Comment by jdietrich

To a half-competent machinist or manufacturing metrologist, half a millimetre of concentricity error on a part of that size might as well be half a mile. It's a huge, grievous error that can be seen with the naked eye. You don't get an error of that scale through normal variation, it's a clear sign of a serious problem with your setup.

This part of the article really leapt out at me:

The tolerance for this bore was supposed to be Ø 0.05 mm according to the design drawings, but was changed to Ø 0.5 mm in the manufacturing drawings without explanation. Even so, the non-conformance on the accident hub was between Ø 0.90 and Ø 0.98 (an offset of 0.45–0.49 mm), which should have been flagged by the machine. The CMM records from the accident hub were not retained, so it was not possible for investigators to confirm that the error was actually registered.

The meaning might not be obvious if you've never worked in a machine shop, but it's crystal clear if you have. Many people at that plant knew that they were delivering out-of-spec parts. Everyone who handled that part could have told you at a glance that the counterbore was badly off-centre. Rather than going back to remake the parts, rather than figuring out why the parts were bad, they just went through the motions of QC, shipped them anyway, falsified documentation and discarded evidence. For all the complexity of the analysis, the root cause is blindingly simple - flagrant negligence, concealed by flagrant deceit.