This was actually a QA problem — a set of design issues starting at the front of the process. All QC can do is identify problems after they have occurred.
As the saying goes, “you can’t test quality into a product.”
I guess I am a bit confused. Someone was supposed to be checking the bolts before the plane left the facility and they didn't. That seems to be a QC process issue more than a QA issue.
But that also seems like splitting hairs. The problem is not one of engineering design, to OP's post.
I disagree somewhat. It should not be possible for a plane to leave the factory without completing all QC checks. People are fallible, so a robust process is critical, and designing/confirming a robust QC process is a QA responsibility.
Sure, but "did the plane leave with all of the bolts it was supposed to" does not seem like a question that needs to be answered by someone with mechanical engineering degree. Let alone the responsibility of someone sitting in a cubicle in Everett.
How do we know that it was just 'someone was supposed to be checking the bolts before the plane left the facility and they didn't'. Because I'm not sure it's actually been fully revealed where the problem was. And despite the production issues, I'm of the opinion that the door-plug design should have been fail safe like the other doors where just pressure prevents them from being opened during flight. And another thing, passing the buck to QA doesn't let engineering off the hook since QC in this setting is a part of the engineering!
But that also seems like splitting hairs. The problem is not one of engineering design, to OP's post.