Heavy Maintenance
It is a common statement made by the layperson that if these MROs' are so dodgy, then why aren't aeroplanes falling out of the sky?
Well the simple answer is that any short cut taken, or deviation from accepted industry practice, or task simply not carried out, or defect missed etc... is like a time bomb buried deep. When and how it goes off, anyones guess. These checks are years appart.
This is not a problem for Singapore Airlines, in particular, because they get rid of their aircraft after about 5 years (D checks 5-6 years apart). Couple this with a world wide shortage of capacity for wide body 3rd party work (yes David Cox and John Vincent closed down the premier heavy line and workshop support, in an environment where no 3rd party MRO had space) so "rushing them through" is paramount. Qantas were lucky they jagged a few slots in Singapore. MAS has 10 lines full, "come back in about 10 years" if you need a check done.
But at the end of the day, the law was broken. Someone is surely culpable. These were not maintenance errors, mistakes, these people deliberately acted in the way they did. They knew what they were doing was wrong. If Cox cannot see this, he must go.