Mean down time

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In organizational management, mean down time (MDT) is the average time that a system is non-operational. This includes all time associated with repair, corrective and preventive maintenance, self imposed downtime, and any logistics or administrative delays. The difference between MDT and MTTR (mean time to repair) is that MDT includes any and all delays involved; MTTR looks solely at repair time.

There are three main ways of reducing MDT:

1. Make the system repairable. 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.
2. 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).
3. 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.