For all those who have never worked in an Aerospace Manufacturing environment, and surely there must be some out there, here is a quick beginners' guide to "Traceability".
When aircraft are assembled the aircraft manufacturer needs to know that the finished product conforms to the definition he Certified. That is to say, the everything in the aircraft is the same as the aircraft that passed the original certification - or individual component certification - and has been manufactured using the same processes. This is a HUGE simplification that doesn't mention the Modification process, variations due to the combined effect of drawing tolerances, accepted alternate processes and accepted non-conformances following a Concessions / Materials Review Board (MRB) / Dérogation procedure. (Pauses to catch breath).
To simplify this for all, purchased components are supplied with a magic piece of paper called a "Certificate of Conformity" (CofC) and if the supplier is authorised to do so they will also issue a Certificate of Release to Service (an EASA Form 1 or FAA Form 8130). The CofC is the link that forms the chain of evidence that helps the aircraft manufacturer to demonstrate to the authorities that all is well with the everything that goes into the aircraft.
These are important, powerful documents.
Except, of course, they're not. They are just bits of paper. What makes them so important is the regulation and control, the vigilance and the best practice of you and of all your suppliers. By accepting the value of the CofC you are accepting the ability of any given supplier and sub-supplier to promptly identify when things have gone awry during the manufacturing and assembly processes, to have isolated all other hardware with the same issue and to rectify by rework or repair every part supplied before each of the CofC's are signed. You are accepting that your supplier will not make changes to his or your design without supporting documentation and testing if required or without informing you. You are trusting that everything that goes into his component and everything that has happened to his component is exactly what he believes it to be. You are trusting that he has read, understood and complies with all of the possibly hundreds of specifications you have quoted as your requirements. It starts to become clear how it could be that a CofC could be signed in good faith for non-conforming hardware.
I am in no means trying to undermine or undervalue this system; it is long tested and robust. The system works because the Industry expends a lot of energy to manage it. Suppliers gain contracts only after they can demonstrate that they have a working Quality and Concessions System. Manufacturers that purchase hardware have themselves a Quality process that includes review and periodic audit of their suppliers.
It suffices to say how important it is that these systems work and work well.
It might be considered easy enough to pass an audit if there are enough documents
available to demonstrate the Quality system is active; but that would be
the big picture and I am talking about details..., that would be the structure and I am talking about the attitude. Once the hardware is
delivered, the magic of the paper starts to work and the aura of
conformity can have the tendency to stick even to hardware that has
since been identified as non-conforming. More than once I have heard
"But it must be conforming, it has a CofC". Lips moving, eyes glazed by
the power of the paper.
"Supplier Quality" is sometimes a small and orphaned department. They are often not directly related to their sibling "Manufacturing Quality" and their cousin "Concessions / MRB". They regularly come under great pressure from their more powerful relation "Manufacturing" or the sometimes overbearing parent "Programmes". When things work well, their employees are quite difficult to track
down as they are out visiting one supplier or another. If not then
their people are mostly fire-fighting Quality "Escapes" discovered once
the supplier parts have already made it to your production line. On their shoulders rests the responsibility of keeping the CofC system working.
It is for this reason I read with great interest the item in Flight by Lori Ranson, "FAA willing to improve oversight of manufacturer-supplier relationships". I will definitely be watching for how this subject develops.