Testing a structure to failure, beyond its design limits, is not typically required. But it sure is exciting to watch.
During the original 767 type cert, the plan had been to test the wing to failure. But the wing was stronger than expected - while well above the predicted wing failure loading, part of the fuselage failed where it was being held down. Since they were already above the required wing loading, the decision was made not to repeat the (rather expensive) test to failure condition. Hence the 767 wing was never tested to actual failure.
We immediately accused the structures guys of building the wing too heavy
