To: lomapaseo
You are mixing a few facts with your faulted idea of what was wrong to support your idea that critical fault analysis could of/should have prevented these accidents. You must have eyes in your backside to see things so clearly post accident. If things were really thought to never fail than there would have been no need for the manufacturers to have issued Service Bulletins against the possible malfunction before these accidents.
The point is that equipment’s, appliances, subsystems and systems fail at a rate far lower than what is predicted in the reliability analyses. The figures derived in the reliability analyses feed into the preparation of the FMECAs and are factored into the safety hazard analysis, which is the basis for certification. If the figures used in the Reliability analyses are not accurate an /or are very optimistic then any element of the analytical process is contaminated and therefore is not a realistic representation of the ultimate safety and /or reliability of the system under analysis. When these contaminated optimistic figures are entered into the hazard analysis and then massaged using Boolean algebra the manufacturer can show that his systems safety far exceeds the safety requirements established by the certification authorities.
The basic rule of reliability, from an FAA perspective, is that if a part fails at a rate higher than predicted a service bulletin it issued and the manufacturer of the component goes back to square 1 and the failure is not chargeable even if it resulted in a crash.
The fact that the manufacturer promulgates service bulletins goes to prove that the component was not properly analyzed for potential defects and that problems arise that were either not predicted or there is another defect in the manufacturing and quality assurance in the manufacturer of that component. All of these things can be predicted and many of them most likely were but the manufacturer declined to incorporate the necessary changes in the part or the manufacturing process or the quality program. In most instances it is to save money and time.
As far as having eyes in my backside I have often been accused of having my head up my butt. However, the real reason I make the charges that I do is because I have been a Reliability, Maintainability and Systems Safety Engineer since 1968 and for thirteen years prior to that I worked in various engineering positions in the aerospace industry. I have seen it all. I have complained loudly and I have experienced the rebuff of engineering when I made a valid suggestion relative to the design. My fellow RMS engineers have often told me to be quiet as not to shake the boat. Their reasoning was that it puts bread and butter on the table. I personally don’t subscribe to that position. That is why I shoot my mouth off on technical forums such as PPRune.