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To: Maurice Winn who wrote (51681)	6/24/2009 4:51:49 AM
From: Elroy Jetson	1 Recommendation Read Replies (2) \| Respond to of 219799

Until de Havilland Comets began to fall from the sky, it was assumed that metal fatigue was not a relevant issue in aircraft aluminum. After all, why would smart aircraft designers build them, then simply wait until they fail while in operation? You aren't suggesting this, are you? But this is exactly what they did, even if they didn't intend to do it, or convinced themselves it was impossible. I'm sure more than one smart person has attempted to find ways to test the degradation of composite materials, it's just that no one has found a solution yet - which is obviously a problem with the material going into wider use. Simply put, Airbus has been relying on "studies" which claim to show that composite materials lose strength in use, but no further than a particular level. Yet this ostensible characteristic of composite materials does little to explain the way they are failing. Airbus convinced themselves they had addressed prior failures in composite tail fin assemblies of various makers by placing computer imposed limitations on the range of movement of these airfoils in various conditions. Firstly, this dangerously assumes the the computer is receiving correct information regarding airspeed and other factors - which we know was not true. Imagine driving a car in which the steering might disintegrate if the speedometer fails. It's not sensible. Second, and I think more importantly, this assumes the reason for the failure of composite materials is misuse rather than degradation through use and time. This is also not sensible. Sadly, the composite material tail assembly on this aircraft could have failed due any of these reasons. Airbus has also been convinced that the junction of composite materials with aluminum and titanium is a special problem, so have been particularly aggressive in using composites as fasteners requiring extreme strength and durability in a way which there is little history of real world use. People who surf know it's very unusual for surfboards to break. But here's a fence made of broken composite material surfboards. Anyone who surfs can tell you there usually doesn't seem to be any way to explain why they break. Some break virtually new, and others after many years of use. A few break when hitting a submerged rock, but are under very little stress when they fail. When the failure of a composite material surfboard causes it to lose a fin, or snap in half, there's little damage beyond the cost of a new board. In a passenger jet built like a surfboard, the consequences are simply unacceptable. It would have been nice to find a method for predicting composite material failure before selling large passenger aircraft made of this material. But it hasn't been found yet, yet the aircraft are in constant use. Many pilots won't let their families fly in aircraft built with extensive use of composite material. .