Why Fasteners Fail

Having spent over a decade working threaded fasteners for Boeing when I hear about a failure involving such items I take note. Unfortunately, the Tee connector that caused this Air Force failure is not a nut, but improper tightening procedures is probably to blame. Of course I suspect when L3 went looking for its fastener engineer to ask what happened or how to correct it they probably found they no longer had such a person. In the quest for Lean-Mean engineering teams the support engineering has been discarded and designers have been tasked to determine installation procedures for their assemblies. When I interviewed with SpaceX over five years ago they didn't want me because all their designers did fastener selection. Besides, as they said, the strongest fastener was the hi-lok pin (which would get a chuckle from some, dropped jaws from others). The reason I mention Space X, Its Falcon 1 launch on march 25th 2006 ended in failure due to a nut failure. Originally they said the nut wasn't properly tightened (like the Air Force incident). In truth they had used an aluminum nut in cryogenic conditions which caused the nut to snap on lift-off. I would never have approved of such a material nut under those conditions.