Function based reliability targets under budgetary constraints

The method presented here as summarized by means of the flow chart in Figure 1 is able to derive subsystem target reliability levels and thereafter the system's reliability target based on value to the customer and warranty budgets. Reliability targets are determined based on value to the customer per function while at the same time considering budgetary constraints. The product to be developed is persistently perceived as a means of fulfilling the functionality the customer desires. The customer thus gets a greater influence in determining target reliability levels. Each subsystem's target reliability level is defined in accordance with its quantitative contribution to fulfilling the product's functions. Statistically inevitable failures before the targeted product lifetime are often compensated by warranty and good-will expenditures. Allocating allowable warranty budgets to each subsystem based on its importance toward fulfilling the system's functions ultimately results in the allowable number of failures per warranty time, whereupon reliability relevant parameters can be derived. This results in a reliability allocation as much in line with the voice of the customer as possible. Contrasting with existing methods, the one presented here combines the determination of the subsystems' reliability targets (which are determined first) with the determination of the system's reliability target. Also, the method does not depend as heavily as e.g. the method ARINC, AGREE, the Feasibility of Objectives or the method by Karmiol, Bracha and Mettas on empirically defined factors. (These methods are summarized in e.g. [1,2,3]). This enhances the method's applicability significantly. Furthermore, the method can be applied in early development stages of either a new product development or of design changes as long as the system structure per function can be determined. How encompassing a function is regarded is scalable. The method is also applicable to arbitrarily complex systems. (c.f. [4])