How is quality built in to a safety-critical project ?

Question: How is quality built in to a safety-critical project !?

There needs to be a "rachet" mechanism to stop quality going backwards!.

Question prompted by :
<<Q/On a safety critical project, might each quality factor decline after reaching perfection !?
A/Very remote chance! Quality factors are, or should be, like non-return valves in a fluid duct system: there should be no question of decline, or a return, after the point of perfection! Absolutely one-way traffic!>>
(insight by swanjarv!.!.)
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Best Answer - Chosen by Asker:

You build a feedback circuit passing through a moderator to monitor the efficiency of the QC!. The moderator applies sufficient pressure to hold QC to goal levlels!.Www@QuestionHome@Com