Statistics for Maintenance Modelling: Repairable Systems

# Repair Time¤

One way of describing the occurrence of failures is to state the mean time between failures, often known as MTBF. The main difference between the MTBF and mean time to failure, known as the MTTF, is in the usage. The MTTF may apply to first failure or a non-repairable failure, whereas the MTBF is used in the context of repairable systems. Note that the MTBF is usually the mean operating time between failures. There is, however, considerable variation in the use of these terms and the definitions should be checked within any given text.

Repair actions taken after system or component failures are corrective maintenance actions. Actions taken before failure are called preventive maintenance actions, which may include regular servicing and replacement of parts before significant wear or total failure has occurred. The modelling of repair time is of considerable interest as this affects the necessary human resources, spares provisioning and operational effectiveness. Some of the issues are considered in the second part of this course, namely maintenance modelling.