The assumption of the constant failure rate can lead to excessive costs and non-optimum design decisions.  As this paper shows, simply summing constant failure rates can produce results which are highly inaccurate.  Highly inaccurate results can introduce significant error in decisions made for everything from product design to logistics support requirements such as spares and maintainers.  If we shift from reliability engineering analysis, the ability to address hazard rates versus time based on root-cause failure mechanisms will become cost-effective and can become an integral part of the concurrent engineering approach to product development.  The notion of the constant failure rate should no longer be accepted as a rule.  In stead, statistical distributions and assumptions must be shown to be appropriate every time they are used.  Simplicity alone is not a sufficient reason to use any given methodology or approach.
 

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