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Comment by jurassicfoxy | Hacker News Reader

One thing I don't understand is the why the door isn't designed so that pressure doesn't seal it tighter. Like a manhold cover. It seems at least the door needs to be "lifted" to be removed, so the missing bolts hold it down (but presumably do not hold against outward pressure).

I guess that's why it doesn't immediately fall out.

Has anyone seen mechanical or assembly drawings of these things?

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My guess is a combination of it would be harder to install that way and designers never considered people would leave the bolts out! Hard to design a plane for such serious assembly oversight.

Competent designers do think about those things.

Competent designers and engineers consider the risks of incorrect assembly, and depending on risk assessment (probability vs severity of failure), and cost-benefit assessment (cost of redesign vs cost of inspection), and based on that decide on if further mitigations are required.

Sure that makes sense.

Generally if it's possible that a complete failure of process happens, designers will plan for that. Anything outside of fully automated assembly processes with interlocks and safety checks warrant that to a decent designer. You cite cost of redesign but we're talking design in the first place. What's on the table in this discussion is design, not response to failures.

My understanding, reading this, is that it is the pressure that holds it in place. The bolts just keep is from sliding off.

The doors are very heavy, the pressure keeps them in place in only one direction. Without the bolts, only friction from the pressure would hold them up.

>One thing I don't understand is the why the door isn't designed so that pressure doesn't seal it tighter.

I guess presumably because the plug does double-duty as a door depending on the floor plan.

The door plug does seal tighter under pressure, but it has to be in the right position to do that.

It's up to chance that the door plug could bounce up, and thus ready to open when the pressure builds.

Chris Brady has a video explaining it:

https://www.youtube.com/watch?v=5FcyvFfHsjQ

It's like a flaky test in CI -- it worked for so many flights because the door is held on rails, and then by pressure at altitude.

based on the Blancolirio explanation, it would have been held in place by the pressure differential, except that on this flight it got jostled just right at a low enough altitude.

What seems odd is the springs that assist opening an emergency exit are left in place. Might not have made a difference.

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