Alaska Airlines NTSB briefing: what broke on the door plug | Hacker News Reader

Alaska Airlines NTSB briefing: what broke on the door plug

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8 pointsgraton7 comments

An important piece of context is the bolts found loose on a United plane:

https://www.reddit.com/media?url=https%3A%2F%2Fi.redd.it%2Fm...

there are three visible on the right in that photo. These bolts don't have a cotter pin and they look like they are essentially part of the plug door assembly itself. It sounds like they are never intended to be loosened for installation, opening, inspection, or access. They bolt the collar that goes around the guide cylinder to the plug door frame itself.

I think if these bolts become loose, then 1) the collar will be free to move upwards, assisted by the spring that you can see in that photo below the collar, and 2) the door plug is basically mechanically untethered and just held in place by friction and air pressure. If the plug door frame itself were nudged up about an inch by the collar spring action, or any other force (like turbulence), it'd push right out like DB Cooper.

In the NTSB briefing, the chair said that the NTSB had offered party status to Spirit Aerospace (who I think make the frame and the plug) and the machinist union.

That is interesting. Though I'm not sure that even if one of those came loose it would allow the door to move. There are supposed to be four bolts installed and if just one of them is installed I'm not sure how the door could move up.

https://www.youtube.com/watch?v=maLBGFYl9_o at around the 7:26 mark has a great explanation of how the door is secured and it seems like as long as there is at least one of the four bolts installed the door can't move. Now as you pointed out those loose nuts could effectively mean that bolt could become useless. And the NTSB didn't mention those other nuts, which I think they would have.

You're right, I'm being misled by the United photo. Even if all 4 of those nuts were loose and the bolts came out, there'd still be the upper holding bolts on the plug itself.

My mildly-informed opinion is that none of the four bolts were installed in the door plug. Otherwise it doesn't seem possible that the door could move up. I guess we will find out in the future as the NTSB said in the briefing that they will be able to tell if there were any bolts installed in the door.

17:33 into the video it is explained "what broke".

The door moved upwards, as is done when it is opened. It became disengaged and allowed it to be expelled from the aircraft. They have not found the four bolts that restrained it from moving and are not sure if the four bolts were installed.

Really good video explaining how the door plugs work with photos: https://www.youtube.com/watch?v=maLBGFYl9_o

The previous video describing all the door options on the MAX series is also a relevant precursor for this door-plug specific video.

I find it amazing that the NTSB has only 437 employees (stated in this video).

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