That is not always and engineering problem. It can be a manufacturing problem. One case[1] of this is the F-86. It was engineered fine, but a worker on the floor didn't follow instructions and installed a bolt incorrectly. This caused the plane's aileron to lock during certain maneuvers killing some pilots. This was a manufacturing problem not an engineering problem.

1) http://characterqualitystories.com/cqs/node/394