A steel eyebolt which attached a rear lift strut to the right wing of a helicopter failed by fatigue. As a contributing factor, thread cutting produced sharp notches at thread roots, reducing fatigue life. Also, design fatigue life may have been exceeded as the part was in use about 10,000 h. Cumulative damage resulting from a previous accident could have occurred too. Because of this accident, inspectors were instructed to examine threaded zones of eyebolts by magnetic particle inspection after every 100 h in service. A maraging steel drive shaft of a helicopter also failed because of corrosion (pits),...