DW, you're right, I phrased it badly. I know that responsibility was apportioned between parties. By 'all blame', I was referring to fact that no other individual human being on the airline's side was convicted of wrongdoing. The mechanic's supervisor was explicitly cleared of blame / responsibility. The implication is that no-one checked the repair, and that this self-certification-type work is considered acceptable. I would have expected the repair to be inspected and cleared by one other person at the very least. The fact that it is apparently OK to have one person sign off his own work, when that work is a repair to a passenger aircraft, is alarming to this passenger.