The investigation into the failure of a Russian Soyuz rocket to place two European Galileo GPS satellites into the correct orbit has found that it was caused by the faulty installation of fuel lines on the Fregat upper stage.
The failure was as simple as clamping together a cold helium line with the hydrazine fuel line, causing the hydrazine to freeze long enough to upset the Fregat stage’s orientation and cause the two satellites’ release into an orbit that is both too low and in the wrong inclination, officials said. One official said the Euro-Russian board of inquiry into the failure discovered that one in four Fregat upper stages at prime contractor Moscow-based NPO Lavochkin had the same faulty installation. ,,,,
Government and officials said the commission is debating how to proceed now that it knows that, as expected, the Fregat failure was not one of design, but of assembly and quality control. [emphasis mine]
In other words, 1 in 4 Fregat upper stations were routinely assembled improperly and no one noticed. The investigation also found that this assembly problem had existed on several past launches but because of the orbital requirements it had fortunately not caused any problems.
I want to emphasize that these kind of sloppy assembly issues have been occurring at a number of different Russian factories and different Russian companies. It seems to be systemic to the entire Russian aerospace industry, and it also appears to be getting worse.