The goal of maintenance should always be to improve operational reliability and personal safety, which in turn produces positive effects in terms of availability. Operational reliability depends on the combined characteristics of reliability , maintainability and maintenance supportability. These can be measured using the following numerical values:


Examples of numerical values:

  • The relationship between scheduled and unscheduled maintenance
  • Maintenance costs divided by production volume or number of units produced
  • MOTBF: Mean Operating Time Between Failures
  • MTTR: Mean Time To Restoration
  • MMDT: Mean Maintenance Down Time
  • MWT: Mean Waiting Time

High operational reliability equals:

  • Lower maintenance costs
  • Higher profitability
  • More stable production
  • Fewer quality losses
  • Lower energy costs
  • Improved working environment
  • More time for improvements


Dependability includes availability, saftey, durability, economics and their influencing factors (reliability, maintainability, supportability, conditions of use and operators influence).


According to the European Standard, availability is defined as:The ability of a unit to perform the required function under specified conditions at a given time or within a set time interval, provided that the required support functions are available.

Note: Availability depends on the combined characteristics of reliability, maintainability and maintenance supportability.





A measure of the reliability is Mean Operating Time Between Failures (MOTBF). That is the period between the last corrective action for an error until the next error occurs. Through machine condition monitoring, the time between failures may be extended which leads to a higher reliability.

Reliability is the ability to perform required functionality under given conditions.




Mean time to restoration (MTTR) measures the system’s maintainability. MTTR is the average time needed to repair a malfunction. Mean time to restoration is easiest to influence when constructing the machine. By improving accessibility and supporting functions you can raise the level of maintainability.

Maintainability is a measure of how easy it is to detect, locate and correct faults in a device or a system.




Maintenance supportability can be described as the average waiting time for a maintenance action. Factors that lead to improved supportability include scheduling maintenance activities and ensuring accessibility, technical documentation of high quality.

Supportability describes the maintenance organization’s ability to provide the resources required for maintenance.


Maintenance Supportability


Reliability and maintainability takes into account the technical system’s ability to meet availability while the maintenance supportability describes the maintenance organization’s ability to effectively correct faults. These three factors, in turn, are determined by a number of subfactors and maintenance activities.


Dependability with Text


European Standard-EN 15341:2007 Maintenance Technology – Key Performance Indicators

To manage maintenance operations effectively, it’s important to measure what we do, how often and how well we do it.

To do this, we must identify a number of numerical values; these are often referred to as key performance indicators (KPIs). The chart below presents a few examples from the standard containing 71 available KPIs defined in three different categories; financial, technical and organizational.

Select an overall key performance indicator from each category that adds value to the maintenance activity over time and to which all staff can relate.



External and Internal KPI

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