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

[OldnGrounded]

Interesting that the bolts securing the rollers to the frame were identified. Can that be done without opening the plug to access and see the rollers? Perhaps the act of QC ing the rollers lead to the lock bolts being removed and not reinstalled. The plot thickens.

The images on the AC story show that at least three of the four bolts securing each roller guide pin to the fuselage frame are visible when the interior panel is removed (or before it's installed). Two of them could probably be tightened/torqued without opening the plug. The other two? Probably not, at least not in an approved manner. At least, that's what it looks like.

https://theaircurrent.com/wp-content/uploads/2024/01/plug-exit-anatomy.jpg

[DType]

Except that it was NOT "a plug type passenger door"

[A0283]

I am hoping that a sufficiently definitive NTSB preliminary report is issued in 30 days or less. All the answers appear to be on the ground with no mysterious interactions between crew, aircraft, weather, et al that are the more frequent and overlapping set of conditions that lead to an investigation.

It seems like a fairly simple path as I previously outlined - design, manufacturing engineering, QA, QC, and the assemblers. Somehow this particular door happened as a result of a procedural disconnect.

The 1 year report can delve into the wider aspects of production controls and make recommendations for systemic improvements, but I at least want to see quite soon a report that Unnamed Person #1 did this and Unnamed Person #2 who was supposed to do that and didn't, so that the rest of aviation can then look to whatever those involved also touched and make sure it is OK.

My impression, trying hard to understand the meaning of what the NTSB chair says, and peek behind the blinders, is that you will not get that. Hope not, but…

Appears the NTSB is focussing on this specific case … eh aircraft… the answer being for example something like “in this specific aircraft a bolt there and there was probably missing“… might get that in 30 days but would not bet on that…

Appears the NTSB leaves it up to the FAA to investigate the manufacturing and production processes. That would mean the FAA should point out your Unnamed persons. Which looks like the FAA investigating its own oversight…

If manufacturing is causal here, then you would want an independent investigator to investigate that.

I get the feeling that the NTSB is focussing on the aircraft side and not taking its role on the potential causal side of the manufacturing process.

This is why installing a specialist work group centred on manufacturing, is something I tried to suggest earlier in the thread.

If manufacturing turns out to be main cause or strong factor, then, in hindsight, it will appear strange that we got a Meteo WG but not a Manufacturing WG.

Would be interesting to hear other’s views on this.

[MechEngr]

A new video from Chris Brady and an explanation of the previous error which apparently was also found in the AMM and was the basis for Chris to use.

Thanks to Chris for all the videos and the timely updates.

https://www.youtube.com/watch?v=kKSNdqtG3dY

[zueriflyer]

TV is boring tonight, hence did some math. Worst case assuming plug rotates into highest frontal area condition once ejected (highest plug deceleration).

Calculated in incremement of 10 msec by the miracle of EXCEL. Plug hits H/S leading edge 0,21 sec after ejection with 160 mph speed difference.

Very simplified, no fancy aero., just considering change of drag with speed, only longitudinal.
Energy is 73 kJ.


Source: USA TODAY Plug Height [m] 1,2192 48 [inch]
Source: USA TODAY Plug Width [m] 0,6604 26 [inch]
calc Plug FrontalArea [m^2] 0,81 1248 [inch^2]
estm. cw Plug [-] 1,2
Source: USA TODAY Mass of Plug [kg] 28,6 63 [pounds]
estm. Air Density @ FL160 [kg /m^3] 0,8
Source NY TIMES Aircraft Speed @incident [m/s] 197 440 [mph]
scaled from 73 pic Distance Plug-Horiz.Stab. [m] 9

calc Initial Drag Force on Plug [N] 14965
calc Initial Deceleration of Plug [m/s^2] 523 53,3 [g]

calc Plug speed @ impact with H/S [m/s] 71,5 equals 160 [mph]
calc Energy [kJ] 73,1

[jimjim1]

Pressurisation issues were unrelated to the incident.

So they say at present. I have no inside info but it is a bit of a coincidence if it turns out to really be unrelated.

It is strange for the NTSB to say this at this early stage. How could they even know?

[DaveReidUK]

The bolts drawn in blue on post 684 hints to a fully threaded bolt, also called a set screw, used for the locking. Which is a lot weaker than a partly threaded actual bolt. This would have been a vulnerability factor when the roller pin regularly hit it on the middle. The sideways or bending strength of a set screw is probably not more than that of a bolt 1 size down.
Is there a picture of the actual "bolt" that is supposed to be used and in the free.

I wouldn't infer anything from that drawing. I'd be amazed if they aren't plain shank bolts.

[DaveReidUK]

So they say at present. I have no inside info but it is a bit of a coincidence if it turns out to really be unrelated.

It is strange for the NTSB to say this at this early stage. How could they even know?

The NTSB said that the cabin pressure controller had gone into Alt mode on 3 occasions. There was no mention of it having had an effect on actual cabin px.

[BFSGrad]

FAA letter to Boeing, no punches pulled:
I’ve seen other comments citing this letter as evidence that NOW the FAA is finally dropping the hammer on Boeing. I see the letter as more of a pro forma document. Wasn’t the FAA supposed to have dropped the hammer on Boeing years ago after the MAX/MCAS debacle? Wasn’t Boeing supposed to be under enhanced scrutiny as a consequence of the deferred prosecution agreement?

Reminds me of some dialogue from an old John Landis movie:

Greg: What do you intend to do, sir? Delta’s already on probation.
Dean W: They are?
Greg: Yes, sir.
Dean W: Oh. Then as of this moment, they’re on double secret probation!

[WillowRun 6-3]

FAA letter to Boeing, no punches pulled:

FAA's letter to Boeing appears (to this SLF/attorney) to reveal a state of alarm within FAA and (despite its total absence of pertinent aviation regulatory knowledge or experience) perhaps the Secretary's office as well.

Why? Because FAA's letter contains no reference whatsoever, let alone any citation, to statutory or administrative regulation provisions which specifically authorize such an investigatory process in a situation of this type. In the aftermath of the first and then second MAX accidents, there certainly were formal investigations by the Inspector General. IIRC the IG documents carried heavy, definitive citations to its authority to investigate. This letter simply announces the inquiry. Perhaps there is some unspecified general authority for this inquiry - if there is, I'll both be surprised and corrected.

I am emphatically not making any suggestion that the inquiry is improper. But it strongly suggests a case of the FAA "wingin' it." Consider also -

Administrative processes in the federal interagency always are spelled out in detail; the time frames for actions to be taken such as submitting filings, the types of information that can be requested of the responding party, any rights of confidentiality protection, and many more subjects. In this instance, however, the entire section describing how this investigation will be conducted reads like it was crafted from whole cloth. Or ad hoc in legal terms. (I'm stating more of an impression based on experience rather than a specifically provable point.)

Though Mech Engr no doubt is correct that the overall situation would benefit from a thorough report at 30 days from NTSB, I seriously doubt such a significantly comprehensive inquiry will be condcuted by the Board or that at 30 days more than facts of the occurence itself will be reported. Even if the jurisdictional line between FAA and NTSB was open to flexibility before the letter announcing FAA's inquiry, the marker has been set down now.

What this all means for FAA funding, and the still-pending FAA reauthorization legislation....what a mess, is about all that emerges at this point. .

[EXDAC]

The bolts drawn in blue on post 684 hints to a fully threaded bolt, also called a set screw, used for the locking.

I have no knowledge of the terminology used in Ireland but FAA AC 41.13-1b has 9 different references to setscrews all of which are fully thread headless fasteners. In my native UK these were known as grub screws, in US as set screws. Clearly these door hinge fasteners have heads.

[lateott]

I’ll first answer question #2: the previously logged cabin pressure controller faults have been mentioned several times in the thread, and they were reported to be not linked to cabin air leakage.
Still, I think I’ve read that hissing noises had been reported nevertheless. Investigators will still have an open ear for this detail!

Pressurisation issues were unrelated to the incident.

I am not aware of any evidence of your statements regarding relevance of the auto pressurization warnings.

The NTSB Chair stated at least 2 times "we don't know." If you have a more current and credible source than NTSB as late as 8-Jan, please provide a source.

[megan]

From Avweb, backs up what I said in post #35, "Maybe Spirit (Boeing) is suffering the same pitfalls, get the aircraft out the door and focus being lost on the process"Weeks before a catastrophic incident involving a Boeing 737 MAX 9, workers had raised warnings about defective production procedures. Reporters at Jacobin.com posted a story (https://jacobin.com/2024/01/alaska-airlines-boeing-parts-malfunction-workers-spirit-aerosystems) yesterday (Jan. 9) citing documents filed in federal court (https://drive.google.com/file/d/1pzxFhXIxXWUjZkAaLGICuyR8Vi-u1HN6/view) from workers at Spirit AeroSystems, the Boeing subcontractor that reportedly manufactured the door plug that departed a Boeing 737 MAX 9 on Jan. 5 over Portland, Oregon.As part of the federal securities lawsuit, a Spirit employee allegedly told higher-ups about an “excessive amount of defects,” later telling a colleague he “believed it was just a matter of time until a major defect escaped to a customer.” According to the court filing, the company ignored the warnings.

Broadly, the lawsuit alleges that Spirit deliberately covered up systemic quality-control deficiencies, encouraged employees to underplay defects and retaliated against workers who spoke out about their safety concerns.

The complaints speak to Boeing’s allegedly insufficient oversight of subcontractors such as Spirit and the FAA’s inability to effectively regulate quality control. According to the Jacobin report, William McGee, former panel member advising the U.S. Department of Transportation (DOT) and now a senior fellow for aviation and travel at the American Economics Liberty Project, said, “The FAA’s chronic, systemic, and longtime funding gap is a key problem in having the staffing, resources, and travel budgets to provide proper oversight. Ultimately, the FAA has failed to provide adequate policing of outsourced work, both at aircraft manufacturing facilities and at airline maintenance facilities.”

According to Jacobin reporters, Spirit received a $75 million public subsidy from the U.S. DOT in 2021 and reported greater than $5 billion in revenues in 2022. A class action lawsuit launched in May 2023 and amended in December claimed that Spirit management “concealed from investors that Spirit suffered from widespread and sustained quality failures. These failures included defects such as the routine presence of foreign object debris [FOD] in Spirit products, missing fasteners, peeling paint, and poor skin quality. Such constant quality failures resulted, in part, from Spirit’s culture, which prioritized production numbers and short-term financial outcomes over product quality.”

One quality control inspector reported in the court filings that management at Spirit was putting inspectors in “a very uncomfortable situation” by asking them to inaccurately record the number of defects. In an ethics complaint, the inspector wrote, “We are being asked to purposely record inaccurate information.” The inspector conveyed his concerns in a direct email to Spirit CEO, Tom Gentile, according to the complaint.

[WHBM]

Assembly crews (such as the folks putting in the interior panels) would be used to seeing those bolt holes in your picture empty on the emergency exit door equipped models. I wonder if this particular airframe was the first after a run of a few airframes equipped with emergency exit doors. Perhaps complacency or rushing though the task of checking all the doors/plugs: then signing off a whole page of sign offs could be a factor.
The fact is that there are hardly any 737-MAX9 being built with proper emergency doors at this position. It is essentially a provision for when they get sold on secondhand in mid-life, and fitted with higher density seating. Of recent MAX9 production the vast majority have been only for Alaska and United, who specify plugs. It has really been a poor seller other than to the US major trunk carriers.

They are interleaved in production with the 737-MAX8, the shorter aircraft, which does not have or need any door at this position at all, and never has any plugs or provision for them..

[lateott]

A new video from Chris Brady and an explanation of the previous error which apparently was also found in the AMM and was the basis for Chris to use.

Thanks to Chris for all the videos and the timely updates.
Thanks for posting.

It is very clear at 3:58 that the springs bear the entire weight of the plug, holding the stop pins above the stop fittings. Clearly the plug must be pushed down, after being pulled into the frame, in order to place the 4 stop bolts.


https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/901x957/springs_bearing_weight_of_plug_b7e5fc8bd8e5f328ea2fb55164889 8e0fd6566bd.jpg

[lateott]

A self-ejecting design!

[incompleteness]

A new video from Chris Brady and an explanation of the previous error which apparently was also found in the AMM and was the basis for Chris to use.

Thanks to Chris for all the videos and the timely updates.



In this latest video, Chris talks about the lack of documentation for cockpit door opening under rapid decompression. The AMM says the door "is able to withstand the pressure difference due to the small area of the flight compartment."

Discussion. In FAR 25.365, the size of the rupture in the pressure shell that you are required to assume, in square feet, is given via a formula. This is fixed for a given model of aircraft. It's the same no matter where the rupture occurrs.

If the rupture occurrs in a large compartment, like the cabin, the time to vent all the air out of that compartment is longer than the time to vent a smaller compartment like the cockpit. That's because the same size hole must be assumed for both compartments.

So if the rupture occurrs in the cabin, the general gaps around the cockpit bulkhead may allow sufficiently fast venting of the cockpit into the cabin to prevent exessive delta-p on the cockpit bulkhead. If the rupture occurs in the cockpit, the decompression is much faster, and the natural venting around the cockpit bulkhead may not be fast enough to prevent high dp's on the bulkhead.

That explains why blowout panels into the cockpit exist, but there are none the other way.

The 25.365 formula gives a size of the required rupture on the MAX 9 of about 4 square feet (caveat: I calculated that myself, so, not an offical value). the Alaska 1282 blowout was much bigger than what the aircraft is required to be designed for.

What I feel this might mean is that the cockpit door is not supposed to open in a decompression that conforms to certification. But this was a much larger decompression opening than Boeing was required to consider. Through either luck, or just good ethical design practice, the door latch was made weaker than the bulkhead, and blew open, thus possibly saving the bulkhead.

It's not that surprising that Boeing didn't put something in the AMM that covers an eventuality not considered in certification.

[OldnGrounded]

Probably too expensive to plug the doorway from inside the fuselage with the plug being larger than the opening, sealing tighter as the cabin pressure differential increases. Also, plugging an exit to fit in a couple of additional seats is like shortening a runway. Safety is compromised again by the accountants!

Plugging those exits is for configurations with fewer seats.

[BigJETS]

I have not seen the maintenance manual but I would expect that the stop fittings are adjusted so the door plug skin is flush with the fuselage skin and all stop fittings are in contact. Photos of the incident aircraft seem to show that the seal is fixed to inside of the fuselage and the door plug would be pulled into it when it was closed. I very much doubt that the fit of the seal is of any consideration in the adjustment of the stop fittings.
After much consideration I may have to agree with you on this. I thought perhaps it was cinched down tight, but I guess it really is conceived to be open 10 times a day if desired (for some reason?). Thanks for the input. Im seeing the plug as a door now...A door with no knob apparently.

[aox]

https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/499x441/image_2024_01_12_010740304_921133a95c0a4daaa048563ef073048e1 0f15fe0.png

I'm looking at the castellated nut at the bottom of the picture in post 764

Maybe my eyesight will be a bit clearer in the morning

[B-757]

What I feel this might mean is that the cockpit door is not supposed to open in a decompression that conforms to certification. But this was a much larger decompression opening than Boeing was required to consider. Through either luck, or just good ethical design practice, the door latch was made weaker than the bulkhead, and blew open, thus possibly saving the bulkhead.

It's not that surprising that Boeing didn't put something in the AMM that covers an eventuality not considered in certification.

..My manual (not 737) clearly states that the whole door may open in case of a rapid cabin decompression..Do not know about Max..

Fly safe,
B-757

[Loose rivets]

I'm looking at the castellated nut Test question. Where's the pin, split or cotter?


EXDAC
but I would expect that the stop fittings are adjusted so the door plug skin is flush with the fuselage skin and all stop fittings are in contact.


If I were charged with the problem, I'd be outside on a hoist holding a big straight-edge against the hull. I'd phone my mate inside. "Tighten . . . bit more . . . bit more." You get the picture.

[Old Ag]

Thanks for posting.

It is very clear at 3:58 that the springs bear the entire weight of the plug, holding the stop pins above the stop fittings. Clearly the plug must be pushed down, after being pulled into the frame, in order to place the 4 stop bolts.


https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/901x957/springs_bearing_weight_of_plug_b7e5fc8bd8e5f328ea2fb55164889 8e0fd6566bd.jpg

Unknown is how much upward force they exert on the plug when its in the closed position. Also unknown is how much of an interference fit there is between the stop pads and the adjustable pins in the stop fittings. It could be that it takes a bit of force to dislodge the door from the stop pads, but when free the springs push the hinge slide fittings up against the washers in the end of the hinge and hold the plug it at its upward limit on the hinges. Conversely, I imagine it would take downward pressure on the plug to overcome the spring and shift it down. Then a little extra force to overcome the interference between the stop pads and stop pins to get it fully closed.

I'm still convinced that someone removed all the stop bolts and never reinstalled them. Somehow they got the door closed and it stayed in place.

Until it didn't.

They built it like a mouse trap.

[AirBill]

How does the door plug seal itself if it is on the external side of the pressurized cabin? It is like looking at a tapered drain plug from the bottom. There must be some seals involved, but the interior air pressure is forcing the door outward away from the seals. What am I missing here?

[dragon6172]

Test question. Where's the pin, split or cotter?

Looks as though it is there to me?

[lateott]

Unknown is how much upward force they exert on the plug when its in the closed position. Also unknown is how much of an interference fit there is between the stop pads and the adjustable pins in the stop fittings. It could be that it takes a bit of force to dislodge the door from the stop pads, but when free the springs push the hinge slide fittings up against the washers in the end of the hinge and hold the plug it at its upward limit on the hinges. Conversely, I imagine it would take downward pressure on the plug to overcome the spring and shift it down. Then a little extra force to overcome the interference between the stop pads and stop pins to get it fully closed.

I'm still convinced that someone removed all the stop bolts and never reinstalled them. Somehow they got the door closed and it stayed in place.

Until it didn't.

They built it like a mouse trap.

1) How much upward force they exert on the plug when it's in the closed position? Not sure what you mean. In the intended "closed position" the answer is zero. In the pulled-closed but not bolted position the answer is > 31.5 lbs for each hinge.
2) There should be zero interference between the stop pads and stop pins on the ground at zero differential pressure
3) IMO there is no way the plug was sealed behind the interior plastic trim without at least one "placed" bolt. Whether that bolt also had a castellated nut with or without a split pin is another question.

[lateott]

I have not seen the maintenance manual but I would expect that the stop fittings are adjusted so the door plug skin is flush with the fuselage skin and all stop fittings are in contact.

If I were charged with the problem, I'd be outside on a hoist holding a big straight-edge against the hull. I'd phone my mate inside. "Tighten . . . bit more . . . bit more." You get the picture.
I would guess they are adjusted only after the plug is installed and bolted. Then a thickness gauge is inserted and they are adjusted to leave a specified gap. I don't think they should be touching at zero pressure differential.

[Old Ag]

I am not aware of any evidence of your statements regarding relevance of the auto pressurization warnings.

The NTSB Chair stated at least 2 times "we don't know." If you have a more current and credible source than NTSB as late as 8-Jan, please provide a source.

In an earlier post someone stated that the NTSB described the "Altn" light coming on during the pressurization events, this means the primary controller detected a a parameter that tripped a fault with the primary controller and the alternate system did not detect the same fault. Actual pressurization events (cabin altitude climb of over 2000fpm, excessive cabin diff pressure <8.75 psi or cabin alt over 15,800 feet) would trip an "Auto Fail" light without the "Altn" light as both controllers would detect those faults if they were real. A pressure leak or failure to pressurize would not trip anything that would cause an "Altn" fault, so it would be easy to deduce that the pressurization controller events were unrelated to a leaky plug door if indeed the "Altn" light was part of the events. That may be where this is coming from.

[lateott]

In an earlier post someone stated that the NTSB described the "Altn" light coming on during the pressurization events, this means the primary controller detected a a parameter that tripped a fault with the primary controller and the alternate system did not detect the same fault. Actual pressurization events (cabin altitude climb of over 2000fpm, excessive cabin diff pressure <8.75 psi or cabin alt over 15,800 feet) would trip an "Auto Fail" light without the "Altn" light as both controllers would detect those faults if they were real. A pressure leak or failure to pressurize would not trip anything that would cause an "Altn" fault, so it would be easy to deduce that the pressurization controller events were unrelated to a leaky plug door if indeed the "Altn" light was part of the events. That may be where this is coming from.
I see your logic.

However, would a transient event that causes the AUTO FAIL indication cause the ALTN system to also indicate if that transient event was no longer present?

Isn't it possible that the condition was no longer present when ALTN was active?

[lateott]

What I feel this might mean is that the cockpit door is not supposed to open in a decompression that conforms to certification. But this was a much larger decompression opening than Boeing was required to consider. Through either luck, or just good ethical design practice, the door latch was made weaker than the bulkhead, and blew open, thus possibly saving the bulkhead.

It's not that surprising that Boeing didn't put something in the AMM that covers an eventuality not considered in certification.

..My manual (not 737) clearly states that the whole door may open in case of a rapid cabin decompression..Do not know about Max..

Fly safe,
B-757
B-757 Based on your username and expereince do you know whether any B-757 or 767 variant has a "plug" solution. It is clear that some variants have mid-cabin emergency exits of a similar floor level, fold-down design, and some seating arrangements seem to have no internal evidence of a door at that position. Do any of them have a plug, or do they all have actual doors fitted, whether covered by internal trim or not.

Follow-up question would be whether those aircraft with a masked inactive door still have the active sensors and annunciators that an active door would have.

[GlobalNav]

An investigation? Good for them. I'd suppose that this door was not intended to depart the plane in midair, so I can intuit that, yes, Boeing failed.

Better close those barn doors. The horse is out.

I get that the enforcement by the FAA has to follow this path, but this is a path that can be put onto a post-it note.

I feel sorry for the FAA employees. They will once again be used as a punching bag by the politicians that short them necessary funds to both fully staff and attract enough top people to oversee every aspect of modern aviation. I guess we can expect a bunch of very concerned Representatives openly asking if they should cut money from the FAA budget until they can prove they can do better with less, knowing that if FAA can the Reps will see that as a reason to keep the funding low, and possibly cut it further.
One possibly beneficial impact of the conspicuous consequences of bad Boeing management practices that led to this and several Boeing issues is that the FAA managers who have continued to treat Boeing with kid gloves will be silenced, in favor of the majority of FAA safety engineers who have been sounding alarm bells with no effect for years. Hopefully the pendulum swings.

[Old Ag]

1) How much upward force they exert on the plug when it's in the closed position? Not sure what you mean. In the intended "closed position" the answer is zero. In the pulled-closed but not bolted position the answer is > 31.5 lbs for each hinge.
2) There should be zero interference between the stop pads and stop pins on the ground at zero differential pressure
3) IMO there is no way the plug was sealed behind the interior plastic trim without at least one "placed" bolt. Whether that bolt also had a castellated nut with or without a split pin is another question.

What I mean under your point number 1 is: How much force is needed to hold the plug into the closed position without any stop bolts? If what you are saying is correct, if you pull the plug into the closed position, then let it go, it will pop up and over the stop pads on its own. Then a little push toward the outside opens it.

This would mean when its closed with stop bolts installed, there will be some pressure on one or more of the stop bolts resisting the upward movement of the door due to the assist spring pressure.

And if what you are saying is correct, it supports the theory that the airplane was flying around with at least one stop bolt somewhat in place, or the door would have never stayed closed. However, pressure on any of the bolts, nut or not, would make it more difficult for the bolt to fall out.

I find it unlikely that all four stop bolts, even with the nuts removed could fall out in less than 200 cycles. The loose bolt theory works better without the stop bolts having to resist the springs forcing the door off the stops.

I keep retuning to the sticky door no bolt theory. This would require a mechanism that would allow the door to be closed and held in place without the stop bolts. That would be an interference fit with the stop pads or maybe friction from the seal.

We shall see.

[A0283]

As expected you can find multiple production-, transport-, and final_assembly-configurations. Would take a lot of time to validate and sequence them.

Prelim - plug config rolling out of Spirit - note opening angle and delivery without escape hatches (papered over):

https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/165x141/img_0666_77a3df1e97d6bd842741ef4f9ac808d75ab240e6.jpeg

Prelim plug during transport:


https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/1242x862/img_0707_cb488a53b9459df177c5d9053088c156c4977614.jpeg


Prelim 737-9 door - posted earlier but - note items as sign ‘no slide installed’ and wiring:


https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/473x801/img_0735_88408a3af6ed49a3fe3df5f6ca33cb223f03b934.jpeg

[lateott]

What I mean under your point number 1 is: How much force is needed to hold the plug into the closed position without any stop bolts? If what you are saying is correct, if you pull the plug into the closed position, then let it go, it will pop up and over the stop pads on its own. Then a little push toward the outside opens it.

This would mean when its closed with stop bolts installed, there will be some pressure on one or more of the stop bolts resisting the upward movement of the door due to the assist spring pressure.

And if what you are saying is correct, it supports the theory that the airplane was flying around with at least one stop bolt somewhat in place, or the door would have never stayed closed. However, pressure on any of the bolts, nut or not, would make it more difficult for the bolt to fall out.

I find it unlikely that all four stop bolts, even with the nuts removed could fall out in less than 200 cycles. The upper stop bolts might even have the threaded end pointed slightly downward making the loose stop bolt theory even more unlikely. The loose bolt theory works better without the stop bolts having to resist the springs forcing the door off the stops.

I keep retuning to the sticky door no bolt theory. This would require a mechanism that would allow the door to be closed and held in place without the stop bolts. That would be an interference fit with the stop pads or maybe friction from the seal.

We shall see.
Yes, your comments make sense.

I was thinking the spring force upwards always remains the same on the plug, until a lower stop bolt is placed, at which time the stop bolt receives all of the spring force. One of the questions (which I think you are getting at) is how much resistance to upward motion is present from the static friction of the seals.

I just had a thought when looking at the photo below. Could a passenger ever dislodge an unbolted plug upward, say with an aggressive window shade lift? Not sure if there is another trim layer that goes on top of the white window cover that we see, which is attached to the plug...


https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/793x960/img_2986_e337b5ea72c70c81e1bb3c63bf63476ddc2ca2d2_2041ff0fa9 170cad71a20f7a7e90cbddb5a27a7d.jpeg

[Pinkman]

I think I have read every post assiduously but didn't see whether 26A was occupied on the inbound to PDX prior to the incident flight. If so, has the occupant been identified and interviewed to see whether they noticed any whistling or temperature change? I recall that the Singapore A380 door incident and Baku diversion which led to the door redesign program was preceeded by pax complaining of cold and whistling noises into LHR. It would help solve the prior px alarm issue which, if you subscribe to occam's razor, is a stretch to disconnect from the incident flight.

[aeromech3]

I have been wondering all along just how they get those upper guide locking bolts into position, without specially made pliers like a forceps it would be the job given to a small fingered Apprentice (at least in my training days) of course some blue tack holding it temporarily in the outer side of the track before the plug was pulled into the aperture might work.
I considered the guide roller being placed in the track before the plug was offered up and then bolted when mated to the frame serrations, but that would entail many loose parts.
My crusty size XL hands are no longer dexterous for such a job; my similar task as an Apprentice was wire locking the recharge
points on a Trident main oleo whilst the night shift rested in the crew room!

[ozaub]

Having reread Seattle Times article and watched Chris Brady’s latest video, there’s sufficient confusion about which way’s up that I’ll risk sticking with my assumption at #678 that thrust from “Lift Assist Springs” is less than weight of plug. Though I thank lateott for telling us that plug weighs 63 lbs., much less than I guessed.

Certainly on proper doors the springs must lift the guide fittings clear of their rollers and stop fittings clear of their pads, so that door can open. But such an arrangement would be quite illogical for plug that must (should) stay shut.

On a side issue raised by Brady and others, the door configuration used on 737 used to be known as “semi-plug”. It was allowed only because door had to move up before it could move out. Whereas a true plug is bigger than its hole.

[EDLB]

Amazing that with 63 lbs a plug, and you have two, one each side, there is no option to get the tube frame without those openings at all. 1kg mass is about 100L Jet-A1 a year for normal airline use. If I assume that without an airframe opening you get 15 lbs we talk about 4T of Jet-A1 every year only two carry two plugs.

[ozaub]

And it’s not just weight of plug. Weight of frame will be at least as much again.

[Beegooodin]

This is my thinking of what could appened in this case :
In the absence of bolts avoiding vertical motion of the plug , you have a system with

a weight the plug (63 Lbs) , 28 Kg
springs with a stifness of 50 Lbs force(the plug weight part taken by the ,springs versus the plug displacement to engage in the upper guide fitting slots (4 inches) ) aprox: 12, 5 lbs/force by inch (2180 N/m)
damping, frictions loads provided by the 12 pads (stop fitting) with the delta pressure loads ) aprox 2400 Lbs/ Psi delta pressure


This give you a dynamic system with a aprox frequency of 50 Hz if the motion is not contradicted that could be the case by the vertical stop on the upper slot when the lug go down in contact.

Also there is no or very low delta pressure in the phases of ground or near ground opreration.

With the taxi, take off flight, landing even low vertical acceleration with low delta pressure, This the plug could ramp up the slot with the vibration frequncy, desangage the 12 pads and have only the slot resistance to conteract the delta pressure loads.

The upper guide seems to not have been designed for those loads and could break when the delta pressure loads exceeded the guide capability with the roller down on the guide.

It is just my thinking.




T

[C2H5OH]

https://cimg3.ibsrv.net/gimg/pprune.org-vbulletin/499x441/image_6e740afba2a61cdec1be03c28448d5c8c2cb0e0e.png


I'm looking at the castellated nut at the bottom of the picture in post 764

Maybe my eyesight will be a bit clearer in the morning
Too many JPG artifacts in that picture to be sure, could be there though as some edge needs to be present to cause these artifacts in the first place - in that cosine transformation which JPG is.

[C2H5OH]

As expected you can find multiple production-, transport-, and final_assembly-configurations. Would take a lot of time to validate and sequence them.

Prelim - plug config rolling out of Spirit - note opening angle and delivery without escape hatches (papered over):

https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/165x141/img_0666_77a3df1e97d6bd842741ef4f9ac808d75ab240e6.jpeg


Good catch, so we know now, that it may still be open, when the fuselage is being prepared for rail transport, for some unknown reason. That means it is not installed, and immediately closed and secured until line maintenance reopens it at some customer, the securing being signed off and documented immediately.

[DaveReidUK]

I think I have read every post assiduously but didn't see whether 26A was occupied on the inbound to PDX prior to the incident flight.

Neither 26A nor 26B was occupied.

[DaveReidUK]

Certainly on proper doors the springs must lift the guide fittings clear of their rollers and stop fittings clear of their pads, so that door can open.

Not quite.

In Chris Brady's videos, he rightly labels them "lift assist springs". It's someone either inside or outside of the aircraft, pulling down the actuation lever, that provides the additional force required to lift the door off the rollers. The springs were originally fitted because of the difficulty in opening the door purely by brute force.

[Pinkman]

...and it isnt just the fuel cost variable... Adding options (was it four in the current case?) increases complexity, maintenance cost, and the chances of a "quality escape" during assembly.

Obviously there's a tradeoff between seat density, weight, lifetime revenue, maintenance and regulatory compliance and you can be sure that TBC beancounters have client spreadsheets so that the airline can pick the option tha suits their route network/traveller profiles (F/J/Y) etc. and maximises profit. But I am willing to bet that the financial and reputational cost of this episode kicks the cost of simply giving the option of a standard door (lose 2 seats?) or a disabled/inop door with no slide empennnage (lose 1 seat?) into touch. Complexity is the enemy of quality and the mantra for TBC might be "Do it simply - do it right - time after time"

[Del Prado]

Neither 26A nor 26B was occupied.


Are you sure Dave/have a reference?

Question was about previous flight not the incident flight. I’d be surprised if 26A and B were unoccupied on consecutive legs.

[rog747]

A poster earlier mentioned did the 757/767 design ever use Door Plugs, the answer is no.

Both of the types were offered with variable options for overwing Exit Window and Exit Door configurations whether ordered for Legacy, or Charter airline seating,
and this was determined on the build line by the Customer/Lessor.

Door Plugs (or window exit plugs) were seen as far back as the three BAC 1-11 400 series built in 1968 for Channel Airways who selected 4 overwing exit windows to enable 99 charter IT pax, but later Operators plugged/deactivated the 2nd extra pair of window exits.

The BEA Trident 3B also had Door Plugs fitted at the deactivated starboard Mid-Cabin door (the Mid-Cabin Pantry area).
Exit limit (as seen on BA Super Shuttle) was up to 146 pax, but could be increased to 170, with this Door activated for IT Charter flights.
180 pax is mentioned in the HS design brochures (I assume 180 pax would need some 7 abreast seating, but no airline ever did this on the Trident 3).
DaveReidUK will no doubt know more about BEA /BA Trident 3's :)

The Boeing 707-320C which had a 'Hat Rack' exit door hatch design akin to today's 737M-9, could have this exit plugged if the 707 Operator did not want to fly it as a Combi, nor want to seat more than 189 Pax, which was the Exit Limit without the Hat Rack door activated (same as 737M8-200 and M9).

At BMA British Midland we had 3 x 707C's reconfigured in 1982 with all new wide-look cabins/galleys/seats to enable 212 pax for IT Charter flights,
and although they were fitted with the original Boeing Hat rack doors, these was actually replaced by a new larger Boeing 757 Type 1 exit drop down door with a Slide.


https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/1200x800/tes_84_17_g_bmaz_7b0c8e06d7ea6ecb3e7568e4e0b4c0d36b0b8209.jp g

***BMA 707C
The new aft exit door is now larger than the original hat rack door

https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/960x665/11040402_812138598881455_1480452611117236690_n_e3b75af9c5ee7 ba58c0457589fccf2633067e66a.jpg


***BMA 707C
You can see the larger new aft exit door fitted 1982

[DaveReidUK]

Are you sure Dave/have a reference?

Question was about previous flight not the incident flight. I’d be surprised if 26A and B were unoccupied on consecutive legs.

Apologies, my comment was re the incident flight. RTFQ. :\

[safetypee]

" Are there aircraft in service which have restraining bolts fitted to exits, but which are meant to be operational ? ! "

It is would be very poor engineering practice to use a disabling device which could be inadvertently misused to prevent a required operation.
The FAA letter identifies Part 21 problems, but the issue also involves Part 25 Mitigating human error in design, engineering, and compliance. Which additionally relates to the overall design, certification, and manufacturing process in both Spirit and Boeing, and also with FAA oversight.

Perhaps another instance of local approval (cf previous MAX grounding), where the FAA delegates their responsibilities to the manufacturer via DER oversight, in-house self-checking, which if in error enables the FAA to blame the manufacturer, whereas the higher responsibility is still that of the regulator.

Modern views of safety in complex systems (any system with human involvement is complex), indicate that active safety responsibility has to move upwards in organisational and certification processes; i.e. fewer delegations.

Ref for info: 'HF guidance for regulators ICAO Doc 10151 Manual on Human Performance (HP) for Regulators' … and manufacturers, and operators, and individuals.

https://www.icao.int/safety/OPS/OPS-Section/Documents/Advance-unedited.Doc.10151.alltext.en.pdf

[DaveReidUK]

Are there aircraft in service which have restraining bolts fitted to exits, but which are meant to be operational ? !

It's by no means certain that that's actually possible.

The upper restraining bolts go through holes in the guide tracks attached to the door plug. There would be no reason for those holes to exist in the guide tracks on a live door (I don't know whether they do or not, does anyone?).

The lower bolts go through holes in the fitting that hinges down as the door opens. The jury still seems to be out re whether it's the same fitting on the live door, because of the debate on how far the respective doors are able to open and, if they're different, whether the holes exist on both.

So may turn out that it's not actually possible to lock the live door in place with those bolts. We need someone with an AMM.

[DTA]

It's by no means certain that that's actually possible.

The upper restraining bolts go through holes in the guide tracks attached to the door plug. There would be no reason for those holes to exist in the guide tracks on a live door (I don't know whether they do or not, does anyone?).

The lower bolts go through holes in the fitting that hinges down as the door opens. The jury still seems to be out re whether it's the same fitting on the live door, because of the debate on how far the respective doors are able to open and, if they're different, whether the holes exist on both.

So may turn out that it's not actually possible to lock the live door in place with those bolts. We need someone with an AMM.
Post 726 shows the live door and the holes in the upper guides are visible. I guess this reduces the spares holding required.

[Thrust Augmentation]

The upper restraining bolts go through holes in the guide tracks attached to the door plug. There would be no reason for those holes to exist in the guide tracks on a live door (I don't know whether they do or not, does anyone?).


https://cimg5.ibsrv.net/gimg/pprune.org-vbulletin/927x800/doors_173c0435247b7bec6e9f2d997cc5d923c26b5175.jpg

[MarineEngineer]

If I were tasked with closing and securing that door, I might pull it inwards and push it down with one foot. Then I would an undersize bolt, welding rod, nail or similar in one of the four holes just to keep it in place while I positioned the proper bolts. If this had been done but the last step had been omitted, it might explain why it took so long for the incident to occur.

[sandringham1]

Not quite.

In Chris Brady's videos, he rightly labels them "lift assist springs". It's someone either inside or outside of the aircraft, pulling down the actuation lever, that provides the additional force required to lift the door off the rollers. The springs were originally fitted because of the difficulty in opening the door purely by brute force.
The spring assist was especially important if the door had an escape slide hanging on it, I guess.
What I don't understand is how the door, that appears to fit tightly into the fuselage skin with a small shut line, is able to move upwards on the rollers/guide fittings enough to allow the 12 stop pads to be cleared. Doesn't the door skin conflict with the fuselage skin at the top.

[Thrust Augmentation]

What I don't understand is how the door, that appears to fit tightly into the fuselage skin with a small shut line, is able to move upwards on the rollers/guide fittings enough to allow the 12 stop pads to be cleared. Doesn't the door skin conflict with the fuselage skin at the top.

There is a gap of sorts at the top, look at post #783.

[sandringham1]

There is a gap of sorts at the top, look at post #783.
I saw that but didn't believe they would do it like that, I wonder where any water getting in there goes?

[D Bru]

Mid-aft emergency exit deployment 737-900ER (referring to the discussion in this thread about how far the emergency exit can open on it’s bottom hinges, in comparison to the "plug"):

https://www.youtube.com/shorts/q1x883EtQkQ

Mid-aft emergency exit deployment 707 (several inside test view tests from 14:30, outside view tests start at 21:40):

https://www.youtube.com/watch?v=LUyKK3mSqPw

Clearly, some things have developed since….

Interesting though that in the 707 this emergency exit door was a proper “plug” type: opening to the inside, impossible to “escape”, the door/plug that is. But as the different tests demonstrate, what to do with such a sizeable object inside the aircraft in case of an emergency (exit)?

[hoistop]

Mid-aft emergency exit deployment 737-900ER (referring to the discussion in this thread about how far the emergency exit can open on it’s bottom hinges, in comparison to the "plug"):

But as the different tests demonstrate, what to do with such a sizeable object inside the aircraft in case of an emergency (exit)?

Pull it in, then throw it out of the airplane. No need to store it inside. (in real emergency)

[rog747]

Mid-aft emergency exit deployment 707 (several inside test view tests from 14:30, outside view tests start at 21:40):

https://www.youtube.com/watch?v=LUyKK3mSqPw

Clearly, some things have developed since….

Interesting though that in the 707 this emergency exit door was a proper “plug” type: opening to the inside, impossible to “escape”, the door/plug that is. But as the different tests demonstrate, what to do with such a sizeable object inside the aircraft in case of an emergency (exit)?

Great 707 archive, thanks - way long before the days of throw it outside rather then place it on the seats, or in this case it went on the floor!

As mentioned above when at BMA we reconfigured our 707C's for 212 pax, a new larger 757 type door (with a slide on the door) was fitted in place of what you see in the old AA 707 video.

[Mac the Mechanic]

The aircraft fuselage is curved as is the door cut-out so when the plug/door goes up it clears the upper edge.

[rog747]

It was pretty standard practice to place Overwing Exit hatches/windows, and hat rack door on to the seats, rather then throw it out -
Later on it became more standard to throw it out over the years...

The 737NG (700 800 and 900) had the novel upward hinging overwing exits hatches....

[DaveReidUK]

https://cimg5.ibsrv.net/gimg/pprune.org-vbulletin/927x800/doors_173c0435247b7bec6e9f2d997cc5d923c26b5175.jpg

Thanks, so it does seem it's possible to lock (i.e. disable) the live emergency exit with at least the top bolts. Though I guess, if that had ever been done, functional checks of the E/E would catch it.

[spornrad]

https://www.avweb.com/aviation-news/boeing-subcontractor-subject-of-lawsuit-over-qc-deficiencies/

[Less Hair]

Could somebody have installed an active emergency door configuration on a plugged door by accident? Like not installing the bolts and leaving the plug room to slide up?

[WHBM]

Amazing that with 63 lbs a plug, and you have two, one each side, there is no option to get the tube frame without those openings at all. 1kg mass is about 100L Jet-A1 a year for normal airline use. If I assume that without an airframe opening you get 15 lbs we talk about 4T of Jet-A1 every year only two carry two plugs.

And it’s not just weight of plug. Weight of frame will be at least as much again.
Back when the 737NG first offered the extended fuselage, from the 737-800 to the 737-900, the exit configuration was kept the same, as the aircraft met the desires of US trunk carriers who didn't need the full exit provision on the -800 for maximum seating, because of their first class, galleys, and extra legroom. The additional length, and seats, still complied with the seating evacuation limit for this fitout. However this variant was a very poor seller, I think they only sold about 50 (ironically Alaska were one of the few to take some), because finance companies didn't like them as they couldn't be remarketed later to anyone who did maximum seating.

Boeing then redid the design as the 737NG-900ER, which among other things introduced this plug/real exit door fitting. The US trunk carriers didn't lose seating at this point, or have the extra maintenance cost (they thought) for a proper exit at the opening, but it could be adapted later if and when required. The approach carried forward to the MAX9.

[Reverse rotation]

This side by side comparison of the door plug and functioning door also shows significant differences in the hinge mechanisms at the bottom of the door.

Post #765 shows the door plug being fully supported by the springs in their fully extended position. The force applied by the springs in their compressed state with the plug fully closed will be significantly more (Hookes law, force is proportional to compression) and, looking at how far off the stops the springs lift the door, the upward force being applied to the door to just clear the stops will be much greater than just the weight of the door.

[DaveReidUK]

Letter from 3 US Senators - Markey (D-MA), Vance (R-OH) and Welch (D-VT) - to Calhoun:

[DaveReidUK]

Could somebody have installed an active emergency door configuration on a plugged door by accident? Like not installing the bolts and leaving the plug room to slide up?

I think you might have hit the nail on the head.

[Thrust Augmentation]

I saw that but didn't believe they would do it like that, I wonder where any water getting in there goes?

I guess in terms of water sealing it's much like a car door seal, water gets under the edges into the area under the surface / outside the seals & drains away from the rear & bottom;


https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/447x600/door_leak_eb435a943dfbf5e6b3e86aa28b7cdc795707b72d.jpg

[CleanerCc]

Why are more people not talking about aar in OKC? I can't post pictures but if you go to Google maps 35.4015987, -97.6023138 you will see they have docking and ground ac carts they put on the left side right at door plug for the wifi mod. It would take nothing to open that door in a maintenance environment. Just because they said they did nothing in that area does not mean someone did not open the door.

[WHBM]

I think you might have hit the nail on the head.
Boeing aren't currently making any MAX9 with the exit door at this point; all currently in production are being built with the plug. The ability to substitute a full exit door is aimed at the secondhand use of the aircraft later in life.

[rog747]

The Emergency Exit door has a small porthole window versus, the Door Plug has a full size passenger cabin window.

[Less Hair]

The active emergency door has a pressure relief opening as well. It is quite different.

[EXDAC]

If I were tasked with closing and securing that door, I might pull it inwards and push it down with one foot. Then I would an undersize bolt, welding rod, nail or similar in one of the four holes just to keep it in place while I positioned the proper bolts. If this had been done but the last step had been omitted, it might explain why it took so long for the incident to occur.

It would be tempting to fit the guide track locking bolts in reverse orientatation (head inwards, shank outwards). That temporary fit would be much easier than the correct orientation and would align the lower locking bolt holes better than an undersize improvised pin. The reversed upper guide bolts would be removed and fitted in the correct orientation after the lower locking bolts were fitted.

If this assembly method was used it's easy to see how it could go bad if interruped by a break or shift change.

[Jhieminga]

I saw that but didn't believe they would do it like that, I wonder where any water getting in there goes?
This illustration from a very different type shows the geometry of such a door. Notice that the top of the door is tapered, so that it can move up and (on this drawing) slighty left to disengage the lugs on the door from the lugs on the frame. The door has a rubber seal that is pressurised so that any water runs around the door and out through drain holes or small gaps between door and frame.


https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/1198x1508/screenshot_2024_01_12_at_14_42_22_d21c9b0b801d9a38cd8fd4b01d cd77801f289012.png

[DaveReidUK]

Boeing aren't currently making any MAX9 with the exit door at this point; all currently in production are being built with the plug. The ability to substitute a full exit door is aimed at the secondhand use of the aircraft later in life.

I read the post to which I was responding as suggesting that the plug door had been configured as if it was a live door (i.e. no lock bolts fitted), not that a live door had been actually fitted, which of course wasn't the case.

[DaveReidUK]

If I were tasked with closing and securing that door, I might pull it inwards and push it down with one foot. Then I would an undersize bolt, welding rod, nail or similar in one of the four holes just to keep it in place while I positioned the proper bolts.

Isn't that what cross-head screwdrivers were invented for ? :O

With the added advantage of being bleeding obvious in situ !

[1southernman]

My attention span sux...Is there a common location/facility for last hands-on all these "doors" with issues?...Surely that's been researched early on and known...Cue "Airplane!" dialogue...

[MarineEngineer]

It would be better if Boeing provided a dowel for the purpose which was attached to a large, orange 'don't forget me' label.

[Ivor_Bigunn]

And from "The Department of Totally Predictable Developments":

https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/886x987/sue_1_832e43945756cfdf26fd92a08f5dc79111fb8045.jpg
https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/645x989/sue_2_7c68b013ab52777de6b3722ed5e167c8c5d52073.jpg


IB

[Longtimer]

So the only loose bolts etc. have been reported on the Left sides plugs, evidently the same plug is also on the right side.... different process at boeing or?
The FAA’s priority is always keeping Americans safe. In that spirit, Boeing 737-9 aircraft will remain grounded until operators complete enhanced inspections which include both left and right cabin door exit plugs, door components, and fasteners. Operators must also complete corrective action requirements based on findings from the inspections prior to bringing any aircraft back into service.

[MechEngr]

The loose pin bracket was reported on the right hand side.

[Longtimer]

The loose pin bracket was reported on the right hand side.
Upon some more research:
https://theaircurrent.com/aviation-safety/undamaged-plug-exit-on-alaska-max-9-had-fasteners-tightened-during-assembly/

​​​​​​​

[MarineEngineer]

I wonder how many pax from AS1282 accepted the replacement flight on an identical plane? I'm not sure I would have! 😁

[OpenCirrus619]

So the only loose bolts etc. have been reported on the Left sides plugs, evidently the same plug is also on the right side.... different process at boeing or?
The FAA’s priority is always keeping Americans safe. In that spirit, Boeing 737-9 aircraft will remain grounded until operators complete enhanced inspections which include both left and right cabin door exit plugs, door components, and fasteners. Operators must also complete corrective action requirements based on findings from the inspections prior to bringing any aircraft back into service.
Personally (though it won't happen) I would feel more confident if the FAA grounded all 737 Max until:

Root cause of the multiple examples of poor assembly / QC / QA have been identified AND remedial action taken / measures put in place to prevent recurrence
All 737 Max undergo a detailed inspection to check that there are none flying with mis-assembled Doors / Plugs / Rudder Controls / ..., no mis-drilled holes (filled with "fasteners"), etc.
There are redundant sensors feeding any systems which can override the pilot

[MechEngr]

Upon some more research:



I was referring to the aircraft that United had inspected and that United had found a loose pin bracket on the right side. There is such a torrent of coverage I don't know if I (aka Google) can find it again, but the investigation is not being limited to left side doors.

[lateott]

Having reread Seattle Times article and watched Chris Brady’s latest video, there’s sufficient confusion about which way’s up that I’ll risk sticking with my assumption at #678 that thrust from “Lift Assist Springs” is less than weight of plug.

This is my thinking of what could appened in this case :
In the absence of bolts avoiding vertical motion of the plug , you have a system with

a weight the plug (63 Lbs) , 28 Kg
springs with a stifness of 50 Lbs force(the plug weight part taken by the ,springs versus the plug displacement to engage in the upper guide fitting slots (4 inches) ) aprox: 12, 5 lbs/force by inch (2180 N/m)
damping, frictions loads provided by the 12 pads (stop fitting) with the delta pressure loads ) aprox 2400 Lbs/ Psi delta pressure




In Chris Brady's videos, he rightly labels them "lift assist springs". It's someone either inside or outside of the aircraft, pulling down the actuation lever, that provides the additional force required to lift the door off the rollers. The springs were originally fitted because of the difficulty in opening the door purely by brute force.

Physics and photos prove the spring force applied is > 31.5 lb each spring, > 63 lb from the pair, when the springs are extended to the stop washers at the end of the hinges
The full weight of the plug is carried by the extended springs. Whether they are called lift "assist" or not, they support the entire weight of the plug when they are fully extended.
Once lifted, the plug will not fall back down below the stop fittings because its entire weight is being supported
If the springs applied less than the mass of the plug, then

the Hinge Guide Fittings would not be held against their upper stop washers when supporting the weight of the plug
one would need to lift the plug over the stop pads to close the plug



It is a self ejecting design, constrained by 4 tiny bolts. How do we know? They did the experiment over Southwest Portland, and it ejected.


https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/1194x661/springs_bearing_weight_of_plug_2_526da6e6893bffe91f40d5f2f8c 6b799b40fdc2a.jpg
https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/901x957/springs_bearing_weight_of_plug_fa89be294dac18dfae6c8d010998c 1190ea4dc48.jpg
https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/1096x1076/plug1_87e7c558e5443e2a29038f976de9ad8a8e41f07b.jpg

[WillowRun 6-3]

FAA Increasing Oversight of Boeing Production and ManufacturingFriday, January 12, 2024WASHINGTON, D.C. — After taking decisive and immediate action to ground approximately 171 Boeing 737-9 MAX planes, the Federal Aviation Administration (FAA) today announced new and significant actions to immediately increase its oversight of Boeing production and manufacturing. These actions come one day after the FAA formally notified Boeing that the FAA has launched an investigation into the company as a result of last Friday’s incident on a Boeing Model 737-9 MAX in which the aircraft lost a passenger door plug while in flight.

The actions announced today include the FAA conducting:


An audit involving the Boeing 737-9 MAX production line and its suppliers to evaluate Boeing’s compliance with its approved quality procedures. The results of the FAA’s audit analysis will determine whether additional audits are necessary.
Increased monitoring of Boeing 737-9 MAX in-service events.
Assessment of safety risks around delegated authority and quality oversight, and examination of options to move these functions under independent, third-party entities.

"It is time to re-examine the delegation of authority and assess any associated safety risks," FAA Administrator Mike Whitaker said. "The grounding of the 737-9 and the multiple production-related issues identified in recent years require us to look at every option to reduce risk. The FAA is exploring the use of an independent third party to oversee Boeing’s inspections and its quality system."

Yesterday, the FAA announced an investigation to determine if Boeing failed to ensure completed products conformed to its approved design and were in a condition for safe operation in compliance with FAA regulations. The letter to Boeing is available here (https://www.faa.gov/newsroom/updates-grounding-boeing-737-max-9-aircraft).

The safety of the flying public, not speed, will determine the timeline for returning the Boeing 737-9 MAX to service.

See the FAA's statements on the grounding of certain Boeing 737-9 MAX aircraft here (https://www.faa.gov/newsroom/updates-grounding-boeing-737-max-9-aircraft).

[MarineEngineer]

So the only loose bolts etc. have been reported on the Left sides plugs, evidently the same plug is also on the right side.... different process at Boeing or?
The FAA’s priority is always keeping Americans safe. In that spirit, Boeing 737-9 aircraft will remain grounded until operators complete enhanced inspections which include both left and right cabin door exit plugs, door components, and fasteners. Operators must also complete corrective action requirements based on findings from the inspections prior to bringing any aircraft back into service.

Surely, FAA's mandate is keeping everyone safe, not just Americans! FAA regulations apply to US registered aircraft and foreign commercial aeroplanes flying in US airspace.
airline

[DType]

Quote:-
Physics and photos prove the spring force applied is > 31.5 lb each spring, > 63 lb from the pair, when the springs are extended to the stop washers at the end of the hinges

If true, what held the plug in situ for two months, some slack bolts?

[lateott]

Quote:-
Physics and photos prove the spring force applied is > 31.5 lb each spring, > 63 lb from the pair, when the springs are extended to the stop washers at the end of the hinges

If true, what held the plug in situ for two months, some slack bolts?
Two very different questions :)

[dragon6172]

Quote:-
Physics and photos prove the spring force applied is > 31.5 lb each spring, > 63 lb from the pair, when the springs are extended to the stop washers at the end of the hinges

If true, what held the plug in situ for two months, some slack bolts?
The lock bolts feed from outside in, with somewhat tight quarters to accomplish. As a mechanic, I would probably close the door, push down against the springs, and temp insert one bolt in reverse fashion to hold the door in place while I got the others bolts installed the proper way, and then flip around the temp installed bolt. Obviously if there was a break or end of shift or whatever after the temp bolt was installed, you can see how this could happen. But... this possibility still means there is a pretty crappy QA system.

[Loose rivets]

Something just doesn't seem right about that hinge assembly.

Physics and photos prove the spring force applied is > 31.5 lb each spring, > 63 lb from the pair, when the springs are extended to the stop washers at the end of the hinges my bold.

That nylon type material has to slide over the black hinge pins, therefore the holes though them must be very nearly as big as the washers under the pairs of bronze-coloured nuts. This makes me assume that the hinge guides are not designed to thump against, or have sustained pressure on, the washers.

Clearly the nylon type material does not slide over the washers, indeed one is reported as having belled up during the 'accident'. Presumably the nuts have to be removed to lift the plug away from the aircraft, so why are the washers so small in diameter?

Dragon6172. That's why I never throw worn PK screwdrivers away. Turned and tapered for a repetitive job makes them valuable. But then, Spirit or Boeing would have those tools . . . wouldn't they?

[MarineEngineer]

I agree, BUT Boeing probably have a written procedure for closing and securing this door and they probably have some special tools for the job. There might be a handle to assist closing and lowering the door and a temporary method for holding it in place while the arrestor bolts are fitted. Mechanics are nor expected to just wing it!

[DaveReidUK]

In Chris Brady's videos, he rightly labels them "lift assist springs". It's someone either inside or outside of the aircraft, pulling down the actuation lever, that provides the additional force required to lift the door off the rollers. The springs were originally fitted because of the difficulty in opening the door purely by brute force.

Physics and photos prove the spring force applied is > 31.5 lb each spring, > 63 lb from the pair, when the springs are extended to the stop washers at the end of the hinges
The full weight of the plug is carried by the extended springs. Whether they are called lift "assist" or not, they support the entire weight of the plug when they are fully extended.
Once lifted, the plug will not fall back down below the stop fittings because its entire weight is being supported
If the springs applied less than the mass of the plug, then
the Hinge Guide Fittings would not be held against their upper stop washers when supporting the weight of the plug
one would need to lift the plug over the stop pads to close the plug


At the risk of stating the obvious (again), they're called "lift assist springs" because, regardless of whether they can support the entire weight of the plug or not, their raison d'etre is to help lift the active door (which unsurprisingly weighs considerably more) over the stops and clear of the roller.

[OldnGrounded]

"It is time to re-examine the delegation of authority and assess any associated safety risks," FAA Administrator Mike Whitaker said. "The grounding of the 737-9 and the multiple production-related issues identified in recent years require us to look at every option to reduce risk. The FAA is exploring the use of an independent third party to oversee Boeing’s inspections and its quality system."

Well, that's interesting. Presumably, Ace Airplane Inspections, Inc. would be paid by Boeing, avoiding the problem of prying more money from Congress to increase FAA staffing.

The regulator may actually be getting serious about this.

[MechEngr]

Something just doesn't seem right about that hinge assembly.
...
That nylon type material has to slide over the black hinge pins, therefore the holes though them must be very nearly as big as the washers under the pairs of bronze-coloured nuts. This makes me assume that the hinge guides are not designed to thump against, or have sustained pressure on, the washers.

Clearly the nylon type material does not slide over the washers, indeed one is reported as having belled up during the 'accident'. Presumably the nuts have to be removed to lift the plug away from the aircraft, so why are the washers so small in diameter?

The washers only need to be slightly larger than the hole in the nylon, which is nearly the same as the diameter of the rod in order to act as a stop. The washers do fit closely around the reduced diameter of the screw threads at the end of the fitting; most washers don't have a significantly large multiplier of ID to get to the OD except for so-called "fender washers" used in conjunction with very thin material where the need is to distribute the pressure over a large area. At most one might ask why the stop washer isn't thicker to avoid a bell, but there looks to be a substantial chamfer on the inside of the nylon that would move the load farther out, so perhaps it was intended that if the load on the door was high enough, the door would be released. That all seems rather tricky, but it did avoid damage to the fuselage, even if that wasn't the plan.

What I haven't seen are clear pictures of the slide-guide rod that seems to be missing that washer. I haven't heard of anyone finding the slide guide bracket that also went missing. Did it cone the washer and gut the nylon bushing or did it strip the nuts or break the threaded section?

I see from news today that at least one shoe and sock were removed from the passenger in the seat along the wall immediately behind the opening, though they did find his phone, also working, and returned to him via Alaska.

[MechEngr]

Part of the FAA Administrator's statement was that authority had been taken from the FAA by legislation, driving the move to self-certification. The link is to 1:39, but the forum doesn't start there.
https://youtu.be/eOFFMIw4_vc?t=99

[lateott]

Something just doesn't seem right about that hinge assembly.

my bold.

That nylon type material has to slide over the black hinge pins, therefore the holes though them must be very nearly as big as the washers under the pairs of bronze-coloured nuts. This makes me assume that the hinge guides are not designed to thump against, or have sustained pressure on, the washers.

Clearly the nylon type material does not slide over the washers, indeed one is reported as having belled up during the 'accident'. Presumably the nuts have to be removed to lift the plug away from the aircraft, so why are the washers so small in diameter?
That is a different question from the spring force, but I agree with you.

The Hinge Guide Fitting looks like a beefy chunk of steel and that is what ultimately would need to deform and slide over those washers. We know that the aft Hinge Guide Fitting was retained on the hinge pin while being ripped over the heads of at least 2 bracket bolts, and somehow escaping the other 2 bracket bolts, if they were present. In the below photo you can at least see the pin diameter relative to the stop washer, but the diameter of the hole in the Hinge Fitting Guide is obscured by the nylon washer.

I believe one of the Chris Brady videos states the maximum local wind specification for the plug (or door when installed). Definitely less than 271 KIAS.

Give Boeing engineers some credit, the self-ejecting plug design has breakaway features.


https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/1018x1030/lower_bolt_13171207507904805fa5a9a9bfed2e7227b833d5.jpg
From Chris Brady video

[incompleteness]

Well, that's interesting. Presumably, Ace Airplane Inspections, Inc. would be paid by Boeing, avoiding the problem of prying more money from Congress to increase FAA staffing.

The regulator may actually be getting serious about this.

Yes this is about the biggest step the FAA could take short of pulling selected Boeing delegations of authority, which it also looks like they are threatening to do.

There are probably some ex Boeing quality people who retired in disgust who wouldn't mind coming back as an overseer in the spirit of schadenfreude.

[lateott]

What I haven't seen are clear pictures of the slide-guide rod that seems to be missing that washer. I haven't heard of anyone finding the slide guide bracket that also went missing. Did it cone the washer and gut the nylon bushing or did it strip the nuts or break the threaded section? I think the nuts and threaded section can be seen in the plastic-draped NTSB photos. I can't make out a "cupped stop washer" but another poster believed they could.

https://cimg4.ibsrv.net/gimg/pprune.org-vbulletin/409x351/_53450362798_491755e612_o_ff018f8815f50962e1704242cd3ca9b146 86ff00.jpg

[lateott]

At the risk of stating the obvious (again), they're called "lift assist springs" because, regardless of whether they can support the entire weight of the plug or not, their raison d'etre is to help lift the active door (which unsurprisingly weighs considerably more) over the stops and clear of the roller.
1) They obviously can and do support the entire weight. Refute it.
2) That is not the raison d'etre according to the Chris Brady videos, although they obviously assist the lifting of the plug or door.

[EXDAC]

The lock bolts feed from outside in, with somewhat tight quarters to accomplish. As a mechanic, I would probably close the door, push down against the springs, and temp insert one bolt in reverse fashion to hold the door in place while I got the others bolts installed the proper way, and then flip around the temp installed bolt. Obviously if there was a break or end of shift or whatever after the temp bolt was installed, you can see how this could happen. But... this possibility still means there is a pretty crappy QA system.

See my post 827 where I laid out exactly the same scenario.

[BFSGrad]

I wonder how many pax from AS1282 accepted the replacement flight on an identical plane? I'm not sure I would have! 😁
Recall that at that time, the 18 MAX 9s that Alaska briefly placed back into service had recently been through heavy maintenance that had verified the proper installation of the plug doors. I would have had no concerns about flying on those MAX 9s.

I do wonder if Alaska has any regrets about paying $100Ms to get our of their A320/321 leases early?

[DaveReidUK]

1) They obviously can and do support the entire weight. Refute it.

The entire weight of what ? The plug door, or the E/E ? Do you think they weigh the same ?

[lateott]

If I were tasked with closing and securing that door, I might pull it inwards and push it down with one foot. Then I would an undersize bolt, welding rod, nail or similar in one of the four holes just to keep it in place while I positioned the proper bolts. If this had been done but the last step had been omitted, it might explain why it took so long for the incident to occur.

See my post 827 where I laid out exactly the same scenario.


If I were working on my boat or RV I would pull the plug in from the top or middle for leverage, step on both hinges to counteract the spring, shove at least 1 bolt in the top to hold it against the spring force, then go about installing all the bolts.

But I suppose the installation/maintenance SOP may be more prescriptive in where to grab/pull/push for proper positioning. ;)

These kinds of adaptations need to consider human factors in install/maintenance. If it were a door, that door would have a proper handle and latch and a logical "closing" sequence that naturally counteracts the springs. The fact that this is a plug adapted to the airframe may cause the technician to improvise.

As did I at #163 :)

[EXDAC]

As did I at #163 :)

Members of the jury, have you decided on your verdict? Yes. (It's about the only plausible explanation that has been proposed so far.)

[lateott]

The entire weight of what ? The plug door, or the E/E ? Do you think they weigh the same ?
1) I was referring to the plug. The weight of the plug door is obviously supported by its springs. The weight of the E/E is designed to be supported by its springs, according to Chris Brady.
2) Of course the E/E door weight is significantly greater than the plug
3) We don't know if the springs for the E/E door are the same as those used for the plug, or if they have different part numbers and compression forces fit for purpose. You have stated that previously and I agree.

But there is absolutely no doubt the springs used for the plug support the weight of the plug. And as I said, according to Chris Brady, the design intent for the spring hinges, their reason to exist, is to prevent re-closing of the E/E door in the event of evacuation.

[lateott]

Members of the jury, have you decided on your verdict? Yes. (It's about the only plausible explanation that has been proposed so far.)
I work in a similarly highly regulated industry. A design change like the plug would result in a risk assessment of "Red," an RPN rating category calculated by multiplying Severity x Occurrence x Detection, and the highest risk category. A risk at that level would require mitigation and surveillance.

At the very least, it would have been very simple to install a positional sensor flagging the existing annunciator in the flight deck. The plug cannot be ejected if it does not "translate" upwards more than a given amount which would be easy to detect if monitored.

(Some redundant attachment would have been appreciated as well!)

So many ways to break a chain of events...

[SRMman]

https://theaircurrent.com/aviation-safety/undamaged-plug-exit-on-alaska-max-9-had-fasteners-tightened-during-assembly/

[DaveReidUK]

1) I was referring to the plug. The weight of the plug door is obviously supported by its springs. The weight of the E/E is designed to be supported by its springs, according to Chris Brady.
2) Of course the E/E door weight is significantly greater than the plug
3) We don't know if the springs for the E/E door are the same as those used for the plug, or if they have different part numbers and compression forces fit for purpose. You have stated that previously and I agree.

But there is absolutely no doubt the springs used for the plug support the weight of the plug. And as I said, according to Chris Brady, the design intent for the spring hinges, their reason to exist, is to prevent re-closing of the E/E door in the event of evacuation.

In that case, we seem to be in general agreement, leaving aside the question of what proportion of the E/E door weight the springs support (which isn't really relevant to discussion of the door plug configuration).

[WHBM]

I do wonder if Alaska has any regrets about paying $100Ms to get our of their A320/321 leases early?
And also paid out many US $100s of millions for the earlier members of their 737-MAX9 fleet, which are now in their second enforced grounding in the few years of their life..

[421dog]

So my understanding is that the people from the manufacturers that signed things off are DAR-Fs… these people have a long history with the company in manufacturing, but are not A&Ps or certainly not IAs. They often did 15+ years as riveters, but have no clue as to how an aircraft comes together otherwise.

I have no compunction about flying on Boeing Aircraft, and have no animosity toward them (except that they have had my 421 520-D cylinder set on hold for 17 months due to their production issues {happy to speak with somebody there}).

[Grummaniser]

All this to-and-fro about whether the lift-assist springs exert a force greater than or less than the weight of the door only applies on the ground or in level (more precisely 1g) flight. It wouldn't take much of an aerodynamic "bump" considerably to reduce the weight of the door, allowing it to translate upwards without the whole weight being supported by the springs.

[xetroV]

I still don’t understand the design decision of keeping the lift-assist spring from the evacuation door in the door plug. Seems like an overly complex solution for a problem that, for this particular purpose, doesn’t even exist (preventing an opened door plug from closing). If any type of spring was required here to begin with, shouldn’t that have been a pulling string (preventing the door plug from opening)? Why lessen the force required to open a door plug?

[DaveReidUK]

All this to-and-fro about whether the lift-assist springs exert a force greater than or less than the weight of the door only applies on the ground or in level (more precisely 1g) flight. It wouldn't take much of an aerodynamic "bump" considerably to reduce the weight of the door, allowing it to translate upwards without the whole weight being supported by the springs.

Subject obviously to there being sufficiently low cabin pressure at that point.

[Old Ag]

https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/901x957/springs_bearing_weight_of_plug_b7e5fc8bd8e5f328ea2fb55164889 8e0fd6566bd.jpg[/Q








https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/473x801/img_0735_88408a3af6ed49a3fe3df5f6ca33cb223f03b934.jpeg

I still don’t understand the design decision of keeping the lift-assist spring from the evacuation door in the door plug. Seems like an overly complex solution for a problem that, for this particular purpose, doesn’t even exist (preventing an opened door plug from closing). If any type of spring was required here to begin with, shouldn’t that have been a pulling string (preventing the door plug from opening)? Why lessen the force required to open a door plug?

Clearly the hinges differ between the plug and the doors. The plug hinge is an intentional design not a reuse of the emergency exit door hinge design. I can’t see any spring in the hinge area of the emergency exit door. I see a very different spring as part of the latching hardware in the emergency exit door. It appears to me that the emergency exit door is assisted upward by the springs that flank the viewport via the latching mechanism.

So we know that Boeing carefully selected the plug assist spring just for the task of keeping the stop fitting and pins from falling behind the stop pads when the plug is opened. So it’s logical to assume that the spring pressure is enough to lift the plug until the hinge fittings are pressed up against the stops in the end of the hinges when the door is open. The above photo demonstrates that the plug is held up by the springs and the stop pads and stop pins are not aligned when open.

Why? Probably to reduce the risk of the back of the stop pins from striking the back of the stop pads if someone tried to close the door in the down position. We don’t know how much force it takes to push the plug pack into place against the spring pressure, but I suspect it isn’t very much. But it may take a bit of force to fully seat the stop pins against the stop pads in the fully closed position. From the above photo, we can see evidence of the stop pins contacting the stop pads and maybe even grease or graphite transfer between the pads and pins. So there is contact and maybe a bit of friction between the two. Probably more friction from the seals. What we don’t know is how much force is needed to close or open the plug. I’ll bet the NTSB is looking into that.

[EXDAC]

Clearly the hinges differ between the plug and the doors.

I have not seen any images that support that assumption. In my opinion the image pair that you posted does not. Do you have a high resolution image of an OPEN emergency exit door showing the hinge arrangement?

My speculation is that, to the greatest extent possible, all components of the door plug and the active door are identical. Why else would locking bolt holes be provided in the guide fittings of active doors?

[421dog]

This looks to me as an impeccable mating connection with a long history, that someone found a way to foul up.

[dragon6172]

I have not seen any images that support that assumption. In my opinion the image pair that you posted does not. Do you have a high resolution image of an OPEN emergency exit door showing the hinge arrangement?

My speculation is that, to the greatest extent possible, all components of the door plug and the active door are identical. Why else would locking bolt holes be provided in the guide fittings of active doors?
I don't think the hinges are the same between the two door types.
https://www.youtube.com/shorts/UGiabqoO6-Q
Not a high resolution photo, but a couple of notes:
- The active door opens nearly 180 degrees, the maintenance crew actually put cushions on the fuselage so that it is not damaged by the door. The door plug would seem to only go 90 degrees, based on the hinges that remained on the accident aircraft, which appear to be fully extended.
-The active door would appear to have some sort of tension/torsion system to "slow" its opening. It appears to be going slower than what I would expect from just gravity. The door plug doesn't appear to have anything similar.

These are just assumptions of course.... nothing definitive

[OldnGrounded]

So we know that Boeing carefully selected the plug assist spring just for the task of keeping the stop fitting and pins from falling behind the stop pads when the plug is opened.

Do we know that? Why would it matter where the fittings and pins fall when the plug is opened? And why would they fall back behind the pads after the plug is opened to its position leaning away from the fuselage at approx. 15 degrees, even if there were no springs at all?

[Old Ag]

I have not seen any images that support that assumption. In my opinion the image pair that you posted does not. Do you have a high resolution image of an OPEN emergency exit door showing the hinge arrangement?

My speculation is that, to the greatest extent possible, all components of the door plug and the active door are identical. Why else would locking bolt holes be provided in the guide fittings of active doors?

Look at the hinge from the plug. Its shaped like a question mark. The end that is "C" shaped attaches to the floor of the plane. The other end has the spring and passes through the fitting in the door. Without the door attached, the plug hinge it is only capable of folding down about 90 degrees before it hits the lower part of the door frame. The only photos Ive seen of that hinge in that position are post incident photos from the incident plane.

Look at the video I posted earlier of the emergency exit in motion. It folds down about 140 degrees. The plug hinge does not have that range of motion.

In my opinion, its pretty obvious that the hinges are different between the plug and the door. And I can tell that from the exit door photo above and any of the dozens of mid exit plug photos like the one in post 843. In fact, stop pin fittings, guide fittings and the perimeter frame they attach to seem to be about the extent of common parts between the plugs and exit doors.

Does that prove they they use different springs. Nope. But it does prove that it cant be assumed that are even springs involved in the exit door hinges. And I haven't seen any photographs that prove the exit doors have similar hinges to the plugs.

Why are the guide fittings identical? Perhaps they didn't see a need to have different parts that serve the same purpose, that is guiding the door up on a bearing in the frame. Perhaps they didn't see a risk that someone would try to bolt an exit shut. Perhaps they do bolt the inactivated emergency exits shut. Reuse of one part doesn't mean they reused as many as possible. Weight and maintenance are much larger issues than maximizing parts commonality.

[Old Ag]

Do we know that? Why would it matter where the fittings and pins fall when the plug is opened? And why would they fall back behind the pads after the plug is opened to its position leaning away from the fuselage at approx. 15 degrees, even if there were no springs at all?

As I stated further on in the post you quoted, they probably though it a good idea that pulling the plug shut wouldn't risk the back of the stop pins being closed on the back of the stop pads. So they added springs as a mechanism to force the plug upwards when it was opened. Otherwise you would have to lift the plug over the stop pads as you pulled it in to close it. Better to keep the plug translated up when its open and make the user push it into position than rely on the user to hold it up and clear of the stop pads as they try to close it.

The phrase "fall back behind the stops" may be referring to the case that if there were no assist springs, and you let go of the door while lifting it up, it would fall back closed. With the springs it wont. Maybe that avoids some type of damage the engineers don't like.

[Solofast]

The most likely scenario is that the bolts were not installed. There is broad agreement on that aspect. If the lower bolts were installed not only would the door not move up, but even if there were no nuts on bolts, the bolts would be trapped but the spring pressure and would not fall out. In the NTSB briefing they stated that the door moved up before it was ejected. As noted that cannot happen if the lower bolts were in place even if there were not nuts on them. If the upper bolts were in place the door could not move upward and would remain on the plug pads. That is the case even if all the lower hinges were not even installed. In that case the plug door would pivot around the upper rollers and it would be held in position by the pads, Based on these conditions there is only one conclusion, that is: None of the four locking bolts were present at the time the door was ejected.

According to the NTSB the tracks were damaged and the bolts were not recovered. Their initial analysis examination was that it was not clear if the bolts had been present. That does not take a rocket scientist to discern. If the bolts were in place both the inside and the outside of the track will be damaged. That is, if the bolt was in place the inside area could be broken by the pressure loads, but if the bolt is in place it there will be damage to the outside area of the track because the bolt will be transferring loads to the outboard side of the track. No damage to the outboard side of the track means that the bolts weren't there in the first place.

I don't believe that it is possible for this event to happen if any two of the safety bolts are installed. This provides a level of redundancy to the design. As has been noted this basic design has been employed on the previous generation 737 and flown for millions of hours with no known previous issues. That alone verifies the fundamental soundness of the basic design.

Calhoun understands all of this, but can't say anything until the NTSB makes its ruling, but note he's saying it was Boeing's responsibility and that's basically saying this was a failure in the process to properly rig the door. The issue here is one of a failure in either assembly or maintenance, most likely at Boeing but possibly at AAR during the WiFI installation. Based on those facts the remedy should be an AD to require an inspection to ensure the doors are rigged per specification and the planes returned to flight status.

[WHBM]

Well, that's interesting. Presumably, Ace Airplane Inspections, Inc. would be paid by Boeing, avoiding the problem of prying more money from Congress to increase FAA staffing.
The trouble with such "oversight", auditing, or regulatory organisations is they quite soon find the easiest way to perform their role is to ask the business they are meant to be checking to do their work for them. There are numerous examples of this, not least "Delegated Authority" at Boeing.

[fscotsman]

Not really my point but I don't think it's proven one way or the other yet. 1 warning on the ground isn't exhaustive that it's not related. As a ga self driver interested if atpls often experience cabin pressure warnings and the sops ? I understand dual redundant CPM on 737m, do we know the exact warnings that came up, did both systems correlate (RA should ground it pending) or was it just discrepancy between the 2 ?

[fscotsman]

You'd think so, but I guess you've come across some shockingly bad RINA, DNV, Lloyds, ABS certified processes in offshore, vis. deepwater horizon ?

[cyrano_de_bergerac]

I don't believe that it is possible for this event to happen if any two of the safety bolts are installed. This provides a level of redundancy to the design. As has been noted this basic design has been employed on the previous generation 737 and flown for millions of hours with no known previous issues. That alone verifies the fundamental soundness of the basic design.

'lateott' also made the observation earlier, that "IMO 4 bolts is not enough redundancy for this design when you consider the risk."

Yes there is redundancy to physical failure of the bolts (and/or nuts), if they are installed. But in view of human factors there's no redundancy at all with respect to their installation, because they are certainly going to be installed (or forgotten) as a set. Thus there is only one level of redundancy to installation (inspection), which is also going to occur WRT the bolts/nuts as a single action. In other words, is very unlikely to fail to install or inspect the first bolt, but then proceed to the next, in sequence.

There are various types of redundancy. In "Practical Reliability Engineering" 4 bolts performing the same function would be termed "Like Redundancy".(identical hardware items performing the same function). The authors go on to state (section 6.9.2 "Common Mode Failures" p. 155) "In the design of redundant systems it is very important to identify and eliminate sources of common mode failures, or to reduce their probability of occurrence to levels an order or more below that of other failure modes." [2 potential bullets from a subsequent list of potential common mode failures are quoted below]:
5 Maintenance actions which are common to different paths, for example, an aircraft engine oil check after
which a maintenance technician omits to replace the oil seal on all engines. (This has actually happened
twice, very nearly causing a major disaster each time.)
6 Operating actions which are common to different paths, so that the same human error will lead to loss of both.

In my view this is missing from the design. What is necessary is a different type of redundancy, what the authors call "Active Redundancy", described as "[a system with] two independent parts with reliabilities R1 and R2, satisfactory operation occurs if either one or both parts function. Therefore, the reliability of the system, R, is equal to the probability of part 1 or part 2 surviving." Note that "parts" in this quote would mean dissimilar (distinct) parts, which would not be installed or inspected as a set, not just more identical bolts added to the design.

With respect to "no accidents in the past", keep in mind past performance is not an indication of sound engineering, as luck may play a part. Regardless of that point, the meaningful statistic to consider would not be number of miles flown, because once the bolts are properly installed, then the door/plug will subsequently be reliable indefinitely. The statistics to consider would be "how many planes have had the bolts forgotten by both installation and inspection?" Very likely 1 out of "N" where N is the number of planes with this design. But obviously, this is a statistically significant value, nowhere near the 99.9999999% reliability necessity for aviation that I believe was quoted earlier. It may have happened at installation time more frequently, but then caught by subsequent inspection.

reference: Patrick D. T. O’Connor, Andre Kleyner, "Practical Reliability Engineering" 5nd Edition, Wiley, 2012

[fscotsman]

We have pressure vessels in subsea, with way higher loading, doesn't replace primary design ethos to minimise points of failure. Polyurethane bushes on the bolts would isolate the load cheaply and efficiently. Sure a couple of extra guide pins for ease of maintenance. 7-figure compliance cost is missing 2 to 3 zeros for fuselage design, assuming plug was integrated.

[DaveReidUK]

But it does prove that it cant be assumed that are even springs involved in the exit door hinges.

We've established that the door plug weighs around 65 lb. How much heavier do you think a live door with the latching mechanism, slide and vent panel weighs ?

Say 50% more, around 100 lb ?

Don't you think some assistance to lift it up in order to open it, in an emergency, would be a good idea ? The initial design of the live door reportedly didn't have any assistance, and then Boeing thought better.

[Pinkman]

The trouble with such "oversight", auditing, or regulatory organisations is they quite soon find the easiest way to perform their role is to ask the business they are meant to be checking to do their work for them. There are numerous examples of this, not least "Delegated Authority" at Boeing.

Exactly! When I went on audits of petrochemical plants and fuelling facilities, usually as part of a team, I lost count of the number of times people "told you what they thought you wanted to hear". This happens whether or not you ingratiate yourself with the facility staff and whether the relationship is antagonistic or cooperative. An experienced auditor can easily spot this and form independent and validated opinions and suggestions for improvement. There are also subtle clues from the moment you walked through security at the start of the visit before you even talked to staff or management. Some sites would be clean as a whistle, others would be litter-strewn. It sounds stupid but the sites where workers and managers collaboratively took pride in their working environment were invariably those with fewer incidents, injuries and fatalities and less re-work because staff took pride in the quality of their work. I know it sounds like motherhood and apple pie but I saw it frequently.

[Eesh]

If the bottom front bolt alone was missing, could the air flow over the door plug have pulled the corner out sufficient to shear off the door plug from the frame?

[DTA]

Thinking further about the way the upper and lower stop bolts work. The lower stop bolts will be much stronger than the upper ones because of the way they are fitted. The upper bolts attached to the guide at their ends. The guide roller then contacts the bolt at its mid point which is its weakest point, being furthest from where it is attached to the guide. The lower bolts again attach at their ends to the green hinge bracket. The force on those is applied by the shaft which should be applied along the length of the bolt and under extreme stress would be split between each end of the bolt at its strongest point.

Assuming this is correct, would it be fair to say that the lower bolts are the important ones and the upper ones are just a secondary insurance? Now if the lower bolts were missing the upper bolts would have to do all the work. There must be some play in the fitting of the upper bolts such that the guide roller can move a little bit between the top of the guide and the bolt. Without that it would be very hard to insert the lock bolt.

If the lower bolts are missing the plug door would be able to bounce between the top of the guide and the lock bolts with any aircraft movement. Eventually would that be enough to cause the two bolts to fail? If they did fail then that could also damage the guide near the fixing holes for the bolt.

This would explain why the failure took some time to happen. From what everyone else has said, it is hard to see how the plug would have popped out after a few months if no bolts were present. Unless they were loose of course.

[DaveReidUK]

If the bottom front bolt alone was missing, could the air flow over the door plug have pulled the corner out sufficient to shear off the door plug from the frame?

I don't think so.

The bolts don't hold the door in, they hold it down.

[Europa01]

Look at the hinge from the plug. Its shaped like a question mark. The end that is "C" shaped attaches to the floor of the plane. The other end has the spring and passes through the fitting in the door. Without the door attached, the plug hinge it is only capable of folding down about 90 degrees before it hits the lower part of the door frame. The only photos Ive seen of that hinge in that position are post incident photos from the incident plane.

Look at the video I posted earlier of the emergency exit in motion. It folds down about 140 degrees. The plug hinge does not have that range of motion.

In my opinion, its pretty obvious that the hinges are different between the plug and the door. And I can tell that from the exit door photo above and any of the dozens of mid exit plug photos like the one in post 843. In fact, stop pin fittings, guide fittings and the perimeter frame they attach to seem to be about the extent of common parts between the plugs and exit doors.

Does that prove they they use different springs. Nope. But it does prove that it cant be assumed that are even springs involved in the exit door hinges. And I haven't seen any photographs that prove the exit doors have similar hinges to the plugs.

Why are the guide fittings identical? Perhaps they didn't see a need to have different parts that serve the same purpose, that is guiding the door up on a bearing in the frame. Perhaps they didn't see a risk that someone would try to bolt an exit shut. Perhaps they do bolt the inactivated emergency exits shut. Reuse of one part doesn't mean they reused as many as possible. Weight and maintenance are much larger issues than maximizing parts commonality.

As this thread developed it seemed likely to me that the same hinge mechanism would have been used for both EE and the non-exit applications. HOWEVER having seen the photos of two types it is quite clear that not just the hinge mechanisms but also the door/plug structures are different in that area. This together with that EE slide deployment video are convincing enough for me.
I also subscribe to the view expressed earlier that closing the door plug from the assisted lift position would be likely to be achieved by pulling down with one hand near the top of the door and pressing down with a boot on the bottom of the door leaving the other hand free to insert a temporary sprag of some sort probably in one of the guide tracks.

[ST Dog]

yet the Hinge Guide Fitting itself was being held to the door plug with only ordinary nuts and lock washers.

What makes you think that?

Every indication is a locking nut plate was used.

Just look at the recovers plug photos showing parts of 2 bolts still present, held by the nut plates.

[SRMman]

Some more from the Seattle Times, including this about Sen Maria Cantwell. Cantwell had asked to see the last 24 months of notices of FAA quality systems audits related to Boeing and one of its suppliers, Spirit AeroSystems.

Spirit, based in Wichita, Kan., builds the entirety of the fuselage for the 737 MAX 9, before sending it to Boeing’s Renton plant by train.

“Recent accidents and incidents … call into question Boeing’s quality control,” Cantwell wrote in the letter to the FAA Thursday. But, she continued, “it appears that the FAA’s oversight processes have not been effective” in ensuring Boeing’s planes are safe.
https://www.seattletimes.com/business/boeing-aerospace/boeing-is-under-fire-after-alaska-airlines-max-9-blowout-so-is-the-faa/

[incompleteness]

Look at the hinge from the plug. Its shaped like a question mark. The end that is "C" shaped attaches to the floor of the plane. The other end has the spring and passes through the fitting in the door. Without the door attached, the plug hinge it is only capable of folding down about 90 degrees before it hits the lower part of the door frame. The only photos Ive seen of that hinge in that position are post incident photos from the incident plane.

Look at the video I posted earlier of the emergency exit in motion. It folds down about 140 degrees. The plug hinge does not have that range of motion.

In my opinion, its pretty obvious that the hinges are different between the plug and the door. And I can tell that from the exit door photo above and any of the dozens of mid exit plug photos like the one in post 843. In fact, stop pin fittings, guide fittings and the perimeter frame they attach to seem to be about the extent of common parts between the plugs and exit doors.

Does that prove they they use different springs. Nope. But it does prove that it cant be assumed that are even springs involved in the exit door hinges. And I haven't seen any photographs that prove the exit doors have similar hinges to the plugs.

Why are the guide fittings identical? Perhaps they didn't see a need to have different parts that serve the same purpose, that is guiding the door up on a bearing in the frame. Perhaps they didn't see a risk that someone would try to bolt an exit shut. Perhaps they do bolt the inactivated emergency exits shut. Reuse of one part doesn't mean they reused as many as possible. Weight and maintenance are much larger issues than maximizing parts commonality.

That kind of c-shaped hinge is usually called a "gooseneck". Looking at the video it seems to me the operable door has dampers that control the opening. Ie, it doesn't just fall open and hit the maximum range of movement, it opens downward in a controlled way.

The door plug has no design features like that, it looks like if you released it when open it would simply fall open until the goosenecks strike the lower sill. You probably have to handle it with care to ensure it doesn't accidentally fall open and damage the sill.

So the hinge apparatuses are quite different between the two, but I don't think you can conclude from that whether or not individual parts, like the springs, are different.

It's just my feeling that the springs would be different on the lighter door, but it's also possible they are less compressed, which would also reduce the lift force. Or maybe the same spring with the same compression works well enough.

Springs are easy enough to source that having a different one on the door plug wouldn't be a big deal.

[Uplinker]

The most likely scenario is that the bolts were not installed. There is broad agreement on that aspect. If the lower bolts were installed not only would the door not move up, but even if there were no nuts on bolts, the bolts would be trapped [by] the spring pressure and would not fall out. In the NTSB briefing they stated that the door moved up before it was ejected. As noted that cannot happen if the lower bolts were in place..........Based on these conditions there is only one conclusion, that is: None of the four locking bolts were present at the time the door was ejected.

No damage to the outboard side of the track means that the bolts weren't there in the first place..........I don't believe that it is possible for this event to happen if any two of the safety bolts are installed. This provides a level of redundancy to the design. As has been noted this basic design has been employed on the previous generation 737 and flown for millions of hours with no known previous issues. That alone verifies the fundamental soundness of the basic design.

On the Ford car production line in the UK in the '70's, there were lots of problems with poor quality control and a disillusioned workforce not assembling the cars properly. There were many instances of components being fitted on the cars but the securing bolts not tightened up; and there was rubbish - including empty drink cans - being left in the actual cars, behind panels.

And after many years at my first employment - nothing to do with car production - it was discovered that one of our colleagues was not doing his job properly - instead of removing and bringing down all the broadcast antennas and dishes that we rigged on the roof of an outside broadcast event, he would leave them up there so the kit would be there for the next event and he wouldn't have to carry it all the way down and back up again. But the next event might have been a year away ! So we had a continual problem with some of our gear not being in the stores when it should have been there, and the reason was this bloke.

I suspect this aircraft manufacturer - or its subcontractors - has both problems; The new bosses have seemingly focussed on making money rather than airliners, so they don't care about their staff and and have accordingly cut costs so much that the dedicated engineers and technicians have left, or retired and not been replaced, and those who remain are disillusioned and don't care, or are not properly trained in the first place.

And the apparent lack of double inspections etc, is presumably 'allowing' corners to be cut unnoticed. I can imagine a worker like my ex colleague saving time by installing this blank plug without these four locking bolts, and signing himself off, with nobody ever knowing, or noticing or inspecting.

I sincerely hope I am wrong !

[Old Ag]

We've established that the door plug weighs around 65 lb. How much heavier do you think a live door with the latching mechanism, slide and vent panel weighs ?

Say 50% more, around 100 lb ?

Don't you think some assistance to lift it up in order to open it, in an emergency, would be a good idea ? The initial design of the live door reportedly didn't have any assistance, and then Boeing thought better.

Does the lift assistance have to be built into the hinge? Could it perhaps be built into the latching mechanism? Could the latching mechanism cam the door upwards with the help of springs integrated into the latching mechanism? Could that be what the visible springs around the view port in the emergency exit photo assist with?

[Easy Street]

If the lower bolts were installed not only would the door not move up, but even if there were no nuts on bolts, the bolts would be trapped but the spring pressure and would not fall out.

I am not sure this can be said with certainty. On the ground, sure, the door plug will be held firmly against the bolts by spring pressure. However, perhaps not so in flight. Look at the inner faces of the door frame stop pads: they appear slightly concave to me, and if so, that would provide a means by which the door plug could be shifted ever so slightly downwards, as increasing differential pressure caused the stop plugs to find the lowest point of the concave stop pads. This might compress the bottom springs just enough to relieve loading on the restraining bolts while pressurised, and allow them to gradually work loose over the course of several flights. Of course, this theory would require castle nuts and cotter pins to be absent as well.

[aeromech3]

It appears to me on the E/E door that has the decal NOT an Exit as re-posted in #870; at the lower sides there looks likely a roller fitting on the door frames and a guide block on the aperture frames, which faces upwards! that
Of course it could be a micro-switch block on the aperture.

[MikeSnow]

That kind of c-shaped hinge is usually called a "gooseneck". Looking at the video it seems to me the operable door has dampers that control the opening. Ie, it doesn't just fall open and hit the maximum range of movement, it opens downward in a controlled way.


Looking at the picture of the EE door from inside, posted earlier in the thread, I see something shiny that could be a hydraulic damper on the bottom left:

https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/234x201/aiqqpsr_1a46fe1b57dc66e8a65173bbc3e4e4d13dd4209f.png

And on the bottom right there is something that looks like a spring, with something shiny at the top, possibly a spring around another damper:
https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/253x250/image_f1344946d7cb14ecdf1800b8e273be28f02d0020.png

[D Bru]

Boeing aren't currently making any MAX9 with the exit door at this point; all currently in production are being built with the plug. The ability to substitute a full exit door is aimed at the secondhand use of the aircraft later in life.

Well, on 15 November 23 they did deliver PH-CDQ (L/N 8802) with exit door (and presently active, the aircraft I mean). So, that's about the same time as Alaska N704AL (L/N 8789).

On a different note, I thought that the plug was first applied by Boeing on the NG-900ER (since 2007), but I now found that Boeing started plugging exits as early as 1970 with the advent of the "Advanced" 727-200. The earlier version (delivered 1967 through 1969) had pre-wing type 2 exits, while these were replaced by plugs on the "Advanced". So, the plug has quite some history at Boeing....

Regards

https://www.airliners.net/photo/United-Airlines/Boeing-727-222/1117348

https://www.airliners.net/photo/United-Airlines/Boeing-727-222/2079350/L

[roger4]

What we really need is a nice clear video of the plug-door, and for contrast the E/E door, being opened from the inside!

[MarineEngineer]

What we really need is a nice clear video of the plug-door, and for contrast the E/E door, being opened from the inside!
I'd like to see a page from the maintenance guide describing how to close and secure the door! And if any tools are used to lower and hold closed the door while the bolts are fitted.

[DaveReidUK]

Does the lift assistance have to be built into the hinge? Could it perhaps be built into the latching mechanism? Could the latching mechanism cam the door upwards with the help of springs integrated into the latching mechanism? Could that be what the visible springs around the view port in the emergency exit photo assist with?

Maybe. But for that to be true, there would need to be something on the door surround, against which the door could lever itself upwards. And whatever the "something" is, it would presumably exist also on aircraft with the door plugs (albeit not used for that purpose).

I can't seen anything on any of the (admittedly poor) photos that resembles the above.

[aeromech3]

D Bru you are not entirely wrong, but the B727-200ADV which I worked on, did not have the removable plug we are discussing; it was a total fuselage plug which made it a longer aircraft.
Not sure of the history of this particular B727.

[helispotter]

...There are probably some ex Boeing quality people who retired in disgust who wouldn't mind coming back as an overseer in the spirit of schadenfreude.

I would say more a case of "There are probably some ex Boeing quality people who retired in disgust who wouldn't mind coming back as an overseer in the spirit of making sure the work is being done properly". They might only see that as possible when being paid and managed independently of Boeing.

[remi]

I would say more a case of "There are probably some ex Boeing quality people who retired in disgust who wouldn't mind coming back as an overseer in the spirit of making sure the work is being done properly". They might only see that as possible when being paid and managed independently of Boeing.
It's not that hard to find someone who wants to be paid for being a literalist pedantic twit without having to manage other humans. It's not even a rare talent.

[RUTUS]

...

The door/plug and two phones have been found. One in working condition still in airplane mode. So they can reassemble the plane and get it in airworthy condition.

Does the phone make a gentle glide path landing if you put it in airplane mode?

[D Bru]

Thanks aeromech3, I grant your memory accurate of course, but on this particular 727 (N7647U), the forward of wing door plug outline is clearly visible, also see this photograph: https://www.airport-data.com/aircraft/photo/000658863.html

https://cimg3.ibsrv.net/gimg/pprune.org-vbulletin/1145x587/screenshot_2024_01_13_at_14_33_33_1d0973a39640c7632b9af73b8b 468146a5b4eb0c.png


Regards

[scifi]

Quote....
Originally Posted by roger4
What we really need is a nice clear video of the plug-door, and for contrast the E/E door, being opened from the inside!

My guess is that it is a two man job to remove the plug, as it has no outward constraint. If one person alone tried to open it, he would have difficulty holding on to it once it was partially open, and could be thrown out of the aircraft. The second person is required on the outside of the plane to lower the plug safely.

[EXDAC]

My guess is that it is a two man job to remove the plug, as it has no outward constraint. If one person alone tried to open it, he would have difficulty holding on to it once it was partially open, and could be thrown out of the aircraft. The second person is required on the outside of the plane to lower the plug safely.

Opening a door plug and removing a door plug from an aircraft would be quite different tasks. We have seen photos of open door plugs that show it is restrained by wire tethers. No need to lower it away from the aircraft.

[DaveReidUK]

My guess is that it is a two man job to remove the plug, as it has no outward constraint. If one person alone tried to open it, he would have difficulty holding on to it once it was partially open, and could be thrown out of the aircraft. The second person is required on the outside of the plane to lower the plug safely.

Leaving aside the fact that it's been shown possible to remove the plug without any human involvement being required :O, I'd be surprised if there's any requirement to remove it during routine maintenance. Why is this an issue?

[OldnGrounded]

It's not that hard to find someone who wants to be paid for being a literalist pedantic twit without having to manage other humans. It's not even a rare talent.

If I were hiring independent inspectors to provide quality assurance in the construction of airliners, "literalist pedantic twits" are exactly the people I'd want. They are also the people future passengers would want, whether they know it or not.

[OldnGrounded]

Leaving aside the fact that it's been shown possible to remove the plug without any human involvement being required :O, I'd be surprised if there's any requirement to remove it during routine maintenance. Why is this an issue?

This, exactly. These plugs aren't intended to be routinely opened and closed. And, on the probably rare occasions when they are opened and closed, it shouldn't matter whether or not the job can be easily performed by a single person or require a second set of hands.

[Alison747]

Perhaps I could be permitted to throw in a couple more rumour-like thoughts :-

There has been discussion about the amount of force provided by the lift springs. There is more than one photo of the open door showing the hinge guide fully against the stop washer at the top.
I was wondering about the logic for this and suggest that it is very much intentional and that the nuts on top are a height adjustment to align the upper guide roller and its door guide when the door is open.
Differential adjustment of the nuts on each guide also aligns the door vertically.

For this to be true, the springs must supply more than the weight of the door to be reliably solid at the top of travel.
The next point then is that the spring force will increase quite a bit as the door is pushed down and this force is only restrained by the rather slim "arrestor" bolts which have a shear force on them as there is nothing for them to clamp.
Any slight play in the sliding action of the hinge can also potentially cause wear at the bolt.

Having seen the construction I don't think I would feel happy sitting next to one of these "unscheduled exit" plugs - I would want big bolts directly between plug and frame!

[twochai]

It's not a 'plug' door - it's a 'semi-plug' door.

[Old Ag]

https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/473x801/img_0735_88408a3af6ed49a3fe3df5f6ca33cb223f03b934.jpeg

Maybe. But for that to be true, there would need to be something on the door surround, against which the door could lever itself upwards. And whatever the "something" is, it would presumably exist also on aircraft with the door plugs (albeit not used for that purpose).

I can't seen anything on any of the (admittedly poor) photos that resembles the above.

Looking at the above photo, you can see the handle attached to a round bar or torque tube that spans the door. On the side of the door, opposite the handle, you can see the bar pass through the door and attach to a lever arm that has some sort of pin on the other end. This pin seems to be engaged in some kind of striker or guide attached to the door frame between the second and third stop pad. This striker/guide is not shared with the plug configuration. The exact configuration is not clear but there are two torsion springs along the torque tube and a further mechanism buried in the door behind the handle with a large spring attached. You can’t see the door frame clearly on the handle side, but what you can see is consistent with the non handle side.

So exactly how this all works in not perfectly clear, but it is easy to imagine that pulling the handle up rotates the torque tube pressing the pins at the ends of the arms down towards the strikers, forcing or at least allowing the door to translate up. Where the assist to move the door upwards is unclear. It could be the visible springs and mechanisms in the middle of the door acting through the torque tube and strikers. There could be springs buried in the door that bear the doors weight, or it could be both.

[DType]

IF the springs do support the total plug weight when extended to the stops, then they must exert significantly greater upthrust when compressed in situ.
In which case when dismantling, after removing the last bolt (when all correctly fitted), the plug would be ejected briskly upwards.
Seems both undesirable and unnecessary, unless the same springs are retained when a door is retrofitted?

[Stagformation]

Looking at the above photo, you can see the handle attached to a round bar or torque tube that spans the door. On the side of the door, opposite the handle, you can see the bar pass through the door and attach to a lever arm that has some sort of pin on the other end. This pin seems to be engaged in some kind of striker or guide attached to the door frame between the second and third stop pad. This striker/guide is not shared with the plug configuration. The exact configuration is not clear but there are two torsion springs along the torque tube and a further mechanism buried in the door behind the handle with a large spring attached. You can’t see the door frame clearly on the handle side, but what you can see is consistent with the non handle side.

So exactly how this all works in not perfectly clear, but it is easy to imagine that pulling the handle up rotates the torque tube pressing the pins at the ends of the arms down towards the strikers, forcing or at least allowing the door to translate up. Where the assist to move the door upwards is unclear. It could be the visible springs and mechanisms in the middle of the door acting through the torque tube and strikers. There could be springs buried in the door that bear the doors weight, or it could be both.
The further mechanism buried behind the handle is probably the external door handle mechanism. The other mechanism attached to the torsion rod —on the opposite side of the window to the handle —is probably a flightlock (sadly a mitigating function that a plug doesn’t have).

[GlobalNav]

Some more from the Seattle Times, including this about Sen Maria Cantwell. Cantwell had asked to see the last 24 months of notices of FAA quality systems audits related to Boeing and one of its suppliers, Spirit AeroSystems.

Spirit, based in Wichita, Kan., builds the entirety of the fuselage for the 737 MAX 9, before sending it to Boeing’s Renton plant by train.

“Recent accidents and incidents … call into question Boeing’s quality control,” Cantwell wrote in the letter to the FAA Thursday. But, she continued, “it appears that the FAA’s oversight processes have not been effective” in ensuring Boeing’s planes are safe.
https://www.seattletimes.com/business/boeing-aerospace/boeing-is-under-fire-after-alaska-airlines-max-9-blowout-so-is-the-faa/

One problem that makes FAA so ineffective is that it’s mostly clerical, i.e., paperwork checks. Then when a potential problem is identified, instead of enforcement, it’s dismissed as “merely a paperwork error”.

[MZoVrsmg]

IF the springs do support the total plug weight when extended to the stops, then they must exert significantly greater upthrust when compressed in situ.

The force will be greater, but *significantly greater*?

Spring force is a linear function of the distance it's been compressed.

Consider these number's I've pulled from my imagination:

Free length of springs is 6" longer than installed length with the door in the open/up position (at the stops)
Springs together exert 64lb when open to fully support the weight of the door

Compressing those springs an additional 1.5" to the closed position is only an additional 25% travel in this scenario, so the total force should be about 80lb with the door in the closed position.

Subtract the weight of the door, and we're talking about less than 20lb to contend with when installing/removing the arrestor bolts. Seems manageable.

[WillFlyForCheese]

Perhaps I could be permitted to throw in a couple more rumour-like thoughts :-

There has been discussion about the amount of force provided by the lift springs. There is more than one photo of the open door showing the hinge guide fully against the stop washer at the top.
I was wondering about the logic for this and suggest that it is very much intentional and that the nuts on top are a height adjustment to align the upper guide roller and its door guide when the door is open.
Differential adjustment of the nuts on each guide also aligns the door vertically.

For this to be true, the springs must supply more than the weight of the door to be reliably solid at the top of travel.
The next point then is that the spring force will increase quite a bit as the door is pushed down and this force is only restrained by the rather slim "arrestor" bolts which have a shear force on them as there is nothing for them to clamp.
Any slight play in the sliding action of the hinge can also potentially cause wear at the bolt.

Having seen the construction I don't think I would feel happy sitting next to one of these "unscheduled exit" plugs - I would want big bolts directly between plug and frame!

The upward force of the springs, through the length of travel, would differ if the springs were progressive versus linear. Does anyone know what type of spring is used in this application?

[Obba]

Interview with pax re shirtless boy at 3:35

https://www.youtube.com/watch?v=OWfKCIMGYOY

I find it hypocritical that this lady passenger is commenting on how scared and terrifying it was - however, she was taking selfies, smiling and grinning away!

[MechEngr]

The upward force of the springs, through the length of travel, would differ if the springs were progressive versus linear. Does anyone know what type of spring is used in this application?
The helix of the extended spring looks to be uniform as is the diameter of the coil and the diameter of the wire. These are all characteristics of linear springs.

Progressive springs tend to have some coils close to decrease the number of open/active coils. In the closed position the coils are still uniformly spaced, the exceptions being the last turn that is used to make a 90 degree end to seat the spring.

[incompleteness]

The next point then is that the spring force will increase quite a bit as the door is pushed down and this force is only restrained by the rather slim "arrestor" bolts which have a shear force on them as there is nothing for them to clamp.


I'm not sure what diameter the arrestor bolts are because my eyeballing skills aren't up to it, but they must at least be 6/32. Your basic vanilla 6/32 bolt has a shear strength around 2000 lbs. The two at the bottom have two shear planes each so each one is good for 4000 lbs.

I won't make things too confused by talking about other failure modes like bearing, because the order of magnitude is what's interesting.

The ones at the top work in bending but still, each one will be able to resist any spring force with ease.

All they have to do is keep the door on its stops. An engineer will look at this and see a quadruple-redundant design that's almost over-designed and will feel pretty good about it.

The problem is, it's not quad-redundant. If we go with the prevailing theory, one mistake prevented the installation of all 4 bolts, instead of 4 independent mistakes.

But to me as a stress guy, I'm thinking if production can't reliably build and install this door, they can't do anything. It's a pretty basic aerostructure. How are we supposed to engineer around not being able to build and install basic things?

Apropos of not this topic, I'll also add they were so lucky the door let go at 16,000 and not 35,000. I suspect the blowout was bigger than what the airplane was designed for, and had the delta-p been higher something very very bad could have happened.

[Solofast]

'
With respect to "no accidents in the past", keep in mind past performance is not an indication of sound engineering, as luck may play a part. Regardless of that point, the meaningful statistic to consider would not be number of miles flown, because once the bolts are properly installed, then the door/plug will subsequently be reliable indefinitely. The statistics to consider would be "how many planes have had the bolts forgotten by both installation and inspection?" Very likely 1 out of "N" where N is the number of planes with this design. But obviously, this is a statistically significant value, nowhere near the 99.9999999% reliability necessity for aviation that I believe was quoted earlier. It may have happened at installation time more frequently, but then caught by subsequent inspection.

reference: Patrick D. T. O’Connor, Andre Kleyner, "Practical Reliability Engineering" 5nd Edition, Wiley, 2012

These plug doors are opened during specific inspections. Consequently the fact that they are opened and secured on a regular (although infrequent basis) is an indication that the process of closing and securing the door, when performed to the prescribed procedure is a safe process. There are literally thousands of bolts on any aircraft that if not properly installed and secured will result in the loss of an aircraft. We cannot make everything idiot proof as idiots are so ingenious. If the FAA wanted to put an emphasis on this they could require a logbook entry noting that the door had been opened and an additional verification of inspection and that could provide another level of redundancy, but there is not need to redesign something that works as designed. A redesign would then require additional certification testing and approvals and there is no need for that.

[SRMman]

An interesting article from Reuters about Boeing workers involvement with the plug door.


Reuter’s source has told them that, contrary to Boeing standard factory procedures, (Renton) workers “usually remove the panel, and use the gap to install pieces of cabin equipment, before replacing the panel and finishing the installation”.

But the source familiar with Boeing's industrial process said on Friday that according to its standard factory procedures, the company only removes or adjusts the panel if there are signs it was installed incorrectly

Boeing does perform certain checks and conducts pressurization tests before delivering the plane to the airline, the source said, adding that interiors are loaded elsewhere in the plane.


Well, if true we have here unauthorised work being carried out, presumably without the normal checks, paperwork, inspections and signatures, leading almost inevitably – in time – to incorrect reassembly and/or missing parts.

https://www.reuters.com/business/aerospace-defense/boeing-performs-pressure-tests-does-not-normally-adjust-max-9-panels-source-2024-01-13/

[MechEngr]

Were I king for a day on that line I would require labeling at each removable fastener location to indicate that a fastener is required and have a QR code to link to the part numbers and any torque requirements and a diagram showing the correct installation. The door would also have a QR code linking to a diagram and assembly process. That main QR code would also include the serial number of the door so that the QC checking the door would be recorded. They would scan the 12 capture screws and the 4 capture bolts. Each one should be linked to the assembler who scanned them as part of their completion of work record. They should all have tamper-proof stripe applied by the QC operator so that anyone removing the door will not be able to sneak it back into place.

[DIBO]

I find it hypocritical that this lady passenger is commenting on how scared and terrifying it was - however, she was taking selfies, smiling and grinning away!
:sad:
I am pretty sure that if you take a vote from persons occupying row 0 up to the rear jump-seats, on whether this experience was "scary and terrifying", you would get an unanimous vote.
Hint: "Neuroscience research suggests that laughter or mirth is a way for us to reduce fear, anxiety, or stress."

I applaud this lady for having the presence of mind, to start communicating by text-writing on her phone, the only practicable way of communicating, when suddenly a shirtless teen dropped in an empty seat next to her, and upon seeing his skin abrasions, was compassionate enough to inquire on his state of well-being.
And this selfie will be treasured by both for a very long time....

[Solofast]

In another forum a Boeing worker who works on installing interiors said that the Reuters quote is not correct. He said that those doors are too small to do much interior installation work. He said that interiors are installed through the front and rear main doors as those are larger and it is much easier to get seats and bins through the main doors. We'll have to wait and see what is determined but there are conflicting rumors as to whether or not those doors are opened or removed during interior assembly.

One aspect that could have fallen through the cracks is that the bolts to fasten the bottom hinges to the door frame were not in some cases correctly fastened (not necessarily "loose" in normal parlance, but not torqued to spec). All of the doors are shipped from in place but Spirit does not consider them "fitted and final". For the main doors this is fine. Boeing removes the main doors, dresses them with slides and other hardware and then rigs them to stringent specifications. Boeing was assuming that the plug doors were "installed" and wasn't checking the fasteners that mount the hinges and this is an apparent lapse and it explains how the loose bolts could have slipped through the system. That's also a relatively simple fix in adding a procedure to inspect, and torque those bolts.

[OldnGrounded]

:sad:
I am pretty sure that if you take a vote from persons occupying row 0 up to the rear jump-seats, on whether this experience was "scary and terrifying", you would get an unanimous vote.
Hint: "Neuroscience research suggests that laughter or mirth is a way for us to reduce fear, anxiety, or stress."

I applaud this lady for having the presence of mind, to start communicating by text-writing on her phone, the only practicable way of communicating, when suddenly a shirtless teen dropped in an empty seat next to her, and upon seeing his skin abrasions, was compassionate enough to inquire on his state of well-being.
And this selfie will be treasured by both for a very long time....

Yup. If I remember correctly, the woman told the interviewer that the teen asked for the selfie after they had been communicating for a while (and presumably were beyond the initial shock of the event) to memorialize their crazy shared experience. I think she deserves loud applause, and I'd bet that she and the kid and his family will have an unbreakable connection.

[remi]

We cannot make everything idiot proof as idiots are so ingenious. If the FAA wanted to put an emphasis on this they could require a logbook entry noting that the door had been opened and an additional verification of inspection and that could provide another level of redundancy, but there is not need to redesign something that works as designed. A redesign would then require additional certification testing and approvals and there is no need for that.

Ain't that the truth. But that's what meticulous inspection (of assembly and maintenance) is for.

I wouldn't be surprised if there are months of delay getting the MAX line going again as new procedures might need to be certified. FAA will probably be okay with existing a/c being rigorously inspected and brought to spec.

[Europa01]

Were I king for a day on that line I would require labeling at each removable fastener location to indicate that a fastener is required and have a QR code to link to the part numbers and any torque requirements and a diagram showing the correct installation. The door would also have a QR code linking to a diagram and assembly process. That main QR code would also include the serial number of the door so that the QC checking the door would be recorded. They would scan the 12 capture screws and the 4 capture bolts. Each one should be linked to the assembler who scanned them as part of their completion of work record. They should all have tamper-proof stripe applied by the QC operator so that anyone removing the door will not be able to sneak it back into place.

Unless I’m much mistaken most of this is already in place on modern car production lines. I’m at a total loss to understand why at least a functioning paperwork version of this was not in place for this door/plug. Surely for a major pressure envelope component we should expect an auditable QA trail with independent verification of the critical steps together with a workforce discipline which prevents messing with something which has been assembled in this way.
This seems all the more relevant given the nasty sting in the tail of post #921 in which incompleteness raises the possibility that at higher altitude this could have been a catastrophic beyond design basis accident. Presumably both Boeing and the FAA (dis)missed this as an incredibility of failure item during design and certification. My guess it was worse than 10E-3

Finally, in the wake of a dreadful smoking hole event somewhere we almost always find a combination of unfortunate circumstance which contributed. This case is the exact reverse - window seat not occupied, event at low altitude, departing door did not impact the horizontal stabiliser. The whole thing screams ‘unbelievably lucky this time’ . Let’s hope that that Boeing and the FAA get it.

[WHBM]

I’m at a total loss to understand why at least a functioning paperwork version of this was not in place for this door/plug ... Presumably both Boeing and the FAA (dis)missed this as an incredibility of failure item during design and certification. My guess it was worse than 10E-3

It seems we are starting to hear that there was a competently documented process for the assembly steps, which is really what you would expect from somewhere like Boeing, but on the ground this was not being followed. I'd be pretty confident that they nevertheless have a paper audit that all was done right. The way to overcome this is called MBWA - Management By Walking Around; just seeing that reality matches.

Regarding Risk Assessments, I have long found these to be alas a way of back-fitting likelihood values to what you have already designed, just to get things accepted.

[A0283]

Some thoughts in general:

In final assembly you ‘never have enough’ space and access.

Getting complete fuselages delivered (as Boeing do with the 737) may well be an overall manufacturing optimum, but reduces available space and accessibility in final assembly even more.

The most critical area with respect to space and access is the cockpit section and E-bay. Call them the “red zone”.

If you take interiors for example, you would expect galley units to be delivered to final assembly on rollers, then lifted onto the level platform outside the left hand forward pax door (the platform railings being foldable or turnable), then pushed into the cabin and rolled to their positions. You would expect cabin wall panels to be delivered in a similar manner with sets of panels on roller carts and through the same door.

These logistics moves of big parts limit available space and access, and in the most critical area.

If you get passengers in from the left and cargo/baggage from the right side of your aircraft, your cargo doors are on the right, and (smaller) service doors too.

So the left side of your plane has 2 big size pax entry door openings, plus 1 (potential) medium plug opening, plus 2 small size escape hatch openings.

So the right side of your plane has 2 medium size service door openings, plus 1 (potential) medium plug opening, plus 2 small escape hatch openings, plus 2 medium/large cargo door openings.

This means that you will be tempted to open these plugs during final assembly, and especially to open the one on the left side. So the probability that you open a plug is higher on the left than on the right.

That probability increases when you have to deal with changes in production rates, and with shortages and delays.

Don’t say this is what happened, but may explain why the left plug was ejected and not the right. Which makes it interesting to find out if on the other planes the loose bolts of AK and UA were found mostly on the left.

[tdracer]

If it does turn out to be IAM workers in Renton doing something (removing the door plug) without following the relevant procedures or doing the associated paperwork, it's going to be a huge blow to the whole IAMs mantra that "union workers do it better".
The IAM spent years (and huge dollars) claiming that the 787 line in Charleston couldn't do the high quality work that the IAM does in the Puget Sound. Before we had the huge embarrassment of FOD left in the KC-46 and other tanker QA failures - done by the IAM's 'superior' work force.

[Solofast]

I wouldn't be surprised if there are months of delay getting the MAX line going again as new procedures might need to be certified. FAA will probably be okay with existing a/c being rigorously inspected and brought to spec.

The Max line is not stopped. The only planes affected are the -9's and Boeing only makes 3 or 4 of those a month. No one has said anything about stopping or slowing Max production. Right now there are only 2 Max-9's that have been built and are awaiting delivery and those will have to be subjected to any inspections called out by the AD. Max-9 production is a small subset of the Max line. It's about 10% of Max production. Since the -9 wasn't impacted by the Spirit bulkhead issue in the last few months they've made a higher percentage of them compared to the -8's but if they didn't make any -9's for month or so it isn't going to have an effect on production rates or Max deliveries.

[remi]

If it does turn out to be IAM workers in Renton doing something (removing the door plug) without following the relevant procedures or doing the associated paperwork, it's going to be a huge blow to the whole IAMs mantra that "union workers do it better".
The IAM spent years (and huge dollars) claiming that the 787 line in Charleston couldn't do the high quality work that the IAM does in the Puget Sound. Before we had the huge embarrassment of FOD left in the KC-46 and other tanker QA failures - done by the IAM's 'superior' work force.
I'm more concerned about whether workers are being exploited than whether they're "superior," but then again the superior cheapness of non union labor is the part that gets Boeing management excited.

[incompleteness]

:sad:
I am pretty sure that if you take a vote from persons occupying row 0 up to the rear jump-seats, on whether this experience was "scary and terrifying", you would get an unanimous vote.
Hint: "Neuroscience research suggests that laughter or mirth is a way for us to reduce fear, anxiety, or stress."

Some people must have looked at the two empty seats beside the big gaping hole and asked themselves "I can't remember, were there people in those seats before?"

People do absolutely random things in situations they never experienced before where adrenaline must have been through the roof. They didn't know if it was a bomb, they didn't know if the airplane was going to continue to fall apart, they didn't know if anyone had actually died, they didn't know if they were going to be alive in one minute. Taking selfies is one if the least strange things someone could have done.

[Mach2point7]

The FAA announcement on Jan 12 begins with the following statement: " WASHINGTON, D.C. — After taking decisive and immediate action to ground approximately 171 Boeing 737-9 MAX planes, the Federal Aviation Administration (FAA) today announced new and significant actions to immediately increase its oversight of Boeing production and manufacturing. These actions come one day after the FAA formally notified Boeing that the FAA has launched an investigation into the company as a result of last Friday’s incident on a Boeing Model 737-9 MAX in which the aircraft lost a passenger door plug while in flight. "

On its own, that sounds reasonable. But I would have thought that the FAA "oversight" was already at the highest level as a result of the MCAS omnishambles. It also states: " Assessment of safety risks around delegated authority......." This is like deja vu all over again. If I was a U.S. taxpayer I would be asking Congress to point the blowtorch at the FAA, as well as at Boeing.

[cyrano_de_bergerac]

These plug doors are opened during specific inspections. Consequently the fact that they are opened and secured on a regular (although infrequent basis) is an indication that the process of closing and securing the door, when performed to the prescribed procedure is a safe process. There are literally thousands of bolts on any aircraft that if not properly installed and secured will result in the loss of an aircraft. We cannot make everything idiot proof as idiots are so ingenious. If the FAA wanted to put an emphasis on this they could require a logbook entry noting that the door had been opened and an additional verification of inspection and that could provide another level of redundancy, but there is not need to redesign something that works as designed. A redesign would then require additional certification testing and approvals and there is no need for that.
True, but off the assembly line is a slightly different situation. Disassembly/reassembly of a component once delivered is self-validating with respect to part inventory. Extra bolts/parts lying around after a job (hmm check the manual)... says confused question mark and call Ikea.

I agree with you on the bulk of your post, and a redesign likely isn't needed. IMO the cockpit and the maintenance hangar have addressed the human-factors element to a large degree, but it seems the assembly line is lagging behind. Maybe a reconsideration there, with a view of the subtleties/nuances of "effective" redundancies might mean additional layers of inspection. Or stronger visual cues - for low-tech ideas maybe contrasting paint where a fastener must go? Or for high-tech, maybe digitalized video inspections, that are processed through A.I. for abnormality detection. Maybe that would solve other problems, such as the foreign object debris problem, I mean if inspections already don't notice extra tools left in an airframe, whatever problems are happening there, it's not going to be solved by the same level of thinking and one more log book.

[C2H5OH]

All of the doors are shipped from in place but Spirit does not consider them "fitted and final". For the main doors this is fine. Boeing removes the main doors, dresses them with slides and other hardware and then rigs them to stringent specifications. Boeing was assuming that the plug doors were "installed" and wasn't checking the fasteners that mount the hinges and this is an apparent lapse and it explains how the loose bolts could have slipped through the system. That's also a relatively simple fix in adding a procedure to inspect, and torque those bolts.
This would be amusing in a peculiar way, because the manufacturer and its supplier would have had the same difficulty of defining this a door or non-door as this forum.
It also would mean that there’s potentially both: A (manufacturing) design issue and a shopfoor discipline and oversight issue.

[SRMman]

A good article in the BBC's Business section summarising the situation.

https://www.bbc.co.uk/news/business-67956244

[639]

:sad:
I am pretty sure that if you take a vote from persons occupying row 0 up to the rear jump-seats, on whether this experience was "scary and terrifying", you would get an unanimous vote.
Hint: "Neuroscience research suggests that laughter or mirth is a way for us to reduce fear, anxiety, or stress."

I applaud this lady for having the presence of mind, to start communicating by text-writing on her phone, the only practicable way of communicating, when suddenly a shirtless teen dropped in an empty seat next to her, and upon seeing his skin abrasions, was compassionate enough to inquire on his state of well-being.
And this selfie will be treasured by both for a very long time....

In a situation of potential peril I invariably find myself scanning for any further information on what may happen next and what actions might lessen the blow, others may be driven to text their friends and family or take a photo of the event. I'm uncertain whether the lady in question is displaying presence of mind or is simply reverting to learned behavior under stress, her actions may be ultimately welcomed but I wouldnt pretend to know her motivation.
Glad they all ended up OK

[remi]

It seems we are starting to hear that there was a competently documented process for the assembly steps, which is really what you would expect from somewhere like Boeing, but on the ground this was not being followed. I'd be pretty confident that they nevertheless have a paper audit that all was done right. The way to overcome this is called MBWA - Management By Walking Around; just seeing that reality matches.

Regarding Risk Assessments, I have long found these to be alas a way of back-fitting likelihood values to what you have already designed, just to get things accepted.
If it was a Stupid Process™ it was probably followed like other Stupid Processes™, that is to say, workers start inventing their own seemingly more sensible processes.

Like instead of taking everything under the wings apart, workers start removing and replacing DC-10 engines directly from pylons with a forklift. Seemed like a great idea at the time, amirite?

Or the guy working on the 737 who apparently didn't reinstall a washer into a location that he couldn't actually see, during a bizarrely difficult maintenance procedure, leading to a bolt coming loose into the slat track and thence being shoved into the wing fuel tank.

Honorable mention to the inspector who pitched in and helped his guys remove the screws from their EMB 120 horizontal stabilizer, although it might have gone better if he had let the next shift know the leading edge needed to be put back together.

And to the guy who just used the screws that were handy to put the windscreen on BA111.

But anyway if you have what seems to be a Stupid Process™, people will sooner or later stop following it, possibly with dire results.

[ozaub]

Is it Legal to Plug Emergency Exits on MAX 9?

Previously I’ve questioned ethics of plugging EEs; it seems wrong to deliberately block an available escape route. I wasn’t questioning legality of doing so, provided maximum passenger load complied with ratings of remaining EEs.

However, on reflection plugging mid-cabin EEs on MAX9 may not comply with FAR §25.813 Emergency Exit Access: “…. Emergency exit distribution must be as uniform as practical….”

If any EEs are plugged surely it should be either pair of over-wing EEs, not those at mid-cabin. Certainly, retaining mid-cabin EEs better meets intent of regulation as discussed in FAA Advisory Circular AC No: 25.807-1 UNIFORM DISTRIBUTION OF EXITS. Note regulation number has changed since AC was written.

[MarineEngineer]

Is it Legal to Plug Emergency Exits on MAX 9?

Previously I’ve questioned ethics of plugging EEs; it seems wrong to deliberately block an available escape route. I wasn’t questioning legality of doing so, provided maximum passenger load complied with ratings of remaining EEs.

However, on reflection plugging mid-cabin EEs on MAX9 may not comply with FAR §25.813 Emergency Exit Access: “…. Emergency exit distribution must be as uniform as practical….”

If any EEs are plugged surely it should be either pair of over-wing EEs, not those at mid-cabin. Certainly, retaining mid-cabin EEs better meets intent of regulation as discussed in FAA Advisory Circular AC No: 25.807-1 UNIFORM DISTRIBUTION OF EXITS. Note regulation number has changed since AC was written.

Four main doors and two overwing E/Es are hardly uniformally distributed!

[hec7or]

If any EEs are plugged surely it should be either pair of over-wing EEs, not those at mid-cabin. Certainly, retaining mid-cabin EEs better meets intent of regulation as discussed in FAA Advisory Circular AC No: 25.807-1 UNIFORM DISTRIBUTION OF EXITS. Note regulation number has changed since AC was written.

No advantage, the overwings don't reduce the seating capacity but the Mid Exits do.

[DaveReidUK]

Is it Legal to Plug Emergency Exits on MAX 9?

Previously I’ve questioned ethics of plugging EEs; it seems wrong to deliberately block an available escape route. I wasn’t questioning legality of doing so, provided maximum passenger load complied with ratings of remaining EEs.

However, on reflection plugging mid-cabin EEs on MAX9 may not comply with FAR §25.813 Emergency Exit Access: “…. Emergency exit distribution must be as uniform as practical….”

If any EEs are plugged surely it should be either pair of over-wing EEs, not those at mid-cabin. Certainly, retaining mid-cabin EEs better meets intent of regulation as discussed in FAA Advisory Circular AC No: 25.807-1 UNIFORM DISTRIBUTION OF EXITS. Note regulation number has changed since AC was written.

Plugging one of the overwing E/E pairs would be pointless - there would be no advantage in terms of space for additional seats.

[Lawk]

The warning light came on during three previous flights: on Dec. 7, Jan. 3 and Jan. 4 — the day before the door plug broke off. Homendy said she didn’t have all the details regarding the Dec. 7 incident but specified the light came on during a flight on Jan. 3 and on Jan. 4 after the plane had landed.

So December 7th. The day the aircraft leaves the MRO AAR after its WiFi install. (cannot post flightaware image, new user)

AAR says they dont touch plug doors. However satellite image shows some kind of ramp near the location of that door on some variant of the 737 unable to see if it is a MAX 9. Look for AAR in Oklahoma on Google maps (i am not allowed to post the image because I am a new user).

I think the NTSB should look into this despite the claims of the MRO.

Especially if the forensics find markings on the bolt holes and where the door rests indicating that there was a bolt there at some point. If not then I guess the most likely scenario is still them being missing from the get go.

You can watch a WiFi retrofit video on youtube by United (for A320) but you can still see that it appears to be a massive job.

[Stagformation]

Is it Legal to Plug Emergency Exits on MAX 9?

Previously I’ve questioned ethics of plugging EEs; it seems wrong to deliberately block an available escape route. I wasn’t questioning legality of doing so, provided maximum passenger load complied with ratings of remaining EEs.

However, on reflection plugging mid-cabin EEs on MAX9 may not comply with FAR §25.813 Emergency Exit Access: “…. Emergency exit distribution must be as uniform as practical….”

If any EEs are plugged surely it should be either pair of over-wing EEs, not those at mid-cabin. Certainly, retaining mid-cabin EEs better meets intent of regulation as discussed in FAA Advisory Circular AC No: 25.807-1 UNIFORM DISTRIBUTION OF EXITS. Note regulation number has changed since AC was written.

Overwing escapes have their benefits too….

https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/1500x1000/img_1027_0669564c1f7ee2cbe0497c305248a3594fdfc37b.jpeg

[SRMman]

Another big Dominic Gates article in the Seattle Times today 14th Jan.

Unfortunately I've reached my limit of free articles but for those with access its entitled "Boeing and U.S. aerospace set back by Alaska Airlines fuselage blowout".

[MarineEngineer]

Just delete the site cookies and you'll be able to read another three, free articles!

[Jet Jockey A4]

Another big Dominic Gates article in the Seattle Times today 14th Jan.

Unfortunately I've reached my limit of free articles but for those with access its entitled "Boeing and U.S. aerospace set back by Alaska Airlines fuselage blowout".

Here we go a link to the article... https://www.seattletimes.com/business/boeing-aerospace/boeing-and-u-s-aerospace-set-back-by-alaska-airlines-fuselage-blowout/

It may take up to a month before United and Alaska can have their MAX 900 aircrafts in the air... Alaska is cancelling between 110 and 150 flights a day because of the MAX 9 being grounded.

[AerocatS2A]

I see your logic.

However, would a transient event that causes the AUTO FAIL indication cause the ALTN system to also indicate if that transient event was no longer present?

Isn't it possible that the condition was no longer present when ALTN was active?
In the NTSB media briefing they say there is “no indication whatsoever that [the pressurisation controller issues] correlate in any way to the expulsion of the door plug”. That’s not “we don’t know”, that’s them saying it’s not related as positively as they can in an investigation that hasn’t been completed.

[DIBO]

AAR says they dont touch plug doors. However satellite image shows some kind of ramp near the location of that door on some variant of the 737 unable to see if it is a MAX 9. Look for AAR in Oklahoma on Google maps (i am not allowed to post the image because I am a new user).
I think the NTSB should look into this despite the claims of the MRO.
https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/759x382/aar_elevated_workplatform_91a93ac4b11827d3083c0e596c177fad45 096b40.jpg
I think, for now, better not call the NTSB...

[DaveReidUK]

specially if the forensics find markings on the bolt holes and where the door rests indicating that there was a bolt there at some point. If not then I guess the most likely scenario is still them being missing from the get go.

Not forgetting the scenario where the bolts were initially fitted, but the nuts were never split-pinned ...

[WillowRun 6-3]

From Senate website:

Chair Cantwell’s letter to FAA Administrator Michael Whitaker:

By letter dated January 26, 2023, I requested that the Federal Aviation Administration (FAA) initiate a new Special Technical Audit of 11 areas related to Boeing’s production systems. In the Agency’s response dated April 4, 2023, former Acting Administrator Billy Nolen stated that such an audit was not needed because “the agency has [already] implemented tools to complete audits [of Boeing] for the bulk of this information at regular intervals.” FAA’s reply pointed to the Quality System Audit (QSA) program, which evaluates manufacturers’ production systems to ensure compliance with FAA regulations.

Recent accidents and incidents—including the expelled door plug on Alaska Airlines flight 1282—call into question Boeing’s quality control. In short, it appears that FAA’s oversight processes have not been effective in ensuring that Boeing produces airplanes that are in condition for safe operation, as required by law and by FAA regulations.

To help the Committee determine whether FAA’s oversight processes are effective, please provide us with copies of notification letters from the last 24 months for all Quality Systems Audits of Boeing and for all Supplier Control Audits of Spirit AeroSystems. Also, please provide us with copies of any reports relating to these audits and any letters of investigation or other documents provided to Boeing or Spirit AeroSystems following the audits.

Specifically regarding Spirit AeroSystems, please provide the Committee with an explanation of FAA’s oversight of Spirit’s production system and of FAA’s oversight of Boeing’s supplier control system as it relates to Spirit. Please identify what, if any, improvements in oversight by FAA that you intend to implement to ensure that Spirit’s future performance meets all FAA regulatory requirements.

In reviewing FAA orders on how oversight processes are to be conducted, it appears that there may be ways for manufacturers to avoid audit accountability. For example, FAA Order 8120.23A requires that, before performing a Quality System Audit, the Agency must provide 50 days advance notice. This generous notice period clears the way for manufacturers to correct noncompliant conditions prior to the audit, ensuring that non-compliant conditions are rarely if ever detected during an audit. In effect, manufacturers must only get their house in order once an audit is announced.

While the order directs FAA audit teams to determine whether the manufacturer has various documented procedures, it is not clear from the order to what depth the audit teams review manufacturers’ performance to determine whether they comply with their own internal requirements. For example, the order requires auditors to “[p]erform, as necessary, a combination of document and product reviews to determine if the quality system element meets applicable requirements,” leaving the depth of the reviews to the audit team’s discretion. How is the FAA ensuring that documented procedures are being routinely and uniformly followed?

Finally, we are aware that several years ago, Boeing initiated a “Verification Optimization” program that resulted in eliminating thousands of quality inspections on each airplane, relying instead on mechanics self-verifying that they performed their work properly. This resulted in the elimination of 900 quality inspector positions. This program was implemented for several years and would appear to be contrary to FAA’s requirements that production certificate holders have inspection programs that are adequate to ensure that products conform to their type design. Has the FAA verified that Boeing’s inspection program complies with FAA requirements for production certificate holders? If so, please explain how FAA has verified Boeing complied?

We are aware that the FAA has initiated at least two investigations in the past in relation to this Verification Optimization program. Under FAA enforcement policy, recurring violations of this type require legal enforcement action. Please advise of the status of any enforcement actions and outcomes. And please advise the Committee as to whether this program has been rescinded and that an adequate inspection program has been restored.

I request that you provide a written response by January 25, 2024. Thank you for your prompt attention to these important matters.

[Editorial note from this SLF/attorney: In the practice of employment and labor law over the course of, let's say close to four decades, many instances of staff reductions, downsizing, reductions in force, and so on were encountered. Still, tagging the elimination of 900 positions, that is 900 quality inspector positions, as "Verification Optimization", . . . well, innovation truly isn't gone from Boeing, it's just moved into cynical manipulation of language, in this instance anyway.]

[WHBM]

In reviewing FAA orders on how oversight processes are to be conducted, it appears that there may be ways for manufacturers to avoid audit accountability. For example, FAA Order 8120.23A requires that, before performing a Quality System Audit, the Agency must provide 50 days advance notice. This generous notice period clears the way for manufacturers to correct noncompliant conditions prior to the audit, ensuring that non-compliant conditions are rarely if ever detected during an audit. In effect, manufacturers must only get their house in order once an audit is announced.

For all that this covers some formalised audits (and there's presumably nothing to prevent giving notice that you will be doing such an audit on the 1st Monday of every month), aircraft in production have always as standard had permanent on-site inspectors from the customer. Alaska Airlines will presumably have (one or more) fully qualified engineers in the Renton plant specifically to oversee assembly of their own aircraft. And far more, Boeing as customer will doubtless have staff at Spirit, overseeing the whole production process of the fuselages. I believe they even put someone on the train taking the fuselages from Wichita to Seattle.

Now these "client representative" staff will be looking absolutely at the manufacturing process in detail, compliance with procedures, seeing the daily work plan, walking round the aircraft for much of their time, etc. An interesting task, one or two who have had this role previously have even posted their experiences on here in the past. Engineers are sent from all over the world to Boeing to oversee what is being built for them - Alaska Airlines doubtless have the easiest time of all, given that their corporate HQ and principal maintenance base is just down the street from Renton.

[OldnGrounded]

https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/759x382/aar_elevated_workplatform_91a93ac4b11827d3083c0e596c177fad45 096b40.jpg
I think, for now, better not call the NTSB...

Right. Looks pretty much like a setup for installing the WiFi system.

[EXDAC]

https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/759x382/aar_elevated_workplatform_91a93ac4b11827d3083c0e596c177fad45 096b40.jpg


Doesn't that image show a work stand and shelter aligned with the position of the antenna system? Doesn't that image also show that the top of the work stand is almost at the top of the door opening and would not provide any useful access to the interior if the plug was open or removed?

I'm not saying the image proves that the door plug is not opened or removed but, as shown, I don't see that it offers any proof that it is opened or removed.

[DIBO]

I think it gives a pretty good indication on where, how and what they were up to, given the roof-top mounted wifi dome was part of their mission. And at first sight, that does not include any plug door activity.:rolleyes:
So that is why I included in my original post (https://www.pprune.org/accidents-close-calls/656760-alaska-airlines-737-900-max-loses-door-flight-out-pdx-48.html#post11576103)
I think, for now, better not call the NTSB...

[vikingivesterled]

I'm not sure what diameter the arrestor bolts are because my eyeballing skills aren't up to it, but they must at least be 6/32. Your basic vanilla 6/32 bolt has a shear strength around 2000 lbs. The two at the bottom have two shear planes each so each one is good for 4000 lbs.


But what if in the confusion of bolt definition they used an available fully threaded bolt (called set screw (with no head they are called grub screw)) instead of one only partially threaded (just called bolt). How much would that reduce the shear strength. And in this case it's bending and hitting/pushing on the middle by the roller pins strength we are talking about, not pull strength.
(Definitions on bolt type names are from the website of the supplier of stainless steel hardware inox.ie)
This could also have been done by a Spirit employee and especially if they thoght Boeing routinely would replace them later.
They could even have used non hardened bolts.

That Alaska plane needs to be taken apart to see if not at least one bolt have fallen into a gap and down into the belly of the plane. If they did fail its unlikely they all failed at the same time.
And I wouldn't worry to much about lose bolts on other planes. It's the precense of the bolt that is important. Not its thightness. And a castellated nut with a split pin would stop it coming out altoghether, unless it was broken in two.

[DaveReidUK]

But what if in the confusion of bolt definition they used an available fully threaded bolt (called set screw (with no head they are called grub screw)) instead of one only partially threaded (just called bolt). How much would that reduce the shear strength. And in this case it's bending and hitting/pushing on the middle by the roller pins strength we are talking about, not pull strength.
(Definitions on bolt type names are from the website of the supplier of stainless steel hardware inox.ie)
This could also have been done by a Spirit employee and especially if they thoght Boeing routinely would replace them later.
They could even have used non hardened bolts.

I could attribute many potential issues to Boeing and/or Spirit. But not knowing the difference between a bolt and a set screw isn't one of them.

[EXDAC]

(Definitions on bolt type names are from the website of the supplier of stainless steel hardware inox.ie)
.

I searched the inox.ie site for "set screw". I found no definition and no products. Where did you find the definition you quoted?

It's easy enough to find specs for set screws that are fully threaded with no head e.g. AN565.

[Pinkman]

Set Screw (US) = Grub Screw (UK/IE)

[DaveReidUK]

Door plug on arrival at NTSB's Materials Lab:

https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/2000x1333/unpacking_door_d2cdc6788e860af328a17cb00efa40b8655b1132.jpg

Fractured roller guide can be clearly seen at the corner nearest the camera.

[Edoil17]

Hmmm. Looking at the setup for Wi-Fi installation, it does not look ideal. I'm sure they would need to cut / drill holes in upper fuselage (all this being done outside, albeit under cover of a tent).
Post installation, would, from experience require some form of cabin pressurisation checks, to confirm that the fuselage was sufficiently airtight to return to service post this work being carried out.

[vikingivesterled]

I searched the inox.ie site for "set screw". I found no definition and no products. Where did you find the definition you quoted?


Under the tab Bolts, then select "Bolts & Set Screw - Hex Head"
It's in the 2 first lines of the Product Details:
"Stainless Steel Set Screws are fully threaded and have hexagon heads.
Stainless Steel Bolts are part threaded and have hexagon heads."

Question is also wether a Clewis Pin would have been the better application for this type of use.
It is what is seen as a stronger part than bolts for holding marine rigging together, also avoiding chance of deformation or fracturing the roller guide in this case, by overthigthening the bolt.
A partly threaded bolt would have had to be made to exact length specification of the non threaded part to avoid pinching. Again these bolts did not pull something together but just acted as a blocker for the rolling pin and the spring load mechanisme. A Clevis Pin would also avoid the possibility of forgetting the split pin since it is the only thing holding it in place. The added castellated nut of a bolt would probably be useless anyway without the split pin.

I alo see some comments on how the split pins before where bent in a certain way. This overbending has been abandoned in the marine industry unless snagging is a factor, because sharp bends is found to weaken the pin. A slight split of the 2 ends to an angle of about 30 degrees between the two is enough to keep it in place in even the storms of the southern polar regions, and simplifies removal.

[incompleteness]

https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/759x382/aar_elevated_workplatform_91a93ac4b11827d3083c0e596c177fad45 096b40.jpg
I think, for now, better not call the NTSB...
That image is weird. The v-stab is perforated and its got odd blobbiness all over like you see in AI images.

[Solofast]

Not forgetting the scenario where the bolts were initially fitted, but the nuts were never split-pinned ...

If the bottom bolts were installed, even without nuts and split pins they won't just fall out. The reason is that the springs would jam the lower fittings up against the bolts and that constant force would prevent them from coming out. Once those bolts are in place if force isn't supplied to push the door down off the bolts, then they are restraining the springs and the bolts aren't moving, let alone falling out. Doesn't matter if the bottom nuts were installed or not, those bolts won't fall out on their own. This is why it is clear the bolts were never installed.

[EXDAC]

Under the tab Bolts, then select "Bolts & Set Screw - Hex Head"
It's in the 2 first lines of the Product Details:
"Stainless Steel Set Screws are fully threaded and have hexagon heads.
Stainless Steel Bolts are part threaded and have hexagon heads."


Thanks for the reference. It includes the statement - "Set Screws are manufactured to DIN 933 and Bolts to DIN 931."

The problem is that DIN 933 does not, at least as far as my search has gone, define set screws or even mention set screws. The primary characteristic of DIN 933 appears to be "full thread". They come with a variety of head types but none are set screws as set screws have no head.

https://www.fastenermart.com/files/DIN931-933-ISO4014-4017-JISB1180-Specifications.pdf

As far as aviation fasteners are concerned I have more confidence in AC 43.13-1B, NAS specs, and MS specs, than an Irish bolt manufacturer's web site that appears to list no aircraft or aviation products.

[OldnGrounded]

https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/1234x944/aar_google_maps_2024_01_14_19_05_48_3ef77bf060c355a37943cc3a 6fc389d1ea28aac4.png
Grabbed from Google Maps just now. https://www.google.com/maps/place/6611+S+Meridian+Ave,+Oklahoma+City,+OK+73159/@35.4027296,-97.6025357,152a,35y,180h,39.33t/data=!3m1!1e3!4m6!3m5!1s0x87b2120e387fa4c5:0xde8df55cb2f208b 7!8m2!3d35.3996039!4d-97.60179!16s%2Fg%2F11bw3zsy9_?entry=ttu
That image is weird. The v-stab is perforated and its got odd blobbiness all over like you see in AI images.

I think it's most likely an AI-assisted enlargement of a 3D satellite image, either not the latest & greatest AI or one in which AI has not been permitted to get too creative. It seems to have filled in some spaces where there was limited information available, but not attempted to paint in every possible detail.

[Loose rivets]

Fractured roller guide can be clearly seen at the corner nearest the camera.

I think the vital thing to notice is just how slight the deformation of the out edge of the guide is. i.e., it really spells out just how short the roller/pin is compared to the available depth.

[BigJETS]

Door plug on arrival at NTSB's Materials Lab:

https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/2000x1333/unpacking_door_d2cdc6788e860af328a17cb00efa40b8655b1132.jpg

Fractured roller guide can be clearly seen at the corner nearest the camera.
Not only are the guides damaged, but both skins at top corner rib structure, appear separated; as if the bottom of the plug let go, pivoting on the upper guides and prying against top of opening until the top guides finally broke out. Perhaps due to both lower hinge guide fittings separated from plug the instant vertical motion clears 12 stops, but before top guides released. ?

Also Re: The wifi install photo, is pretty definitive. The plug occupies the 10th window placement from aft. Would appear to be sealed in this photo.

[Oro-o]

Not only are the guides damaged, but both skins at top corner rib structure, appear separated; as if the bottom of the plug let go, pivoting on the upper guides and prying against top of opening until the top guides finally broke out. Perhaps due to both lower hinge guide fittings separated from plug the instant vertical motion clears 12 stops, but before top guides released. ?….

I was just about to ask about that. I had marked up the photo to highlight it. It would not have happened on impact in soft water-logged ground; it had to have been pre-existing or during separation.


https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/925x500/cdbffa27_6363_46a3_b383_f2304718dd99_b82fa62c7c08534e7bb8a51 24197290e16876ce0.jpeg
Red indicators for highlighting.

[Solofast]

But what if in the confusion of bolt definition they used an available fully threaded bolt (called set screw (with no head they are called grub screw)) instead of one only partially threaded (just called bolt). How much would that reduce the shear strength. And in this case it's bending and hitting/pushing on the middle by the roller pins strength we are talking about, not pull strength.
(Definitions on bolt type names are from the website of the supplier of stainless steel hardware inox.ie)
This could also have been done by a Spirit employee and especially if they thoght Boeing routinely would replace them later.
They could even have used non hardened bolts.

That Alaska plane needs to be taken apart to see if not at least one bolt have fallen into a gap and down into the belly of the plane. If they did fail its unlikely they all failed at the same time.
And I wouldn't worry to much about lose bolts on other planes. It's the precense of the bolt that is important. Not its thightness. And a castellated nut with a split pin would stop it coming out altoghether, unless it was broken in two.

The bolts used here would never be full threaded bolts. The bolts used would have unthreaded shanks and are clearly drilled for split (cotter) pins. To be drilled for split pins they aren't #6 and most likely aren't #10's (although they could be but I highly doubt it). It's far more likely that these are 1/4 inch AN bolts with an ultimate strength of 125ksi. They could even be A286 material as that is more corrosion resistant. A286 bolts have an ultimate strength of 160 ksi. A quarter inch bolt in double shear is good for about 5500 pounds of force each. That would apply to the lower bolts. You're looking at it requiring 11000 pounds of force to shear just the lower bolts, never mind that you have to get past the upper bolts too. The upper bolts are in bending since they are loaded by the roller, The person who designed this was very smart. In this design the upper bolts can bend some and thus share the load with the lower bolts. If the upper bolts were in pure shear then all of the bolts need to be in contact at the same time to make sure they share the load. With this design it's going to take significantly more load to get past the bolts if they are in place. The amount of vertical force to move the door off of the pads is likely well over 15,000 pounds. That is the lower bolts require bout 11000 pounds to fail in shear, and the upper botls are likely about half that and they fail in a combination of shear and bending since they're essentially a simply supported beam with a center loading. The bottom line is that if the bolts are in there the door isn't moving since there are no appreciable loads in that direction and it will require more than 7 TONS of load to move the door up with the bolts in palce.

[MechEngr]

Not only are the guides damaged, but both skins at top corner rib structure, appear separated; as if the bottom of the plug let go, pivoting on the upper guides and prying against top of opening until the top guides finally broke out. Perhaps due to both lower hinge guide fittings separated from plug the instant vertical motion clears 12 stops, but before top guides released. ?

Also Re: The wifi install photo, is pretty definitive. The plug occupies the 10th window placement from aft. Would appear to be sealed in this photo.

Perhaps the last gasp from the restraining cables after the guide brackets let go.

[jimjim1]

I was just about to ask about that. I had marked up the photo to highlight it. It would not have happened on impact in soft water-logged ground; it had to have been pre-existing or during separation.


https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/925x500/cdbffa27_6363_46a3_b383_f2304718dd99_b82fa62c7c08534e7bb8a51 24197290e16876ce0.jpeg
Red indicators for highlighting.

If the door was freed from the 12 stop pegs the roller pin might still be retained within the top guide. If the bottom moved out under the influence of cabin pressure then damage to the top consistent with the images could occur. The very top lip would be forced inboard, pivoting round the guide, causing the separation of the skin from the frame shown until eventually the guide failed. Then both the top and bottom of the door would be free to open.

In this scenario the door's upward translation would be interrupted by being jammed between the outward force on the guide roller and the inward force on the top edge of the door on the frame.

[aox]

Thanks for the reference. It includes the statement - "Set Screws are manufactured to DIN 933 and Bolts to DIN 931."

The problem is that DIN 933 does not, at least as far as my search has gone, define set screws or even mention set screws. The primary characteristic of DIN 933 appears to be "full thread". They come with a variety of head types but none are set screws as set screws have no head.

https://www.fastenermart.com/files/DIN931-933-ISO4014-4017-JISB1180-Specifications.pdf

As far as aviation fasteners are concerned I have more confidence in AC 43.13-1B, NAS specs, and MS specs, than an Irish bolt manufacturer's web site that appears to list no aircraft or aviation products.

Reminder

Set Screw (US) = Grub Screw (UK/IE)

And from other posts in the thread, set screws here have heads

There is something similar happening with split pins (UK) and cotter pins (USA). However here, and I suspect also in USA, a cotter pin is wedge tapered pin that secures a crank arm to a shaft or axle, such as old style bicycle cranks to the bottom bracket spindle before the development of tapered, square ended, cotterless crank systems.

[DaveReidUK]

The reason is that the springs would jam the lower fittings up against the bolts and that constant force would prevent them from coming out.

That's partly dependent on the weight of the door plug at any given point versus the spring force.

We know its mass, but I'd be very surprised if it's never subjected to more than 1g during flight.

This is why it is clear the bolts were never installed.

We'll find that out soon enough from the NTSB's metallurgists.

[NSEU]

That is a different question from the spring force, but I agree with you.


I believe one of the Chris Brady videos states the maximum local wind specification for the plug (or door when installed). Definitely less than 271 KIAS.

Give Boeing engineers some credit, the self-ejecting plug design has breakaway features.
From Chris Brady video

What is the dynamic pressure at 271 KIAS at 16,000 feet?

Is this the right calculator for computing this?

https://www.spaceworks.aero/fcc/index.html

If so, I only get 1.05psi.

How tall/deep is the plug? i.e the side profile

[MarineEngineer]

I note that the lift assist brackets are completely missing.

[Jhieminga]

You need to convert the 271 KIAS to TAS (use https://indoavis.co.id/main/tas.html for example) and then convert that to ft/s. I have guessed at some of the values or used standard values, but that gets me 283.75 lbf/ft^2 or 1.97 psi.

[DTA]

Unfortunately there are still no photos that show what if anything remains of the forward green hinge bracket. The NTSB lady managed to get her arm in just the wrong place.
I was just about to ask about that. I had marked up the photo to highlight it. It would not have happened on impact in soft water-logged ground; it had to have been pre-existing or during separation.



Red indicators for highlighting.
I think there was a photo showing that the plug ended up in a tree or bush. Not that it makes any difference.
Not only are the guides damaged, but both skins at top corner rib structure, appear separated; as if the bottom of the plug let go, pivoting on the upper guides and prying against top of opening until the top guides finally broke out. Perhaps due to both lower hinge guide fittings separated from plug the instant vertical motion clears 12 stops, but before top guides released. ?

Also Re: The wifi install photo, is pretty definitive. The plug occupies the 10th window placement from aft. Would appear to be sealed in this photo.
Whilst having the bottom of the door plug move out would explain the separation of the skin at the top it is hard to see how the bottom could have moved out first. The two shafts remain attached and the rear bracket mounting bolts appear to have been broken by considerable force suggesting the rear bracket at least was correctly in place (though probably not with a lock bolt).

[Oro-o]

…
I think there was a photo showing that the plug ended up in a tree or bush. Not that it makes any difference.

….

I agree, I don’t think that makes any difference. For reference, here is the reported position in which it was it was found. It passed through some canopy above, I believe. This was in the Seattle Times article yesterday.


https://cimg3.ibsrv.net/gimg/pprune.org-vbulletin/2000x1504/41ba4e83_a3c1_41dc_9bdf_8b69f3d5ed83_3fb1b915a7057bd5e460d07 86fe1e49e396ee367.png

[aox]

Sidetrack question: if a lot of the aircraft is made of carbon fibre, why isn't that door/plug?

[Less Hair]

It is not made mostly of carbon fibre but aluminium.

[DTA]

I agree, I don’t think that makes any difference. For reference, here is the reported position in which it was it was found. It passed through some canopy above, I believe. This was in the Seattle Times article yesterday.



This is the image I was thinking of.

https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/767x1023/kweirhlstzfobpvohyvdibabw4_3cdf5654c901b801bf3adaa14f21fc19a e9e4790.jpg
I think the one in your post is where it was moved to after being found.

[aox]

Ok. Maybe only the later designs.

[Oro-o]

I note that the lift assist brackets are completely missing.

And if you look at the bottom of the plug, the aft hinge assembly apparently put up a little fight, and the forward one not as much. You can note the aft, lower inner frame is bent outwards from contact with the aft hinge pin assembly, and some of the outer paint is rubbed through to the zinc chromate layer underneath (inside blue circle). Or it at least looks like abrasion in the low-res photo, and not paint popping off from deformation.

Perhaps the last gasp from the restraining cables after the guide brackets let go.

I don’t think that could cause an issue between the skin and the frame - the yellow arrow shows the restraining cable attachment, via that ring to the frame. Looks like the cable parted at the door end, which was connected to the frame.

So both aft connection points did not let go cleanly, but were forced - 1) the forced upper guide track and 2) the bent lower hinge area. I’m sure the NTSB people already know how this happened, with access to the whole unit and ability to examine the whole assembly, bolt holes, etc.

https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/1134x691/40f91990_e354_4378_8aed_cd1a9c4cc444_ac4983d9eed9b62685c8c40 0cde2bde45ce1de3a.jpeg

[incompleteness]

One thing the NTSB lab photo shows, I think, is that the lower hinge post guide fittings are attached to the door with one-lug nutplates. You can see them beside the NTSB lady's arm.

Something like MS21061. It's interesting because the places I've worked usually avoid one-lug nut plates when possible due to the risk of attachment rivet breakage. Non-trivial disassembly of structure is usually required to replace them.

[A0283]

Fractured was word used by Mrs H early on for the top guides… photo not good quality, but looks a bit more like folded open… was not much flesh on the bracket there in the first place…

scenario option … 14,830ft 271kt 14.09psi.. top opens up …press 11.64 psi…plug caught be airflow opens wider, rips steel wire… 15,859ft 271kt 9.08psi … plug flips 90 deg down, then ripped off, … low hinges departure prevents plug from hitting the horizontal stabiliser …

forward (in DOF) hinge stripped, aft hinge ripped,

[TryingToLearn]

Why does the door plug look overdesigned, with heavy machinged members? The main reason is because it works as a curved plate to carry the pressure, which means there is a lot of plate bending in the structure. Baseline fuselage structure works as a pessure vessel with primary loads in tension. Plate bending is structurally inefficient.

Why don't they bolt together the stop pads and stop fittings? That's because it would change the load paths. Doors are designed not to pick up general fuselage loads, they sort of "float". So if you created bolted connections to the fuselage at 12 points, the door would become primary structure and you would have to redesign local fuselage frames, intercostals, and skins, and add a nontrivial certification item to cover just the plug doors. For design, analysis, and testing, you are potentially looking at 7 figures.
This statement made me think of another possible chain of events:
The tension in the fuselage (along the circumference) will expand the doorframe, increasing the distance between roller pin and hinges.
Bending of the door will do the opposite to the upper guide track and hinge brackets.
If there is not enough play in the bolts and roller guide (remember the slotted holes on the hinge brackets which allow adjustment), the plug will take over fuselage tension due to pressure differential.
If this tension is strong enough to break/shear the lower bolts, stored energy may just be enough to snap the plug up off the lower pads and/or break the upper bolts or guide track.

Just another theory which would imply wrong adjustment (or design), not missing parts. But it somehow fits to the pictures so far.

This failure mode would be unique to the plugs, not applicable to the emergency doors. The 'real' emergency door design does not limit the 'floating' of the door on the pads as the plug does since the hinges are not blocked. Four bolts in all four corners on the plug counteract the intention of having the door/plug float on pads and decoupling it from the fuselage tension. Maybe they accidentially bolted the plug in the fuselage tension load path trying to have redundancy on the bolts.

Is there any difference in fuselage stiffness between NG/ER/MAX versions equipped with plugs? Could this be a contributing factor?

Are those loose nuts on the other planes really loose or did excessive tension stretch the screws, actually preventing further accidents?

I hope they will find the right answer.

[safetypee]

Without learning, history will repeat;
"Boeing was really, really bad at building airplanes"

https://valkstrat.com/the-myth-of-old-boeing/

[EXDAC]

I wonder when "UP" and FWD" with corresponding arrows were marked on the door plug. Would those marking have been required for production assembly or only for someone unfamiliar with how the plug was fitted.

[DTA]

I wonder when "UP" and FWD" with corresponding arrows were marked on the door plug. Would those marking have been required for production assembly or only for someone unfamiliar with how the plug was fitted.
They were not visible on the earlier photos.

[MarineEngineer]

It's to differentiate it from any right-hand doors that fall off!

[D Bru]

I wonder when "UP" and FWD" with corresponding arrows were marked on the door plug. Would those marking have been required for production assembly or only for someone unfamiliar with how the plug was fitted.

Photos from Bob's garden are w/o those markings. So I presume it was the NTSB putting them after retrieval "out a an abundance of caution" ;)

[retiredCSE]

After installing WIFI antenna they must have done a pressure test of the cabin . After that the Warnings from the pressure systems started . What if the test moved or damaged something in the door plug . It has happened before on a Boeing in Oklahoma City that too much pressure during test caused big cracks in the fuselage . USAF KC-135. In 1999 .

[BigJETS]

One thing the NTSB lab photo shows, I think, is that the lower hinge post guide fittings are attached to the door with one-lug nutplates. You can see them beside the NTSB lady's arm.

Something like MS21061. It's interesting because the places I've worked usually avoid one-lug nut plates when possible due to the risk of attachment rivet breakage. Non-trivial disassembly of structure is usually required to replace them.
Agree, I would not expect nutplates to be used for attaching the guide blocks here. They are much weaker compared to a tension nut. Its not a blind access location either. In this case however, it appears the bolts were never tightened/installed because the nutplates seem intact. If this had any to do with the nutplates, they would be pulled or deformed. Still seems odd to use them there. Its assumed those blocks are never required to retain the plug once its captured by the 12 stop lugs.
We still cant explain the missing fwd guide. The easiest explanation: it was never there.

[MechEngr]

The fasteners would have been subject to shear loads rather than tension loads. This would have put the screws against the sides of the holes in the door. If they are replaceable element nut plates, the float of the nut plates would isolate the nutplate rivets from load. They may even have just turned with the rivet as the pivot to allow that contact.

[BigJETS]

Whilst having the bottom of the door plug move out would explain the separation of the skin at the top it is hard to see how the bottom could have moved out first. The two shafts remain attached and the rear bracket mounting bolts appear to have been broken by considerable force suggesting the rear bracket at least was correctly in place (though probably not with a lock bolt).
I agree its difficult to explain anything related to the lower hinge assys and the connection to the plug via guide blocks. I am going on the assumption that mutiple hardware was missing or not installed, in addition to at least the top two lockbolts. If the guide blocks are not fully attached to the plug, then the hinges are not much of a factor.
The damages on the bottom rib are when the hinges were ripped out of the plug. It appears to me, they didnt pull straight out cleanly, but rather the plug was released bottom first, and pivoted on the top guides perhaps 10 degrees, which caused the bottom hinges to be removed violently against the rib structure. (It is this chain of events which dictated whether the plug went around, or straight into the H.Stab)

[Yogi62]

If the bottom of the plug pivoted out, causing the top of the plug skin to hit against the opening at the top and causing the observed separation damage in the lab photo, would there not be witness marks on the the top of the plug door frame/fuselage skin? Are there any good pictures of the outside of the plane at the top of the opening?

[ScandinavianInterest]

When comparing the picture from the NTSC lab to a Seattle Times entry "Boeing and U.S. aerospace set back by Alaska Airlines fuselage blowout" (I am not allowed to include URL, sorry) then I observe on the ST picture that all of the bolts are locked with a green locking compound, including the 12 studs. This I cannot find on the studs of the plug at the NTSC lab. I do as well miss the hole for the locking bolt in the guide track. Is it hidden due to warping of the of the guide track?

[ewumnrr]

There are witness marks on the stop pads from the door resting on them. Could be damage from the departure but could also be rub marks over a longer period.
I think the door first went up a bit and the pins were no longer resting against the stop pads but the flange that holds the stop pins. During that period, there were probably leaks around the door which would explain the pressure system detecting fluctuations.
The question arises then if it would have been possible to see the plug sticking out a quarter inch during that time which might have been days / weeks. It would have been up half an inch as well.

[remi]

Without learning, history will repeat;
"Boeing was really, really bad at building airplanes"

https://valkstrat.com/the-myth-of-old-boeing/
Requirements and production systems are different in aerospace, where extreme requirements are placed on both traceability AND safety AND even reliability. Defense programs can often make do with less safety. Transportation networks can make do with less traceability and reliability.

Any system that is working well to fulfill the above is doing its job better than one that is newer and more efficient but less good at fulfilling key needs.

Replacing old but tried and true processes in commercial aerospace is hard to do right. It might seem right from a financial and ability perspective, but those are not what keep large, deliberate aerospace enterprises running successfully.

Boeing would be better off with a corporate structure that has no shareholders.