Boeing 737-9 Max - two months old plane loses cabin window and panel

[flashcrash]

Blown-out plug door found in a backyard in Portland.

Plane part lost in dramatic mid-air blowout found (bbc.com)

[Gabriel]

That will be interesting. I hope they share photos soon.

[Evan]

Looks to me like 14 bolts holding it in place.

[sjwk]

Speaking at a news conference, Ms Homendy said pilots reported pressurisation warning lights on three previous flights made by the specific Alaska Airlines Max 9 involved in the incident.

The decision to restrict lengthy flights over water was so that the plane "could return very quickly to an airport" in the event the warnings happened again, the NTSB chief added.

It is not clear if there is a link between the issues that led to those warnings, and the issue that caused the blowout on 5 January.

"An additional maintenance look" was requested but "not completed" before the incident, Ms Homendy said.

https://www.bbc.co.uk/news/world-us-canada-67909417

[Highkeas]

Looks to me like 14 bolts holding it in place.

The video in post #26 says the panel is held in place by four bolts. Four bolts seems inadequate to me.

[Gabriel]

Looks to me like 14 bolts holding it in place.

12 of the 14 that you are counting are just stops, and they are what are holding the pressurization forces. Read the explanation below and I highly recommend watching the video in post #26.
Here the link again: https://www.youtube.com/watch?v=maLBGFYl9_o

The video in post #26 says the panel is held in place by four bolts. Four bolts seems inadequate to me.

That's not exactly correct. The panel is definitively not held in place by 4 bolts.

The following explanation, which is what I understood from the video, may be not 100% accurate but it will be close. From what I understood:

All the pressurization force (which is the big force that the plug needs to withstand) is taken by the 12 stops (6 on each side).
To open the door or plug, you need to slide the door/plug up 1.5 inches first to clear these stops.
The door's / plug's hinges are mounted in a kind of is spring-loaded "piston)" to help with this up-motion.
But the up motion is impeded by the rolling pins and tracks on the upper part of the sides.

Up to that point, the system is identical for the door or plug. Now the differences:
In the door, the rolling pins are kept in the locked position by the door handle mechanism.
In the plug, the rolling pins are kept in place by the bolts (1 bolt goes through each pin) and there is an additional bolt in each hinge's piston so even if the bolts of the pins are not installed the spring will not move the door up.

The force in the bolts, or in the handle mechanism, is very small. It is just holding the door down against the springs which, in turn, are compressed with a force that is not much greater than the weight of the door or plug. In my "engineering intuition" estimation just 1 of the 4 bolts would be more than enough (and with margin) to keep the door down.
Once the airplane is pressurized, the bolts, door handle mechanism and rolling pins and tracks can all magically disappear and the door in not going anywhere, held firmly against the 12 stops by the pressurization force.

In the picture above you can see, on the right edge of the plug, the 6 stops, the tracks that house the rolling pins (between the 1st and 2nd stop from the top), the bolt that goes through the track and rolling pin, the hinge with the spring-loaded piston (the vertical black cylinder on the bottom edge) and the bolt that keeps that piston compressed. On the left side you can see top 3 stops, the track, you can even see a little bit of the pin, and the bolt that goes through the pin and track, and, between the 2nd and 3rd stops, the strap that limits how much this plug can be swing opened for maintenance access to the frame, to prevent that the door just swings/falls down pivoting on the bottom hinges and hits the fuselage (which is what happens, apparently, when you pop open the actual emergency exit door).

[flashcrash]

Once the airplane is pressurized, the bolts, door handle mechanism and rolling pins and tracks can all magically disappear and the door in not going anywhere, held firmly against the 12 stops by the pressurization force.

Thanks for clarifying this, and for providing the link to that very helpful video. And yet, the door-plug clearly did decouple from the fuselage. Based on the NTSB photos released so far, all 12 of the stops appear to be present on the aircraft frame and are, at least to my untrained eye, apparently undamaged. I've seen plenty of speculation about the possibility that the bolts were not re-inserted correctly after the initial delivery inspection, but even if that were true, wouldn't the stops alone have made a blow-out impossible at altitude?

[sjwk]

Question - would the plane have been delivered with the plug fitted from the factory, or would it have come with a door, and the replacement of door with plug been an after-market fitting? I'd guess that fitting of seats etc is done by the airline after delivery, and number of seats determines if a plug or door is required - or are all the aircraft individually specced and configured by the airline but built to order by Boeing?

Just wondering whether if, say, it's found that it was missing bolts, that's a Boeing construction issue, or potentially the fault of a 3rd party on behalf of the airline?

[Evan]

Question - would the plane have been delivered with the plug fitted from the factory, or would it have come with a door, and the replacement of door with plug been an after-market fitting? I'd guess that fitting of seats etc is done by the airline after delivery, and number of seats determines if a plug or door is required - or are all the aircraft individually specced and configured by the airline but built to order by Boeing?

Just wondering whether if, say, it's found that it was missing bolts, that's a Boeing construction issue, or potentially the fault of a 3rd party on behalf of the airline?

The Boeing contractor, Spirit Aerosystems, who install the plug, also build the 737 fuselage. It might be that they build it with the emergency door and then it is returned for the refit, but I doubt that because the plane is sold before it is built and the build order should have specified the door plug. But that is speculation.

[BoeingBobby]

The Boeing contractor, Spirit Aerosystems, who install the plug, also build the 737 fuselage. It might be that they build it with the emergency door and then it is returned for the refit, but I doubt that because the plane is sold before it is built and the build order should have specified the door plug. But that is speculation.

They build parts for Boeing and Airbus. I used to fly 787 fuselage parts out of their McConnell AFB facility in the DreamLiner.

[Evan]

They build parts for Boeing and Airbus. I used to fly 787 fuselage parts out of their McConnell AFB facility in the DreamLiner.

Yes, they build the 737 and the nose and cockpit sections for most Boeing aircraft, as well as Airbus components. They are the old Wichita Boeing plant that built everything from the B-29's to the 727's. Boeing sold it off in 2005. Probably to prop up numbers for the shareholders.

[Evan]

Looks intact...

[baxterboy]

Clearly, there is a great deal of valuable information in the thread; however, unlike most posters, I know virtually nothing about the technical aspects of planes, making it a bit difficult to decipher the info.

In a few weeks, my wife and 3 children under six are scheduled to travel on an Alaska Airline Boeing 737-900. They are seated in row 25. I believe the problem with the plugged door on the Max occurred on row 26.
Therefore, I am concerned about their safety on the plane - particularly at cruising altitude. If there is a plugged door on a 737-900 and it came off at cruising altitude, from what I understand, there's a strong possibility they could be sucked out of the plane.

It is virtually impossible to get through to Alaska Airlines on the phone to get information.

I am unsure if there is a plugged door on the 737-900 similar to the one on the Max.

Information and recommendations would be appreciated.
Cheers

[sjwk]

Just saw on avherald and subsequently on BBC that United have found loose bolts in door plugs on a number of their aircraft which needed tightening.

https://www.bbc.co.uk/news/world-us-canada-67919436

[Evan]

Clearly, there is a great deal of valuable information in the thread; however, unlike most posters, I know virtually nothing about the technical aspects of planes, making it a bit difficult to decipher the info.

In a few weeks, my wife and 3 children under six are scheduled to travel on an Alaska Airline Boeing 737-900. They are seated in row 25. I believe the problem with the plugged door on the Max occurred on row 26.
Therefore, I am concerned about their safety on the plane - particularly at cruising altitude. If there is a plugged door on a 737-900 and it came off at cruising altitude, from what I understand, there's a strong possibility they could be sucked out of the plane.

It is virtually impossible to get through to Alaska Airlines on the phone to get information.

I am unsure if there is a plugged door on the 737-900 similar to the one on the Max.

Information and recommendations would be appreciated.
Cheers

You'll be relieved to know that there is no safer plane than one that has just been inspected. Whatever caused that plug to depart the plane (most likely loose, missing or damaged bolts), it won't happen to yours. FAA Airworthiness Directives require very specific measures to be taken. All Alaska planes will be carefully checked before being returned to service.