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Alaska Airlines 737-900 MAX loses a door in-flight out of PDX

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Alaska Airlines 737-900 MAX loses a door in-flight out of PDX

Old 17th Jan 2024, 10:21
  #1061 (permalink)  
 
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Hi TryingToLearn... I think you have a good understanding of the workings of the door plug, especially the bit about the Coefficient of Friction of metal on metal being 0.2. I had originally thought that the pads were rubber covered, so giving a CoF of 1.0. until I saw the close up picture of the plug laying on the ground.
Maybe the ultimate design fault is that as the differential pressure rises, the plug moves outwards, away from the support frame. In most of the doors used, they are on the inside of the door frame, so any outward movement increases the sealing force.
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Old 17th Jan 2024, 10:48
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Originally Posted by TryingToLearn
To me logic does!
Think back to the MCAS issue:
One mayor concept error during the SW design lead to a latent fault. Wrong input could make the SW feature go mad.
Normal defects (birdstrike...) made the fault show up and caused a situation almost impossible to control. One or two close calls, 2 fatal incidents.
At first, everybody pointed at the pilots, but the number of incidents was just to high to make it plausible.
First everybody (here) pointed at missing pilot training, piece of cake stab runaway...
Yes, it's true that MCAS was a design issue that didn't manifest itself until the Max had been in service for some time.

But there's no logic at all in asserting (at this stage, at least) that the fact the plug door problem only emerged six years after service entry means that it must therefore also have been a design issue.

Maybe it was, maybe it wasn't.
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Old 17th Jan 2024, 10:48
  #1063 (permalink)  
 
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The door frame is riveted or bolted to the fuselage skin. There is distortion there and the paint has cracked and possibly the sealant.
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Old 17th Jan 2024, 11:46
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TryingToLearn
. . . That's how the MCAS fault showed up . . .
Just a small nit-pick. MCAS didn't fail. At all times the software did exactly what it was written to do. The vane failures happened to parts that were at the time NOT designated in the 'Catastrophic' range. The final two failures of the vanes were cause by completely disparate mechanical issues. To be on that close timescale was a bizarre coincidence but one that may have caused a much more rapid and accurate set of investigations. Saying that two accidents being close together is a good thing becomes a rather unsavoury philosophic argument.
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Old 17th Jan 2024, 11:51
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Surfaces of Al alloy, which are permanently assembled in aircraft assembles are treated with a polymer which was known as Thiokol (the parent Co.).
Depending on application and drying times needed to complete the assembly or in wet fuel or hydraulic areas the spec was different; we used PR1422, 1431 in my days of heavy maintenance; mostly the colour of the PR was a sh*tty brown, but some were more grey; what you are seeing as cracks could well be the sealant that the paint has not covered or adhered to.
My spec #'s could be wrong.
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Old 17th Jan 2024, 12:04
  #1066 (permalink)  
 
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Originally Posted by D Bru
Commensurate with the cracks on the top corners of the door plug (in the picture posted #963 by DaveReidUK of the door plug's delivery to NTSB's facility), there are also cracks near the top corners of the door frame
Does NTSB say these pictures show cracks in the door frame? If not, is it possible the marked cracks are gaps between the door seal and the door seal retainer?
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Old 17th Jan 2024, 14:10
  #1067 (permalink)  
 
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Could be cracks....

Originally Posted by aeromech3
Surfaces of Al alloy, which are permanently assembled in aircraft assembles are treated with a polymer .... what you are seeing as cracks could well be the sealant that the paint has not covered or adhered to. My spec #'s could be wrong.
Originally Posted by EXDAC
Does NTSB say these pictures show cracks in the door frame? If not, is it possible the marked cracks are gaps between the door seal and the door seal retainer?
Thanks to both, I've edited the post so as to make my observation less definitive. However, EXDAC, the door seal at that hight already seems to be completely on the outside part of the doorframe.

Regards
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Old 17th Jan 2024, 14:10
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I can picture that the large segment of the interior cladding might get hung up for a few milliseconds on the door opening and pry it out a bit before finally giving up.

Recall the experiment of putting a cheap paint stirring stick overhanging a table edge and putting cheap newspaper over the end so that a karate chop to the extended stick snaps it off. The paper alone isn't very sturdy, but for the short time it provides a barrier to air getting under the part of the stick on the table and that air pressure is enough.

It could also be that the metal was elastically bent, pulled on the sealant that then shed its paint over a disproportionate area, but those dark areas have the tapered look that a deformed section produces when it breaks the paint film loose.
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Old 17th Jan 2024, 14:25
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This image is a crop of a previously posted image of a de-activated door. I believe the gray material that spans the image is the flexible door seal not the fuselage skin.


Last edited by EXDAC; 17th Jan 2024 at 14:37.
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Old 17th Jan 2024, 14:34
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FAA Latest holding statement

Apparently the results of the first 40 inspections are complete. "The FAA will thoroughly review the data from them".

Pending this review, approval of inspection and maintenance processes, and the delivery of said inspection and maintenance all 737-9s with door plugs [sic] will remain grounded

Expensive

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Old 17th Jan 2024, 14:39
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Originally Posted by MarineEngineer
There are none, because there is nothing wrong with the time-proven design. The issue is with Quality Control.
With all due respect, some points:
1. “Nothing” is an absolute term, aerospace is more about probabilities, … example: structures are not systems, which moves them to another ball park,
2. If design is at fault … we don’t know, … there are a number of open design questions…
3. If QC is at fault … we don’t know, … but we know both Spirit and Boeing have had serious QA/QC problems over the last few years… even O’Leary says it’s not right…
4. … most important …in aerospace there are a number of significant steps between design and QC… (you can’t compare aerospace in this respect to marine or automotive design & manufacture .. )…
5. theoretically speaking, based on the original definitions of Quality… you might say that if the whole integral process would run as it is meant to, you would not need QA/QC at all, it is like a “buffer” which theoretically should be empty… in line with that the term “quality escape” used by Calhoun sounds non-sensical to some, they would say from their viewpoint “it was so bad, not even QA/QC caught it” … that organisations may push activities into QA/QC that theoretically don’t belong there muddies the waters …blaming QX moves you away from fundamental causes…

we still need much more and much better information… would be interesting to have the docket filling up with checked factual information during the investigation…. hope to see that in my lifetime ;-)

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Old 17th Jan 2024, 14:47
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Originally Posted by A0283
would be interesting to have the docket filling up with checked factual information during the investigation…. hope to see that in my lifetime ;-)
I have found a review of the docket to sometimes be far more informative than even the final report. Does NTSB ever open the docket to public access before the final report is issued?
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Old 17th Jan 2024, 14:53
  #1073 (permalink)  
 
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But we do know that QC was lacking. United found several planes with loose hardware. There can be no doubt of this fact.
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Old 17th Jan 2024, 14:59
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Originally Posted by EXDAC
I have found a review of the docket to sometimes be far more informative than even the final report. Does NTSB ever open the docket to public access before the final report is issued?
you would expect :

a. 30 day prelim
b. 365 day annual update
c. Publication of final report

to be such opening moments, have not found them earlier than final IIRC … but …

in some cases the docket is indeed (far) more interesting for understanding and learning than the report…

the fact that the NTSB has a docket at all makes them the gold standard for me personally in that respect … seems that some countries are moving in that direction… all should

sometimes some Asian (Japan) reports are more informative than the NTSB one … but that will depend on the user … they give more information on the investigative process for example, and some data sets are more consistent and more complete…





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Old 17th Jan 2024, 15:29
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Originally Posted by EXDAC
Does NTSB say these pictures show cracks in the door frame? If not, is it possible the marked cracks are gaps between the door seal and the door seal retainer?
Are you sure that's a seal retainer? I have to admit I've stared at that thing that goes up over the door cutout for a few hours and my best guess is it provides attachment points for interior panels on the operational door installation. I think the seal is quite a small bonded-on thing that seems to be missing, although you can see it in some pictures of the bottom of the cutout.

Edit: It actually makes sense, that "seal" at the top actually fills the 3-4" gap at the top of the door. It must be quite a beefy thing which explains that big retainer structure.

Last edited by incompleteness; 17th Jan 2024 at 15:45.
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Old 17th Jan 2024, 15:31
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Alaska customers received an email link to this video:

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Old 17th Jan 2024, 16:04
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Good point (, but/and...)

Originally Posted by EXDAC
This image is a crop of a previously posted image of a de-activated door. I believe the gray material that spans the image is the flexible door seal not the fuselage skin.

Good point! Indeed, in a picture of a closed door plug on another MAX-9 (see below) that I now found, the flexible seal from the side of the door frame clearly continues and bends over the top, exactly as you indicate. So the cracks I perceived are in the sealant between the "flexible" rubber and the metal strips next to the top of the door opening, not in the door frame it self. But, taken together with the cracks at the top of the door plug itself at approximately the same hight, it indicates IMO that something frictioneous happened there in the process of the door plug blow out.




BTW, concerning this for me at least new picture (of as said another Max-9's inspected), I note that:
1. (and I well realise it was discussed earlier on) with the space between the roller guide (on the door plug) and the roller plate (on the door frame), given what we've seen about the actual roller length, the roller end itself IMO can hardly reach more than halfway to the centre of the arrestor bolt;
2. the three of four visible bolts (and washers) securing the roller plate on the door frame show manipulation (broken paint). Probably as a result of torquing at regular maintenance. But I read somewhere (can't find it anymore) that supposedly also some of these bolts have been found loose at the ongoing inspections, apart from the bolts which attach the brackets guiding the lower vertical spring rods to the door plug frame. To note that the roller plate bolts of the accident plane don't seem to show any manipulation after having been painted following installation.

Last edited by D Bru; 17th Jan 2024 at 16:08. Reason: Typo
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Old 17th Jan 2024, 17:01
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Fairly typical now is the response to Kirkland Donald, the US nuclear safety procedures expert, being appointed as Calhoun's direct adviser on safety procedures.

Boeing names independent adviser, shares dive 8%

Boeing names independent adviser, shares dive 8% (msn.com)

So there we go; Boeing makes a mainstream move to address and enhance QA and air safety in their products, and what does Wall Street do ? "Hey guys, mark them down, this is going to have an impact on their cost-revenue balance. Probably not by anything like 8%, but hey, let's Send A Message to their board that we don't care for that. It will impact this year's earnings. Calhoun's gotta increease margins regardless. May prevent an accident in future years, but so what - we're short term people here, next quarters' earnings are king. In those future years we'll have offloaded our stocks to some other sucker".
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Old 17th Jan 2024, 17:09
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Note the green torque-stripe material on these fasteners that was not on the ones shown as loose. The paint chips on the corners of the bolts indicate they were removed and replaced after the initial installation.

Had the upper capture bolts been able to sneak past the rollers, those bolts would still be with the door.
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Old 17th Jan 2024, 17:16
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This from The Financial Times and is on a paywall, so may not be fully visible.
RyanAir doubles number of engineers overseeing Boeings production lines
I read that they went from 6 to 12 FR engineers and did so at Boeings request. As oft reported, FR are best buddies - not necessarily best customer!
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