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MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures

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MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures

Old 16th Dec 2019, 05:29
  #4541 (permalink)  
 
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The set screws and gears everyone is blaming don't play any part in the operation of the sensor when the A/C is in flight.
They keep the sensor in a faired position on the ground.
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Old 16th Dec 2019, 06:31
  #4542 (permalink)  
 
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Originally Posted by 568 View Post
"The AoA system that feeds it lies and also lies to the stall warning and stick shaker does not make sense".

With respect, how do you know the AoA lies?
Have you flown the 737?
Thanks.
We have two crashes because the AoA system lied. I don't need to fly a plane to know that.
It should have told the truth and signaled the equivalent of "The data is wrong" instead of reporting an erroneous 70 degree nose up AoA (ET302).

In both crashes the stall warning system, based on the AoA lie, caused aural and stick shaker warnings and disabled the autopilot, confusing the pilots about the status of the planes, which were not near stalling. The pilot's ability to detect MCAS actuation was adversely affected by the false warnings. Had that status been available to the MCAS systems engineers they are very likely to have added that state as a consideration in inhibiting the operation of the stabilizer trim motor, but they apparently believed AoA was reliable. It was an error to believe that, but the AoA subsystem developers would be the ones most familiar with the reliability of the AoA system.

So why didn't the aural stall warning group, the stick shaker group, or the autopilot group ever notice that the AoA could be unreliable and force the development of a clear indicator to the pilots about the reason for all three of them dumping on the pilots at the same time?
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Old 16th Dec 2019, 07:15
  #4543 (permalink)  
568
 
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Originally Posted by MechEngr View Post
We have two crashes because the AoA system lied. I don't need to fly a plane to know that.
It should have told the truth and signaled the equivalent of "The data is wrong" instead of reporting an erroneous 70 degree nose up AoA (ET302).

In both crashes the stall warning system, based on the AoA lie, caused aural and stick shaker warnings and disabled the autopilot, confusing the pilots about the status of the planes, which were not near stalling. The pilot's ability to detect MCAS actuation was adversely affected by the false warnings. Had that status been available to the MCAS systems engineers they are very likely to have added that state as a consideration in inhibiting the operation of the stabilizer trim motor, but they apparently believed AoA was reliable. It was an error to believe that, but the AoA subsystem developers would be the ones most familiar with the reliability of the AoA system.

So why didn't the aural stall warning group, the stick shaker group, or the autopilot group ever notice that the AoA could be unreliable and force the development of a clear indicator to the pilots about the reason for all three of them dumping on the pilots at the same time?
As you don't fly the type I will try to keep this comment on a level playing field.
Sensors installed on most modern transport aircraft "don't lie". That's why I asked the question regarding your comment. Systems that are not in agreement in data feeds generally provide pilot (s) "feedback" either through EICAS or by alerting the pilots through respective PFD's (or ND's) such as a horizontal amber line drawn through the respective failed modes on the PFD for LOC/VNAV/LNAV or VTK (inop FMC) on respective pilots ND.

When you consider the vast amount of users reading these posts, it is very easy to draw conclusions from posts, such as yours, that systems "lie", which may not be correct, so I wanted to clarify your post.
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Old 16th Dec 2019, 07:17
  #4544 (permalink)  
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Yes indeed.
But Airbus flight control law doesn't compare with 737 and I flew the Diesel-9/15/32, which is so far removed from both types with regard to flight control law, hydraulics, etc etc!
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Old 16th Dec 2019, 07:19
  #4545 (permalink)  
 
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Originally Posted by MechEngr View Post

So why didn't the aural stall warning group, the stick shaker group, or the autopilot group ever notice that the AoA could be unreliable and force the development of a clear indicator to the pilots about the reason for all three of them dumping on the pilots at the same time?
In a word: profit.
Doing any sort of AoA comparison, would require a warning to the crew, and any new warning would have reduced the probability of a common type endorsement without simulator time for the training. This was a key design criteria for the MAX, no crew training beyond a short iPad course. Southwest included a $1 million per airframe penalty in the contract for the MAX if simulator training was required.

I don't know how much of the MAX threads you have read, the key name you want to search for is Rick Ludtke on this issue (pprune.org search). He documents internal Boeing design mandate. There hasn't been a denial from Boeing as far as I am aware.

Yes, it is really that simple, to maximise sales and profit, every change had to be viewed through the prism of continued commonality.
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Old 16th Dec 2019, 08:18
  #4546 (permalink)  
 
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Originally Posted by 568 View Post
As you don't fly the type I will try to keep this comment on a level playing field.
Sensors installed on most modern transport aircraft "don't lie". That's why I asked the question regarding your comment. Systems that are not in agreement in data feeds generally provide pilot (s) "feedback" either through EICAS or by alerting the pilots through respective PFD's (or ND's) such as a horizontal amber line drawn through the respective failed modes on the PFD for LOC/VNAV/LNAV or VTK (inop FMC) on respective pilots ND.

When you consider the vast amount of users reading these posts, it is very easy to draw conclusions from posts, such as yours, that systems "lie", which may not be correct, so I wanted to clarify your post.
Was the 70 degree nose up report to the other systems true?
The AoA sensor did not electrically fail. Nothing was inoperative. It was reporting the wrong information. Is there some other term for not reporting the truth?
Since the 737 only used one AoA sensor at a time for each side, there was no way to detect disagreement and display that.
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Old 16th Dec 2019, 08:47
  #4547 (permalink)  
 
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Originally Posted by MechEngr View Post
Was the 70 degree nose up report to the other systems true?
The AoA sensor did not electrically fail. Nothing was inoperative. It was reporting the wrong information. Is there some other term for not reporting the truth?
Since the 737 only used one AoA sensor at a time for each side, there was no way to detect disagreement and display that.
My working definition of a "lieing" is "knowingly telling an untruth". It is doubtful whether an AoA sensor is capable of knowledge.

Other than that I think you chaps are in danger of furiously agreeing with each other
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Old 16th Dec 2019, 09:37
  #4548 (permalink)  
 
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Originally Posted by CurtainTwitcher View Post
In a word: profit.
Doing any sort of AoA comparison, would require a warning to the crew, and any new warning would have reduced the probability of a common type endorsement without simulator time for the training. This was a key design criteria for the MAX, no crew training beyond a short iPad course. Southwest included a $1 million per airframe penalty in the contract for the MAX if simulator training was required.

I don't know how much of the MAX threads you have read, the key name you want to search for is Rick Ludtke on this issue (pprune.org search). He documents internal Boeing design mandate. There hasn't been a denial from Boeing as far as I am aware.

Yes, it is really that simple, to maximise sales and profit, every change had to be viewed through the prism of continued commonality.
The customer drumbeat of "no new training/no new endorsement" was clear.

The Max was supposed to ship with the AoA disagree alert, but it does not appear that it specifically alerts that that's the reason for other systems to be unreliable, nor does it appear to pass that status within the FCC currently in control of the stabilizer trim functions. It's this latter function that is being added to the new software.

https://www.satcom.guru/2018/11/737-...n-command.html description claims that each FCC gets data from both ADIRUs, including AoA data, but that description seems to be about autopilot operations. Other information says that each FCC was dependent on the same-side AoA sensor for handling MCAS when it was their turn. Quite confusing.
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Old 16th Dec 2019, 10:20
  #4549 (permalink)  
 
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Originally Posted by MechEngr View Post
The customer drumbeat of "no new training/no new endorsement" was clear.

The Max was supposed to ship with the AoA disagree alert, but it does not appear that it specifically alerts that that's the reason for other systems to be unreliable, nor does it appear to pass that status within the FCC currently in control of the stabilizer trim functions. It's this latter function that is being added to the new software.

https://www.satcom.guru/2018/11/737-...n-command.html description claims that each FCC gets data from both ADIRUs, including AoA data, but that description seems to be about autopilot operations. Other information says that each FCC was dependent on the same-side AoA sensor for handling MCAS when it was their turn. Quite confusing.
Short answer: The autopilot and MCAS are different sub-systems running on each FCC.

The autopilot is a 3-axis system, and demands high integrity data from muliple sensors to operate safely.

MCAS is a subroutine of the speed-trim system, and both operate on a single axis of pitch via the horizontal stabiliser.

IMO this is where things went wrong. Speed trim is a closed-loop system, with limited authority in pitch, and failure is not catastrophic. MCAS was supposed to be closed-loop, but due to AOA failure it became open-loop. It also had larger authority, and unlimited scope.

Thus a safe and trusted sub-system became a monster, due to a combination of hardware error, faulty design, and lack of foresight.
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Old 16th Dec 2019, 12:13
  #4550 (permalink)  
 
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Originally Posted by CurtainTwitcher View Post
In a word: profit.
Doing any sort of AoA comparison, would require a warning to the crew, and any new warning would have reduced the probability of a common type endorsement without simulator time for the training. This was a key design criteria for the MAX, no crew training beyond a short iPad course. Southwest included a $1 million per airframe penalty in the contract for the MAX if simulator training was required.

I don't know how much of the MAX threads you have read, the key name you want to search for is Rick Ludtke on this issue (pprune.org search). He documents internal Boeing design mandate. There hasn't been a denial from Boeing as far as I am aware.

Yes, it is really that simple, to maximise sales and profit, every change had to be viewed through the prism of continued commonality.
Didn't the NG ship with a (non-optional) AoA comparison and disagree warning? And wasn't the omission of this warning in the Max discovered by Boeing late in development (or after certification)? And didn't they tell the FAA they were going to add it back in with the next update to the display software?

If so, then this has nothing to do with common type endorsements or Rick Ludtke, right?
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Old 16th Dec 2019, 13:41
  #4551 (permalink)  
 
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Since the 737 only used one AoA sensor at a time for each side, there was no way to detect disagreement and display that.
Not true- NG had as standard an AOA disagree light-note-display. But due to a software screwup- the MAX did not. Boeing knew this, but decided it was not a safety item ( still arguing ) and planned to change- update software ' eventually ' ..
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Old 16th Dec 2019, 13:48
  #4552 (permalink)  
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I think we've drifted back into discussion about what MCAS did vs. what it should have done if it were even needed, how the AoA might have failed, etc. It's interesting and since there are plenty of competing views and differing understandings, it can go on for a very long time. (I'm biting my virtual tongue to keep from prolonging the AoA argument.)

However, all of this is based upon an MCAS system that will never fly again, so its really a tech discussion relevant mostly to the two accident flights -- extremely important, obviously, but not really on-point WRT the currently-pressing issues of the effects of the grounding, investigations, the fix and testing, certification etc. on Boeing, customers, crews and pax, and worldwide civil aviation.

Boeing stock is approaching 3 million shares traded in a few minutes since the open. Average daily volume is less than 4.5 million.

Last edited by OldnGrounded; 16th Dec 2019 at 14:46.
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Old 16th Dec 2019, 13:51
  #4553 (permalink)  
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Originally Posted by Grebe View Post
Not true- NG had as standard an AOA disagree light-note-display. But due to a software screwup- the MAX did not. Boeing knew this, but decided it was not a safety item ( still arguing ) and planned to change- update software ' eventually ' ..
That's correct. On the MAX the disagree alert was inadvertently linked to the optional AoA indicator.
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Old 16th Dec 2019, 13:52
  #4554 (permalink)  
 
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My MAX FRM says "AOA Disagree Alert (amber) [shows a picture] Indicates the Captain's (left) and First Officer's (right) angle of attack values disagree by more than 10 degrees for more tha 10 continuous seconds." I guess the AOA can't lie, but the manuals can.

However, all of this is based upon an MCAS system that will never fly again...
I am not so sure. For starters, Boeing STILL has not submitted MAX 2.0 for approval. The descriptions of it that they did submit left me with some serious questions, like one activation only (until reset). The original MCAS was supposed to be one activation only (until reset). What is the reset condition? How much has it changed? And the biggest question is, do we trust Boeing to tell us the truth?

Last edited by Takwis; 16th Dec 2019 at 14:11.
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Old 16th Dec 2019, 14:17
  #4555 (permalink)  
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Quote:However, all of this is based upon an MCAS system that will never fly again...
Originally Posted by Takwis View Post
I am not so sure. For starters, Boeing STILL has not submitted MAX 2.0 for approval. The descriptions of it that they did submit left me with some serious questions, like one activation only (until reset). The original MCAS was supposed to be one activation only (until reset). What is the reset condition? How much has it changed? And the biggest question is, do we trust Boeing to tell us the truth?
I meant that MCAS 1.0 won't fly again. I think that's a pretty safe bet -- unless, of course, we are indeed lied to by Boeing and anyone else who actually knows what's going on with the MCAS fix. I wouldn't trust Boeing, but I think the scrutiny it's under would make it hard for a lie to fly.
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Old 16th Dec 2019, 14:49
  #4556 (permalink)  
 
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From WSJ just now:
Boeing Co. is considering either suspending or cutting back production of the 737 MAX amid growing uncertainty over the troubled plane’s return to service and could disclose a decision as soon as Monday, according to people familiar with the matter.

Sorry, cannot link the article as it is paywalled.
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Old 16th Dec 2019, 14:55
  #4557 (permalink)  
 
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more about posible shutdown 737 Max production here: https://simpleflying.com/boeing-737-...tion-shutdown/
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Old 16th Dec 2019, 15:32
  #4558 (permalink)  
 
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The set screws and gears everyone is blaming don't play any part in the operation of the sensor when the A/C is in flight. They keep the sensor in a faired position on the ground.
Unless the screw falls out and jams the gears?

There is an interesting design point here; nothing in the real world is independent. You would think that the ECU of an electronically controlled engine would be completely independent from a marine hot water heater, or that a freshwater toilet and an autopilot would have nothing in common. Yet, a small leak in the cooling system circuit (which is used to heat the hot water under way) dripped down a wire loom and into the wiring of the ECU, causing unexpected acceleration at random times depending upon which set of throttles was being used to control the engine. The rate compass which was used to set the ships' course for the autopilot was installed just a little too close to the DC pump for the freshwater toilet, leading to a magnetic field interference issue that caused large swings in course when the toilet was flushed. There are examples everywhere; at my sister's workplace they were prohibited from changing the screen color on their work PCs because it would cause their application to crash (back in pre-win95 days.) One NT bug that I never figured out at work had to do with setting the date to before the 1700s which caused death deep in the operating system only if a certain application was in use at the same time.

However, the managers still love to draw little boxes on the whiteboards to show how simple it all is and how any idiot can react within five seconds...
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Old 16th Dec 2019, 15:41
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Water pilot The rate compass which was used to set the ships' course for the autopilot was installed just a little too close to the DC pump for the freshwater toilet, leading to a magnetic field interference issue that caused large swings in course when the toilet was flushed.
Bringing that back to the 737, in the NG and MAX, we can tell when the lav is flushed, airborne, because the cabin air pressure rate of change gauge shows about a 500 fpm drop, and then rise. (fortunately, the compass is a little farther away.)
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Old 16th Dec 2019, 19:30
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Originally Posted by Water pilot View Post
Unless the screw falls out and jams the gears?
There was a Comet crash on take-off in Turkey around 1960 because a screw worked loose in the artificial horizon and stopped the pitch pointer going past a certain point. It was night and the pilot kept pulling...
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