Citing a 2007 accident that followed the in-flight separation of a section of a Eurocopter EC 130B4 main rotor blade, the U.S. National Transportation Safety Board (NTSB) has recommended daily checks of main rotor blades on specific helicopters for cracks and surface deterioration. The pilot and seven passengers were not injured in the July 7 accident, but the helicopter was substantially damaged during the emergency descent and autorotation into the Hudson River in New York. The NTSB said the probable causes of the accident were "the fatigue fracture and in-flight separation of a section of the composite main rotor blade trailing edge aft of the spar, due to inadequate manufacture, and the manufacturer's failure to detect an out-of-specification deviation in the rotor blade's trailing-edge roving." (A "roving" is defined by the NTSB as a "collection of fibers in a parallel bundle with little or no twist.") The NTSB said that because the fibers were misaligned, loads were transferred to the skin, which is more susceptible than the fibers to cracking.
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