| The parts are designed for "ultimate load" which is 150% of the worst case maximum load expected to ever see in service. I used to work at Boeing on the 757 stabilizer trim system. There's the design group and the stress group. I was in the design group, the stress group double checks the design work. One day the stress group called me on the carpet, and asked me why my designs consistently just barely exceeded 150%. I said I started with the ultimate load, and worked backwards to size the part. The stress groups said they prefered designs to be 10% over the ultimate load. I replied that I designed to the requirements, as adding 10% makes the airplane overweight. If they didn't like the design requirements, change them. They grumbled, but I got my way :-/ A few months later, they offered me a position on the stress group. It was a nice compliment, as they normally required a masters' degree and I only had a bachelors. I told them I was honored by the offer, but my heart was in design. Some time later, my parts were put on the torture rack to see if they passed the ultimate load test. All of them passed on the first try. I also had the privilege in being mentored by some really fine engineers at Boeing, such as J Burton Berlin and Erwin Schweizer. Am I proud of that? Yes. I love flying in the 757. Best airplane Boeing ever made. Whenever I fly in them I chat a bit with the flight crew, and they love it, too. |