When an aircraft was lifted,its forebody fell down to the ground accidently. It was found that the hanger bolt of the front hanging point had fractured. Macro and micro appearance observation,metallographic examination,hardness and chemical composition analysis were performed on the fractured hanger bolt. The results show that the fracture of the hanger bolt was brittle overload facture. Through examining the design,production and installation of the bolt,it was found that the fracture of the bolt was caused by the co-effect of abnormal structure（ the matrix of tempered sorbite contains a large amount of ferrite）,excessive brittleness and insufficient safety margin. It was suggested that the bolts should be replaced with synthetic fiber hoisting belt.Onsite test results show that three point lifting is more simple,stable and reliable.
Failure Analysis and Prevention