I'm wondering why the tolerances for the oil pipe were so small in the first place. Why not make the pipe one or two mm thicker?
That said it seems like did have a poor process where a part could be out of spec and they had no good way to check it. As they mentioned about Swiss cheese, you want as many layers as possible, and checks like that are needed.
Why not counterbore the pipe before installation, so it’s a trivial process?
Would it then not survive welding perhaps?
It’s very interesting that there were not wall thickness measurements. That would have solved this whole issue.
The failures were more with the whole process (like the reference points with different tolerances and the inadequate paperwork) rather than machinist incompetence. They are just the guys at the bottom.
There was no correcting mechanism and nothing to catch the issue. This is a system failure. The person who set the second datum for a different operation did nothing wrong: a new reference was needed for production reasons and that new reference did not need the same tight tolerance. They were not responsible for what happened later. Then, as the author mentions in the article, the software should have flagged the tolerance mismatch when that datum was used for something else.
> The machinist would have seen with the naked eye very easily that the hole was not close to center, an old salt would have raised it up.
No machinist is ever going to eyeball tolerance violations by a fraction of a millimetre on all the measures of every piece they build. That’s science fiction. Checking should have been in the manufacturing check list. Again, a system failure.
> The machinist not being aware that moving the jig was ruining the setpoint. Incompetence number 3.
Moving it was more or less required for another operation, which is the reason why there were different reference points for seemingly the same thing. Again, that is not the problem. The fundamental problem was that the second datum was used instead of the first.
Besides, if a machinist being aware that a bit of metal must not move at all is required to keep aircrafts flying, the real failure is not to specify that. I don’t know where you live, but in most of the world humans do what they can but are not perfect. That’s why there are checks and procedures to correct mistakes. No single decision or action should result in a crashed aircraft. Otherwise the whole system is just creating death traps.
> There were clearly incompetent individuals working at the facility.
You call them incompetent without seemingly understanding the actual problems, even though they were explained in detail in the article. There will always be out-of-specs pieces and random issues everywhere. If your system depends on humans being perfect, then your system is the problem.
Even great people are bound to make a mistake sometimes. You need to reduce it, sure, and I hope that this specific failure never happens again, but we need to take a broader view.
The article mentioned some of these tubes being rejected, and yet this one made it through.