Alaska Airlines 737-900 MAX loses a door in-flight out of PDX
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And yet again we see the reluctance for U.S. pilots to declare MAYDAY!! MAYDAY!! MAYDAY!! that gets EVERYBODYS immediate attention rather than a mumbled call and where a controller had to ask "are you an emergency or do you just wish to return to Portland" that was after he stopped their descent at 7000' from what I could hear on the R/T recording, posted earlier. Unless, of course, you don't consider having a piece of your aeroplane falling off causing an explosive decompression (or should that be an unplanned pressure operated, gravity assisted, removal of a fuselage panel and internal atmosphere) A342
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Stupid question but..
Have a question about the plug.
In the video that MechEngr linked to, you don't see if the stop fittings will be on the inside of the stop pads or no.
If you compare with the door model, you can clearly see that it is on the inside in the closed position.
Can't link but search for "Climb on board Boeing's new 737 Max 9" on Google, it's the first link from Cnet, picture no.12.
Have a question about the plug.
In the video that MechEngr linked to, you don't see if the stop fittings will be on the inside of the stop pads or no.
If you compare with the door model, you can clearly see that it is on the inside in the closed position.
Can't link but search for "Climb on board Boeing's new 737 Max 9" on Google, it's the first link from Cnet, picture no.12.
Last edited by Intecler; 6th Jan 2024 at 22:57.
I guess this will put back the certification of the Max 10 by a few months. Also I wonder how many carriers use that as a proper emergency exit complete with slide equipment.
But the 737-9 is free to fly once the inspection that relates to the AD has been carried out.
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Informative video: https://www.youtube.com/watch?v=nw4eQGAmXQ0
Indicates a non-functional door was used rather than in-oping an exit door and suggest retaining bolts were missing. If so, then there will be a paper trail back to whoever signed off that the bolts were installed.
Indicates a non-functional door was used rather than in-oping an exit door and suggest retaining bolts were missing. If so, then there will be a paper trail back to whoever signed off that the bolts were installed.
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Facts and speculations:
1) This aircraft included a bottom-hinged mid-cabin plug, there was no mid-cabin door (fact)
2) At altitude the plug is normally retained against pressure differential by its 12 stop fittings positioned inside the frame's 12 stop pads (fact)
3) The plug design is spring loaded to lift itself 1.5 inch, clear its stop fittings from the frame's stop pads, swing down, and eject itself from the plane at flight speeds (facts with hyperbole)
4) Only 4 horizontal bolts are in place to counteract the spring-and-eject action of this plug design, 2 in the lower hinge brackets and 2 in the upper guide fittings* (believed to be fact)
5) 1 to 3 of the 4 bolts must have been missing, loose, over torqued, defective, wrong size, etc.** (speculation)
6) The 1 to 3 remaining bolt(s) loosened or sheared during the flight, allowing the plug to lift and eject (speculation)
7) Either the aircraft came from the factory that way or Alaska Air performed some improper maintenance on the plug in the last 2 months (speculation)
* Not entirely true, because if the plug is properly positioned during pressure differential there is also friction of the stop fittings against the stop pads which acts against the lifting spring force. Therefore, there may have been only a narrow window of pressure differential in which the plug lift-and-eject could have occurred. It's possible at higher altitude this could not have occurred, thereby somewhat limiting the potential consequences from (more) explosive decompression, altitude plunge, etc.
**I will speculate 2 bolts were missing, either the top 2 in the upper guide fittings, or the bottom 2 in the lower hinge brackets. Otherwise 2 or all 4 were over torqued or wrong size. If 4 bolts were missing, they never would have had any cycles, and it is unlikely a random defect would hit 4 bolts in the same plug. Therefore, human error during assembly or less likely maintenance.
IMO 4 bolts is not enough redundancy for this design when you consider the risk.
1) This aircraft included a bottom-hinged mid-cabin plug, there was no mid-cabin door (fact)
2) At altitude the plug is normally retained against pressure differential by its 12 stop fittings positioned inside the frame's 12 stop pads (fact)
3) The plug design is spring loaded to lift itself 1.5 inch, clear its stop fittings from the frame's stop pads, swing down, and eject itself from the plane at flight speeds (facts with hyperbole)
4) Only 4 horizontal bolts are in place to counteract the spring-and-eject action of this plug design, 2 in the lower hinge brackets and 2 in the upper guide fittings* (believed to be fact)
5) 1 to 3 of the 4 bolts must have been missing, loose, over torqued, defective, wrong size, etc.** (speculation)
6) The 1 to 3 remaining bolt(s) loosened or sheared during the flight, allowing the plug to lift and eject (speculation)
7) Either the aircraft came from the factory that way or Alaska Air performed some improper maintenance on the plug in the last 2 months (speculation)
* Not entirely true, because if the plug is properly positioned during pressure differential there is also friction of the stop fittings against the stop pads which acts against the lifting spring force. Therefore, there may have been only a narrow window of pressure differential in which the plug lift-and-eject could have occurred. It's possible at higher altitude this could not have occurred, thereby somewhat limiting the potential consequences from (more) explosive decompression, altitude plunge, etc.
**I will speculate 2 bolts were missing, either the top 2 in the upper guide fittings, or the bottom 2 in the lower hinge brackets. Otherwise 2 or all 4 were over torqued or wrong size. If 4 bolts were missing, they never would have had any cycles, and it is unlikely a random defect would hit 4 bolts in the same plug. Therefore, human error during assembly or less likely maintenance.
IMO 4 bolts is not enough redundancy for this design when you consider the risk.
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Thanks, that explains in detail the working of the plug type door. Door must slide upwards to de-align the stop fittings. Door was thus creeping up by vibration during ground ops until it popped open after some cycles. So a massive quality problem in assembly, since they most likely forgot to install the four safety bolts (no damage to the fittings)
I think you can see the hinges hanging out of the doorframe in post-incident photos at the gate.
If we knew assembly or maintenance procedures we might be able to better guess whether the top 2 or bottom 2 bolts were missing. You would need to put 1 or 2 bolts in just to hold the plug in the frame. Seems like for installation, the plug must be pulled into the frame from the mid/top of the plug, pushed down at the hinges to counteract the spring and align the stop fittings, then a bolt installed to hold it against the upward spring force while the remaining bolts placed and tightened.
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Comments section is very instructive. Boeing gaining criminal reputation by the minute. Justifiably so.
https://www.nytimes.com/2024/01/05/b...mentsContainer
https://www.nytimes.com/2024/01/05/b...mentsContainer
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Spring-eject is disabled at pressure difference by friction and on ground was probably avoided via glue by paint / stickiness of seals. These plugs are never opened. Maybe the springs not installed? Vibration in ground ops overcame the sticking after some cycles. At least the upper two bolts were clearly not installed or fell out, since the stop fitting eyes are completely undamaged on the pics.
Last edited by spornrad; 6th Jan 2024 at 22:18.
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Fortunately the area around door frames is strengthened, this is why a rear door is a least risk bomb location for a suspect package. It looks like a quality control issue.
From the video in post #131, the MAX 10 does not use the plug-type mid-cabin exit door that is central to this accident. Regardless, the MAX 7 is in the on-deck circle, not the MAX 10. Even though unrelated, this accident will make it much more politically problematic for the FAA to grant the engine anti-ice exemption for MAX 7 certification.
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As has been alluded to, it looks like the most likely explanation is Boeing neglected to put any bolts in! Of course, there will have to be detailed investigation to confirm if any bolts were fitted, but the pictures do not appear to show any evidence that any bolts were there at all. Other unlikely possibilities could be that the bolts were severely over torqued and fractured after a few pressurization cycles. The evidence may have been blown out the door. It highlights the importance of finding the dummy door plug to see if there are any remaining bolt stems or none at at all. Either way, it is likely the Boeing will have further explaining to do in respect of their procedures, safety and quality control. It is incredibly lucky that the incident happened at relatively low altitude. It is worrying that there have been a series of issues on this type that have, or could have, resulted in fatalities. I avoid these aircraft as a matter of principle. In my opinion, Boeing have got away with knowingly putting peoples lives at risk and there have been insufficient consequences. Passengers should vote with their feet and simply stop flying 737 Max as a protest.
There's what looks like quite an informative contribution by a former Boeing engineering guy (jimpalmer1969) in the comments section below Juan Browne's initial analysis.
https://www.youtube.com/watch?v=I9EvHpf8jZg
https://www.youtube.com/watch?v=I9EvHpf8jZg