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Old 13th Apr 2024, 10:47
  #41 (permalink)  
 
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Gentlemen, are You sure that this is not a red herring?

The issue with MCAS, as far as I can see it, is the following:

Slice 1:
It uses the most powerful control surface on the aircraft to force the nose down. On the accident aircraft (plural!), it was triggered not by multiple AOA vanes that all agreed about an approaching high AOA condition. The system was fired due to one single input from a quietly failed sensor without any checks, redundancy, whatever in place to keep it from happening. This was by design, not by a further system error. And unlike what has been written about the B707-400 above, it certainly introduced more than a tiny nose-down nudge.

Slice 2:
This protection system (for that is what it is, I consider it similar to the Airbus alpha protection in normal law in essence) has not been told about to the flight crews. It is said that this was due to cost cutting in training and intended to keep the Max under the same type rating as the previous models.

Slicee 3:
Self-certification, minimum authority supervision, ...

These are all cheese slices that had their holes lined up even before any crew set foot into the aircraft. Please take care not to bark up wrong trees.
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Old 13th Apr 2024, 10:53
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Old 13th Apr 2024, 12:56
  #43 (permalink)  
 
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TU.144 and WR6-3,

What I wrote is not a red herring and certainly does not absolve Boeing and the FAA from blame. All I was doing was pointing out that previous generations of pilots and airline training departments were well aware of, and used to dealing with, 1960s certificated aircraft and their deficiences. If you listen to what DPD had to say in the RAeS podcasts, the FAA was 'rather too lenient' in the application of its certification requirements for the 707, hence the changes DPD required for the rudder and the addition of a stick nudger.

Again, I think the FAA has had a rather too cosy arrangement with Boeing which, over the years, allowed Boeing to use grandfather rights for the 737. That, in itself, allowed later variants of the 737 to be built to less stringent requirements than would have been the case had it been a totally new type. But, so long as the training departments continued to apply training standards consistent with those earler requirements, safety was not significantly affected.

Come the Max, Boeing decided to correct for the longitudinal stability problems using the MCAS which operated on the whole stabilsier rather than a stick nudger operating on the elevators alone. Furthermore, allowing such a powerful control to be activated through inputs derived from a sole-source AoA sensor rather than having this duplicated or even triplicated, meant that there was now a gaping hole in the Swiss cheese. Thus, in no way, am I absolving Boeing and the FAA.

My comments regarding pilot proficiency concern the fact that, over time, flight operations departments may (probably?) have become less stringent regarding the awareness of, and training for, a runaway stabilser when compared with the way this was treated in the early days of the 707. I speak as an antique aviator and so am not aware of how much emphasis was placed on the runaway stabiliser drill on the 737Max.

And, WR6-3, I fully endorse your three likes above :-
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Old 13th Apr 2024, 14:33
  #44 (permalink)  
 
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No disagreement here in principle.

However, the core of the issue may then be summed up by stating that the 737 Max is an 1960s aircraft at heart coming with 1960s style issues and, consequently, an 1960s safety record. All thanks to the grandfathering rights and obviously some reluctance to spend money on a whole new modern design instead of squeezing what can be squeezed out of an available model...
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Old 13th Apr 2024, 19:38
  #45 (permalink)  
 
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Originally Posted by Tu.114
However, the core of the issue may then be summed up by stating that the 737 Max is an 1960s aircraft at heart coming with 1960s style issues and, consequently, an 1960s safety record. All thanks to the grandfathering rights and obviously some reluctance to spend money on a whole new modern design instead of squeezing what can be squeezed out of an available model...
Sorry, but "1960s safety record" is a demonstrably false statement.
Hull loss statistics for the 737NG series is nearly identical to the A320 series (stats as of 2022 - they may have changed a bit since).
Hull loss rate/million departures (fatal/total):
737NG: 0.08/0.18
A320 Series: 0.08/0.17
(knowing a little bit about statistics, the difference is not statistically significant)

In contrast, the true 1960's safety record 737-100/200: 0.87/1.78

There is plenty to criticize about the 737 MAX MCAS system and how it was certified, but to say the 737 is inherently unsafe because of its basic design heritage simply doesn't hold water.
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Old 13th Apr 2024, 22:09
  #46 (permalink)  
 
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I would suggest that both MCAS accidents would not have occurred if the airplane was certified to modern certification standards. So yes in this case grandfathering 1960 certification standards directly lead to both tragic accidents. The airplane is full of systems that are completely uncertifable under today’s certification standards.
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Old 13th Apr 2024, 22:42
  #47 (permalink)  
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Tu

The system was fired due to one single input from a quietly failed sensor without any checks, redundancy, whatever in place to keep it from happening
Quietly failed? The vane was wildly out of alignment with the shaft it rotates. The result was chaos.

I too am an old guy with far too much time on my hands. I read every post, some many times, in that two intensive years.

The replacement of the nearly new sensor with a refurbished one from somewhere in Florida still leaves me stunned. It's exactly the kind of trap fault-finders fall in to. It's vital to assume the new part might also be faulty, though the aviation industry is unlikely to provides time for a test flight for such a small part. Again, I question what was in the minds of the first crew and technicians in those first two days? Remember, it followed a grievously under-played emergency from the day before. In fairness, no one knew about the part's 'chaotic' status, simply because it didn't fall into that catagory yet.

The 707 nosing up at the late stages of a stall sounds related to the reason for MCAS. However, despite routinely reading duff gen about the reason MCAS was introduced, I only know about the inability to certify the MAX while nacelle lift was making the late stages of pulling back much too light on the pole. This was nearing the stall, and in certain turns - the latter being vitally important to get right.
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Old 13th Apr 2024, 22:47
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Originally Posted by Big Pistons Forever
I would suggest that both MCAS accidents would not have occurred if the airplane was certified to modern certification standards. So yes in this case grandfathering 1960 certification standards directly lead to both tragic accidents. The airplane is full of systems that are completely uncertifable under today’s certification standards.
Also demonstrably false. MCAS met current certification standards - but only because of some very bad assumptions regarding pilot reactions and training. MCAS failure was classified as "MAJOR" (classifications are MINOR, MAJOR, HAZARDOUS, and CATASTROPHIC). MAJOR failures are allowed to occur at ~10-5/hr (for example, 'routine' engine failures are considered MAJOR) - which basically means 'increased crew workload', and redundancy is not required. The regulations regarding such faults haven't materially changed in decades.
In 20-20 hindsight, MCAS should have been classified as at least HAZARDOUS (and probably CATASTROPHIC) - which means probability of occurrence of 10-7/hr (or 10-9 for catastrophic) and require redundancy.
The problem wasn't the cert rules, it was the interpretation of the seriousness of the fault (which, to some extent, was hidden from the FAA).
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Old 14th Apr 2024, 12:05
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Originally Posted by tdracer
Also demonstrably false. MCAS met current certification standards - but only because of some very bad assumptions regarding pilot reactions and training. MCAS failure was classified as "MAJOR" (classifications are MINOR, MAJOR, HAZARDOUS, and CATASTROPHIC). MAJOR failures are allowed to occur at ~10-5/hr (for example, 'routine' engine failures are considered MAJOR) - which basically means 'increased crew workload', and redundancy is not required. The regulations regarding such faults haven't materially changed in decades.
In 20-20 hindsight, MCAS should have been classified as at least HAZARDOUS (and probably CATASTROPHIC) - which means probability of occurrence of 10-7/hr (or 10-9 for catastrophic) and require redundancy.
The problem wasn't the cert rules, it was the interpretation of the seriousness of the fault (which, to some extent, was hidden from the FAA).
In my opinion it was noncompliance because the analysis did not apply to the actual design, which why the hazard classification was insufficient. Perhaps one can consider this unintended but it is a consequence of deliberate obfuscation and a rush to certification of the design for financial purposes. Inexcusable.

The ineffectiveness of FAA oversight due to the new processes surrounding ODA is a major contributing factor. ODA should be eliminated, particularly in Boeing’s case.
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Old 14th Apr 2024, 17:02
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The ineffectiveness of FAA oversight due to the new processes surrounding ODA is a major contributing factor. ODA should be eliminated, particularly in Boeing’s case.
I don't think that is realistic or even desirable and I say that as as someone who used to work for an aviation regulator. The reality is that the expertise exists in industry not the FAA, especially in this era of rapid technological advancements. The problem was regulatory capture of the ODA by Boeing. That, that was happening should have been obvious to the FAA and they should have taken action.
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Old 14th Apr 2024, 17:47
  #51 (permalink)  
 
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Cherry picking statistics is pretty poor form. Deciding to choose only the 737NG to compare it with the A320 series is frankly embarrassing. How about comparing the 737NG to the A318 alone? Zero hull losses for the A318. You would agree that is an unfair and unrealistic comparison?

The discussion is about the 1960s era 737 that is a dead horse that continues to be beaten by Boeing. So compare apples to apples. The Boeing 737 is demonstrably less safe than the Airbus A320. Boeing’s own statistics show it, you even acknowledge the rate of the 100/200 being so much worse than the NG. What about the 3/4/500? Again much worse than the A320 family. And look at the Max - 1.48! So how about we compare that to the A320 NEO for most modern variants?

A320 NEO 0.11/0.11 versus 737 Max 1.48/1.48. Your own data confirms it. Do better.

https://www.boeing.com/content/dam/b...df/statsum.pdf
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Old 14th Apr 2024, 20:19
  #52 (permalink)  
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I think it was Winston Churchill who once said :" never trust a statistic you have not manipulated yourself .." or something similar.
Simple example : are Germanwings and Sully's US Air counting as A320 hull losses accidents in that comparison?
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Old 14th Apr 2024, 21:39
  #53 (permalink)  
 
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Originally Posted by BoeingDriver99
Cherry picking statistics is pretty poor form. Deciding to choose only the 737NG to compare it with the A320 series is frankly embarrassing. How about comparing the 737NG to the A318 alone? Zero hull losses for the A318. You would agree that is an unfair and unrealistic comparison?

The discussion is about the 1960s era 737 that is a dead horse that continues to be beaten by Boeing. So compare apples to apples. The Boeing 737 is demonstrably less safe than the Airbus A320. Boeing’s own statistics show it, you even acknowledge the rate of the 100/200 being so much worse than the NG. What about the 3/4/500? Again much worse than the A320 family. And look at the Max - 1.48! So how about we compare that to the A320 NEO for most modern variants?

A320 NEO 0.11/0.11 versus 737 Max 1.48/1.48. Your own data confirms it. Do better.

https://www.boeing.com/content/dam/b...df/statsum.pdf
Talk about cherry picking stats! There are substantial systems differences between the various 737 versions (-1/200, -3/4/500, -6/7/8/900NG, and MAX). The -1/200 really was a 1960s design, and it's hull loss stats are comparable to other models from that period. Newer versions of the 737 incorporated various safety systems that simply were not available or feasible with then existing technology of the early versions. Newer technology has made aircraft safer, and the various 737 models have incorporated newer technologies that were available at the time the various models were designed - making them safer. That's why aircraft in general are so much safer today than they were in the 1960s - it's new systems such as TCAS and GPWS, along with improved crew training and ATC improvements.
The basic issue is - are derivative aircraft certified under the Changed Product Rule (CPR) meaningfully less safe than all-up new designs of the same vintage. By that metric, there is absolutely nothing wrong with the 737NG.
Yes, mistakes were made with the MAX, and Boeing deserves criticisms for the way they designed and certified it. But those are not related to the grandfathered aspects of the cert that were allowed by CPR (nearly all of the grandfathered cert aspects of the 737 are related to structures, not systems).
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Old 14th Apr 2024, 21:41
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Originally Posted by tdracer
Also demonstrably false. MCAS met current certification standards - but only because of some very bad assumptions regarding pilot reactions and training. MCAS failure was classified as "MAJOR" (classifications are MINOR, MAJOR, HAZARDOUS, and CATASTROPHIC). MAJOR failures are allowed to occur at ~10-5/hr (for example, 'routine' engine failures are considered MAJOR) - which basically means 'increased crew workload', and redundancy is not required. The regulations regarding such faults haven't materially changed in decades.
In 20-20 hindsight, MCAS should have been classified as at least HAZARDOUS (and probably CATASTROPHIC) - which means probability of occurrence of 10-7/hr (or 10-9 for catastrophic) and require redundancy.
The problem wasn't the cert rules, it was the interpretation of the seriousness of the fault (which, to some extent, was hidden from the FAA).
For the benefit of others, Unicode includes code points for superscripted numerals and 'plus' and 'minus' signs.

10⁺⁻¹²³⁴⁵⁶⁷⁸⁹⁰

So the maximum failure rates can be rendered as:

MAJOR: ~10⁻⁵
HAZARDOUS: ~10⁻⁷
CATASTROPHIC: ~10⁻⁹

The relevant code points are
Superscripted 'plus' sign: U+207A
Superscript 'minus' sign: U+207B
Superscript Left Parenthesis: U+207D ⁽
Superscript Right Parenthesis: U+207E ⁾
Superscript Numeral One: U+00B9
Superscript Numeral Two: U+00B2
Superscript Numeral Three: U+00B3
Superscript Numeral Four: U+2074
Superscript Numeral Five: U+2075
Superscript Numeral Six: U+2076
Superscript Numeral Seven: U+2077
Superscript Numeral Eight: U+2078
Superscript Numeral Nine: U+2079
Superscript Numeral Zero: U+2070

Copying and pasting from this post should work.
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Old 14th Apr 2024, 21:43
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Originally Posted by ATC Watcher
I think it was Winston Churchill who once said :" never trust a statistic you have not manipulated yourself .." or something similar.
Simple example : are Germanwings and Sully's US Air counting as A320 hull losses accidents in that comparison?
Sully, yes (although as a hull loss, not a fatal hull loss since no one died). "Bad Luck" accidents are included, as is blatant crew error.
Germanwings - probably not. The stats specifically exclude intentional acts such as war or terrorism and I suspect pilot suicide would qualify.
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Old 15th Apr 2024, 02:10
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So stick with the Max statistics alone then. Approximately twice as dangerous as the 100/200. And approximately 15 times as dangerous as the Neo. But I’m sure you’d make another argument that those statistics don’t apply.

Hey ho - I can see where you sit on the issue. Such a shame to see the destruction of such a successful brand.

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Old 15th Apr 2024, 04:22
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The problem with statistics of small numbers of events is that probabilities based on them have huge problems determining the confidence interval.

It's better to focus on the sequence that led to the accident and identify any places where the same initiator might start onto a different path. Like, before MCAS was involved, why did the last crew do exactly all the opposite things in response to a simple stall warning? Nice day, plenty of visibility, engines running fine. Set pitch and power and go on with the day. Or just concentrate on the autopilot to the exclusion of lowering the thrust until Vmo is exceeded?

What fault in the training allowed the crew the understanding that only autopilot could possibly be the answer to a problem that demanded autopilot be given no authority?

No point on continuing worry over MCAS as that software has been altered to perform a different function, but this won't be the last stall warning a crew gets on an airplane.
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Old 15th Apr 2024, 07:50
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I think we've thrashed the MAX issue to death elsewhere

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Old 15th Apr 2024, 12:20
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Originally Posted by Asturias56
I think we've thrashed the MAX issue to death elsewhere
Yes, here we go again ...
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Old 15th Apr 2024, 14:43
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"The problem with statistics of small numbers of events is that probabilities based on them have huge problems determining the confidence …"

Which is why the use of outcome - fatalities, as a measure of safety is of little value in a very safe industry.

Alternatively, risk based safety - reducing the level of risk of harm to an acceptable minimum, considers current activity. The process looks to the future based on what has happened, and what is happening now; neither measure absolute, but a useful a guide for judgement of an uncertain future.

The 737 Max recent history should not be overly projected forward because of the mitigations from modifications.
However, the continuing manufacturing issues involving several types, and the difficulties in providing a quick fix for culture, etc, suggest that there is an increased level of risk which may take time to reduce.
Furthermore, the regulator who should oversee these aspects has suffered similar problems.

Thus the current situation has to be judged relative to the excellent historical record of Boeing aircraft and the industry in general; better than most forms of transport.
Flying is 'safe', and flying in Boeing aircraft is sufficiently comparable with other aircraft not to be concerned relative to other transport activities.
The issue remains about who and how risk based judgements are made:- manufacturing governance, regulator oversight, and the context of presentation - media and personal, human bias.

http://john-adams.co.uk/wp-content/u...onsibility.pdf
,,
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