organization An organization or organisation (Commonwealth English; see spelling differences), is an entity—such as a company, an institution, or an association—comprising one or more people and having a particular purpose. The word is derived from ...

management Management (or managing) is the administration of an organization, whether it is a business, a nonprofit organization, or a government body. It is the art and science of managing resources of the business. Management includes the activities o ...

, mean down time (MDT) is the

average In ordinary language, an average is a single number taken as representative of a list of numbers, usually the sum of the numbers divided by how many numbers are in the list (the arithmetic mean). For example, the average of the numbers 2, 3, 4, 7, ...

time that a system is non-operational. This includes all downtime associated with

repair The technical meaning of maintenance involves functional checks, servicing, repairing or replacing of necessary devices, equipment, machinery, building infrastructure, and supporting utilities in industrial, business, and residential installa ...

, corrective and

preventive maintenance The technical meaning of maintenance involves functional checks, servicing, repairing or replacing of necessary devices, equipment, machinery, building infrastructure, and supporting utilities in industrial, business, and residential installa ...

, self-imposed

downtime The term downtime is used to refer to periods when a system is unavailable. The unavailability is the proportion of a time-span that a system is unavailable or offline. This is usually a result of the system failing to function because of an un ...

, and any

logistics Logistics is generally the detailed organization and implementation of a complex operation. In a general business sense, logistics manages the flow of goods between the point of origin and the point of consumption to meet the requirements of ...

or administrative delays.

Description

The inclusion of delay times distinguishes mean down time from

mean time to repair Mean time to repair (MTTR) is a basic measure of the maintainability of repairable items. It represents the average time required to repair a failed component or device. Expressed mathematically, it is the total corrective maintenance time for ...

(MTTR), which includes only downtime specifically attributable to repairs. Mean Down Time key factors: # SYSTEM FAILURE ## ''Identification & Recovery Time.'' First, the fact that the system is down must be identified, and maintainers notified & brought to action ## ''

Fault detection and isolation Fault detection, isolation, and recovery (FDIR) is a subfield of control engineering which concerns itself with monitoring a system, identifying when a fault has occurred, and pinpointing the type of fault and its location. Two approaches can be ...

.'' The problem must be identified and the faulty part identified. ## ''Parts Procurement.'' Replacement parts needed (if any) must be obtained ## ''System Repair.'' Faulty parts must be replaced or repaired. # SCHEDULED DOWNTIME ## ''Preventive Maintenance.'' Preventive maintenance checks are often intrusive and require the system to be down (unless

prognostics Prognostics is an engineering discipline focused on predicting the time at which a system or a component will no longer perform its intended function. This lack of performance is most often a failure beyond which the system can no longer be used to ...

are used), e.g., checking oil in a car engine. ## ''System Upgrade.'' System downtime is usually required to bring new features to the system. ## ''Calibration.'' Many forms of mechanical or electronic equipment require periodic intrusive calibration. ## ''Other administrative actions'' There are four main ways of reducing MDT: # ''Design the system to fail less often.'' A more reliable system that doesn't fail often reduces the Down Time. # ''Make the system

repairable A repairable component is a component of a finished good that can be designated for repair. Overview Repairable components tend to be more expensive than non-repairable components (consumables). This is because for items that are inexpensive to ...

.'' If an item is repairable, it will be used for a longer time, and the user will become more familiar with its operation. This will decrease the MDT because the user will be able to detect abnormal operation sooner, and the system will be repaired before the problem becomes too serious. # ''Let the user repair the system.'' By designing a system to be user-repairable, the MDT will be considerably decreased, as it will not have to be taken out of service for long periods of time while it is being repaired by the manufacturer (which of course includes time spent in transit to and from the manufacturer). # ''Provide the user with a repair support system.'' The closer critical spare parts are to the system, the faster it will be able to be repaired, as this eliminates the delay involved in ordering parts from the manufacturer and waiting to receive them. Also, the clarity of any instructions on how to repair an item will greatly contribute to the speed at which it is repaired.

References

Engineering failures Reliability engineering {{Business-stub