MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures
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First I'd like to say that we should be careful in our use of the term "supporting evidence." Discussions on PPRuNe seem to function reasonably well with a fairly loose set of rules as to what constitutes "evidence." Most of that said evidence is actually, from a strictly legal standpoint, a bunch of hearsay, large harvested from various new agencies and online sites. If we are going to start enforcing evidentiary standards, then that standard needs to apply across the board regardless of whether one agrees or disagrees with a certain point. From my perspective, I think we are doing fine with the general understanding that the information on which we are basing these discussions are being supplied by various parties with various viewpoints, all subject to later revision. At some point we should also acknowledge that all of this information will eventually be examined and adjudicated by official agencies who actually do have to comply with rules of evidence.
Second, as you noted, each point I listed was presented without supporting evidence - to include the conclusion that Boeing really screwed this one up. I assume you are not taking issue with point #1? There is an underlying assumption that the reader has kept up with a reasonable amount of the evidence already presented and that there is no need to extensively recap this information.
Re MCAS design, from what has be been attributed to reliable description, the theory of MCAS is consistent with methods of enhancing stability shortfalls, e.g. Mach trim. However the design engineering implementation of MCAS, single system, etc, fell short of what was required or that which should have been detected - the debate goes on.
Re FAA weaknesses in oversight and certification process; most likely, but these deficiencies have been noted, investigated, and action is expected. They are central to the accidents, but apparently not unique - a continuing concern.
Re ‘glaring deficiencies’ in operator maintenance; the scant information relating to the accidents published so far indicates that maintenance activity could be judged as good as might be expected given the lack of published information about MCAS - or of its existence at all, at that time.
Re crew training relating to the accidents; no evidence provided at all. Pure supposition based on hindsight, reinforced by the ongoing debate as to how much credit should be allocated to crew intervention, alerting systems, procedures, and the apparent inability to manually move the trim from extreme positions.
These accidents should provide many lessons to be learnt; the first and very important is to beware hindsight bias.
Last edited by Tomaski; 20th Oct 2019 at 01:03.
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Tomaski: ". . . I think we are doing fine with the general understanding that the information on which we are basing these discussions are being supplied by various parties with various viewpoints, all subject to later revision. At some point we should also acknowledge that all of this information will eventually be examined and adjudicated by official agencies who actually do have to comply with rules of evidence."
With the House committee hearings looming, and with the multiplicity of issues, the layers of issues, it's worth noting something about evidence in our (U.S.) system. That is: there is a difference, sometimes large, between rules of evidence, and standards for evidence. To illustrate, calling some info hearsay isn't quite meaningful. There are exemptions - carved out of the basic definition of what hearsay is - for things that ostensibly are or should be hearsay. But the rule(s) say they're "not hearsay". And then there also are many exceptions to the general rule barring hearsay, in which, indicia of reliability is a major, major factor.
The point is, if information is presented and developed in a q&a format, with persons testifying sworn and under penalty of perjury, even absent ANY formal rules of evidence, standards for evidence can still be applied. Labor arbitration is a pretty relevant example. And about the last congressional hearing I can think of where the impression of reliability seemed strong was back in 1996. Michael Chertoff, and Richard Ben-Veniste, were special counsel who questioned the witnesses (the subject was Whitewater scandal stuff, iirc). Maybe the House hearings - which now have a great deal more ground to cover, a lot more than one day with the airframer's C.E.O., should requisition two similar special counsel to conduct the questioning, not the Congress members who.....well, standards for reliability aren't their strong suit.
With the House committee hearings looming, and with the multiplicity of issues, the layers of issues, it's worth noting something about evidence in our (U.S.) system. That is: there is a difference, sometimes large, between rules of evidence, and standards for evidence. To illustrate, calling some info hearsay isn't quite meaningful. There are exemptions - carved out of the basic definition of what hearsay is - for things that ostensibly are or should be hearsay. But the rule(s) say they're "not hearsay". And then there also are many exceptions to the general rule barring hearsay, in which, indicia of reliability is a major, major factor.
The point is, if information is presented and developed in a q&a format, with persons testifying sworn and under penalty of perjury, even absent ANY formal rules of evidence, standards for evidence can still be applied. Labor arbitration is a pretty relevant example. And about the last congressional hearing I can think of where the impression of reliability seemed strong was back in 1996. Michael Chertoff, and Richard Ben-Veniste, were special counsel who questioned the witnesses (the subject was Whitewater scandal stuff, iirc). Maybe the House hearings - which now have a great deal more ground to cover, a lot more than one day with the airframer's C.E.O., should requisition two similar special counsel to conduct the questioning, not the Congress members who.....well, standards for reliability aren't their strong suit.
So, Mark Forner, had issues in the SIM with MCAS, but later convinced the FAA not to include MCAS in the manual, because it could confuse pilots(like it confused him in the SIM). When asked for info he plead the fifth, to prevent these texts coming out. Currently, he is a line pilot for SWA, whose pilots are suing Boeing for lost wages due to the MAX debacle. I would love to be on the JS when he is flying!
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indeed. I am not a physics guy. So i just say the probability of an MCAS failure is p; probability of flight without failure is (1-p).
So, probability of n flights without failure (1-p)**n.
This statistic allows us ro estimate how long MCAS us going to take before it kills someone.
Maybe pilots would profit from knowing Bernouilli’s OTHER works
Edmund
So, probability of n flights without failure (1-p)**n.
This statistic allows us ro estimate how long MCAS us going to take before it kills someone.
Maybe pilots would profit from knowing Bernouilli’s OTHER works
Edmund
Sadly the root cause of this tragedy seems increasingly apparent. A company run by MBA bean counters who know the price of everything and the value of nothing combined with a regulator who was so lacking in personnel and financial resources that they had effectively delegated their responsibility to the companies that they were supposed to provide oversight to.
Boeing returned over 90 BILLION dollars to shareholders in the form of dividends and share buybacks in the last 10 years. That money came from a company top to bottom emphasis on cheap and fast, instead of spending the money and taking the time to do things right.
Like Exxon and BP the Boeing C suite executives got their fat bonus cheque’s as the stock price soared oblivious to fact they were destroying the company......
Boeing returned over 90 BILLION dollars to shareholders in the form of dividends and share buybacks in the last 10 years. That money came from a company top to bottom emphasis on cheap and fast, instead of spending the money and taking the time to do things right.
Like Exxon and BP the Boeing C suite executives got their fat bonus cheque’s as the stock price soared oblivious to fact they were destroying the company......
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IMO the THS - the single most powerful control surface - should have never been used in this kind of control loop. It is a bad idea and that idea should have been killed instantly.
Once it was accepted - the rest of the bad things start to come up (like different understandings and acceptance of weird behaviour).
Once it was accepted - the rest of the bad things start to come up (like different understandings and acceptance of weird behaviour).
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indeed. I am not a physics guy. So i just say the probability of an MCAS failure is p; probability of flight without failure is (1-p).
So, probability of n flights without failure (1-p)**n.
This statistic allows us ro estimate how long MCAS us going to take before it kills someone.
Maybe pilots would profit from knowing Bernouilli’s OTHER works
Edmund
So, probability of n flights without failure (1-p)**n.
This statistic allows us ro estimate how long MCAS us going to take before it kills someone.
Maybe pilots would profit from knowing Bernouilli’s OTHER works
Edmund
Source: Boeing Statistical Summary of Commercial Jet Airplane Accidents Worldwide Operations | 1959 – 2017
Another source, Airsafe.com has compiled 737-MAX departures at 0.65 million, and quotes a hull loss rate of 3.08 per million departures.
source: Airsafe.com Plane crash rates by model
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So, Mark Forner, had issues in the SIM with MCAS, but later convinced the FAA not to include MCAS in the manual, because it could confuse pilots(like it confused him in the SIM). When asked for info he plead the fifth, to prevent these texts coming out. Currently, he is a line pilot for SWA, whose pilots are suing Boeing for lost wages due to the MAX debacle. I would love to be on the JS when he is flying!
On the other hand, if he felt that he raised the alarm loud enough after this discovery, he would probably not have invoked the 5th this year.
Last edited by spornrad; 20th Oct 2019 at 07:56.
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Pegase Driver
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CurtainTwitcher :
These list are biased because they do not separate events where technical issues are a factor with events which have nothing to do with the model type , for instance it says on a foot note ::
.
The second list also excludes Cargo flights for instance.
These list are biased because they do not separate events where technical issues are a factor with events which have nothing to do with the model type , for instance it says on a foot note ::
As of 25 March 2015, the order of the airline models with the five lowest crash rates (for models with at least two million flights) has changed, with the Airbus A320 dropping to fifth place due to the March 2015 Germanwings crash in France:
The second list also excludes Cargo flights for instance.
MCAS was in the Maintenance Manuals as reported in one of the earliest MAX threads on PPRuNe - to what detail I am not sure. The maintenance training from the NG to the MAX was far greater than the pilot training for the same, if I recall correctly it was 3 weeks in the class.
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A few Non-Technical Questions
Amidst the learned technical discourse on this thread, may I be permitted to raise a couple of non-technical issues that may be of general interest:
1) Are Boeing still assembling the MAX 8 and if so, how many per month ?
2) Where are Boeing storing the completed aircraft ?
3) What impact is the above having on Boeings main sub-contractors and partners ?
If the above should be in a different thread, mods, please feel free to move it!
1) Are Boeing still assembling the MAX 8 and if so, how many per month ?
2) Where are Boeing storing the completed aircraft ?
3) What impact is the above having on Boeings main sub-contractors and partners ?
If the above should be in a different thread, mods, please feel free to move it!
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So, I'm not a 737 pilot or engineer, but have followed this thread from the outset. Something that's been nagging at me the last little bit, which I don't think has been answered;
Boeing has described MCAS, and it seems to be the general belief of most of the folks on this board based on available information, as being there to cope with a small portion of the envelope - low speed, high AoA, clean turns, to maintain stick force gradient while increasing AoA. What has been highlighted by the Forkner IM exchange is that this was the NEW low speed regime MCAS was extended to (and where its authority and rate were increased).
What does it do at higher speeds? It's clear from the comments that it was originally intended for use at higher speeds only, but to what end, exactly? Just enhanced STS to massage some stability concerns outside of straight speed stability that STS was originally added to address? Also, earlier information mentioned STS came from the KC-46A - I'm thinking that again, this may have been in higher speed regimes, to address stability concerns....
-Colin
Boeing has described MCAS, and it seems to be the general belief of most of the folks on this board based on available information, as being there to cope with a small portion of the envelope - low speed, high AoA, clean turns, to maintain stick force gradient while increasing AoA. What has been highlighted by the Forkner IM exchange is that this was the NEW low speed regime MCAS was extended to (and where its authority and rate were increased).
What does it do at higher speeds? It's clear from the comments that it was originally intended for use at higher speeds only, but to what end, exactly? Just enhanced STS to massage some stability concerns outside of straight speed stability that STS was originally added to address? Also, earlier information mentioned STS came from the KC-46A - I'm thinking that again, this may have been in higher speed regimes, to address stability concerns....
-Colin
So, I'm not a 737 pilot or engineer, but have followed this thread from the outset. Something that's been nagging at me the last little bit, which I don't think has been answered;
Boeing has described MCAS, and it seems to be the general belief of most of the folks on this board based on available information, as being there to cope with a small portion of the envelope - low speed, high AoA, clean turns, to maintain stick force gradient while increasing AoA. What has been highlighted by the Forkner IM exchange is that this was the NEW low speed regime MCAS was extended to (and where its authority and rate were increased).
What does it do at higher speeds? It's clear from the comments that it was originally intended for use at higher speeds only, but to what end, exactly? Just enhanced STS to massage some stability concerns outside of straight speed stability that STS was originally added to address? Also, earlier information mentioned STS came from the KC-46A - I'm thinking that again, this may have been in higher speed regimes, to address stability concerns....
-Colin
Boeing has described MCAS, and it seems to be the general belief of most of the folks on this board based on available information, as being there to cope with a small portion of the envelope - low speed, high AoA, clean turns, to maintain stick force gradient while increasing AoA. What has been highlighted by the Forkner IM exchange is that this was the NEW low speed regime MCAS was extended to (and where its authority and rate were increased).
What does it do at higher speeds? It's clear from the comments that it was originally intended for use at higher speeds only, but to what end, exactly? Just enhanced STS to massage some stability concerns outside of straight speed stability that STS was originally added to address? Also, earlier information mentioned STS came from the KC-46A - I'm thinking that again, this may have been in higher speed regimes, to address stability concerns....
-Colin
Given Boeing's "transparency" to date, those concerns are probably extremely warranted.
From the day of the second crash Boeing have never gained any ground on being credible, honest or transparent - in fact lots of the opposite.
indeed. I am not a physics guy. So i just say the probability of an MCAS failure is p; probability of flight without failure is (1-p).
So, probability of n flights without failure (1-p)**n.
So, probability of n flights without failure (1-p)**n.
The culprit was a SINGLE AoA vane that sent erroneous data to the MCAS. If the vane had a duplicate then MCAS would not be seen as the villain it currently is.
Imagine if a single vane activated a stick pusher at low altitude. Would you blame the stick push system or the design of a single vane having so much authority?
Just for the record. MCAS did not fail in these incidents (with available information so far).
The culprit was a SINGLE AoA vane that sent erroneous data to the MCAS. If the vane had a duplicate then MCAS would not be seen as the villain it currently is.
Imagine if a single vane activated a stick pusher at low altitude. Would you blame the stick push system or the design of a single vane having so much authority?
The culprit was a SINGLE AoA vane that sent erroneous data to the MCAS. If the vane had a duplicate then MCAS would not be seen as the villain it currently is.
Imagine if a single vane activated a stick pusher at low altitude. Would you blame the stick push system or the design of a single vane having so much authority?
I did not think so, but interesting comment.
You are correct MCAS operated exactly as it was instructed - a child doing what both it's parents guided it to do.
The child is not the villain but maybe the parents are.
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MEL = Minimum Equipment List
CDL = Configuration Deviation List
Both of these documents provide the operator the authority to dispatch an aircraft with certain systems or components that are inoperative, degraded or missing. There are usually some maintenance actions and operational limitations associated with a particular inoperative component. If a system is not listed in either of these two documents, then that system must be fully operational for dispatch. There are many aircraft systems and components that are not in the MEL or CDL.
That said, Boeing considered MCAS to be a sub-function of the Speed Trim System (STS). In the original design, Speed Trim (and hence MCAS) used two independent controllers that alternated every flight. The MEL allows dispatch with one STS controller inoperative as long as the other was verified as operative. I assume this MEL item will be removed or substantially altered before the MAX returns to service.