Fleet-level Reliability of Multiple Repairable Units: A Parametric Approach using the Power Law Process
Volume 10, Number 3, May 2014 - Paper 01 - pp. 239-250
JAN BLOCK, ALIREZA AHMADI, TOMMY TYRBERG and UDAY KUMARDivision of Operation, Maintenance and Acoustics, Luleå University of Technology, SE-971 87, Luleå, SWEDEN
(Received on May 05, 2012, revised on Sept. 09, 2013 and Jan. 13, 2014)
The application of parametric reliability analysis methods for repairable units, such as Power law process, is quite clear and straightforward for a single repairable unit. However, in practice, the analyst needs to know the reliability characteristics of units at a fleet level. The application of parametric reliability analysis methods at the fleet level, even if it is limited in scope, is quite complex. The aim of this paper is to describe the use of the power law process for multiple repairable units with differing reliability characteristics, to predict the expected number of failures at fleet level. The empirical data used in the paper are based on field data gathered during the operational life of two types of multi repairable units used in the Swedish military aircraft system FPL 37 Viggen from 1977 to 2006. The paper performs the trend test using TTT-based MIL-HDBK-189 and Laplace tests, and assesses the equality of shape-parameters for the intensity function of the power law process for multiple units. Estimation of the scale- and shape-parameters using maximum likelihood estimation is also performed. The parametric approach using power law process was found to yield relatively accurate estimations of number of failures, compared to empirical data.
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