Operational Testing Example

This example appears in the Reliability growth reference.

Consider two systems that have been placed into operational testing. The data for each system are given below. Do the following:


 * 1) After estimating the parameters, verify the assumption of $$\beta = 1\,\!$$.
 * 2) Estimate the instantaneous MTBF of the system at the end of the test (demonstrated MTBF).
 * 3) Estimate the MTBF that can be expected after the BD failure modes are addressed (projected MTBF) and the maximum MTBF that can be achieved if all BD modes that exist in the system were discovered and fixed according to the current maintenance strategy (growth potential MTBF).

The BD modes are implemented at the end of the test and assume a fixed effectiveness factor equal to 0.6 (i.e., 40% of the failure intensity will remain after the fixes are implemented).

Solution  The entered operational testing data and the estimated parameters are given below.



The assumption of $$\beta = 1\,\!$$ can be verified by looking at the confidence bounds on $$\beta\,\!$$ via the Quick Calculation Pad (QCP). The 90% 2-sided Crow confidence bounds on $$\beta\,\!$$ are shown next.



Since the confidence bounds on $$\beta\,\!$$ include one, then you can fail to reject the hypothesis that $$\beta = 1\,\!$$.

 From #1, the demonstrated MTBF (DMTBF) equals 33.7097 hours. 

The projected MTBF and growth potential values can be displayed via the Growth Potential MTBF plot.



The plot shows that the projected MTBF equals 42.3824 hours, and the growth potential MTBF equals 62.9518 hours.  