Also - need to ensure that all testing methodologies were up to scratch. Here is an article about a KC-135 pressure test that ended up making the plane pop like a balloon [0] - all because the pressure gauge used by the tester didn't have a 'stop' peg and he missed the fact that the needle had cycled around.

A door hatch from the aircraft was found 70 yards away.

[0] - https://theaviationgeekclub.com/time-kc-135-stratotanker-air...