Good thread performance hinges on proper thread inspection and gage calibration as well as meeting current thread inspection standards. In the mid 1980s, the Department of Defense grounded a fleet of UH-60 helicopters when spindles securing the rotor blade to the main mast continued to separate from helicopters in flight. An automotive manufacturer lost an entire day's production of engines when the threads produced to affix the engine block to the frame would not hold. A commercial airliner plunged into the ocean when its horizontal stabilizer failed to respond to the pilot's commands. Prior to this, there were six separate incidents when commercial aircraft made emergency landings due to in-flight engine separations. In these seemingly unrelated accidents, the underlying problem was thread failure.
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