The optimization of RPN criticality analysis method in FMECA

Aiming at the defect of traditional risk priority number (RPN) method in FMECA, a RPN assessment method is put forward which bases on the fault propagation probability and cost, then a corrective actions choice method is presented by gray correlation theory. Firstly, the occurrence probability and cost are calculated according to fault propagation tree. RPN is assessed by the overall risk of the events. This method avoids the subjectivity and inaccuracy of O,S and D' ranking assessment in traditional RPN. Then a gray correlation theory is introduced in to implement corrective actions choice for the failure mode whose RPN value is higher than the acceptable risk. The choice method has made up for the lack of corrective actions choice method in traditional RPN. Finally, an aircraft elevator control sub-systems is taken as an example and RPN assessment method and actions choice method above are used, a better result is obtained.