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737 MAX future

Old 10th May 2019, 20:08
  #21 (permalink)  
 
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Originally Posted by Eddie Dean View Post
Boeing for a lot of reasons, believe that two serviceable aircraft were flown into the ground.

There is a mammoth thread on the military side about an RAF CH47 crash some 20 years ago. Suffice to say, there's a big difference between Serviceable and Airworthy.
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Old 10th May 2019, 20:44
  #22 (permalink)  
 
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Originally Posted by Eddie Dean View Post
Boeing for a lot of reasons, believe that two serviceable aircraft were flown into the ground.
A serviceable aircraft was flown into the ground -- by the software.

As a pax I do not really care if a particular type of plane is crashing because of a technical flaw or because current pilots are not skilled enough to fly it. It is all a black box to me, with two possible outcomes; I make it home safely and on time or I do not. If there is some other type that is less likely to crash with the pilots that we have (rather than the pilots that we wish we had), I'll take it and let the enthusiasts bemoan how I selfishly ruined the Pinto a perfectly fine plane.

I find a lot of the actions taken by Boeing to be inexplicable. I'm not particularly of the "hate big companies crowd" (I did quite well at big companies and while executives are not particularly useful in my opinion neither are they particularly venial.) News stories that have come out indicate that the culture is pretty sick right now, and it does lead one to question all of their new projects. I mean really, our meetings would have gone much more easily if we had simply reorganized our test group (the test pilots in Boeing's case) away from engineering! Those testers ask so many annoying questions...

My interest is in design, especially bad design and how we can avoid inflicting more of it on humans. I though that this crash would come down to what appeared to be perfectly reasonable decisions that fit prevailing standards but indicate a generic flaw in the prevailing standards. Instead it seems to be a product of FUBAR engineering which is not what I expected from Boeing or any company not based in San Jose run by three 'bros and a bunch of beer.
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Old 10th May 2019, 21:32
  #23 (permalink)  
 
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Originally Posted by Ian W View Post
Assumptions made on how pilots would behave have proved unsafe -
Lion air and Ethiopian being two stark and terrible examples of this fact.

The perception, at least that being portrayed by the media, is that the truth is far from out there yet and that skeletons remain in the Boeing closet around this entire MAX project.

It has to get worse before it gets better. A lot of very good people stand to suffer if that does not happen
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Old 10th May 2019, 23:49
  #24 (permalink)  
 
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The 'fix' includes using 2 AoA sensors. That is not a fix. The ac needs 3, so Boeing is minimizing the cost and impact of the fix.

They almost always disagree, so a 3rd is needed in the decision process. What happens if, like in the crash, one is damaged on DEP?

If MCAS is inop can the ac be dispatched? How does a pilot know MCAS INOP?
If the system is not active until 400 AGL, how does a pilot know the system is inop?

Since the first Lion Air incident was on final, where are the parameters for that?
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Old 11th May 2019, 00:08
  #25 (permalink)  
 
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Let's face it, the fix is in and nobody cares. Pilots with the right suff are going to pretend they are sure can fly this thing when it fights them, airlines are going to pretend their pilots can fly it without additional sim training, and Boeing is going to pretend they fixed it, and the FAA is going to pretend it's fixed, and the Inspector General is going to believe that the FAA certified the type correctly the first time round, and everyone is going to kick Airbus very hard under the table to make sure the Europeans accept the fix.

After reading this forum, I have come to realize that pilots are smart professionals who care bout flying planes, but do not understand that a bad design puts them in a bad place, and every pilot is convinced that *he* would find the right solution to the mechanical issue that killed his colleagues. The first pages of Tom Wolfe's book The Right Stuff come to mind.

Edmund
PS. I say "he" on purpose. I think the female pilots are probably less testosterone-fueled.

Edmund
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Old 11th May 2019, 00:09
  #26 (permalink)  
 
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We have 3 artificial horizons in order to have a tie breaker if 1 goes wrong, same with the air speed indicators and usually IRSs. I can't see how 2 AoA sensors will meet requirements if 1 starts acting up. Boeing may have to come up with a completely new stall avoidance system, even if it means recertifying the aircraft as a new type and requiring pilots to obtain a new rating.
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Old 11th May 2019, 00:20
  #27 (permalink)  
 
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Let's face it, the fix is in and nobody cares. Pilots with the right suff are going to pretend they are sure can fly this thing when it fights them, airlines are going to pretend their pilots can fly it without additional sim training, and Boeing is going to pretend they fixed it, and the FAA is going to pretend it's fixed, and the Inspector General is going to believe that the FAA certified the type correctly the first time round, and everyone is going to kick Airbus very hard under the table to make sure the Europeans accept the fix.

And then it will crash again.

Edmund
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Old 11th May 2019, 00:20
  #28 (permalink)  
 
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Originally Posted by Smythe View Post
The 'fix' includes using 2 AoA sensors. That is not a fix. The ac needs 3, so Boeing is minimizing the cost and impact of the fix.

They almost always disagree, so a 3rd is needed in the decision process. What happens if, like in the crash, one is damaged on DEP?

If MCAS is inop can the ac be dispatched? How does a pilot know MCAS INOP?
If the system is not active until 400 AGL, how does a pilot know the system is inop?

Since the first Lion Air incident was on final, where are the parameters for that?
I got a brief on the new software yesterday. First, I would point out that while a third AOA would be nice, it is not necessary. The 737 has a number of double redundant systems. If there is a disagreement, we get a warning and we refer to a procedure to determine the bad system. We don't need a third AOA to figure out the bad one because we can cross check the airspeeds, mach numbers, altitudes, and power settings for reasonableness. The pilots are, in effect, the "third" system that sorts the good from the bad.

MCAS is part of the Speed Trim System (STS). There are two STS channels, and one is always required for dispatch. If one or both STS/MCAS systems became inop, we receive a warning annunciator on the flight deck. If both systems are inop, the annunciator comes on immediately - it doesn't wait until 400'. If both STS channels fail in flight, we have a non-normal procedure to address it - just like we have non-normals to address the failure of engines, hydraulics, electrics and all sorts of other things we would require for dispatch.

The new Flight Control Computer (FCC) software will inhibit any STS/MCAS input if the difference between AOA's is greater than about 5 degrees. This is more stringent that the current "AOA Disagree" trigger of greater than 10 degrees. The new software also has some other tests for reasonableness. and the total nose down input is adjusted for the conditions - it will input more stab trim at low airspeeds and less at high airspeeds.

Not sure what you are asking with your last question, but maybe it would be a helpful reminder that MCAS only activates with the flaps retracted. If the flight crew is operating the aircraft normally, the flaps will always be extended below 1000 feet.
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Old 11th May 2019, 00:24
  #29 (permalink)  
 
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Originally Posted by edmundronald View Post

After reading this forum, I have come to realize that pilots are smart professionals who care bout flying planes, but do not understand that a bad design puts them in a bad place,
Edmund
Trust me, we understand fully. There is a saying that goes, "The pilot is usually the first one to the scene of the accident." Pilots all want to operate planes that don't malfunction, but we also understand that some days we don't get our wish.
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Old 11th May 2019, 00:41
  #30 (permalink)  
 
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Any fix is going to have to be belt and braces, bullet proof if confidence is going to be restored in the MAX. It will have to cover the lowest denominator airline flying the type not just major airlines in first world countries. A minimum standard solution might get it back in the air but cause future orders to dry up and heaven help Boeing if another one crashes.
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Old 11th May 2019, 01:15
  #31 (permalink)  
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At the end of the day, MCAS will still be able to make inputs to a 47' flying surface. We read that these commands are to be substantially modified, fine, but still that black box has the potential to house HAL. Just how does one construct an impenetrable wall that will stop millions of junction gates from a catastrophic conspiracy - one that no one has filtered out of thousands of lines of code - one that won't show up for months or even years? My feeling is that its connection to the stabilizer should be totally removed and do nothing but warn. But then of course there's STS, MCAS's senior logic layer. That's worked okay for years but it's the sheer power of that flight surface that makes my aged sphincter-system lock up.

Even the basic premise seems bizarre to me: in certain circumstances we want to stop the elevators becoming steadily lighter, so we pitch an entire aircraft nose down? Height, flaps zero, AP off, speed within range and a complex system of relays etc., should all stop that signal going to the tail, but the potential for unwanted activation is hard wired into that aircraft for life.
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Old 11th May 2019, 01:28
  #32 (permalink)  
 
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Originally Posted by 737 Driver View Post
I got a brief on the new software yesterday.

MCAS is part of the Speed Trim System (STS). There are two STS channels, and one is always required for dispatch. If one or both STS/MCAS systems became inop, we receive a warning annunciator on the flight deck. If both systems are inop, the annunciator comes on immediately - it doesn't wait until 400'. If both STS channels fail in flight, we have a non-normal procedure to address it - just like we have non-normals to address the failure of engines, hydraulics, electrics and all sorts of other things we would require for dispatch.

The new Flight Control Computer (FCC) software will inhibit any STS/MCAS input if the difference between AOA's is greater than about 5 degrees. This is more stringent that the current "AOA Disagree" trigger of greater than 10 degrees. The new software also has some other tests for reasonableness. and the total nose down input is adjusted for the conditions - it will input more stab trim at low airspeeds and less at high airspeeds.

Not sure what you are asking with your last question, but maybe it would be a helpful reminder that MCAS only activates with the flaps retracted. If the flight crew is operating the aircraft normally, the flaps will always be extended below 1000 feet.
There was the Boeing spokesman that said the AoA disagree only worked above 400ft after they found it actually was not active all all.

So if that is true, then how can the MCAS part of the STS be tested before flight? Lion Air seems faulty AoA fitted - would the annunciation illuminate in this case?
The current MCAS AoA had no limit of disagree, and there was no problem withe the STS operation previously - MCAS really looks more than just a sub-sytem of STS.
Now the that is worrying - variable amounts of input! So if you are going slow with a high angle of attack - how long do you watch that trim wheel spin for?

From the previous thread Mr Driver your instinct would be to trim have you then disabled MCAS and stopped it from its certification requirement?

Would your current practice still stand? - keep flap out, or Autopilot on to bypass MCAS from being able to activate?
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Old 11th May 2019, 01:28
  #33 (permalink)  
 
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Originally Posted by Loose rivets View Post
At the end of the day, MCAS will still be able to make inputs to a 47' flying surface. We read that these commands are to be substantially modified, fine, but still that black box has the potential to house HAL. Just how does one construct an impenetrable wall that will stop millions of junction gates from a catastrophic conspiracy - one that no one has filtered out of thousands of lines of code - one that won't show up for months or even years? My feeling is that its connection to the stabilizer should be totally removed and do nothing but warn. But then of course there's STS, MCAS's senior logic layer. That's worked okay for years but it's the sheer power of that flight surface that makes my aged sphincter-system lock up.

Even the basic premise seems bizarre to me: in certain circumstances we want to stop the elevators becoming steadily lighter, so we pitch an entire aircraft nose down? Height, flaps zero, AP off, speed within range and a complex system of relays etc., should all stop that signal going to the tail, but the potential for unwanted activation is hard wired into that aircraft for life.
I assume that you understand that there's nothing but software between the flight deck and the rest of the aircraft in more contemporary aircraft designs? At least the 737 has a set of braided steel cables between the flight deck and every primary flight control surface that is needed to get the aircraft back down on the ground.
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Old 11th May 2019, 01:37
  #34 (permalink)  
 
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Originally Posted by Alchad View Post
Bend Alot

Would you mind sharing the link?

thanks
But if I were speaking as a non-flying member of the public, and as a politician who must answer to them, I would say: ground the fleet now. As far as the public is concerned, the industry had its chance and blew it. I would have no confidence in the plane nor the industry until an explanation is found and the design changed. Nor would I buy a ticket on such a plane.

https://www.theatlantic.com/notes/20...HKWMiGTRbWIC3c
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Old 11th May 2019, 01:37
  #35 (permalink)  
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Re 737 Driver's post.

Yes, but it's the initial unwanted command to the H-Stabilizer that I take issue with. Should all the protection fail again, and that jack-screw run its full distance, then those braided steel cables seemingly still won't save the day.

I've thought long and hard about fly by wire since 'flying' a model in a box at Farnborough in the 70's Given the sophistication of the electronics, I concede the probabilities make my worries all but groundless, but then there's a hefty lighting strike into the electrics bay scenario which would indeed put Boeing way ahead.

.

Last edited by Loose rivets; 11th May 2019 at 01:50.
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Old 11th May 2019, 01:48
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737, Sorry, but I am not in agreement here. I understand you are a pilot, and so are many of us. The parameters and the if/then scenario have never been properly detailed. We would not have 3 incidents and 2 crashes if it had been.

While MCAS is part of the Speed Trim System (STS), the parameters appear completely different.

I know the Boeing ac, but are not current like I am on Airbus ac..

From what I have seen on the STS system, STS Mach gain is fully enabled between 100 KIAS and Mach 0.60 with a fadeout to zero by Mach 0.68. 10 seconds after takeoff, 5 seconds following release of trim switches, and Autopilot not engaged.

IF STS utilizes AoA , then why was MCAS required?

What are the parameters that engage MCAS?

I really do not agree with 2 AoA sensors, and the pilot is not the 3rd sensor, especially if there is only one left for whatever reason (as in the Ethiopian crash). As I have stated before, the AoA's are always in disagreement in many conditions, such as climbout and short final ,and while you claim the pilot has a decision, well, where or what is that decision based?
Lose 1 out of 2 sensors, and what is your decision based on?

Those AoA vanes always have issues and you know it.

Last edited by Smythe; 11th May 2019 at 02:44.
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Old 11th May 2019, 01:53
  #37 (permalink)  
 
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Originally Posted by Bend alot View Post
There was the Boeing spokesman that said the AoA disagree only worked above 400ft after they found it actually was not active all all.

So if that is true, then how can the MCAS part of the STS be tested before flight? Lion Air seems faulty AoA fitted - would the annunciation illuminate in this case?
The current MCAS AoA had no limit of disagree, and there was no problem withe the STS operation previously - MCAS really looks more than just a sub-sytem of STS.
Now the that is worrying - variable amounts of input! So if you are going slow with a high angle of attack - how long do you watch that trim wheel spin for?

From the previous thread Mr Driver your instinct would be to trim have you then disabled MCAS and stopped it from its certification requirement?

Would your current practice still stand? - keep flap out, or Autopilot on to bypass MCAS from being able to activate?
In this operator's opinion, certainly not shared by all, the "AOA Disagree" alert that has captured so much attention is not that bid of a deal. If the AOA's are really that far apart, there will be sufficient other indications because of how the AOA information is integrated into other aircraft systems. In the case of both Lion Air flights and ET302, an active stick shaker while the aircraft is accelerating and climbing normally is the big, annoying, and very obvious indication that something is amiss with your AOA system - and that becomes active as soon as the aircraft lifts off the ground.

I'm not sure about what you mean about testing STS/MCAS before flight. There are various logic tests going on in the background for many of our onboard systems, and we will get warning annunciators if one of those self-tests fails. Otherwise, most of our systems are assumed to be working until proven otherwise.

I don't see what is worrying about variable amounts of input. If the system is working and you really are approaching a stall, then that is what you want. If the system somehow got past the new software checks, then MCAS would be making an input when there was no stall while the pilot was hand-flying. As discussed in other threads, the pilot should notice such an anomalous input and take corrective action. At some point, you have to assume that someone is minding the store. If not, there are other systems on the plane that you should be far more worried about.

To your question of what I would do with an unwanted MCAS input, it would be the exact same thing I would do with any unwanted stab trim input. By my count, there are six different sources of input into the electrically-driven trim system on the MAX (five on the 737NG). Our runaway stab procedures are completely agnostic to the source of the undesired trim. Step 2 of that procedure is to oppose and counter the unwanted trim with the yoke trim switch. It is not until Step 5 that the cutout switches are used. This was one of the errors the ET302 crew made - they went right to Step 5. Once MCAS is disabled, yes, the aircraft no longer meets its certification dispatch requirement. That statement also applies when we lose engines, hydraulic systems, generators, and so forth. That is why we have non-normal procedures to get the aircraft back on the ground where it can be fixed.

The technique I spoke of before about engaging the autopilot before flap retraction was an interim approach until Boeing rolled out a long term fix. That will no longer be necessary with the new software.
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Old 11th May 2019, 01:55
  #38 (permalink)  
 
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Originally Posted by Loose rivets View Post
Re 737 Driver's post.

Yes, but it's the initial unwanted command to the H-Stabilizer that I take issue with. Should all the protection fail again, and that jack-screw run its full distance, then those braided steel cables seemingly still won't save the day.
.
If the jackscrew reaches the limit, then someone was very seriously not paying attention. The problem in that case is not with MCAS.
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Old 11th May 2019, 02:06
  #39 (permalink)  
 
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Originally Posted by Smythe View Post
737, Sorry, but I am not in agreement here. I understand you are a pilot, and so are many of us. The parameters and the if/then scenario have never been properly detailed. We would not have 3 incidents and 2 crashes if it had been.

While MCAS is part of the Speed Trim System (STS), the parameters appear completely different.

I know the Boeing ac, but are not current like I am on Airbus ac..

From what I have seen on the STS system, STS Mach gain is fully enabled between 100 KIAS and Mach 0.60 with a fadeout to zero by Mach 0.68. 10 seconds after takeoff, 5 seconds following release of trim switches, and Autopilot not engaged.

What are the parameters that engage MCAS?

I really do not agree with 2 AoA sensors, and the pilot is not the 3rd sensor, especially if there is only one left for whatever reason (as in the Ethiopian crash). As I have stated before, the AoA's are always in disagreement in many conditions, such as climbout and short final ,and while you claim the pilot has a decision, well, where or what is that decision based?
Lose 1 out of 2 sensors, and what is your decision based on?

Those AoA vanes always have issues and you know it.
I can't quote chapter and verse the MCAS engagement parameters since that information has yet to be published. As a practical matter, however, pilots don't memorize all these numbers and then mentally cross-check what the STS/Mach Trim/MCAS is doing. The trim wheel is making adjustments all the time during a normal flight (probably the same on an Airbus), and the trim is either appropriate for the conditions or it isn't. If the trim isn't appropriate, then it should become apparent fairly quickly - again if someone is paying attention. And if someone is not paying attention, then there are much bigger potential issues than MCAS waiting in the wings.

Yes, it would be great if we had triple-redundancy on everything on the 737. However, I must point out that it has relied on double-redundancy with a pilot as tiebreaker for, well, ever since the plane has been flying. It is pretty much a fact of life on the 737, and it really hasn't been an issue. If I lose one of anything, there is always a way to figure out which one is working and which one isn't.
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Old 11th May 2019, 02:16
  #40 (permalink)  
 
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My sad prediction:

The next Max crash will involve a 3rd world airline without mature Western Airline training and experience with a crew so hyper vigilant about a MCAS runway that they will misdiagnose something else as a MCAS failure go to the stab cut out switches and now have to manually trim an out of trim aircraft, which is basically never done, get behind the airplane and fly it into the ground......
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