Back in the early 1950s two Marines were folding the blades on a HRS (S-55) and when they turned the left blade over it fractured at the intersection of the spar and the first pocket. This helicopter had just completed a flight. The crack had propagated from a very shallow cut into the anodized coating on the spar and had resulted from an employee removing excess bonding agent using an Exacto knife. The helicopter I was crewing was aboard ship and we were to fly back to our base, which was about ten miles away. Our flight was cancelled until a Sikorsky rep could come out to inspect our blades. He found the mark of the Exacto knife on one of our blades. After he had ground the cut out we flew back to the base and we scrapped the blade.
But then again it also happens to aircraft. This was filmed on TV. A B-52 had just returned to base after a lengthy flight and the crew was walking away from the plane when the left wing broke away from the wing box.
