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PW100
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 8:46 am

DenverTed wrote:
PW100 wrote:
It is not clear, but this new problem may apply also to MCAS 1.0. It could be that FAA found this issue because of extensive diligence after two accidents. Perhaps the first time aorund they (or Boeing = self-certitifying . . . ) were not so thorough in testing/validating such scenarios.

Right? Look at any skyscraper or stadium. If they inspect it or the plans long enough, there will always be flaws and code violations to be found if they look long enough.
My question is always, does this apply to the NG as well? Not that I wish for the grounding of the NG, just that if it is put under scrutiny, I'm sure there are some similar defects hiding in there. Same with the 787 or A350. The increasing complexity of the systems would take years for a second party to review. To some extent, I think that the safety is because of people getting it right the first time, and the numerous uncaught failure modes being low occurring enough that they never rear their ugly heads for 30 years of service.


Of course you will always find issues, when digging deep enough. In my mind the "Boeing falsifying records" thing may be just that. We all know that from time to time stamps get missed/forgotten on assembly records. And we all know that shouldn't happen. And we all know that it does, sometimes. And we all know that if that occurs not always the perfect world is followed (disassembly, inspect and re-assembly).
But that's in different league than missing important steps in a (D)FMEA, or FAI.

I'm not so much interested whether the failure is present in the NG, for the very simple reason that the NG has a very proven track record, and any dormant issues are so remote, that is should not be such a big deal in terms of grounding the fleet (out-of-trim manual trim wheel forces fall into that category). I think the NG is accumulating around 25M flight hours each year, and the total fleet should be closing in on 250M flight hours. Have we had any reports on the NG (let alone accidents) due to excessive manual trim wheel forces? So while the issue might still be present on the NG, the design around it, and flight ops are so good, that such a situation would occur so rarely, that it could be deemed acceptable, or at least (very) low risk

For me, it is important to understand if such issues may be present on existing MCAS (1.0), as that may put a totally different light on the claims that the accident crews did not do their thing properly (third-world-pilots / poorly trained / could not happen to american crews). If it turns out that manual electric trimming was not working, or limited in travel (to say 2.3 units stabilizer pitch), for reasons now uncovered in MCAS 2.0 testing, then a lot of folks here should be eating lots of crow. And crews all over the planet should realize that they had been very lucky not to have encountered rogue AoA . . .
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XRAYretired
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 8:49 am

PW100 wrote:
XRAYretired wrote:
PW100 wrote:
In my mind, but that may just be me, single-sensor thing correlates to each parameter. If MCAS x.x needs AoA and G to do its thing, that would be two parameters. But if one (or both) of these parameters only rely on one sensor (i.e. one AoA sensor), its architecture is still what I would call, single-sensor. Never mind the second parameter sensor (G-sensor), the AoA input is still depending on one single sensor. And that would still require single-sensor failure mode effect analyses (FMEA).

So to me the removal of G-sensor is a bit of a red herring in terms of single-sensor thing, and associated system requirements in terms of reliability, crew actions, fale-safe etc. Of course, MCAS algorithms would be different for such g-sensor, and the associated failure modes and effects would also be different. But the fact in itself that there is a second parameter, doesn't change the principals of FMEA, and I would still consider it as a single-sensor system.

My understanding of STS is, that it is an auto(pilot) functionality, active when autopilot is disengaged, to assist the pilot in pitch trimming when flying manually with changing speeds. Speed changes (and resulting AoA effects) will change the aerodynamic centre of lift, and results in changes to neutral trimming. Under manual copntrol, the pilot would be adjusting the trim constantly during acceleration from take-off to cruise and vv. Using a smart algorithm, this task can be automated, which is what STS is all about. STS manipulates the same control function as the trim switch and manual trim wheel (ie. stabilizer trim jackscrew).

Apologies, seem to be responding to posts in reverse order today for some reason.

Anyway, this is terminology. We can call them both parameters or apples if you like. The point is MCAS V0.0 requires both apples to fail in the same direction to erroneously initiate MCAS - ~10E-10 (or in the order of E-10 if you prefer). Failure to initiate requires only apple to fail ~10E-05, but is reported only to be hazardous in wind up turn estimated at 10E-05, so 10E-10 for it to occur. G apple is not a red herring in this respect since whilst failure to initiate remains in the order 10E-10, erroneous initiation is reduced to 10E-05. The failure effects are the same irrespective of sensors or apples.


Ray


OK, I see and agree. It is important to distinguish between failure to work, and false activation.
I agree that the second apple(s) will still prevent false activation when the first apple(s) fails.
Thanks.


Good O. Just rough estimates of course cos we dont have the real numbers. We could put a better guess on erroneous operation since we have had two events in around 500K hours, so say ~4*10E-06.

Ray
 
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PW100
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 8:53 am

XRAYretired wrote:
PW100 wrote:
OK, I see and agree. It is important to distinguish between failure to work, and false activation.
I agree that the second apple(s) will still prevent false activation when the first apple(s) fails.
Thanks.


Good O. Just rough estimates of course cos we dont have the real numbers. We could put a better guess on erroneous operation since we have had two events in around 500K hours, so say ~4*10E-06.

Ray


Yep. Needless to say that such odds and consequences would overwhelmingly blind all other issues on any decent FMEA.
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XRAYretired
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 9:19 am

PW100 wrote:
XRAYretired wrote:
PW100 wrote:
OK, I see and agree. It is important to distinguish between failure to work, and false activation.
I agree that the second apple(s) will still prevent false activation when the first apple(s) fails.
Thanks.


Good O. Just rough estimates of course cos we dont have the real numbers. We could put a better guess on erroneous operation since we have had two events in around 500K hours, so say ~4*10E-06.

Ray


Yep. Needless to say that such odds and consequences would overwhelmingly blind all other issues on any decent FMEA.

And the presumption would be to design it out, especially when the solution is relatively easy and cheap as would have been for MCAS, rather than mitigate on the basis that the pilot will catch it as the first option.

Ray

PS It is assuming that false operation was actually identified as a failure mode, which is in doubt at this point.
 
planecane
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 10:32 am

IADFCO wrote:
planecane wrote:
packsonflight wrote:


So how is it possible to certify 737 MAX without addressing the stall behaviour with MCAS ioperative?


Because MCAS inoperative will be a non-normal situation and have a non-normal checklist for the pilots to follow. If certification was impossible because an aircraft behaves differently in non-normal situations then no aircraft could be certified.

[...]


Wrong! MCAS will be inoperative by design (= not a "non-normal" situation) after one activation in a wind-up turn -- plausible scenario: evasive maneuver. Hopefully the FAA will test this situation in flight (not in the simulator) through stall.

You are aware that a wind-up turn is a test maneuver to measure stick force gradient and not something that would be performed as an evasive maneuver in flight, correct?

If you are going to make statements like "MCAS will be inoperable by design" you can't just say "plausible scenario: evasive maneuver."

Please describe in detail a scenario where MCAS would need more than one cycle to maintain the required stick force gradient without first leaving the trigger condition.
 
planecane
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 10:36 am

BoeingVista wrote:
planecane wrote:

Remember from the WSJ report that the "old school" test pilot was ok with MCAS because it would almost never activate in normal service. It had to be included because it is possible to get the 737 into those parts of the flight envelope, not because it is normal.



Not true, on two counts

1) The old school test pilot wanted vortex generators to alleviate the problem rather than a software solution, he was told it couldn't be fixed that way.

2) MCAS had to be included to satisfy a certification criteria of equal stick pressure when approaching a stall.


On count 2, what did I ever say that contradicted that fact? If you are going to call me out for something untrue at least do it for something I posted. I am well aware of why it was required.

In count 1, I know he originally preferred an aerodynamic solution like vortex generators but my memory of the article is that he was ok with MCAS because it would rarely, if a ever be needed in a normal flight.

Edit: upon rereading my post I can see why you thought I was contradicting the certification need for MCAS. I was making that statement with respect to the how rare the need for MCAS would be in normal flight and the rest pilot's perspective.
 
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PW100
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 10:59 am

planecane wrote:
IADFCO wrote:
Please describe in detail a scenario where MCAS would need more than one cycle to maintain the required stick force gradient without first leaving the trigger condition.


Well, it's easy to ask that question to a fellow member here. But in the end it was Boeing's that decided to do it just like that (and FAA accepted). So there must be some reason to do it. I won't expect fellow members here to know that reason.

The question should therefore be directed at Boeing, I would think.
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XRAYretired
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 11:17 am

oschkosch wrote:
More bad press!

https://www.businessinsider.com/boeing- ... ogy-2019-6

And meanwhile in India, engineers are protesting at being even associated with the max.

https://interestingengineering.com/indi ... ax-failure

And Somon Air has cancelled its planned lease.

https://simpleflying.com/somon-air-boeing-737-max/

Gesendet von meinem SM-G950F mit Tapatalk

I think the Indians have called it just about right. Well worth a watch.
https://www.newsclick.in/are-indian-eng ... max-fiasco

Ray
 
planecane
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 11:18 am

PW100 wrote:
planecane wrote:
IADFCO wrote:
Please describe in detail a scenario where MCAS would need more than one cycle to maintain the required stick force gradient without first leaving the trigger condition.


Well, it's easy to ask that question to a fellow member here. But in the end it was Boeing's that decided to do it just like that (and FAA accepted). So there must be some reason to do it. I won't expect fellow members here to know that reason.

The question should therefore be directed at Boeing, I would think.

No, the question should be directed at the poster that stated MCAS 2.0 is inoperable by design because it only activates once per event and then goes on to say that an extreme maneuver is a plausible scenario where this is an issue.

The premise is ridiculous. If it had to activate for more than one cycle to maintain the specified stick force gradient then it couldn't pass the wind-up turn test which it has to pass for certification. Assuming it passes the test then there is no "plausible scenario" where more than one cycle of activation is needed after exceeding the trigger conditions but before exiting the trigger conditions.
 
Ertro
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 11:24 am

planecane wrote:
Please describe in detail a scenario where MCAS would need more than one cycle to maintain the required stick force gradient without first leaving the trigger condition.


I have not followed this "one cycle is enough" discussion so deeply as to me this is another issue that should be left Boeing engineers to solve and trying to be very assertive about it in forums is just creating chaos which might cause problems for Boeing if they try to convince public that they have a real fix and this real fix happens to be something completely different.

But now that we have gone to somehow have some need to really work out the details could you please start by explaining me whether this "one cycle" that is enough and is okay to render MCAS inoperative means one cycle per 1 second, per 10 seconds, per 1 minute, per 10 minutes, per 1 hour, per flight, per week, per month, per year or per decade?

For example if a flight lasts 4 hours and there is an event in the end of the flight which would need MCAS functionality I don't see any significant difference to the severity of the situation based on whether there was another event in the beginning of the flight 4 hours earlier than also needed this MCAS functionality and burned this one time feature inoperable? And if this logic is valid would the same argument hold equally true for somebody to say that the one time event was used last year so we don't need MCAS funtionality any more for the rest of the decade? Or a minute or 10 seconds?

Somehow this one time event discussion sounds like somebody calculating roulette probabilities so that we got black now and that means the next roll cannot be black. However in the reality probabilities are totally unaffected by previous events.

*Edit: I see in later comment you talk about entering and exiting trigger conditions. However it is very easy to imagine situation where these trigger conditions are being constantly entered and exited as every MCAS activation is probably going to cause exiting of the trigger condition either by real or by some error situation where the AoA signal sensor in unstable and gives random readings. So in this case some extra "one time" activation rule in SW is totally meaningless and is just adding some hard to understand complexity into the system.
Last edited by Ertro on Wed Jul 03, 2019 11:48 am, edited 2 times in total.
 
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PW100
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 11:26 am

planecane wrote:
BoeingVista wrote:
planecane wrote:
Remember from the WSJ report that the "old school" test pilot was ok with MCAS because it would almost never activate in normal service. It had to be included because it is possible to get the 737 into those parts of the flight envelope, not because it is normal.

Not true, on two counts
1) The old school test pilot wanted vortex generators to alleviate the problem rather than a software solution, he was told it couldn't be fixed that way.
2) MCAS had to be included to satisfy a certification criteria of equal stick pressure when approaching a stall.

On count 2, what did I ever say that contradicted that fact? If you are going to call me out for something untrue at least do it for something I posted. I am well aware of why it was required.

In count 1, I know he originally preferred an aerodynamic solution like vortex generators but my memory of the article is that he was ok with MCAS because it would rarely, if a ever be needed in a normal flight.


On the highlighted tekst: that sounds very plausable. But then he probably did not consider false activation, he was probably only concerned about the winding turn effects. False activation of course may not be the concern of his/her/function to start with.
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PW100
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 11:35 am

planecane wrote:
PW100 wrote:
Well, it's easy to ask that question to a fellow member here. But in the end it was Boeing's that decided to do it just like that (and FAA accepted). So there must be some reason to do it. I won't expect fellow members here to know that reason.

The question should therefore be directed at Boeing, I would think.

No, the question should be directed at the poster that stated MCAS 2.0 is inoperable by design because it only activates once per event and then goes on to say that an extreme maneuver is a plausible scenario where this is an issue.

The premise is ridiculous. If it had to activate for more than one cycle to maintain the specified stick force gradient then it couldn't pass the wind-up turn test which it has to pass for certification. Assuming it passes the test then there is no "plausible scenario" where more than one cycle of activation is needed after exceeding the trigger conditions but before exiting the trigger conditions.


Perhaps the premise is dubious when the scope of MCAS is expanded beyond the winding turn?
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packsonflight
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 12:16 pm

planecane wrote:
packsonflight wrote:


So how is it possible to certify 737 MAX without addressing the stall behaviour with MCAS ioperative?


Because MCAS inoperative will be a non-normal situation and have a non-normal checklist for the pilots to follow. If certification was impossible because an aircraft behaves differently in non-normal situations then no aircraft could be certified.

Remember from the WSJ report that the "old school" test pilot was ok with MCAS because it would almost never activate in normal service. It had to be included because it is possible to get the 737 into those parts of the flight envelope, not because it is normal.

I don't know if anybody has stats but I'd guess that the incidence of near stall situations on aircraft in commercial service is infinitesimal.

The cases (AF447, colgan 3407) where there were stalls weren't helped by having stable aircraft.

Honestly, if they had not included MCAS and faked the certification paperwork, there would likely never been a crash due to an easier to enter stall during an extreme maneuver.


How is the pilot suppose to follow non-normal checklist for the MCAS when there is no such checklist? In fact MCAS was not disclosed, no training and no checklist.
 
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PixelFlight
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 12:37 pm

planecane wrote:
PW100 wrote:
planecane wrote:
Please describe in detail a scenario where MCAS would need more than one cycle to maintain the required stick force gradient without first leaving the trigger condition.


Well, it's easy to ask that question to a fellow member here. But in the end it was Boeing's that decided to do it just like that (and FAA accepted). So there must be some reason to do it. I won't expect fellow members here to know that reason.

The question should therefore be directed at Boeing, I would think.

No, the question should be directed at the poster that stated MCAS 2.0 is inoperable by design because it only activates once per event and then goes on to say that an extreme maneuver is a plausible scenario where this is an issue.

The premise is ridiculous. If it had to activate for more than one cycle to maintain the specified stick force gradient then it couldn't pass the wind-up turn test which it has to pass for certification. Assuming it passes the test then there is no "plausible scenario" where more than one cycle of activation is needed after exceeding the trigger conditions but before exiting the trigger conditions.

It's not the "poster that stated MCAS 2.0 is inoperable by design [...]" that decided to limit MCAS V2 to a single activation per high AoA cycle.

This situation could even be totally new to the FAA and others administrations. I will not be surprised if this point is part of the discussion between them. At some point those administrations will reach a common position and we will known it. Until them we can only speculate, even if to date I failed to identify any administration statement against one activation per high AoA cycle.
 
kalvado
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 12:49 pm

Ertro wrote:
For example if a flight lasts 4 hours and there is an event in the end of the flight which would need MCAS functionality I don't see any significant difference to the severity of the situation based on whether there was another event in the beginning of the flight 4 hours earlier than also needed this MCAS functionality and burned this one time feature inoperable? And if this logic is valid would the same argument hold equally true for somebody to say that the one time event was used last year so we don't need MCAS funtionality any more for the rest of the decade? Or a minute or 10 seconds?

The assumption behind MCAS single-shot design is that it is rarely, if ever, needed in flight. That makes some sense, actually; the airplane is not supposed to go into outer edges of the envelope. Most what I heard so far, MCAS is for extreme collision-avoidance manuring and few similar situations. It is unlikely to get multiple events on a single flight. Boeing's statement that regular line pilot is unlikely to encounter MCAS situation in their career is probably right.
Now, when it rains - it pours. Getting in a totally messed up airspace (say some extreme event in NYC/LON/LAX control center) with many evasive moves, flying on the edge due to a problem (mechanical problem on a plane, CoG way off, severe piloting problem, entering crazy weather pattern) is a situation MCAS may be genuinely needed more than once per flight. How often that may happen, what kind of scenarios are being considered in this regard is a big question.
MCAS role is mostly known from NYT article - a journalist leak, not an engineering assessment....
 
Ertro
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 1:01 pm

kalvado wrote:
The assumption behind MCAS single-shot design is that it is rarely, if ever, needed in flight. That makes some sense, actually; the airplane is not supposed to go into outer edges of the envelope. Most what I heard so far, MCAS is for extreme collision-avoidance manuring and few similar situations. It is unlikely to get multiple events on a single flight. Boeing's statement that regular line pilot is unlikely to encounter MCAS situation in their career is probably right.


It sure is rare event and single pilot is unlikely to encounter it ever. However that does not mean anything whether MCAS is a needed functionality on a plane. There are multiple other systems on a plane that one pilot is never going to need but they still better be onboard for the next pilot that does encounter a situation where they are needed.
 
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seahawk
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 1:22 pm

kalvado wrote:
Ertro wrote:
For example if a flight lasts 4 hours and there is an event in the end of the flight which would need MCAS functionality I don't see any significant difference to the severity of the situation based on whether there was another event in the beginning of the flight 4 hours earlier than also needed this MCAS functionality and burned this one time feature inoperable? And if this logic is valid would the same argument hold equally true for somebody to say that the one time event was used last year so we don't need MCAS funtionality any more for the rest of the decade? Or a minute or 10 seconds?

The assumption behind MCAS single-shot design is that it is rarely, if ever, needed in flight. That makes some sense, actually; the airplane is not supposed to go into outer edges of the envelope. Most what I heard so far, MCAS is for extreme collision-avoidance manuring and few similar situations. It is unlikely to get multiple events on a single flight. Boeing's statement that regular line pilot is unlikely to encounter MCAS situation in their career is probably right.
Now, when it rains - it pours. Getting in a totally messed up airspace (say some extreme event in NYC/LON/LAX control center) with many evasive moves, flying on the edge due to a problem (mechanical problem on a plane, CoG way off, severe piloting problem, entering crazy weather pattern) is a situation MCAS may be genuinely needed more than once per flight. How often that may happen, what kind of scenarios are being considered in this regard is a big question.
MCAS role is mostly known from NYT article - a journalist leak, not an engineering assessment....


You are missing the point, the problem is the MCAS behaviour during a malfunction in the system. The actual designed function of MCAS was not the problem, the undesired side effect of a faulty sensor was.
 
kalvado
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 1:25 pm

Ertro wrote:
kalvado wrote:
The assumption behind MCAS single-shot design is that it is rarely, if ever, needed in flight. That makes some sense, actually; the airplane is not supposed to go into outer edges of the envelope. Most what I heard so far, MCAS is for extreme collision-avoidance manuring and few similar situations. It is unlikely to get multiple events on a single flight. Boeing's statement that regular line pilot is unlikely to encounter MCAS situation in their career is probably right.


It sure is rare event and single pilot is unlikely to encounter it ever. However that does not mean anything whether MCAS is a needed functionality on a plane. There are multiple other systems on a plane that one pilot is never going to need but they still better be onboard for the next pilot that does encounter a situation where they are needed.

If we assume MCAS events are randomly and uniformly distributed over time, then single pilot per lifetime probability means actuation rate is below 0.5e-4 per hour; so double actuation per flight is in the range where rules allow for pretty much anything.
Now this is about random vs common-cause situation.
 
planecane
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 1:31 pm

PixelFlight wrote:
planecane wrote:
PW100 wrote:

Well, it's easy to ask that question to a fellow member here. But in the end it was Boeing's that decided to do it just like that (and FAA accepted). So there must be some reason to do it. I won't expect fellow members here to know that reason.

The question should therefore be directed at Boeing, I would think.

No, the question should be directed at the poster that stated MCAS 2.0 is inoperable by design because it only activates once per event and then goes on to say that an extreme maneuver is a plausible scenario where this is an issue.

The premise is ridiculous. If it had to activate for more than one cycle to maintain the specified stick force gradient then it couldn't pass the wind-up turn test which it has to pass for certification. Assuming it passes the test then there is no "plausible scenario" where more than one cycle of activation is needed after exceeding the trigger conditions but before exiting the trigger conditions.

It's not the "poster that stated MCAS 2.0 is inoperable by design [...]" that decided to limit MCAS V2 to a single activation per high AoA cycle.

This situation could even be totally new to the FAA and others administrations. I will not be surprised if this point is part of the discussion between them. At some point those administrations will reach a common position and we will known it. Until them we can only speculate, even if to date I failed to identify any administration statement against one activation per high AoA cycle.

I didn't say that the poster made the decision. However, he asserted that having the limit was akin to it not even existing because there are plausible scenarios where it needs to activate more than once per event.

If people are going to make this type of assertion then they should at least lay out the "plausible scenario" in detail. I'm relatively certain that at the time the post was made the poster didn't even know what a wind-up turn is.

The anti-Boeing contingent on here certainly backs each other up.
 
kalvado
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 1:33 pm

seahawk wrote:
kalvado wrote:
Ertro wrote:
For example if a flight lasts 4 hours and there is an event in the end of the flight which would need MCAS functionality I don't see any significant difference to the severity of the situation based on whether there was another event in the beginning of the flight 4 hours earlier than also needed this MCAS functionality and burned this one time feature inoperable? And if this logic is valid would the same argument hold equally true for somebody to say that the one time event was used last year so we don't need MCAS funtionality any more for the rest of the decade? Or a minute or 10 seconds?

The assumption behind MCAS single-shot design is that it is rarely, if ever, needed in flight. That makes some sense, actually; the airplane is not supposed to go into outer edges of the envelope. Most what I heard so far, MCAS is for extreme collision-avoidance manuring and few similar situations. It is unlikely to get multiple events on a single flight. Boeing's statement that regular line pilot is unlikely to encounter MCAS situation in their career is probably right.
Now, when it rains - it pours. Getting in a totally messed up airspace (say some extreme event in NYC/LON/LAX control center) with many evasive moves, flying on the edge due to a problem (mechanical problem on a plane, CoG way off, severe piloting problem, entering crazy weather pattern) is a situation MCAS may be genuinely needed more than once per flight. How often that may happen, what kind of scenarios are being considered in this regard is a big question.
MCAS role is mostly known from NYT article - a journalist leak, not an engineering assessment....


You are missing the point, the problem is the MCAS behaviour during a malfunction in the system. The actual designed function of MCAS was not the problem, the undesired side effect of a faulty sensor was.

False actuation malfunction probability is strongly reduced with 2 sensor approach, and severity of the outcome is limited with the single-shot actuation. I would say, proposed MCAS logic is as good as it can be with an existing set of hardware. Both false-actuation and false-non-actuation probabilities seem low enough.
 
XRAYretired
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 1:38 pm

Ertro wrote:
kalvado wrote:
The assumption behind MCAS single-shot design is that it is rarely, if ever, needed in flight. That makes some sense, actually; the airplane is not supposed to go into outer edges of the envelope. Most what I heard so far, MCAS is for extreme collision-avoidance manuring and few similar situations. It is unlikely to get multiple events on a single flight. Boeing's statement that regular line pilot is unlikely to encounter MCAS situation in their career is probably right.


It sure is rare event and single pilot is unlikely to encounter it ever. However that does not mean anything whether MCAS is a needed functionality on a plane. There are multiple other systems on a plane that one pilot is never going to need but they still better be onboard for the next pilot that does encounter a situation where they are needed.

Whether it is okay to decide MCAS to be sometimes inoperable I am not convinced this kind of one time rule makes any more sense than to decide that MCAS is inoperable on mondays. After all it is very unlikely it is ever going to be needed and especially on mondays.


I'm afraid this is all based around miss-interpretation. There is no 'one time rule' except in the case of AOA sensors, both of them, failing permanently high instantaneously and above the threshold for MCAS initiation i.e. if the AOA remains above threshold, MCAS will be inhibited after 1 cycle (9.26 secs, 2.5units trim max). Assuming an activation is triggered, by the combined two sensor and previous measurement transitioning from below to above the threshold, MCAS will operate for the time needed such that the value drops below the threshold to a maximum of 1 cycle. If the trigger threshold is passed through again, at any point later in the flight or any subsequent flight, MCAS will trigger again. This is entirely consistent with the Boeing statement and entirely reasonable solution in my view.

MCAS is also inhibited by AOA Disagree of more than 5.5degrees, a much more likely proposition than both failing high instantaneously. But any failure mode will only be present for a maximum of one flight since both sensors operable is required for despatch.

Ray
 
FluidFlow
Posts: 256
Joined: Wed Apr 10, 2019 6:39 am

Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 1:43 pm

kalvado wrote:
Ertro wrote:
For example if a flight lasts 4 hours and there is an event in the end of the flight which would need MCAS functionality I don't see any significant difference to the severity of the situation based on whether there was another event in the beginning of the flight 4 hours earlier than also needed this MCAS functionality and burned this one time feature inoperable? And if this logic is valid would the same argument hold equally true for somebody to say that the one time event was used last year so we don't need MCAS funtionality any more for the rest of the decade? Or a minute or 10 seconds?

The assumption behind MCAS single-shot design is that it is rarely, if ever, needed in flight. That makes some sense, actually; the airplane is not supposed to go into outer edges of the envelope. Most what I heard so far, MCAS is for extreme collision-avoidance manuring and few similar situations. It is unlikely to get multiple events on a single flight. Boeing's statement that regular line pilot is unlikely to encounter MCAS situation in their career is probably right.
Now, when it rains - it pours. Getting in a totally messed up airspace (say some extreme event in NYC/LON/LAX control center) with many evasive moves, flying on the edge due to a problem (mechanical problem on a plane, CoG way off, severe piloting problem, entering crazy weather pattern) is a situation MCAS may be genuinely needed more than once per flight. How often that may happen, what kind of scenarios are being considered in this regard is a big question.
MCAS role is mostly known from NYT article - a journalist leak, not an engineering assessment....


If you hit a strong microburst in a bad weather approach you might be toast without MACS. Imagine you are on approach, before flaps are down at around 5000ft agl and you are hit by a strong microburst. Autopilot is immediately off and when you realized what happened you are 3500ft agl descending. You pull on the joke as well as trim ANU as much as you can to avoid terrain. AoA increases and MCAS activates. MCAS prevents a stall but also reduces the effectivity of your manoeuvre to avoid terrain, you are still in a high AoA position and you keep pulling back on the yoke and start trimming again with the thumb switch, which deactivates MCAS. Ground proximity warning still goes off and suddenly it becomes easier to pull on the yoke. Unfortunately you do not realize this because a sh*t ton of warnings go off in the cockpit and you never experienced this in your career on a 737, plus you have no visuals in the bad weather. Stick shaker activates, but you are still concentrated on avoiding terrain. Then you stall 2500ft above ground level.

Would something like this happen often? NO, not but it would not be the first microburst that downs an aircraft and as well with the only aid to help you feel the aircraft not active (probably without warning) it is not a good situation to be in, because at that stage you need to feel the aircraft to fly it.
 
kalvado
Posts: 1878
Joined: Wed Mar 01, 2006 4:29 am

Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 1:50 pm

FluidFlow wrote:
kalvado wrote:
Ertro wrote:
For example if a flight lasts 4 hours and there is an event in the end of the flight which would need MCAS functionality I don't see any significant difference to the severity of the situation based on whether there was another event in the beginning of the flight 4 hours earlier than also needed this MCAS functionality and burned this one time feature inoperable? And if this logic is valid would the same argument hold equally true for somebody to say that the one time event was used last year so we don't need MCAS funtionality any more for the rest of the decade? Or a minute or 10 seconds?

The assumption behind MCAS single-shot design is that it is rarely, if ever, needed in flight. That makes some sense, actually; the airplane is not supposed to go into outer edges of the envelope. Most what I heard so far, MCAS is for extreme collision-avoidance manuring and few similar situations. It is unlikely to get multiple events on a single flight. Boeing's statement that regular line pilot is unlikely to encounter MCAS situation in their career is probably right.
Now, when it rains - it pours. Getting in a totally messed up airspace (say some extreme event in NYC/LON/LAX control center) with many evasive moves, flying on the edge due to a problem (mechanical problem on a plane, CoG way off, severe piloting problem, entering crazy weather pattern) is a situation MCAS may be genuinely needed more than once per flight. How often that may happen, what kind of scenarios are being considered in this regard is a big question.
MCAS role is mostly known from NYT article - a journalist leak, not an engineering assessment....


If you hit a strong microburst in a bad weather approach you might be toast without MACS. Imagine you are on approach, before flaps are down at around 5000ft agl and you are hit by a strong microburst. Autopilot is immediately off and when you realized what happened you are 3500ft agl descending. You pull on the joke as well as trim ANU as much as you can to avoid terrain. AoA increases and MCAS activates. MCAS prevents a stall but also reduces the effectivity of your manoeuvre to avoid terrain, you are still in a high AoA position and you keep pulling back on the yoke and start trimming again with the thumb switch, which deactivates MCAS. Ground proximity warning still goes off and suddenly it becomes easier to pull on the yoke. Unfortunately you do not realize this because a sh*t ton of warnings go off in the cockpit and you never experienced this in your career on a 737, plus you have no visuals in the bad weather. Stick shaker activates, but you are still concentrated on avoiding terrain. Then you stall 2500ft above ground level.

Would something like this happen often? NO, not but it would not be the first microburst that downs an aircraft and as well with the only aid to help you feel the aircraft not active (probably without warning) it is not a good situation to be in, because at that stage you need to feel the aircraft to fly it.

That is sort of what I mean with "crazy weather pattern". But now this is approach, likely flaps-out - and that may be the saving grace as you're likely in configuration where MCAS assistance is not required (at least Boeing told us so)
 
planecane
Posts: 1069
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 1:50 pm

FluidFlow wrote:
kalvado wrote:
Ertro wrote:
For example if a flight lasts 4 hours and there is an event in the end of the flight which would need MCAS functionality I don't see any significant difference to the severity of the situation based on whether there was another event in the beginning of the flight 4 hours earlier than also needed this MCAS functionality and burned this one time feature inoperable? And if this logic is valid would the same argument hold equally true for somebody to say that the one time event was used last year so we don't need MCAS funtionality any more for the rest of the decade? Or a minute or 10 seconds?

The assumption behind MCAS single-shot design is that it is rarely, if ever, needed in flight. That makes some sense, actually; the airplane is not supposed to go into outer edges of the envelope. Most what I heard so far, MCAS is for extreme collision-avoidance manuring and few similar situations. It is unlikely to get multiple events on a single flight. Boeing's statement that regular line pilot is unlikely to encounter MCAS situation in their career is probably right.
Now, when it rains - it pours. Getting in a totally messed up airspace (say some extreme event in NYC/LON/LAX control center) with many evasive moves, flying on the edge due to a problem (mechanical problem on a plane, CoG way off, severe piloting problem, entering crazy weather pattern) is a situation MCAS may be genuinely needed more than once per flight. How often that may happen, what kind of scenarios are being considered in this regard is a big question.
MCAS role is mostly known from NYT article - a journalist leak, not an engineering assessment....


If you hit a strong microburst in a bad weather approach you might be toast without MACS. Imagine you are on approach, before flaps are down at around 5000ft agl and you are hit by a strong microburst. Autopilot is immediately off and when you realized what happened you are 3500ft agl descending. You pull on the joke as well as trim ANU as much as you can to avoid terrain. AoA increases and MCAS activates. MCAS prevents a stall but also reduces the effectivity of your manoeuvre to avoid terrain, you are still in a high AoA position and you keep pulling back on the yoke and start trimming again with the thumb switch, which deactivates MCAS. Ground proximity warning still goes off and suddenly it becomes easier to pull on the yoke. Unfortunately you do not realize this because a sh*t ton of warnings go off in the cockpit and you never experienced this in your career on a 737, plus you have no visuals in the bad weather. Stick shaker activates, but you are still concentrated on avoiding terrain. Then you stall 2500ft above ground level.

Would something like this happen often? NO, not but it would not be the first microburst that downs an aircraft and as well with the only aid to help you feel the aircraft not active (probably without warning) it is not a good situation to be in, because at that stage you need to feel the aircraft to fly it.

Are you a pilot? I'm not asking to be difficult, I'm wanting to know how much expertise is behind your post.
 
FluidFlow
Posts: 256
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 2:16 pm

planecane wrote:
FluidFlow wrote:
kalvado wrote:
The assumption behind MCAS single-shot design is that it is rarely, if ever, needed in flight. That makes some sense, actually; the airplane is not supposed to go into outer edges of the envelope. Most what I heard so far, MCAS is for extreme collision-avoidance manuring and few similar situations. It is unlikely to get multiple events on a single flight. Boeing's statement that regular line pilot is unlikely to encounter MCAS situation in their career is probably right.
Now, when it rains - it pours. Getting in a totally messed up airspace (say some extreme event in NYC/LON/LAX control center) with many evasive moves, flying on the edge due to a problem (mechanical problem on a plane, CoG way off, severe piloting problem, entering crazy weather pattern) is a situation MCAS may be genuinely needed more than once per flight. How often that may happen, what kind of scenarios are being considered in this regard is a big question.
MCAS role is mostly known from NYT article - a journalist leak, not an engineering assessment....


If you hit a strong microburst in a bad weather approach you might be toast without MACS. Imagine you are on approach, before flaps are down at around 5000ft agl and you are hit by a strong microburst. Autopilot is immediately off and when you realized what happened you are 3500ft agl descending. You pull on the joke as well as trim ANU as much as you can to avoid terrain. AoA increases and MCAS activates. MCAS prevents a stall but also reduces the effectivity of your manoeuvre to avoid terrain, you are still in a high AoA position and you keep pulling back on the yoke and start trimming again with the thumb switch, which deactivates MCAS. Ground proximity warning still goes off and suddenly it becomes easier to pull on the yoke. Unfortunately you do not realize this because a sh*t ton of warnings go off in the cockpit and you never experienced this in your career on a 737, plus you have no visuals in the bad weather. Stick shaker activates, but you are still concentrated on avoiding terrain. Then you stall 2500ft above ground level.

Would something like this happen often? NO, not but it would not be the first microburst that downs an aircraft and as well with the only aid to help you feel the aircraft not active (probably without warning) it is not a good situation to be in, because at that stage you need to feel the aircraft to fly it.

Are you a pilot? I'm not asking to be difficult, I'm wanting to know how much expertise is behind your post.


No I am not a pilot. So it is just a theoretical thought. Flew a few times in a simulator and as a "co-Pilot" in a Cessna. I worked a few years in research of airflow especially concerning canard - wing interaction. And have a background in fluid dynamics with focus on large scale weather models.
 
planecane
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 2:22 pm

FluidFlow wrote:
planecane wrote:
FluidFlow wrote:

If you hit a strong microburst in a bad weather approach you might be toast without MACS. Imagine you are on approach, before flaps are down at around 5000ft agl and you are hit by a strong microburst. Autopilot is immediately off and when you realized what happened you are 3500ft agl descending. You pull on the joke as well as trim ANU as much as you can to avoid terrain. AoA increases and MCAS activates. MCAS prevents a stall but also reduces the effectivity of your manoeuvre to avoid terrain, you are still in a high AoA position and you keep pulling back on the yoke and start trimming again with the thumb switch, which deactivates MCAS. Ground proximity warning still goes off and suddenly it becomes easier to pull on the yoke. Unfortunately you do not realize this because a sh*t ton of warnings go off in the cockpit and you never experienced this in your career on a 737, plus you have no visuals in the bad weather. Stick shaker activates, but you are still concentrated on avoiding terrain. Then you stall 2500ft above ground level.

Would something like this happen often? NO, not but it would not be the first microburst that downs an aircraft and as well with the only aid to help you feel the aircraft not active (probably without warning) it is not a good situation to be in, because at that stage you need to feel the aircraft to fly it.

Are you a pilot? I'm not asking to be difficult, I'm wanting to know how much expertise is behind your post.


No I am not a pilot. So it is just a theoretical thought. Flew a few times in a simulator and as a "co-Pilot" in a Cessna. I worked a few years in research of airflow especially concerning canard - wing interaction. And have a background in fluid dynamics with focus on large scale weather models.
My question would be under your scenario if a pilot would trim while continuing to lift the nose? It was my understanding (from one simulator session in a 737NG Sim and no other experience flying) that you would trim when in a static state. i.e. you would trim once reaching the desired pitch for the climb. In your scenario it seems like the pilot would be controlling pitch with the stabilizer instead of the elevator.

I'd like a pilot to give some insight on this.
 
FluidFlow
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 2:38 pm

planecane wrote:
FluidFlow wrote:
planecane wrote:
Are you a pilot? I'm not asking to be difficult, I'm wanting to know how much expertise is behind your post.


No I am not a pilot. So it is just a theoretical thought. Flew a few times in a simulator and as a "co-Pilot" in a Cessna. I worked a few years in research of airflow especially concerning canard - wing interaction. And have a background in fluid dynamics with focus on large scale weather models.
My question would be under your scenario if a pilot would trim while continuing to lift the nose? It was my understanding (from one simulator session in a 737NG Sim and no other experience flying) that you would trim when in a static state. i.e. you would trim once reaching the desired pitch for the climb. In your scenario it seems like the pilot would be controlling pitch with the stabilizer instead of the elevator.

I'd like a pilot to give some insight on this.


Right I see your point. Theoretically it would help for a quick rotation to trim aswell but it could be even more reasonable that the pilot will not trim because it pulling is already a demanding job in that situation.
I would like to know aswell what would be the right action to escape a microburst.
 
JBirdAV8r
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 2:48 pm

planecane wrote:
FluidFlow wrote:
planecane wrote:
Are you a pilot? I'm not asking to be difficult, I'm wanting to know how much expertise is behind your post.


No I am not a pilot. So it is just a theoretical thought. Flew a few times in a simulator and as a "co-Pilot" in a Cessna. I worked a few years in research of airflow especially concerning canard - wing interaction. And have a background in fluid dynamics with focus on large scale weather models.
My question would be under your scenario if a pilot would trim while continuing to lift the nose? It was my understanding (from one simulator session in a 737NG Sim and no other experience flying) that you would trim when in a static state. i.e. you would trim once reaching the desired pitch for the climb. In your scenario it seems like the pilot would be controlling pitch with the stabilizer instead of the elevator.

I'd like a pilot to give some insight on this.


It’s not a plausible scenario. Trimming nose up would not be a pilot reaction in this case. We trim to alleviate control pressure, not to add elevator authority.

Theoretically, you would be relatively close to in-trim anyway in that scenario, even considering a 20-30kt airspeed loss. You would have more than enough elevator authority at that point to get the nose up, especially considering that in a windshear escape, you’ve firewalled the engines. That alone provides a significant nose-up pitching moment. Yanking back as hard as you could, AND adding trim, would only make things much worse. Plus, we are respecting the stick shaker anyway. We won’t continue to pitch up when we hit the PLIs because we know that won’t do us any good anyway.
I got my head checked--by a jumbo jet
 
FluidFlow
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 2:58 pm

JBirdAV8r wrote:
planecane wrote:
FluidFlow wrote:

No I am not a pilot. So it is just a theoretical thought. Flew a few times in a simulator and as a "co-Pilot" in a Cessna. I worked a few years in research of airflow especially concerning canard - wing interaction. And have a background in fluid dynamics with focus on large scale weather models.
My question would be under your scenario if a pilot would trim while continuing to lift the nose? It was my understanding (from one simulator session in a 737NG Sim and no other experience flying) that you would trim when in a static state. i.e. you would trim once reaching the desired pitch for the climb. In your scenario it seems like the pilot would be controlling pitch with the stabilizer instead of the elevator.

I'd like a pilot to give some insight on this.


It’s not a plausible scenario. Trimming nose up would not be a pilot reaction in this case. We trim to alleviate control pressure, not to add elevator authority.

Theoretically, you would be relatively close to in-trim anyway in that scenario, even considering a 20-30kt airspeed loss. You would have more than enough elevator authority at that point to get the nose up, especially considering that in a windshear escape, you’ve firewalled the engines. That alone provides a significant nose-up pitching moment. Yanking back as hard as you could, AND adding trim, would only make things much worse. Plus, we are respecting the stick shaker anyway. We won’t continue to pitch up when we hit the PLIs because we know that won’t do us any good anyway.


Thanks sounds reasonable. It was just the only situation where from an atmospheric point of view MCAS could be needed a second time without dropping under the critical AoA.
 
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aerolimani
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 5:27 pm

XRAYretired wrote:
Ertro wrote:
kalvado wrote:
The assumption behind MCAS single-shot design is that it is rarely, if ever, needed in flight. That makes some sense, actually; the airplane is not supposed to go into outer edges of the envelope. Most what I heard so far, MCAS is for extreme collision-avoidance manuring and few similar situations. It is unlikely to get multiple events on a single flight. Boeing's statement that regular line pilot is unlikely to encounter MCAS situation in their career is probably right.


It sure is rare event and single pilot is unlikely to encounter it ever. However that does not mean anything whether MCAS is a needed functionality on a plane. There are multiple other systems on a plane that one pilot is never going to need but they still better be onboard for the next pilot that does encounter a situation where they are needed.

Whether it is okay to decide MCAS to be sometimes inoperable I am not convinced this kind of one time rule makes any more sense than to decide that MCAS is inoperable on mondays. After all it is very unlikely it is ever going to be needed and especially on mondays.


I'm afraid this is all based around miss-interpretation. There is no 'one time rule' except in the case of AOA sensors, both of them, failing permanently high instantaneously and above the threshold for MCAS initiation i.e. if the AOA remains above threshold, MCAS will be inhibited after 1 cycle (9.26 secs, 2.5units trim max). Assuming an activation is triggered, by the combined two sensor and previous measurement transitioning from below to above the threshold, MCAS will operate for the time needed such that the value drops below the threshold to a maximum of 1 cycle. If the trigger threshold is passed through again, at any point later in the flight or any subsequent flight, MCAS will trigger again. This is entirely consistent with the Boeing statement and entirely reasonable solution in my view.

MCAS is also inhibited by AOA Disagree of more than 5.5degrees, a much more likely proposition than both failing high instantaneously. But any failure mode will only be present for a maximum of one flight since both sensors operable is required for despatch.

Ray

I hope you don’t mind, Ray, but I’m going to quickly summarize the most important details of your writeup, in slightly less technical language.

With function AOA sensors:
When the sensors read above a certain level, MCAS 2.0 will activate once. If all is well with the plane, MCAS will reduce the AOA below the threshold, and the MCAS system resets. So, if there is another event, it is able to activate again.

*In addition, once the AOA reading falls below threshold, the MCAS actually restores the trim to its previous setting.* Source: http://www.b737.org.uk/mcas.htm

With malfunctioning sensors:
With both reading high, and stuck at that reading, MCAS will activate. If the sensors continue to malfunction high, MCAS will not activate again. This is the only scenario in which MCAS would only activate once in a flight, assuming the sensors don’t somehow recover. Most assuredly, the plane will now be displaying lots of warnings, and there will be NNC’s to follow.
 
hivue
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 5:56 pm

FluidFlow wrote:
If you hit a strong microburst in a bad weather approach you might be toast without MACS. Imagine you are on approach, before flaps are down at around 5000ft agl and you are hit by a strong microburst. Autopilot is immediately off and when you realized what happened you are 3500ft agl descending. You pull on the joke as well as trim ANU as much as you can to avoid terrain. AoA increases and MCAS activates. MCAS prevents a stall but also reduces the effectivity of your manoeuvre to avoid terrain


It appears that the myth that MCAS is a stall prevention system persists. It was not a stall prevention system in MCAS 0.0 and 1.0, and will not be a stall prevention system in MCAS 2.0. MCAS is there to provide proper stick forces when the situation -- and the certification requirements -- require some augmentation for that.
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
XRAYretired
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 6:06 pm

aerolimani wrote:
XRAYretired wrote:
Ertro wrote:

It sure is rare event and single pilot is unlikely to encounter it ever. However that does not mean anything whether MCAS is a needed functionality on a plane. There are multiple other systems on a plane that one pilot is never going to need but they still better be onboard for the next pilot that does encounter a situation where they are needed.

Whether it is okay to decide MCAS to be sometimes inoperable I am not convinced this kind of one time rule makes any more sense than to decide that MCAS is inoperable on mondays. After all it is very unlikely it is ever going to be needed and especially on mondays.


I'm afraid this is all based around miss-interpretation. There is no 'one time rule' except in the case of AOA sensors, both of them, failing permanently high instantaneously and above the threshold for MCAS initiation i.e. if the AOA remains above threshold, MCAS will be inhibited after 1 cycle (9.26 secs, 2.5units trim max). Assuming an activation is triggered, by the combined two sensor and previous measurement transitioning from below to above the threshold, MCAS will operate for the time needed such that the value drops below the threshold to a maximum of 1 cycle. If the trigger threshold is passed through again, at any point later in the flight or any subsequent flight, MCAS will trigger again. This is entirely consistent with the Boeing statement and entirely reasonable solution in my view.

MCAS is also inhibited by AOA Disagree of more than 5.5degrees, a much more likely proposition than both failing high instantaneously. But any failure mode will only be present for a maximum of one flight since both sensors operable is required for despatch.

Ray

I hope you don’t mind, Ray, but I’m going to quickly summarize the most important details of your writeup, in slightly less technical language.

With function AOA sensors:
When the sensors read above a certain level, MCAS 2.0 will activate once. If all is well with the plane, MCAS will reduce the AOA below the threshold, and the MCAS system resets. So, if there is another event, it is able to activate again.

*In addition, once the AOA reading falls below threshold, the MCAS actually restores the trim to its previous setting.* Source: http://www.b737.org.uk/mcas.htm

With malfunctioning sensors:
With both reading high, and stuck at that reading, MCAS will activate. If the sensors continue to malfunction high, MCAS will not activate again. This is the only scenario in which MCAS would only activate once in a flight, assuming the sensors don’t somehow recover. Most assuredly, the plane will now be displaying lots of warnings, and there will be NNC’s to follow.


No probs. I guess it also highlights one of the things we have no idea about so far and that is - if MCAS completes a full cycle in fault condition or not in fault condition, would it return trim to previous setting as well? V1.0 clearly did not do so in fault condition in our two events. It may have saved the flights if it did (another simple safeguard missed?).

Ray
 
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hilram
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 6:13 pm

Boeing pays out to relatives of Crash Victims: https://boeing.mediaroom.com/2019-07-03 ... -Accidents

At least Boeing seems now to have moved on from the stance that "we hold no blame". Good. Paints them in a better light.
Flown on: A319, 320, 321, 332, 333, 343 | B732, 734, 735, 736, 73G, 738, 743, 744, 772, 77W | BAe-146 | DHC-6, 7, 8 | F50 | E195 | MD DC-9 41, MD-82, MD-87
 
kalvado
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 6:19 pm

hivue wrote:
FluidFlow wrote:
If you hit a strong microburst in a bad weather approach you might be toast without MACS. Imagine you are on approach, before flaps are down at around 5000ft agl and you are hit by a strong microburst. Autopilot is immediately off and when you realized what happened you are 3500ft agl descending. You pull on the joke as well as trim ANU as much as you can to avoid terrain. AoA increases and MCAS activates. MCAS prevents a stall but also reduces the effectivity of your manoeuvre to avoid terrain


It appears that the myth that MCAS is a stall prevention system persists. It was not a stall prevention system in MCAS 0.0 and 1.0, and will not be a stall prevention system in MCAS 2.0. MCAS is there to provide proper stick forces when the situation -- and the certification requirements -- require some augmentation for that.

It appears that some people still believe Boeing without hard data at hand.
 
MSPNWA
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 6:21 pm

hilram wrote:
At least Boeing seems now to have moved on from the stance that "we hold no blame".


They never had that stance.
 
sillystrings
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 6:28 pm

MSPNWA wrote:
hilram wrote:
At least Boeing seems now to have moved on from the stance that "we hold no blame".


They never had that stance.


"This is an ongoing and relentless commitment to make safe airplanes even safer."
 
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SamYeager2016
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 6:36 pm

MSPNWA wrote:
hilram wrote:
At least Boeing seems now to have moved on from the stance that "we hold no blame".


They never had that stance.

Absolutely! Of course none of this would have happened if those pesky pilots had just run the trim runaway NNC. :sarcastic:
 
hivue
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 6:36 pm

kalvado wrote:
It appears that some people still believe Boeing without hard data at hand.


I (along with a number of others) have been making the "MCAS is not stall prevention" point often in these threads. But if I'm wrong and MCAS is a Boeing alpha prot/alph floor equivalent, minus the FBW, I will genuinely be impressed.

But I don't expect to be impressed.
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
sillystrings
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 6:49 pm

hivue wrote:
FluidFlow wrote:
If you hit a strong microburst in a bad weather approach you might be toast without MACS. Imagine you are on approach, before flaps are down at around 5000ft agl and you are hit by a strong microburst. Autopilot is immediately off and when you realized what happened you are 3500ft agl descending. You pull on the joke as well as trim ANU as much as you can to avoid terrain. AoA increases and MCAS activates. MCAS prevents a stall but also reduces the effectivity of your manoeuvre to avoid terrain


It appears that the myth that MCAS is a stall prevention system persists. It was not a stall prevention system in MCAS 0.0 and 1.0, and will not be a stall prevention system in MCAS 2.0. MCAS is there to provide proper stick forces when the situation -- and the certification requirements -- require some augmentation for that.



I don't know. To me this argument sounds like "the purpose of a wall switch is to provide current to the light bulb, not to turn the light on".

What exactly is the purpose of the stick force requirement then?
 
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aerolimani
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 6:50 pm

XRAYretired wrote:
aerolimani wrote:
XRAYretired wrote:

I'm afraid this is all based around miss-interpretation. There is no 'one time rule' except in the case of AOA sensors, both of them, failing permanently high instantaneously and above the threshold for MCAS initiation i.e. if the AOA remains above threshold, MCAS will be inhibited after 1 cycle (9.26 secs, 2.5units trim max). Assuming an activation is triggered, by the combined two sensor and previous measurement transitioning from below to above the threshold, MCAS will operate for the time needed such that the value drops below the threshold to a maximum of 1 cycle. If the trigger threshold is passed through again, at any point later in the flight or any subsequent flight, MCAS will trigger again. This is entirely consistent with the Boeing statement and entirely reasonable solution in my view.

MCAS is also inhibited by AOA Disagree of more than 5.5degrees, a much more likely proposition than both failing high instantaneously. But any failure mode will only be present for a maximum of one flight since both sensors operable is required for despatch.

Ray

I hope you don’t mind, Ray, but I’m going to quickly summarize the most important details of your writeup, in slightly less technical language.

With function AOA sensors:
When the sensors read above a certain level, MCAS 2.0 will activate once. If all is well with the plane, MCAS will reduce the AOA below the threshold, and the MCAS system resets. So, if there is another event, it is able to activate again.

*In addition, once the AOA reading falls below threshold, the MCAS actually restores the trim to its previous setting.* Source: http://www.b737.org.uk/mcas.htm

With malfunctioning sensors:
With both reading high, and stuck at that reading, MCAS will activate. If the sensors continue to malfunction high, MCAS will not activate again. This is the only scenario in which MCAS would only activate once in a flight, assuming the sensors don’t somehow recover. Most assuredly, the plane will now be displaying lots of warnings, and there will be NNC’s to follow.


No probs. I guess it also highlights one of the things we have no idea about so far and that is - if MCAS completes a full cycle in fault condition or not in fault condition, would it return trim to previous setting as well? V1.0 clearly did not do so in fault condition in our two events. It may have saved the flights if it did (another simple safeguard missed?).

Ray

Having MCAS restore the trim before the aircraft has left the state of high AOA would defeat the purpose of MCAS.

As to the accidents, limiting MCAS to only one activation per high AOA event would have likely saved them.

I believe the fact that only one activation is needed, in a high AOA event, is evidence that MCAS is really not intended to directly prevent a stall. I believe that with only one MCAS activation, the pilot can still pull the plane into a stall. However, that would be a willful disregard of all proper flying, were the pilot to do that, not to mention ignoring a whole host of warnings.

AFAIK, MCAS 1.0 was supposed to return the trim after the AOA sensors show that the aircraft AOA has fallen below the activation threshold. Of course, in our accident scenarios, the AOA sensors were giving false information, thus the the indicated AOA never lowered at all, thus never getting to where MCAS would restore the trim.

As to MCAS 2… for what it's worth, here's some of what http://www.b737.org.uk/mcas.htm has to say regarding Boeing's proposed fix:

A modification to the activation and resynchronization schedule. MCAS will be limited to operate only for one cycle per high AoA event, rather than multiple. At present it will operate for 10s, pause for 5s and repeat for as often as it senses the high AoA condition is present. Furthermore the logic for MCAS to command a nose up stab trim to return to trim following pilot electric trim intervention or exceeding the forward column cutout switch, will also now be improved.
 
MSPNWA
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 6:59 pm

sillystrings wrote:
"This is an ongoing and relentless commitment to make safe airplanes even safer."


That is not a stance of having no fault. You'll have to keep searching. And searching. And searching. Etc.
 
sillystrings
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 7:15 pm

MSPNWA wrote:
sillystrings wrote:
"This is an ongoing and relentless commitment to make safe airplanes even safer."


That is not a stance of having no fault. You'll have to keep searching. And searching. And searching. Etc.


to make safe airplanes even safer

The implication is quite clear. To state otherwise is simply gas-lighting.
 
MSPNWA
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 7:30 pm

sillystrings wrote:
The implication is quite clear. To state otherwise is simply gas-lighting.


Even "safe" airplanes crash with the airplane itself being a factor. I'm guessing you made a conclusion first and are trying to find evidence to support it. That leads to distortions like this.

What you won't find is anything like "we have no blame", "we are not at fault", "we have nothing to do with the crashes", etc. But keep searching if you wish.
 
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seahawk
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Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 7:39 pm

kalvado wrote:
seahawk wrote:
kalvado wrote:
The assumption behind MCAS single-shot design is that it is rarely, if ever, needed in flight. That makes some sense, actually; the airplane is not supposed to go into outer edges of the envelope. Most what I heard so far, MCAS is for extreme collision-avoidance manuring and few similar situations. It is unlikely to get multiple events on a single flight. Boeing's statement that regular line pilot is unlikely to encounter MCAS situation in their career is probably right.
Now, when it rains - it pours. Getting in a totally messed up airspace (say some extreme event in NYC/LON/LAX control center) with many evasive moves, flying on the edge due to a problem (mechanical problem on a plane, CoG way off, severe piloting problem, entering crazy weather pattern) is a situation MCAS may be genuinely needed more than once per flight. How often that may happen, what kind of scenarios are being considered in this regard is a big question.
MCAS role is mostly known from NYT article - a journalist leak, not an engineering assessment....


You are missing the point, the problem is the MCAS behaviour during a malfunction in the system. The actual designed function of MCAS was not the problem, the undesired side effect of a faulty sensor was.

False actuation malfunction probability is strongly reduced with 2 sensor approach, and severity of the outcome is limited with the single-shot actuation. I would say, proposed MCAS logic is as good as it can be with an existing set of hardware. Both false-actuation and false-non-actuation probabilities seem low enough.


Probably yes, but we do not know the consequences of the using 2 sensors, it opens a lot of new questions.

For example you suddenly create a connection between the ADIRU of the pilot and that of the co-pilot, those system are totally independent at the moment. You know need to connect ADMs to both ADIRUS, which then begs the question if a failure in any of those components could fry all connected components. Ist the ADIRU able to handle data from 3 ADMs and not only 2, etc.
 
sillystrings
Posts: 28
Joined: Thu May 30, 2019 7:06 pm

Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 7:45 pm

MSPNWA wrote:
sillystrings wrote:
The implication is quite clear. To state otherwise is simply gas-lighting.


Even "safe" airplanes crash with the airplane itself being a factor. I'm guessing you made a conclusion first and are trying to find evidence to support it. That leads to distortions like this.

What you won't find is anything like "we have no blame", "we are not at fault", "we have nothing to do with the crashes", etc. But keep searching if you wish.


There is a serious problem with your logic. If MAX was safe, it would be flying right now. So we have to assume it is not safe. When Muilenburg states that MAX is "safe", he is implying there is nothing wrong with it. If there is nothing wrong with it, then it certainly cannot be a cause, or partly a cause of a crash, right?
 
planecane
Posts: 1069
Joined: Thu Feb 09, 2017 4:58 pm

Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 8:08 pm

sillystrings wrote:
hivue wrote:
FluidFlow wrote:
If you hit a strong microburst in a bad weather approach you might be toast without MACS. Imagine you are on approach, before flaps are down at around 5000ft agl and you are hit by a strong microburst. Autopilot is immediately off and when you realized what happened you are 3500ft agl descending. You pull on the joke as well as trim ANU as much as you can to avoid terrain. AoA increases and MCAS activates. MCAS prevents a stall but also reduces the effectivity of your manoeuvre to avoid terrain


It appears that the myth that MCAS is a stall prevention system persists. It was not a stall prevention system in MCAS 0.0 and 1.0, and will not be a stall prevention system in MCAS 2.0. MCAS is there to provide proper stick forces when the situation -- and the certification requirements -- require some augmentation for that.



I don't know. To me this argument sounds like "the purpose of a wall switch is to provide current to the light bulb, not to turn the light on".

What exactly is the purpose of the stick force requirement then?


So that it does not become easier to reach stall attitude under certain high AoA conditions. It is somewhat semantics but there is a distinction. A stall prevention system would do something to prevent the pilot from being able to get to stall attitude. In the case of the 737 that would be something like not allowing the elevator to move past a certain point so that no matter what the pilot does it is impossible to stall.

Airbus FWB does this (at least in normal mode) where no matter what the pilot does, they can't stall the aircraft. That is a stall prevention system.

MCAS does not make it impossible to stall.
 
planecane
Posts: 1069
Joined: Thu Feb 09, 2017 4:58 pm

Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 8:10 pm

seahawk wrote:
kalvado wrote:
seahawk wrote:

You are missing the point, the problem is the MCAS behaviour during a malfunction in the system. The actual designed function of MCAS was not the problem, the undesired side effect of a faulty sensor was.

False actuation malfunction probability is strongly reduced with 2 sensor approach, and severity of the outcome is limited with the single-shot actuation. I would say, proposed MCAS logic is as good as it can be with an existing set of hardware. Both false-actuation and false-non-actuation probabilities seem low enough.


Probably yes, but we do not know the consequences of the using 2 sensors, it opens a lot of new questions.

For example you suddenly create a connection between the ADIRU of the pilot and that of the co-pilot, those system are totally independent at the moment. You know need to connect ADMs to both ADIRUS, which then begs the question if a failure in any of those components could fry all connected components. Ist the ADIRU able to handle data from 3 ADMs and not only 2, etc.


Clearly there must already be a physical connection of some type. Otherwise MCAS 2.0 would require hardware changes.
 
XRAYretired
Posts: 553
Joined: Fri Mar 15, 2019 11:21 am

Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 8:13 pm

aerolimani wrote:
XRAYretired wrote:
aerolimani wrote:
I hope you don’t mind, Ray, but I’m going to quickly summarize the most important details of your writeup, in slightly less technical language.

With function AOA sensors:
When the sensors read above a certain level, MCAS 2.0 will activate once. If all is well with the plane, MCAS will reduce the AOA below the threshold, and the MCAS system resets. So, if there is another event, it is able to activate again.

*In addition, once the AOA reading falls below threshold, the MCAS actually restores the trim to its previous setting.* Source: http://www.b737.org.uk/mcas.htm

With malfunctioning sensors:
With both reading high, and stuck at that reading, MCAS will activate. If the sensors continue to malfunction high, MCAS will not activate again. This is the only scenario in which MCAS would only activate once in a flight, assuming the sensors don’t somehow recover. Most assuredly, the plane will now be displaying lots of warnings, and there will be NNC’s to follow.


No probs. I guess it also highlights one of the things we have no idea about so far and that is - if MCAS completes a full cycle in fault condition or not in fault condition, would it return trim to previous setting as well? V1.0 clearly did not do so in fault condition in our two events. It may have saved the flights if it did (another simple safeguard missed?).

Ray

Having MCAS restore the trim before the aircraft has left the state of high AOA would defeat the purpose of MCAS.

As to the accidents, limiting MCAS to only one activation per high AOA event would have likely saved them.

I believe the fact that only one activation is needed, in a high AOA event, is evidence that MCAS is really not intended to directly prevent a stall. I believe that with only one MCAS activation, the pilot can still pull the plane into a stall. However, that would be a willful disregard of all proper flying, were the pilot to do that, not to mention ignoring a whole host of warnings.

AFAIK, MCAS 1.0 was supposed to return the trim after the AOA sensors show that the aircraft AOA has fallen below the activation threshold. Of course, in our accident scenarios, the AOA sensors were giving false information, thus the the indicated AOA never lowered at all, thus never getting to where MCAS would restore the trim.

As to MCAS 2… for what it's worth, here's some of what http://www.b737.org.uk/mcas.htm has to say regarding Boeing's proposed fix:

A modification to the activation and resynchronization schedule. MCAS will be limited to operate only for one cycle per high AoA event, rather than multiple. At present it will operate for 10s, pause for 5s and repeat for as often as it senses the high AoA condition is present. Furthermore the logic for MCAS to command a nose up stab trim to return to trim following pilot electric trim intervention or exceeding the forward column cutout switch, will also now be improved.



Yup, and then waiting 5 secs to before continuing AND is contrary to the purpose if the condition has not been resolved in the first 10. V2.0 will not continue after 1 cycle if the value remains above the threshold and therefore does not support the position that 1 cycle is not satisfactory.

I will not comment on stall prevention/protection, pitch stability/linearity, or just plain 'so it handles in the same way as an NG', the later being still the formal position of Boeing on their website page for MCAS update, since it can be and has been twisted any way by anyone. Sufficient to say it was found necessary, and is still found necessary to have the system. What was unnecessary was incompetent implementation perhaps even willful disregard for good design practices.

Ray
 
MSPNWA
Posts: 3338
Joined: Thu Apr 23, 2009 2:48 am

Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 8:18 pm

sillystrings wrote:
There is a serious problem with your logic. If MAX was safe, it would be flying right now. So we have to assume it is not safe. When Muilenburg states that MAX is "safe", he is implying there is nothing wrong with it. If there is nothing wrong with it, then it certainly cannot be a cause, or partly a cause of a crash, right?


"Safe" is a subjective term. What's safe to one may be unsafe to another. We would expect Boeing to stand behind their product, and believe it's safe (particularly before all the facts come in). That is not an explicit denial of all fault, which is what many were trying to blame Boeing for. It's quite the opposite, because you can't make a "safe" airplane "safer" without the "safe" airplane having faults! You're now admitting that all you have is a subjective assumption of the term "safe". That belies the fact that consensus "safe" aircraft have crashed due in some part to manufacturer fault.

The fact of the matter is that Boeing has never explicitly denied all fault/blame in the accidents. But keep searching for it if you wish.
 
XRAYretired
Posts: 553
Joined: Fri Mar 15, 2019 11:21 am

Re: Boeing 737MAX Grounded Worldwide Q3 2019

Wed Jul 03, 2019 8:21 pm

seahawk wrote:
kalvado wrote:
seahawk wrote:

You are missing the point, the problem is the MCAS behaviour during a malfunction in the system. The actual designed function of MCAS was not the problem, the undesired side effect of a faulty sensor was.

False actuation malfunction probability is strongly reduced with 2 sensor approach, and severity of the outcome is limited with the single-shot actuation. I would say, proposed MCAS logic is as good as it can be with an existing set of hardware. Both false-actuation and false-non-actuation probabilities seem low enough.


Probably yes, but we do not know the consequences of the using 2 sensors, it opens a lot of new questions.

For example you suddenly create a connection between the ADIRU of the pilot and that of the co-pilot, those system are totally independent at the moment. You know need to connect ADMs to both ADIRUS, which then begs the question if a failure in any of those components could fry all connected components. Ist the ADIRU able to handle data from 3 ADMs and not only 2, etc.


You need to think data rather than wires. They already share data sources including each others outputs for some function checking.

Ray

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