Statistics for Maintenance Modelling: Repairable Systems

# Example of Fitting a NHPP Model to Failure Repairs and Estimating Parameters¤

The following data are a subset of the times in operating hours of unscheduled maintenance actions (failure repairs) for a diesel engine of USS Grampus: 860, 1258, 1317, 1442, 1897, 2011, 2122, 2439, 3203, 3298, 3902, 3910, 4000, 4247, 4411, 4456, 4517, 4899, 4910, 5676, 5755, 6137, 6221, 6311, 6613, 6975, 7335, 8158, 8498, 8690, 9042, 9330, 9394, 9426, 9872, 10191, 11511, 11575, 12100, 12126, 12368, 12681, 12795, 13399, 13668, 13780, 13877, 14007, 14028, 14035, 14173, 14176, 14449, 14587, 14610, 15070.

The plot of ln MCNF against ln t, shown below, looks roughly linear, suggesting a power law model may be suitable. You can see from the plot that the slope of the line is roughly 1 so a constant ROCOF may be suggested. We can fit
(t) = 2(t) = to this data set using the equations on the previous screen to estimate and . This gives
= 4.93E -07 and = 1.2178 which suggests that ROCOF is slightly increasing. However, is extremely small which may mean it's not a good model choice (this is explored in exercise 3 on screen 27 at the end of this session).

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