Talking about metal fatigue brought to mind an airplane I have been working on the past couple of days. It is a Boeing 777-200 and was delivered in (I think) year 2000. We are in the process of conducting its most exhaustive check to date, and I noticed in thw work center, the hours and cycles that are on it. I do not recall the exact numbers, but it was 32,000+ flight hours, and 5200+ cycles! Now we flew DC-9's for 30+ years and I think the high time aircraft accumulated something around 70,000 hrs, but the cycles were something close to that also. Cycles on a large airplane are the defining factor, due to the stresses placed on all parts of the pressure hull by the pressurization system. Still, this aircraft is as clean as a new one, and I've been amazed at the amount of composites used in it. The horizontal and vertical tail structure is almost all composite.
Charles
