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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 20th Oct 2019, 00:48
  #3221 (permalink)  
 
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Originally Posted by Grebe View Post
"So far we where told that MCAS was initially designed to work only at very low speeds"

Nope just the opposite - at near cruise at altitude and a steep bank ' windup' turn at edge of normal- extreme flight envelope

Go look up satguru stuff or seattle times

Thats why only .6 degrees change in stab was needed. But at low speeds, they needed more deflection- changed it by a factor of 4- never notified FAA re the 2.4 degree whack.
Thank you, that is interesting. So it was just the other way around. That also makes more sense with regards to the need to extend MCAS authority.
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Old 20th Oct 2019, 01:27
  #3222 (permalink)  
 
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Originally Posted by PEI_3721 View Post
Re Tomaski’s post #3192, and subsequent discussions.
The points made are prefixed as ‘possible’, but subsequently argued as fact without supporting evidence.
Guilty as charged, but with reasonable grounds.

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.
Agree

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.
Agree.

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.
In the case of Lion Air, the actual maintenance issue had nothing to do with MCAS, so it is unlikely the knowledge (or not) of this system would have made any difference. In response to a history of write-ups, maintenance personnel took several actions to include replacing the left AOA vane. This AOA vane malfunctioned from the start on the penultimate Lion Air 610 flight which seems to imply that the installation of the AOA vane was not performed correctly. This procedure is quite well known, so much so that we now have reports of an attempt to falsify photographic evidence purporting to show that the AOA work was done correctly. There is understandable debate as to what the maintenance technicians actually knew regarding the problems on this flight and whether that should have known to re-examine the AOA sensor. In any event, this aircraft was once again released into service with a faulty AOA sensor, this time with tragic results.

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.
First, the entire discussion regarding the state of flight crew training, and the need for improvement in various areas, can be made without a single reference to either of the MAX accidents. There have been various threads over the years, many closed, some still ongoing that have provided lots of (admittedly hearsay) testimony as to these problems. IMHO, the fact that there have not been more incidents/accidents tied to these deficiencies can largely be attributed to the multiple layers of protection built into the aviation safety system. As I stated in a separate post, I submit that the high levels of reliability and safety provided by these other areas has created a perverse incentive for airlines to cut corner on pilot training. Some of the issues regarding the crews' actions in the MAX accidents are simply another set of data points on the very long list of data points that indicate that not all is well with flight crew training.

These accidents should provide many lessons to be learnt; the first and very important is to beware hindsight bias.
By its very nature, an accident investigation tends to look back at what went wrong in the past that led to the particular event. It is much harder to look at current day actions and state with any authority that they will inevitably lead to an accident or incident. I can think a few times where I or someone I knew expressed a legitimate concern with a particular procedure only to be told that there was no data to suggest it was an issue worth worrying about (i.e. nothing bad had happened). In some of those cases, nothing bad ever did happen (well, at least not yet), and as a result nothing changed. Foresight is, at times, ineffective. What I am saying is that while hindsight does have its limitations, it does a pretty good job of identifying what should be changed in the future. Too late for those who died or suffered, but progress nonetheless.

Last edited by Tomaski; 20th Oct 2019 at 02:03.
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Old 20th Oct 2019, 02:27
  #3223 (permalink)  
 
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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.
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Old 20th Oct 2019, 04:40
  #3224 (permalink)  
 
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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!
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Old 20th Oct 2019, 05:22
  #3225 (permalink)  
 
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Originally Posted by Ancient Mariner View Post
He too, an a few others. 😉
Per
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

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Old 20th Oct 2019, 05:41
  #3226 (permalink)  
 
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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......
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Old 20th Oct 2019, 06:52
  #3227 (permalink)  
 
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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).
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Old 20th Oct 2019, 07:16
  #3228 (permalink)  
 
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Originally Posted by edmundronald View Post
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
Edmund, I posted this earlier.

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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Old 20th Oct 2019, 08:30
  #3229 (permalink)  
 
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Originally Posted by hans brinker View Post
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!
Forkner did convince the FAA to leave MCAS unmentioned in March 2016, before his discovery of the high trim authority / low airspeed variant described in those messages. Thus his remark "I lied to the regulators".
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 08:56.
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Old 20th Oct 2019, 08:48
  #3230 (permalink)  
 
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Originally Posted by Ex Cargo Clown View Post
I assume there must be some substantial evidence behind this, or it's a "see you in court" job from Boeing.

Err this is the commercial world.
You cannot take your biggest customer to court....

Silver
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Old 20th Oct 2019, 09:14
  #3231 (permalink)  
 
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Was the MCAS system in the maintenance manuals. Was it in the MEL or the CDL?
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Old 20th Oct 2019, 09:17
  #3232 (permalink)  
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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 ::
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.
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Old 20th Oct 2019, 09:36
  #3233 (permalink)  
 
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Originally Posted by icarus sun View Post
Was the MCAS system in the maintenance manuals. Was it in the MEL or the CDL?
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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Old 20th Oct 2019, 09:50
  #3234 (permalink)  
 
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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!
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Old 20th Oct 2019, 09:54
  #3235 (permalink)  
 
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Originally Posted by icarus sun View Post
Was the MCAS system in the maintenance manuals. Was it in the MEL or the CDL?
It's hard to see how a system, the existence of which pilots were initially unaware of, could appear in the MEL/CDL.

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Old 20th Oct 2019, 12:33
  #3236 (permalink)  
 
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Originally Posted by DaveReidUK View Post
It's hard to see how a system, the existence of which pilots were initially unaware of, could appear in the MEL/CDL.
I believe MCAS is purely software which, regrettably, would not be a maintenance item save for update procedures would it?
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Old 20th Oct 2019, 12:37
  #3237 (permalink)  
 
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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
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Old 20th Oct 2019, 12:53
  #3238 (permalink)  
 
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Originally Posted by sgs233a View Post
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
Recent reports seem to indicate some regulators have concerns MCAS maybe a stall prevention system.

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.
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Old 20th Oct 2019, 13:10
  #3239 (permalink)  
 
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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.
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?
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Old 20th Oct 2019, 13:19
  #3240 (permalink)  
 
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Originally Posted by Icarus2001 View Post
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?
Interesting - Is MCAS seen as the villain?

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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