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

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

Old 7th Jan 2024, 22:53
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Castle nut for installed upper bolt (From the Chris Brady video)
Edit to add: In this image the door is on the left and aircraft door frame is on the right.


Last edited by lateott; 7th Jan 2024 at 22:56. Reason: Additional description
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Old 7th Jan 2024, 22:56
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Originally Posted by lateott
The bolt is not in that location. From the most recent Chris Brady video it is actually perpendicular and its nut is visible in the photo as marked by the blue arrow below:
Yes, I now agree. But why the appearance of an internal thread to the stub post. Maybe there is the small bolt you show and the bolt I envisioned.
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Old 7th Jan 2024, 22:57
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Originally Posted by OldnGrounded
"It's not our fault, it was the subcontractor!" Not a very persuasive defense argument.

Perhaps, since there is a known, ongoing QA problem at Spirit, someone at Renton should be doing those inspections.
Maybe it would be better to say 'Perhaps, since there is a known, ongoing QA problem at Spirit, someone at Renton should be doing lots more of those inspections'.
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Old 7th Jan 2024, 23:11
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Originally Posted by Equivocal
Maybe it would be better to say 'Perhaps, since there is a known, ongoing QA problem at Spirit, someone at Renton should be doing lots more of those inspections'.
Last time that occurred, the Renton QA Staff visited the supplier to Boeing who was doing the ring frames for the NG, and noted that the frames which the production approvals had been based on CAM milling, were being done by hand, over an unapproved homemade jig. The supplier had stated the components were CAM fabricated, and they didn't own a CAM unit. Upshot, Boeing sacked the QA inspectors, and Boeing actually won in court against wrongful dismissal action by the inspectors. The FAA did... nothing. The bogus parts are still flying around today.

Great system. Great company. Great concept of QA.
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Old 7th Jan 2024, 23:23
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Originally Posted by Feathered
All technically correct, but Boeing will proudly say that they are responsible for the entire aircraft delivered. I believe Boeing owns the type certificate for the entire airframe,not just parts not built by Spirit.
If Spirit is building junk and delivering it to Boeing Renton without proper QA, why is Boeing accepting junk without proper QA?

What other flaws, problems, defects, missing fastener nuts, oval bulkhead holes, flawed flight control software, extra wrenches, bonus rags, and other rubbish is Boeing also accepting and happily delivering as-is to customers?
PRECISELY
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Old 7th Jan 2024, 23:27
  #306 (permalink)  
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Flynerd You're looking straight at the locking bolt, end on. I'd imagine the centre hole is a machine turning indent, though I'm surprised it's there at all.


The length of that roller pin is still worrying me. Given that the door can move forward/aft a tad, the locking bolt is very near the end edge of that roller pin.

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Old 8th Jan 2024, 00:11
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I think we will find out that the lift assist springs were out of adjustment. I would guess they are not designed to be providing a constant upward force on the door, which would put a constant force on that locking bolt.

It's right there in the name, lift assist spring. So, for example, if the plug weighs 100 lb, then the spring may provide 70 lb of upward force, and a mechanic opening the plug would only have to provide 30 lb of force to lift the plug high enough for the door stop fittings to clear the fuselage stop pads. This setup would cause a constant downward force (from the weight of the plug) keeping the upper guide roller in the door upper guide track fitting. And no constant force on the locking bolts

If the lift assist spring was adjusted in such a way that there was a constant force applied to the locking bolts, then I could see how after 3 months of vibrations the two bolts wear down and eventually fracture, which would allow the door open on its own.
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Old 8th Jan 2024, 00:16
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The locking pins on the upper assemblies appear to hold the roller pin only at the tangential point where the roller pin contacts the locking pin, which rather than being limited to the normal perpendicular shear force, is able to flex against the pressure from the roller pin. Is there a chance that, in the absence of the locking pins on the lower hinge slides, that this pressure point - in the absence of a radius block to spread that shear force at perpendicular points of contact on the locking pin, cause the locking pin to fail, moving just enough to gradually unseat the 12 stop brackets?

Just speculation at this point. Hopefully they find the door somewhere around Beaverton or Lake Oswego soon.
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Old 8th Jan 2024, 00:18
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Relating to the question of why the plug opened on this particular flight an not any of the earlier ones:
As I understand it, while the springs provide an assist to lifting the door upward, they aren't sufficient to do it on their own. The weight of the door/plug is near, but still greater than, the force of the springs. The door needs someone to manually push it upwards to open. If this is true (and I stand eager to be corrected) then what kept the plug in place all this time is simply gravity. What caused the plug to finally move upwards may have just been a peculiarly angled jostle of the plane while airborne, imparting enough force in the right direction to move it past the stop fittings, and with enough pressure difference to then force it out.
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Old 8th Jan 2024, 00:31
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Boeing has dispatched a team of finance MBAs, lawyers and PR flacks to the scene to address the situation.
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Old 8th Jan 2024, 00:44
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Originally Posted by Loose rivets
Flynerd You're looking straight at the locking bolt, end on. I'd imagine the centre hole is a machine turning indent, though I'm surprised it's there at all.


The length of that roller pin is still worrying me. Given that the door can move forward/aft a tad, the locking bolt is very near the end edge of that roller pin.
That was my first observation also. The pin appears to barely reach to where the locking bolt is located. Given the (apparent) lightweight construction of this door (composite?) it would not take much central outward flex, shortening the lateral distance between the guides, to clear them completely.

Last edited by LapSap; 8th Jan 2024 at 00:56. Reason: corrected "door" not "plug"
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Old 8th Jan 2024, 00:47
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A couple comments:
1) Can we all agree that the missing part of the plane is a "door" that replaces an emergency exit "door, That it is NOT a "plug"?, it is not designed as a "plug", does not function as a "plug" under pressurization of the hull. In fact, it performs exactly the opposite. The outward forces work to stress the door against its retainers not the frame in any intrinsic or hermetic manner..

2) The missing door is fitted with a larger window than the emergency door it replaces. It seems from photos that there is less cross bracing in that design. However I am not jumping to conclusions that the door failed. It is more likely that the low altitude and missing bolts conspired to eject this door (not a plug).
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Old 8th Jan 2024, 01:21
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My first jet course was in the mid 60's. I've spent the rest of the time thinking a plug fit was a door that is pushed outward by pressure and plugs the hole. i.e., the BAC 1-11 had a front door with lugs and a g lock, while the back door was a plug fit. (the back door went to a ventral staircase through the pressure bulkhead.)

For what it's worth, I think the bolts were not fitted. However, the point I raised about the safety bolt being near to the end of the roller pin still nags. The end edge of that pin would make a modest but real cutting tool if it were playing on the curved side of the bolt. Having said this, I'd imagine just about all taxiing would be done with the aircraft pressurised and pad friction stopping relative movement. I can't imagine any other force jarring the door sufficiently vertically.
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Old 8th Jan 2024, 01:24
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Need the door itself to answer most questions. Dimension between LH and RH upper roller guides ( existing opening) would be of interest. Too far apart implies too wide of a door opening.
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Old 8th Jan 2024, 01:29
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Brady's video really helps understanding of the mechanism.

Speculation: If all four bolts are missing, the odd thumped on landing with minimal if any pressurisation could allow the springs to push up the plug. Whether it was one thumped landing or a few, the door ended up off the pads and let go the next time there was enough pressure.

Whatever the cause, the interior panel prevented crew and/or maintenance from seeing the plug was coming loose.

Most likely crews will in future promptly descend and evacuate seats if there's noise from the plug.

The inside panel needs to have view ports to allow verification the plug is properly seated. A paint stripe across the plug and adjacent fuse would show up during external inspection.
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Old 8th Jan 2024, 01:30
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Originally Posted by JamaicaJoe
A couple comments:
1) Can we all agree that the missing part of the plane is a "door" that replaces an emergency exit "door, That it is NOT a "plug"?, it is not designed as a "plug", does not function as a "plug" under pressurization of the hull. In fact, it performs exactly the opposite. The outward forces work to stress the door against its retainers not the frame in any intrinsic or hermetic manner..

2) The missing door is fitted with a larger window than the emergency door it replaces. It seems from photos that there is less cross bracing in that design. However I am not jumping to conclusions that the door failed. It is more likely that the low altitude and missing bolts conspired to eject this door (not a plug).
A door has handles you can use to open it. It’s a plug in the sense it fills the space a functioning door could also be installed. Focusing on wither it ‘plugs’ the hole like a bathtub stopper or not is getting pedantic.
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Old 8th Jan 2024, 01:35
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Passenger cell phone was found at this location:

https://maps.app.goo.gl/q7eg88CNRqgzFWDL9

Last edited by dragon6172; 8th Jan 2024 at 01:40. Reason: Format
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Old 8th Jan 2024, 01:36
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737 max emergency exit holding panel

Door sized hole blown off in flight.

When did the pressure sealing holes become latch held holes and why?
The old over wing exits used to require unlatching, pulling into the plane, then throwing onto the wing. New ones just pop the latch and pressure will open it. There is a solenoid latch to keep unwanted door operation now. Have given up design safety and security of the door pressure sealing for an interlock on a shaft.

And, now it seems that the panel holding the extra emergency exit was fastened from the outside? By bolts?

Someone please clarify this for me.
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Old 8th Jan 2024, 01:52
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Originally Posted by dragon6172
Someone here pointed out that the flying door/plug would probably give a clear primary radar return. Yesterday, NTSB Chair Homendy told the press briefing that the door/plug was likely to be found around Barnes Road and Highway 217.
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Old 8th Jan 2024, 01:56
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Originally Posted by OldnGrounded
Someone here pointed out that the flying door/plug would probably give a clear primary radar return. Yesterday, NTSB Chair Homendy told the press briefing that the door/plug was likely to be found around Barnes Road and Highway 217.
Interesting that this location is about 2 miles lateral separation from the aircrafts ground track according to flightaware/flightradar24. That seems quite a bit....
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