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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum ( )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Posted by: Lae Won Kim ( )
Organization:Rotem Company
Date posted: Tue May 6 10:51:12 US/Eastern 2003
Subject: MTTR
What is the distributon type of MTTR statistically? If it is a normal distribution, who first demonstrate the ditribution type? Thank you


Subject: Maintenance Distributions
Reply Posted by: BWD ( )
Organization: RAC
Date Posted: Wed Apr 16 15:04:55 US/Eastern 2003
The log-normal distribution is most often used in maintainability modeling because it is considered representative of the distribution of most repair time, especially complex repair actions. It applies to most maintenance tasks and repair actions consisting of several subsidiary tasks of unequal frequency and duration. Analysis of past system data indicates that the maintenance times for the majority of complex systems and equipment indicates are log-normally distributed. Relatively simple maintenance tasks and repair actions that consistently require a fixed amount of time to complete (remove and replace) are usually normally distributed. I would suggest that you obtain a copy of the RAC Maintainability Toolkit as a reference source for these type of questions. As far as who first demonstrated that maintenance tasks were log- normal or normally distributed, I suggest that you look at the 1965 book “Maintainability Engineering’ authored by J. Geise University of Pittsburgh and W. W. Holler, Duke University.

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