To: widgeon
The FAA requirements for a single point failure that would cause death or the loss of the aircraft and its' crew / passengers is 1 10-9 or one time in a billion hours of fleet operation.
That would lead you to believe that the aircraft is very safe. However on complex designs there may be 20-30 or more items that if they failed it would result in catastrophic loss of personnel or the entire aircraft. Let's take those 30 items and divide them into the 1 10-9 requirement and you get 33,333,333 hours of fleet operation. Now you add in failures caused by manufacturing defects or maintenance errors or overstress by the pilot in maneuvering and the time between failure drops even further. The FAA requirement is meaningless and the engineers are yet to meet that requirement. The product assurance group cooks the numbers in order to meet the requirements. The loss of the rudder on the AA A-300-600 had the 1 10-9 requirement and it failed long before the meeting of the 1 10-9 allowable failure rate. S-76s lost rotor blades and a BV 234 was lost due to a defect in the transmission design long before the respective helicopters accumulated 1,000,000,000 hours. It gets worse on commercial aircraft because of fleet size and the rate of accumulation of hours. I could go on and on but I think you get the Idea. This is the reason I don’t like to fly any more.