runaway stab situation. The sentence from the article is "Boeing concluded there would be little risk in the event of an MCAS failure — in part because of an FAA-approved assumption that pilots would respond to an unexpected activation in a mere three seconds." This could be interpreted as the assumption being Boeing's, and the FAA merely approved it. And, with the FAA/manufacturer self-approval system in place, I think it's more than possible that the 3-second assumption was never mentioned to the actual FAA, and not just Boeing's self-appointed FAA rep. As to where the 3-second idea might come from, perhaps some misguided person at Boeing read the 3-second assumption in the TCAS documentation and mis-applied it to the MCAS situation.

So, from my reading… no, we do not need to re-certify every Part 25 aircraft, as I don't believe that a 3-second reaction time is specified in the Part 25 document. However, it still leaves open the question of how and where this 3-second idea came about, in responding to a runaway stabilizer situation. Would anybody else like to chime in on where this 3-second idea comes from?

Just in case someone wants to review that article again: https://www.seattletimes.com/seattle-ne ... afeguards/

The 3 second thing has got nothing to do whatsoever with any specific failure mode of the A/C or its systems or atmospheric effects that cause an upset but all or any. It is the reaction time required to recover from the upset in the aircraft attitude and conditions specified.

The ACA is there to provide guidance upon how and what is required to demonstrate that the A/C complies with Part 25 requirement. It is quite likely the relevant Part 25 requirement does not actually say 3 seconds. OAG can probably tell us of the top of his head but is more likely to post the full reference. You have to demonstrate the 3 second ACA requirement compliance to get the pass.

Ray
 
kalvado
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 7:29 pm

OldAeroGuy wrote:
aerolimani wrote:
While reading technical documents is not my forté, I also did not find where this document suggests anything about requiring a 3-second reaction time from pilots. As far as I can tell, the 3-second references in this Part 25 document are merely about defining how tests ought to be conducted.

Searching around a bit, there is some FAA documentation around the TCAS system where pilots response is expected to be around three seconds. That, however, is a totally different situation. TCAS gives a specific aural and visual instruction; no analysis required. On the other hand, detecting a runaway stabilizer is is an analytical task. For a system that normally (and frequently) moves autonomously, three seconds is a pretty small window, especially when many other distracting events are occurring simultaneously.

I'd like to know where this three second concept comes from, in relation to recognizing a runaway stab situation. The sentence from the article is "Boeing concluded there would be little risk in the event of an MCAS failure — in part because of an FAA-approved assumption that pilots would respond to an unexpected activation in a mere three seconds." This could be interpreted as the assumption being Boeing's, and the FAA merely approved it. And, with the FAA/manufacturer self-approval system in place, I think it's more than possible that the 3-second assumption was never mentioned to the actual FAA, and not just Boeing's self-appointed FAA rep. As to where the 3-second idea might come from, perhaps some misguided person at Boeing read the 3-second assumption in the TCAS documentation and mis-applied it to the MCAS situation.

So, from my reading… no, we do not need to re-certify every Part 25 aircraft, as I don't believe that a 3-second reaction time is specified in the Part 25 document. However, it still leaves open the question of how and where this 3-second idea came about, in responding to a runaway stabilizer situation. Would anybody else like to chime in on where this 3-second idea comes from?

Just in case someone wants to review that article again: https://www.seattletimes.com/seattle-ne ... afeguards/


Here's an excerpt using the direct language from AC25-7C:

QUOTE
33. Out-Of-Trim Characteristics - § 25.255.
a. Explanation. Certain early, trimmable stabilizer equipped jet transports experienced “jet
upsets” that resulted in high speed dives. When the airplane was mistrimmed in the nose-down
direction and allowed to accelerate to a high airspeed, it was found that there was insufficient
elevator power to recover. Also, the stabilizer could not be trimmed in the nose-up direction,
because the stabilizer motor stalled due to excessive airloads imposed on the horizontal
stabilizer. As a result, a special condition was developed and applied to most part 25 airplanes
with trimmable stabilizers. With certain substantive changes, it was adopted as § 25.255,
effective with Amendment 25-2. While these earlier problems seem to be generally associated
with airplanes having trimmable stabilizers, it is clear from the preamble discussions to
Amendment 25-42 that § 25.255 applies “regardless of the type of trim system used in the
airplane.” Section 25.255 is structured to give protection against the following unsatisfactory
characteristics during mistrimmed flight in the higher speed regimes:

(1) Changes in maneuvering stability leading to overcontrolling in pitch.
(2) Inability to achieve at least l.5 g for recovery from upset due to excessive control
forces.
(3) Inability of the flightcrew to apply the control forces necessary to achieve recovery.
(4) Inability of the pitch-trim system to provide necessary control force relief when
high control force inputs are present.
b. Reference Regulation. Section 25.255.
c. Discussion of the Regulation.
(1) Section 25.255(a) is the general statement of purpose. Maneuvering stability may
be shown by a plot of applied control force versus normal acceleration at the airplane c.g..
Mistrim must be set to the greater of the following:
(a) Section 25.255(a)(l). A 3-second movement of the longitudinal trim system at
its normal rate for the particular flight condition with no aerodynamic load.
Since many modern
trim systems are variable rate systems, this subsection requires that the maneuver condition be
defined and that the no-load trim rate for that condition be used to set the degree of mistrim
required. For airplanes that do not have power-operated trim systems, experience has shown a
suitable amount of longitudinal mistrim to be applied is that necessary to produce a 30 pound
control force, or reach the trim limit, whichever occurs first.
UNQUOTE

Note the bold, italic text above. This describes how the airplane is put into a condition that it must be shown the the airplane is recoverable. The stabilizer is assumed to run nose up (airplane nose down) before pilot recovery is attempted. In real world service, the 3 sec corresponds to a pilot recognition and reaction time.

The 3 sec time bears no relationship to TCAS except for a general assumption as to pilot reaction time but is written directly into the mis-trim stabilizer condition.

But what exactly are the symptoms to be determined within 3 seconds? Sts is another source of trim movement without direct pilot command, and it happens often. So how to ensure response to actual runaway without many false alarms?
 
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PW100
Posts: 3719
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 7:36 pm

planecane wrote:
PW100 wrote:
Is 3 seconds sufficient to recognize a runaway trim in a stand-alone failure scenario (leaving aside that usually other issues be present at the same time)?
If we look at MCAS, it has a 9 second cycle. Should pilots be expected to disable MCAS after only 3 seconds, or should they allow at least a full MCAS cyce, and take action at the next cycle (after 3 seconds)?
Leaving aside the question whether the intermittent behaviour of MCAS would be recognizable as runaway trim (prior to the accidents).


The expectation is/was that the pilots were expected to recognize a runaway stabilizer (caused by MCAS or otherwise) within 3 seconds and begin the NNC. That's why, to me, it has always been completely irrelevant that MCAS was intermittent. The big failure that was missed is that the same thing that would cause MCAS cause a runaway stabilizer ALSO caused other issues simultaneously. This factor is the reason that I believe the lack of documentation of MCAS and specific training played a huge factor. The training could have been part of the iPad course. Simple instructions that if there was uncommanded nose down trim that the runaway stabilizer NNC should be performed first, regardless of other issues would have gone a long way. The information should have been provided that other alerts (single side stick shaker, unreliable airspeed, etc.) would likely occur simultaneously but that responding to the runaway stabilizer should take priority. This should have been part of the training and the QRH.


I understand what you're saying with the intermittent behaviour.
But then it would make not much sense to schedule MCAS cycle for 9 seconds, if Boeing at the same time expected the crew to shut it down after 3 seconds . . .
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par13del
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 7:38 pm

art wrote:
Anyone want to hazard how much longer it would have taken to get NSA rolling off the line rather than MAX?

No need to guess, just ask the airlines who ordered the MAX, they are the ones who told Boeing that they were not willing to wait the additional years for a clean sheet whose advantage over the NEO would be minimal at best.
Damn Boeing trying to listen to their customers, should have stuck to their guns, we all know if you build it they will come.
 
OldAeroGuy
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 7:45 pm

aerolimani wrote:
OldAeroGuy wrote:
XRAYretired wrote:
Just imagine for a moment spending a few seconds finding the QRH which then tells you to repond within 3 seconds. No it doesnt, nor does the EID because it is ludicrous.

Ray


No need to find the QRH as the response to a Stab Trim Runaway is a memory item, as stated many times on this thread..

Except that we have a pilot telling us that their airline has no memory items. Instead, they have the NNC's on flashcards. I'll refer you to post 2716: viewtopic.php?f=3&t=1421471&p=21426351#p21426351


And Mentour Pilot says the Stab Trim Runaway NNC is a Memory Item:

https://video.search.yahoo.com/yhs/sear ... tion=click
Last edited by OldAeroGuy on Thu Jun 27, 2019 8:06 pm, edited 1 time in total.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
OldAeroGuy
Posts: 3870
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 7:52 pm

kalvado wrote:

But what exactly are the symptoms to be determined within 3 seconds? Sts is another source of trim movement without direct pilot command, and it happens often. So how to ensure response to actual runaway without many false alarms?


As Mentor Pilot says in his video, STS is making control forces easier. Runaway Stab is making it more difficult to control the airplane. If you're having to hold an increasing amount of uncommanded column force, it's a Runaway Stab.

Watch the video:

https://video.search.yahoo.com/yhs/sear ... tion=click
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
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LX015
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 7:55 pm

In all seriousness, I wonder if IAG is now having 2nd thoughts about the LOI for 200 MAXs...
 
morrisond
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 8:01 pm

For what it's worth (Boeing's word) - CNBC just reported a source told them Boeing expects to have the fix done and submitted in September.
 
Paolo18
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 8:06 pm

So what processor is Boeing using for mcas?

8 bit, 16 bit, 32 bit?
 
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Revelation
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 8:28 pm

morrisond wrote:
For what it's worth (Boeing's word) - CNBC just reported a source told them Boeing expects to have the fix done and submitted in September.

https://www.reuters.com/article/us-ethi ... SKCN1TS26Q provides an interesting best case time line:

Boeing will not conduct a certification test flight, a necessary step before formally requesting FAA approval of new software until July 8, under a best-case scenario.

That means the eventual return of the jets for flight may drag into the fourth quarter of the year, analysts said.

If WN is already saying Oct 1 then we are in to the fourth quarter.

On the other hand, no one seems to be suggesting years of delays which suggests that no one (yet?) is getting the word that a new processor is needed.
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mham001
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 8:30 pm

kalvado wrote:
They should be approaching 200 planes in inventory, that is $10B or so. Partially paid for, but with limited new orders (1 LOI with unclear down payment) and possibly reduced progress payments. Compensations. $10B cash were reported at the beginning of the mess, probably mostly depleted.


Nonsense, It reads more like wishful thinking.. We have good reason to believe each plane costs ~$20 million to build. This is not even close to $10 billion and does not account for sales of other products.
 
smartplane
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 8:51 pm

mham001 wrote:
kalvado wrote:
They should be approaching 200 planes in inventory, that is $10B or so. Partially paid for, but with limited new orders (1 LOI with unclear down payment) and possibly reduced progress payments. Compensations. $10B cash were reported at the beginning of the mess, probably mostly depleted.


Nonsense, It reads more like wishful thinking.. We have good reason to believe each plane costs ~$20 million to build. This is not even close to $10 billion and does not account for sales of other products.

Including engines and fitout?
 
ArgentoSystems
Posts: 295
Joined: Sun Mar 24, 2019 12:05 am

Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 8:57 pm

mham001 wrote:
kalvado wrote:
They should be approaching 200 planes in inventory, that is $10B or so. Partially paid for, but with limited new orders (1 LOI with unclear down payment) and possibly reduced progress payments. Compensations. $10B cash were reported at the beginning of the mess, probably mostly depleted.


Nonsense, It reads more like wishful thinking.. We have good reason to believe each plane costs ~$20 million to build. This is not even close to $10 billion and does not account for sales of other products.

I don't know, BA has profit margin of about 20%. Assuming each plane sells for 50M, I would estimate 40M cost. So ok, it is not 10B in cost. But, it is 10B of income they did not receive.
 
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PixelFlight
Posts: 506
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 8:59 pm

BoeingVista wrote:
I disagree with that assessment its quite possible that Boeing has just run out of processing power for the amount of tasks the computer is required to perform.

Freefall wrote:
I think they will need change both (software and hardware) upgrades probably needed because now MCAS software needs to deal with more situations/scenarios and for that more processing power and memory will be needed.

RickNRoll wrote:
The problem is that the processor is an old one that does not appear to have enough power to run more complex time critical calculations.

StTim wrote:
I suspect that what happened was processor overload rather than BSOD type failure.
The "out of processing power" is very hard to believe in the context of a DO-178 compliant software development, especially for the transition from MCAS v1 to MCAS v2. From what have been released so far, the differences between the MCAS v1 and MCAS v2 is just a couple of relatively simple conditions. Even on a 30 years old processors those condition will not add more than a fraction of millisecond of processing time. It's not possible to properly certify for flight operation a computer + software combo with a such insanely small processing margin time.

XRAYretired wrote:
To us, it sounds as though code in the MCAS update either forces the processor into a locked state, such as a tight unbreakable and uninterruptable infinite loop, or triggers an exception that can't be handled and the CPU halts. It is remotely possible the code encounters a design flaw in the unidentified microprocessor that causes the circuitry to freeze.
IMHO, the scenario is far more probable.

Revelation wrote:
you have to consider things like the newer processor may demand more power than you can (reliably) supply, or generate more heat than you can get rid of, or generate more electrical noise than you can block, or have different physical layer characteristics (i.e. voltage levels, bit rates, etc) than the old one.
Very very unlikely. Replacing a 30 old CPU by even most rugged technology available today will almost certainly take less power supply, generate less heat, less noise, and outrageously supersede all physical layers characteristics with a few interface chips.

Revelation wrote:
I have a graduate degree in computer science, and guess what, there effectively are an infinite number of possibilities and testing cannot cover them all. There was a lot of work in the 70s on "provably correct" programs (one example is the software that is in the space shuttle flight computer) but industry walked away from that because it was such expensive and special purpose stuff.
DO-178 define "structural coverage criteria". This document resume well enough the subject on page 12 https://pdfs.semanticscholar.org/ba18/3 ... 3c6f1d.pdf
"
structural coverage criteria have to be achieved depend on the software level:
• Level C: 100% statement coverage is required, which means that every statement in the
program has been exercised.
• Level B: 100% decision coverage is required. That means that every decision has taken all
possible outcomes at least one (ex: then/else for an if construct) and that every entry and exit
point in the program has been invoked at least one.
• 100% MCD/DC (Modified Condition/Decision Coverage) is required for level A software,
which means that:
o Every entry and exit point in the program has been invoked at least once
o Every decision has taken all possible outcomes
o Each condition in a decision has been shown to independently affect that decision’s
outcome (this is shown by varying just that condition while holding fixed all other
possible conditions).
"
 
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aerolimani
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Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 9:05 pm

OldAeroGuy wrote:
aerolimani wrote:
While reading technical documents is not my forté, I also did not find where this document suggests anything about requiring a 3-second reaction time from pilots. As far as I can tell, the 3-second references in this Part 25 document are merely about defining how tests ought to be conducted.

Searching around a bit, there is some FAA documentation around the TCAS system where pilots response is expected to be around three seconds. That, however, is a totally different situation. TCAS gives a specific aural and visual instruction; no analysis required. On the other hand, detecting a runaway stabilizer is is an analytical task. For a system that normally (and frequently) moves autonomously, three seconds is a pretty small window, especially when many other distracting events are occurring simultaneously.

I'd like to know where this three second concept comes from, in relation to recognizing a runaway stab situation. The sentence from the article is "Boeing concluded there would be little risk in the event of an MCAS failure — in part because of an FAA-approved assumption that pilots would respond to an unexpected activation in a mere three seconds." This could be interpreted as the assumption being Boeing's, and the FAA merely approved it. And, with the FAA/manufacturer self-approval system in place, I think it's more than possible that the 3-second assumption was never mentioned to the actual FAA, and not just Boeing's self-appointed FAA rep. As to where the 3-second idea might come from, perhaps some misguided person at Boeing read the 3-second assumption in the TCAS documentation and mis-applied it to the MCAS situation.

So, from my reading… no, we do not need to re-certify every Part 25 aircraft, as I don't believe that a 3-second reaction time is specified in the Part 25 document. However, it still leaves open the question of how and where this 3-second idea came about, in responding to a runaway stabilizer situation. Would anybody else like to chime in on where this 3-second idea comes from?

Just in case someone wants to review that article again: https://www.seattletimes.com/seattle-ne ... afeguards/


Here's an excerpt using the direct language from AC25-7C:

QUOTE
33. Out-Of-Trim Characteristics - § 25.255.
a. Explanation. Certain early, trimmable stabilizer equipped jet transports experienced “jet
upsets” that resulted in high speed dives. When the airplane was mistrimmed in the nose-down
direction and allowed to accelerate to a high airspeed, it was found that there was insufficient
elevator power to recover. Also, the stabilizer could not be trimmed in the nose-up direction,
because the stabilizer motor stalled due to excessive airloads imposed on the horizontal
stabilizer. As a result, a special condition was developed and applied to most part 25 airplanes
with trimmable stabilizers. With certain substantive changes, it was adopted as § 25.255,
effective with Amendment 25-2. While these earlier problems seem to be generally associated
with airplanes having trimmable stabilizers, it is clear from the preamble discussions to
Amendment 25-42 that § 25.255 applies “regardless of the type of trim system used in the
airplane.” Section 25.255 is structured to give protection against the following unsatisfactory
characteristics during mistrimmed flight in the higher speed regimes:

(1) Changes in maneuvering stability leading to overcontrolling in pitch.
(2) Inability to achieve at least l.5 g for recovery from upset due to excessive control
forces.
(3) Inability of the flightcrew to apply the control forces necessary to achieve recovery.
(4) Inability of the pitch-trim system to provide necessary control force relief when
high control force inputs are present.
b. Reference Regulation. Section 25.255.
c. Discussion of the Regulation.
(1) Section 25.255(a) is the general statement of purpose. Maneuvering stability may
be shown by a plot of applied control force versus normal acceleration at the airplane c.g..
Mistrim must be set to the greater of the following:
(a) Section 25.255(a)(l). A 3-second movement of the longitudinal trim system at
its normal rate for the particular flight condition with no aerodynamic load.
Since many modern
trim systems are variable rate systems, this subsection requires that the maneuver condition be
defined and that the no-load trim rate for that condition be used to set the degree of mistrim
required. For airplanes that do not have power-operated trim systems, experience has shown a
suitable amount of longitudinal mistrim to be applied is that necessary to produce a 30 pound
control force, or reach the trim limit, whichever occurs first.
UNQUOTE

Note the bold, italic text above. This describes how the airplane is put into a condition that it must be shown the the airplane is recoverable. The stabilizer is assumed to run nose up (airplane nose down) before pilot recovery is attempted. In real world service, the 3 sec corresponds to a pilot recognition and reaction time.

The way I read this section is that it is defining the power and capability that a trim system must have. To my reading, it's determining how much capability the system needs to have so that the pilot can achieve a fast enough response from the system. In other words, the 3 seconds is defining what the system needs to be capable of, not what the pilot's response time needs to be. This section also defines how the forces should not behave erratically as the system moves through its trim degrees.

I will post here the opening explanation for the section you are quoting. Not anywhere in this whole section, and certainly not in the explanation, is there mention of the actions of an automatic trim system, or its expected characteristics as regards pilot response time. I think it's important to quote the section's opening explanation, as it gives context to everything else contained in the section.

33. Out-of-Trim Characteristics - § 25.255.
a. Explanation. Certain early, trimmable stabilizer equipped jet transports experienced “jet upsets” that resulted in high speed dives. When the airplane was mistrimmed in the nose-down direction and allowed to accelerate to a high airspeed, it was found that there was insufficient elevator power to recover. Also, the stabilizer could not be trimmed in the nose-up direction, because the stabilizer motor stalled due to excessive airloads imposed on the horizontal stabilizer. As a result, a special condition was developed and applied to most part 25 airplanes with trimmable stabilizers. With certain substantive changes, it was adopted as § 25.255, effective with amendment 25-2. While these earlier problems seem to be generally associated with airplanes having trimmable stabilizers, it is clear from the preamble discussions to amendment 25-42 that § 25.255 applies “regardless of the type of trim system used in the airplane.” Section 25.255 is structured to give protection against the following unsatisfactory characteristics during mistrimmed flight in the higher speed regimes:
(1) Changes in maneuvering stability leading to overcontrolling in pitch.
(2) Inability to achieve at least l.5g for recovery from upset due to excessive control forces.
(3) Inability of the flightcrew to apply the control forces necessary to achieve recovery.
(4) Inability of the pitch-trim system to provide necessary control force relief when high control force inputs are present.
 
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aerolimani
Posts: 1132
Joined: Tue Jun 18, 2013 5:46 pm

Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 9:08 pm

Just for the record, I am merely trying to understand where this 3-second assumption comes from. At best, when it comes to recognizing runaway stab, it seems very optimistic to me.
 
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PixelFlight
Posts: 506
Joined: Thu Nov 08, 2018 11:09 pm

Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 9:10 pm

Revelation wrote:
If WN is already saying Oct 1 then we are in to the fourth quarter.

Yes, and this will more and more be close to the JT610 12 months report. I expect that report to list in the findings all related defects identified so far at Boeing. Could be a devastating public perception effect on a release of the grounding.
 
kalvado
Posts: 1809
Joined: Wed Mar 01, 2006 4:29 am

Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 9:16 pm

OldAeroGuy wrote:
kalvado wrote:

But what exactly are the symptoms to be determined within 3 seconds? Sts is another source of trim movement without direct pilot command, and it happens often. So how to ensure response to actual runaway without many false alarms?


As Mentor Pilot says in his video, STS is making control forces easier. Runaway Stab is making it more difficult to control the airplane. If you're having to hold an increasing amount of uncommanded column force, it's a Runaway Stab.

Watch the video:

https://video.search.yahoo.com/yhs/sear ... tion=click

That is a great symptom, but is it actually detectable within 3 seconds and differentiated from turbulence offset or gradient of force in maneuver?
I can imagine 3 seconds response to engine warning sound on takeoff, but I suspect force feeling is largely a closed loop which can be consciously understood only when things are very wrong. I know where I want my car to go, and I don't really notice small glitches like a piece of stone under the wheel. It takes curb or a good pothole to start noticing
 
hivue
Posts: 1903
Joined: Tue Feb 26, 2013 2:26 am

Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 9:16 pm

Revelation wrote:
Leak? Boeing itself made a statement to the capital markets which is not a leak but is the whole dam busting!


But it was leaked before that -- and Boeing didn't leak it:

https://www.cnbc.com/video/2019/06/27/b ... issue.html?

The 2:50 mark.
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
Alfons
Posts: 252
Joined: Sun Feb 03, 2013 1:17 am

Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 9:18 pm

LX015 wrote:
In all seriousness, I wonder if IAG is now having 2nd thoughts about the LOI for 200 MAXs...


That's why they did a LOI.
 
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PixelFlight
Posts: 506
Joined: Thu Nov 08, 2018 11:09 pm

Re: Boeing 737MAX Grounded Worldwide Q2 2019

Thu Jun 27, 2019 9:21 pm

hivue wrote:
CNBC were emphasizing this morning that the fact that the FAA chose to leak the microprocessor issue is very significant (sorry, no link to that story yet). I have to agree.

Yes. Given the transparency the FAA promised to the administrations that have authority on others regions of the world, there have no other choice to regain credibility. I don't think that the FAA "chose to leak", there are now expected to promptly communicate to the others administrations any important finding on the subject and consequently would loss credibility if there are not the first to announce the finding to the public.

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