MP thnx for some sensible questions/comments.
The STC (supplemental type certificate) says that the door must comply with its design documents including the section on requirements for continued airworthiness. In that approved document it states that -
"The cockpit and deadbolt assembly must function properly at all times in order to maintain a secure flight deck"
In his ruling the judge completely ignored these documents that formed part of the case and only addressed the Industrial side of things. The evidence shows that this part fitted to the aircraft was no longer in a condition to allow continued airworthiness (not airworthy to Type design standards) because it could no longer maintain a secure flight deck.
It should also be known that the managers who signed these aircraft out also changed the locks on each door first. If there was no defect they would not have done a thing. If it was not airworthiness they would have deferred.
Regardless of whether the defect was airworthness or not, all Engineers are obligated to report defects under CASA Regs. Airworthiness defects just need to be addressed differently.