Ethiopian airliner down in Africa
[snip]
18. (Opinion) If there are regions of the 737 flight envelope (e.g. extreme trim, opposing elevator) under which pilots lose vertical authority, the whole 737 fleet, both maxs and NGs (assuming that they are also affected by the same issue), should be grounded until such a time as trim deflection is mechanically limited to prevent entry into these uncontrollable regions of the flight envelope.
[snip]
18. (Opinion) If there are regions of the 737 flight envelope (e.g. extreme trim, opposing elevator) under which pilots lose vertical authority, the whole 737 fleet, both maxs and NGs (assuming that they are also affected by the same issue), should be grounded until such a time as trim deflection is mechanically limited to prevent entry into these uncontrollable regions of the flight envelope.
[snip]
My reading of this whole catastrophe is that the certification of the B737MAX and the B737NG may now be thrown into question.
The FAA will undoubtedly approve "MCAS 2.0" in as quick a time as they consider respectable, but the evidence shows that there is such a degree of regulator capture that this will be hard to see as an objective evidence-based process.
Others, particularly CAAC and EASA, may not be so easily convinced. The Russian regulator would probably be onside with that judging by their actions a couple of years ago to attempt remove certification from the B737NG.
That would be catastrophic for Boeing and for the air transport industry world-wide: half the global narrow-body fleet grounded indefinitely hardly bears thinking about.
My reading of this whole catastrophe is that the certification of the B737MAX and the B737NG may now be thrown into question.
The FAA will undoubtedly approve "MCAS 2.0" in as quick a time as they consider respectable, but the evidence shows that there is such a degree of regulator capture that this will be hard to see as an objective evidence-based process.
Others, particularly CAAC and EASA, may not be so easily convinced. The Russian regulator would probably be onside with that judging by their actions a couple of years ago to attempt remove certification from the B737NG.
The FAA will undoubtedly approve "MCAS 2.0" in as quick a time as they consider respectable, but the evidence shows that there is such a degree of regulator capture that this will be hard to see as an objective evidence-based process.
Others, particularly CAAC and EASA, may not be so easily convinced. The Russian regulator would probably be onside with that judging by their actions a couple of years ago to attempt remove certification from the B737NG.
However if they start getting expert whistle blower testimony that brings in to question the whole certification process of MCAS and the reasons for its existence the FAA will be out of options other than some sort of re certification process which is a whole new can of worms.
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To be honest I would be fairly confident that given the amount of scrutiny that the redesigned MCAS has, it would be "safe enough".
What concerns me would be any other, as yet unknown/undisclosed "features" that are lurking in the background that haven't yet been disclosed because they haven't yet contributed to a smoking hole in the ground - essentially have any other corners been cut or sub-optimal design or engineering decisions been made. I would hope that this is what the FAA and other regulators are scrutinising right now.
I would also be fascinated if a gap analysis has been done between the MAX and what would need to change, were it a new aircraft type being certified today - several people have commented that "it would never be certified today" and "it relies on grandfather certification" - so in what ways does the MAX come up short to today's expected regulations?
What concerns me would be any other, as yet unknown/undisclosed "features" that are lurking in the background that haven't yet been disclosed because they haven't yet contributed to a smoking hole in the ground - essentially have any other corners been cut or sub-optimal design or engineering decisions been made. I would hope that this is what the FAA and other regulators are scrutinising right now.
I would also be fascinated if a gap analysis has been done between the MAX and what would need to change, were it a new aircraft type being certified today - several people have commented that "it would never be certified today" and "it relies on grandfather certification" - so in what ways does the MAX come up short to today's expected regulations?
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What a truly superb analysis. I suspect this could very well be plaigerised in its entirety and feature in various court cases in the future.
Regards
I think Alchad that you would have to say that only a few of the Comments 1-33 are accurate and even then, were not the cause of the crashes. Only factors leading to the events. I will look at the 33 comments as will others and I am sure they will be examined one by one for accuracy, relevancy and bias. I look forward to that input from others wiser than I.
Happy flying
ps - would fly on a Max today if I could fine one going somewhere, provided the pilot had been trained in multiple error warnings and knew his pitch and power settings for each phase of flight. The airlines I fly on do that. Someone said today "are we going back to the Cessna 152?" Well, the 737 is a large 152 and that is its beauty in my view. It flies with very little working except it needs the engines, and even without them, has made many safe landings. But, the pilots HAVE to know how to fly. The 737 is not an Xbox. But then nor is an A330 as we saw in the AF 447 crash where the pilots had no idea what was happening to them.
We are not going to get away from the issue of world wide movement towards minimalist training supplemented by smarter and smarter avionics which can save the pilots from their own errors. An old but not bold pilot.
Y
Regards
I think Alchad that you would have to say that only a few of the Comments 1-33 are accurate and even then, were not the cause of the crashes. Only factors leading to the events. I will look at the 33 comments as will others and I am sure they will be examined one by one for accuracy, relevancy and bias. I look forward to that input from others wiser than I.
Happy flying
ps - would fly on a Max today if I could fine one going somewhere, provided the pilot had been trained in multiple error warnings and knew his pitch and power settings for each phase of flight. The airlines I fly on do that. Someone said today "are we going back to the Cessna 152?" Well, the 737 is a large 152 and that is its beauty in my view. It flies with very little working except it needs the engines, and even without them, has made many safe landings. But, the pilots HAVE to know how to fly. The 737 is not an Xbox. But then nor is an A330 as we saw in the AF 447 crash where the pilots had no idea what was happening to them.
We are not going to get away from the issue of world wide movement towards minimalist training supplemented by smarter and smarter avionics which can save the pilots from their own errors. An old but not bold pilot.
Y
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737 Driver
This is a very revealing quote. I can see how the procedures evolve, or de-evolve. But I can also see how it could lead even attentive crews down a very dark garden path.
#845 on the parallel thread
we have promise of a further probing into the AV H's list and circuits. I haven't woken up yet.
737 Driver's comments about the need to know levels I concede completely though as I say, if I were young . . .
FrequentSLF #843 on parallel thread.Well, I found it hard to reconcile the MAX system as described in the AV H's question list - with the outline wiring we'd all been lead to believe was simply a series BackUp configuration. It was too late last night to trace circuits, but 737 Driver did protest it doesn't matter about the details, as long as the crew take the right actions. I have never thought like that and if I'd been on type, (and 40 years younger) I would have known exactly what that circuit did. At least, I hope I would, given I'd got the first clue that something like MCAS was lurking in the background. But then, I'd spent sproghood on the electronics workbench.
Now to another issue in the Herald's list. They go back to the black box taking in good AoA data and corrupting it - in both if not all, cases. Certainly, the chance failure of three vanes stretches the old credulity, though the balance weight hypothesis in the ET flight is very compelling. But along a pure logic line, I would have looked very carefully at the prior reports - in addition to the three major vane issues. The more I read the more I'm not satisfied the Herald's suggestion is not correct. It leaves me with a deep concern about what I've described as a ghost in the machine.
Apart from the digital errors fitting nicely with the three vane positions - they take the very rapid change of angle as being more electronic than a pendulous swing. But as I say, the latter is good fault modelling. It's just that slight angle change from a long steady error state, to a slightly different long steady state. That's odd.
. . . On the NG, the left switch disables the main electric (pilot actuated) trim and the right switch disable all automatic inputs (Speed Trim/Mach Trim/Autopilot Trim). We used to try to identify the offending system and actuate these switches separately in the runaway stab trim procedure depending on the situation. Somewhere along the way, Boeing changed their philosophy on the procedure (probably part of a larger trend of moving away from “troubleshooting” type actions) and now we always use both switches when necessary. I have previously speculated that two switches were retained in the MAX for both redundancy against possible relay welding and to simply harmonize the procedural aspects of runaway trim between the NG and the MAX. That is, both aircraft have two switches (for different reasons) and you always use both switches at the same time.
#845 on the parallel thread
we have promise of a further probing into the AV H's list and circuits. I haven't woken up yet.
737 Driver's comments about the need to know levels I concede completely though as I say, if I were young . . .
FrequentSLF #843 on parallel thread.
Quote:
I am not a pilot, but I have eletrical and automation background.
Based on the wirings that are available on the net the systems are as stated.
MCAS is not stopped by column switches!
MCAS cannot be disabled without cutting off manual electrical trim, which means only wheel cranking can be used if CUT OFF switches are used.
CUT OFF switches are connected in series, and renamed PRI and B/U, either one will CUTOFF all electrical controls (manual thumb on control column, autopilot, STS, MCAS), while on NG one switch will cut off automatic trim, while the other whole cut off the electrics.
Based on the wirings that are available on the net the systems are as stated.
MCAS is not stopped by column switches!
MCAS cannot be disabled without cutting off manual electrical trim, which means only wheel cranking can be used if CUT OFF switches are used.
CUT OFF switches are connected in series, and renamed PRI and B/U, either one will CUTOFF all electrical controls (manual thumb on control column, autopilot, STS, MCAS), while on NG one switch will cut off automatic trim, while the other whole cut off the electrics.
Now to another issue in the Herald's list. They go back to the black box taking in good AoA data and corrupting it - in both if not all, cases. Certainly, the chance failure of three vanes stretches the old credulity, though the balance weight hypothesis in the ET flight is very compelling. But along a pure logic line, I would have looked very carefully at the prior reports - in addition to the three major vane issues. The more I read the more I'm not satisfied the Herald's suggestion is not correct. It leaves me with a deep concern about what I've described as a ghost in the machine.
Apart from the digital errors fitting nicely with the three vane positions - they take the very rapid change of angle as being more electronic than a pendulous swing. But as I say, the latter is good fault modelling. It's just that slight angle change from a long steady error state, to a slightly different long steady state. That's odd.
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Now to another issue in the Herald's list. They go back to the black box taking in good AoA data and corrupting it - in both if not all, cases. Certainly, the chance failure of three vanes stretches the old credulity, though the balance weight hypothesis in the ET flight is very compelling. But along a pure logic line, I would have looked very carefully at the prior reports - in addition to the three major vane issues. The more I read the more I'm not satisfied the Herald's suggestion is not correct. It leaves me with a deep concern about what I've described as a ghost in the machine.
Apart from the digital errors fitting nicely with the three vane positions - they take the very rapid change of angle as being more electronic than a pendulous swing. But as I say, the latter is good fault modelling. It's just that slight angle change from a long steady error state, to a slightly different long steady state. That's odd.
As to the slight change in steady state in ET trace:
The first significant) downward bump in vertical G was at 05:41:15 coincident with the change. Assuming the AoA (sans vane) sensor was wedged at a limit (bird innards even) it was jostled and settled slightly lower.
I don't really understand the drive to make both instances have the same cause since the traces are totally different.
Both Lion air flights had an active AoA with a fixed offset. This 'might' be electronics but could also be explained by a mechanical issue.
ET had a sudden swing to full scale and then tracked G at the end. The speed of the initial swing is hard to read from the graph but does not look faster than the random variations on the working unit.
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737 Driver
This is a very revealing quote. I can see how the procedures evolve, or de-evolve. But I can also see how it could lead even attentive crews down a very dark garden path.
Quote:
. . . On the NG, the left switch disables the main electric (pilot actuated) trim and the right switch disable all automatic inputs (Speed Trim/Mach Trim/Autopilot Trim). We used to try to identify the offending system and actuate these switches separately in the runaway stab trim procedure depending on the situation. Somewhere along the way, Boeing changed their philosophy on the procedure (probably part of a larger trend of moving away from “troubleshooting” type actions) and now we always use both switches when necessary. I have previously speculated that two switches were retained in the MAX for both redundancy against possible relay welding and to simply harmonize the procedural aspects of runaway trim between the NG and the MAX. That is, both aircraft have two switches (for different reasons) and you always use both switches at the same time.
. . . On the NG, the left switch disables the main electric (pilot actuated) trim and the right switch disable all automatic inputs (Speed Trim/Mach Trim/Autopilot Trim). We used to try to identify the offending system and actuate these switches separately in the runaway stab trim procedure depending on the situation. Somewhere along the way, Boeing changed their philosophy on the procedure (probably part of a larger trend of moving away from “troubleshooting” type actions) and now we always use both switches when necessary. I have previously speculated that two switches were retained in the MAX for both redundancy against possible relay welding and to simply harmonize the procedural aspects of runaway trim between the NG and the MAX. That is, both aircraft have two switches (for different reasons) and you always use both switches at the same time.
The initial 737NG safety analysis used the availability of separate cutouts (automation and all) to justify smaller wheel/harder to move under high loading since in most cases pilot electrical trim would still be available.
This may also have been a factor in dropping training on the 'unloading' technique.
Over time training was simplified, not by itself a bad thing, but did not take the above into account.
When MAX was designed the fact that training always used both switches was used to justify removing the seperate functions for whatever reason.
Some have suggested that the training was changed to accomodate the upcoming MAX, I highly doubt this was true since there was no technical need to change the functionality to add MCAS.
Last edited by MurphyWasRight; 2nd May 2019 at 12:25. Reason: 787 > 737
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It is not clear what the current published FDR traces are actually reporting... I am not saying that your interpretation is wrong but it is not absolutely certain. Does the thumb switch have absolute authority in all circumstances (save for when electric trim is disabled)? The wiring schematics available suggests otherwise and the detailed software logic is not publicly known. The FDR data is not clear whether it is reporting inputs or final outputs or something in between. I have read what is available in this thread and still have doubts that there is sufficient information to be sure. What is certain is that the MCAS system was not properly or adequately designed. It is inherently dangerous and should never have been approved. Whether the pilots should or could be expected to resolve the defective system is a secondary issue. It is simply unacceptable for a critical system to continue to rely on plainly unreliable sensor information. The common factor is unreliable AoA that is easily detected but the system ignores. Autopilot is disabled but why on earth is MCAS allowed to continue to operate?
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I had a discussion in that I suggested pulling the CB for the stick shakers once you knew it was a false warning but the answer was that "Boeing doesn't say that in the checklist". I would call that action airmanship though!
Cheers
Y
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Originally Posted by meleagertoo 
I did my 737-3/400 initial course in 1998 and have no recollection at all of ever using just one of STAB TRIM CUTOUT switches. They were always, unless seniity has completely overtaken me, used together. Seems rather more than 'a few years ago' to me.
I did my 737-3/400 initial course in 1998 and have no recollection at all of ever using just one of STAB TRIM CUTOUT switches. They were always, unless seniity has completely overtaken me, used together. Seems rather more than 'a few years ago' to me.
I had a discussion in that I suggested pulling the CB for the stick shakers once you knew it was a false warning but the answer was that "Boeing doesn't say that in the checklist". I would call that action airmanship though!
Cheers
Would take a while to find the post I was referring too, doesn't really matter though; as the total number of years increases sense of elapsed time does seem to compress.
This does totally put to bed any idea that training was changed to accomodate MAX.
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[...]
Every time you say 'just fly the plane' or 'basic airmanship' or 'get another career' you're completely ignoring human factors. This is as dangerous as not knowing how to fly the aircraft. And this is why you're getting such a deservedly robust response from others on here.
[...]
Every time you say 'just fly the plane' or 'basic airmanship' or 'get another career' you're completely ignoring human factors. This is as dangerous as not knowing how to fly the aircraft. And this is why you're getting such a deservedly robust response from others on here.
The human mind does not, ironically, work in the ways most people think it does - it has well-documented limitations and sources of error plumbed into its design. A human factors expert can I believe pretty trivially design a scenario where most (if not all) humans will consistently fail to correctly solve even relatively trivial problems, regardless of their competence under normal conditions.
Thus, when asking "why didn't they just fly the plane?", one possible answer is undoubtedly some variant on "they were incompetent". But another possible answer is "they were put into a scenario in which any human being would consistently fail to solve the problem, regardless of competence". Probably the truth is somewhere between those two points.
*See Wikipedia article "Human factors and ergonomics"
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Thanks all, interesting that it has been that way for many years,
Would take a while to find the post I was referring too, doesn't really matter though; as the total number of years increases sense of elapsed time does seem to compress.
This does totally put to bed any idea that training was changed to accomodate MAX.
Would take a while to find the post I was referring too, doesn't really matter though; as the total number of years increases sense of elapsed time does seem to compress.
This does totally put to bed any idea that training was changed to accomodate MAX.
Yo gums,
‘… still looking for the aero explanation that is more relevant than basic control column feel.’
Ethiopian airliner down in Africa
Ethiopian airliner down in Africa
Nothing more specific to add; no detailed knowledge or reasoning in the public domain.
I suspect that the aerodynamic issue caught Boeing by surprise - late in flight testing; the existence or extent of change of pitching moment (stick force stability), its origin - engine nacelle, nacelle / wing interaction. Possibly a judgement that the handling characteristics would be ‘good enough’ - FAA association.
The need for modification - increased stick force to meet stability requirements at a few specific points in the flight envelope could be achieved with a range alternative approaches; hardware fixes - cf Mach trim, STS, feel shift. These progressively require ‘controlling’ parameters best achieved with software, thence use of ‘full’ software, but it wasn’t ‘full’ or comprehensively protected - faster, better, cheaper; NASA got that wrong; how we fail to learn, how quickly we forget.
The comparisons with modern FBY wire systems and the aerodynamics of those aircraft, adds little to this debate. The 737 airframe and systems design are very old, progressively enhanced, adapted to market demand - with the perception of new shiny technologies are better, at least cheaper.
A more suitable comparison would be with the 707 / 727; in my case the Comet. I recall that the Comet, or its derivatives had a ‘pitch gear change’, (not a manual shift), a smooth electrical repositioning of a mechanical cam which changed the ratio of stick to elevator (also used in the Sea Vixen to cope with transonic trim change). The need for Mach trim in commercial aircraft emerged as speeds increased (stability, stick force reversal), but due to its novelty, solutions were carefully thought through with reliable implementation.
The recent events will go down in history. History, as with war crimes, is written by the victors (lawyers, politicians).
The most important aspect for the industry is in what we learn, how this is to be learnt and implemented. The issues with certification processes may dominate - how to certificate modern systems, common standards, international approval, … trust.
The industry is transitioning from the generally knowable, to more uncertainty. How do we manage aircraft and people in an uncertain world.
https://www.farnamstreetblog.com/201...r-uncertainty/ (Three parts linked)
FAA / Boeing could reconsider their relationship with ICAO, aviation language, safety culture.
More Integration opposed to dominating Assimilation:- https://www.dropbox.com/s/7425e8yykg...20%2B.pdf?dl=0 (use website option)
‘… still looking for the aero explanation that is more relevant than basic control column feel.’
Ethiopian airliner down in Africa
Ethiopian airliner down in Africa
Nothing more specific to add; no detailed knowledge or reasoning in the public domain.
I suspect that the aerodynamic issue caught Boeing by surprise - late in flight testing; the existence or extent of change of pitching moment (stick force stability), its origin - engine nacelle, nacelle / wing interaction. Possibly a judgement that the handling characteristics would be ‘good enough’ - FAA association.
The need for modification - increased stick force to meet stability requirements at a few specific points in the flight envelope could be achieved with a range alternative approaches; hardware fixes - cf Mach trim, STS, feel shift. These progressively require ‘controlling’ parameters best achieved with software, thence use of ‘full’ software, but it wasn’t ‘full’ or comprehensively protected - faster, better, cheaper; NASA got that wrong; how we fail to learn, how quickly we forget.
The comparisons with modern FBY wire systems and the aerodynamics of those aircraft, adds little to this debate. The 737 airframe and systems design are very old, progressively enhanced, adapted to market demand - with the perception of new shiny technologies are better, at least cheaper.
A more suitable comparison would be with the 707 / 727; in my case the Comet. I recall that the Comet, or its derivatives had a ‘pitch gear change’, (not a manual shift), a smooth electrical repositioning of a mechanical cam which changed the ratio of stick to elevator (also used in the Sea Vixen to cope with transonic trim change). The need for Mach trim in commercial aircraft emerged as speeds increased (stability, stick force reversal), but due to its novelty, solutions were carefully thought through with reliable implementation.
The recent events will go down in history. History, as with war crimes, is written by the victors (lawyers, politicians).
The most important aspect for the industry is in what we learn, how this is to be learnt and implemented. The issues with certification processes may dominate - how to certificate modern systems, common standards, international approval, … trust.
The industry is transitioning from the generally knowable, to more uncertainty. How do we manage aircraft and people in an uncertain world.
https://www.farnamstreetblog.com/201...r-uncertainty/ (Three parts linked)
FAA / Boeing could reconsider their relationship with ICAO, aviation language, safety culture.
More Integration opposed to dominating Assimilation:- https://www.dropbox.com/s/7425e8yykg...20%2B.pdf?dl=0 (use website option)
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The direction of this thread is difficult to understand. There seems to be a surprising focus on the cut-out switches but no rational explanation for the changes in the MAX series. If there are no circumstances that only one cut-out should be operated there, is clearly no point in having two cut-out switches. If two contacts are needed to be operated it could be mechanically interlocked into one lever. The current information suggest the two switches are a product of muddled thinking... hardly a confidence builder.
Purely speculating, the reason that MCAS is not automatically disabled in the event of conflicting sensor inputs may be because MCAS needed to be permanently active to comply with 14CFR §25.203(a) "Stall characteristics". However, it is difficult to believe that the designers could have considered it a better option to leave it to the pilots to disable MCAS rather than by the automatic system that would be immediately aware of AoA sensor malfunction. It seems to be possible that focus was on conforming to wording of regulations rather than designing an adequate system.
A critical system that is intended to work in all circumstance must be designed in a way that reduces risks of malfunction to an acceptable level. Reliance on a single sensor or system does not appear to satisfy this obvious requirement. In the event that a critical sensor is no longer reliable, the system must automatically fall back to an alternate. That could be an alternate duplicate system or the manual control of the pilot or a combination or several nested fall-back options. The evidence so far is quite clear that Boeing failed to properly consider these options and required pilot intervention on scant information. In my view, it was negligent design and I suspect that I am not alone.
Many of the comments on this thread focus on the failure of the pilots to resolve the situation. There is good evidence that if the captain had handed control to the right hand seat or used the cut-outs earlier that they would have been successful. However, it does not excuse the fundamental design defects. In actual fact, Boeing could have easily prevented any uncertainty created by unreliable AoA through additional training automation and notification. There is no excuse for the design defects.
Further, much has been made of additional pilot training or improved memory items, QRH etc. Unfortunately, it is trying to close the stable door after the horse has bolted. The existing MCAS system will never be used again and any training or manuals will be based on a substantially different systems. Really all the focus at this stage must be on correcting the design defects... any manuals and training will fall from the new systems and will hopefully learn from the inadequacy of the previous systems and training.
I look forward to learning exactly how the MCAS electric trim system worked and how the situation will be resolved. One of the issues that I would like to further understand is why the pilots only appeared to make shortly electric trim corrections when it seemed likely that they would be trying to make large corrections. The FDR trace combines MCAS and electric trim... it is therefore uncertain what the thumb switch position was in.
Would permanently holding the thumb switch for nose-up, override AND from MCAS? Does MCAS cyclically override the thumb switch input in the 10s 5s cycle that requires further release and activation of the thumb switch. ie is the Boeing Ops Manual Bulletin TBC-19 entirely accurate... namely:
In the event of erroneous AOA data, the pitch trim system can trim the stabilizer
nose down in increments lasting up to 10 seconds. The nose down stabilizer trim
movement can be stopped and reversed with the use of the electric stabilizer trim
switches but may restart 5 seconds after the electric stabilizer trim switches are
released.
If this is true then it would be possible (not desirable) to use electric trim to override MCAS without using the cutout switches. MCAS could be interrupted and corrected every time it kicked in. I suspect it is not entirely accurate... I wonder if anyone has an authoritative answer? None of this excuses MCAS remaining active with unreliable AoA information.
Purely speculating, the reason that MCAS is not automatically disabled in the event of conflicting sensor inputs may be because MCAS needed to be permanently active to comply with 14CFR §25.203(a) "Stall characteristics". However, it is difficult to believe that the designers could have considered it a better option to leave it to the pilots to disable MCAS rather than by the automatic system that would be immediately aware of AoA sensor malfunction. It seems to be possible that focus was on conforming to wording of regulations rather than designing an adequate system.
A critical system that is intended to work in all circumstance must be designed in a way that reduces risks of malfunction to an acceptable level. Reliance on a single sensor or system does not appear to satisfy this obvious requirement. In the event that a critical sensor is no longer reliable, the system must automatically fall back to an alternate. That could be an alternate duplicate system or the manual control of the pilot or a combination or several nested fall-back options. The evidence so far is quite clear that Boeing failed to properly consider these options and required pilot intervention on scant information. In my view, it was negligent design and I suspect that I am not alone.
Many of the comments on this thread focus on the failure of the pilots to resolve the situation. There is good evidence that if the captain had handed control to the right hand seat or used the cut-outs earlier that they would have been successful. However, it does not excuse the fundamental design defects. In actual fact, Boeing could have easily prevented any uncertainty created by unreliable AoA through additional training automation and notification. There is no excuse for the design defects.
Further, much has been made of additional pilot training or improved memory items, QRH etc. Unfortunately, it is trying to close the stable door after the horse has bolted. The existing MCAS system will never be used again and any training or manuals will be based on a substantially different systems. Really all the focus at this stage must be on correcting the design defects... any manuals and training will fall from the new systems and will hopefully learn from the inadequacy of the previous systems and training.
I look forward to learning exactly how the MCAS electric trim system worked and how the situation will be resolved. One of the issues that I would like to further understand is why the pilots only appeared to make shortly electric trim corrections when it seemed likely that they would be trying to make large corrections. The FDR trace combines MCAS and electric trim... it is therefore uncertain what the thumb switch position was in.
Would permanently holding the thumb switch for nose-up, override AND from MCAS? Does MCAS cyclically override the thumb switch input in the 10s 5s cycle that requires further release and activation of the thumb switch. ie is the Boeing Ops Manual Bulletin TBC-19 entirely accurate... namely:
In the event of erroneous AOA data, the pitch trim system can trim the stabilizer
nose down in increments lasting up to 10 seconds. The nose down stabilizer trim
movement can be stopped and reversed with the use of the electric stabilizer trim
switches but may restart 5 seconds after the electric stabilizer trim switches are
released.
If this is true then it would be possible (not desirable) to use electric trim to override MCAS without using the cutout switches. MCAS could be interrupted and corrected every time it kicked in. I suspect it is not entirely accurate... I wonder if anyone has an authoritative answer? None of this excuses MCAS remaining active with unreliable AoA information.
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I would also be fascinated if a gap analysis has been done between the MAX and what would need to change, were it a new aircraft type being certified today - several people have commented that "it would never be certified today" and "it relies on grandfather certification" - so in what ways does the MAX come up short to today's expected regulations?
The certification basis of an aircraft is a list of which regulations it has been demonstrated to comply with, and at which amendment level of that particular regulation is being used to show compliance. The certification basis is agreed to by the manufacturer and the FAA at the beginning of the certification process. The manufacturer has 5 years to complete certification of the aircraft, and the manufacturer is not required to comply with regulations that are changed within that 5 year period.
The cert basis is documented in the Type Certificate Data Sheet. Here's the 737 TCDS, the MAX 8 is on page 71. http://www.airweb.faa.gov/Regulatory...6WE_Rev_64.pdf
For each regulation, the center column lists the amendment level that the airplane complies with. NA indicates "No Amendment."
Then, you can go to the CFR and compare the most current amendment level to the amendment level in the TCDS. https://www.govinfo.gov/content/pkg/...tle14-vol1.pdf
For example, the MAX complies with 25.107 amendment 135 for Takeoff Speed, and that is the current amendment level in the CFR.
Another example, go in the TCDS and look at 25.807 for emergency exits. For some of the doors, the MAX complies with the most current amendment level 114. For others, it complies with amt. 72. Additionally, they are compliant with 25.807(c)(3) at amt. 15, because this section was removed from newer versions of the regulation.
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... would be possible (not desirable) to use electric trim to override MCAS without using the cutout switches. MCAS could be interrupted and corrected every time it kicked in. I suspect it is not entirely accurate... I wonder if anyone has an authoritative answer? None of this excuses MCAS remaining active with unreliable AoA information.
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From something Ive just read MCAS was to compensate for the fact that due to the new engine nacelles the pitch stablity was so poor that it would tighten up in a turn at low airspeed and that it actually required a push on the control column to defeat this which is quite unaceptable in an airliner, not so much in a Pitts.
Obviously this could not have been corrected by adjusting the elevator cct feel so it explains the why of why did they do it this way
Obviously this could not have been corrected by adjusting the elevator cct feel so it explains the why of why did they do it this way
From something Ive just read MCAS was to compensate for the fact that due to the new engine nacelles the pitch stablity was so poor that it would tighten up in a turn at low airspeed and that it actually required a push on the control column to defeat this which is quite unaceptable in an airliner, not so much in a Pitts.
Obviously this could not have been corrected by adjusting the elevator cct feel so it explains the why of why did they do it this way
Obviously this could not have been corrected by adjusting the elevator cct feel so it explains the why of why did they do it this way
Thats interesting Rod - what was is that you read?
