Definition
Mean Down Time (MDT) is the average duration of a single downtime event (from the moment an asset stops to the moment it resumes production) averaged across a set of observed events. Unlike MTTR, which specifically measures repair time (the active fixing work), MDT can include the full stop duration: diagnosis, waiting for parts, repair, and restart.
Key facts
- Averages the full stop-to-resume duration, which can include diagnosis and wait time, not only active repair work.
- Distinct from MTTR, which specifically isolates repair time and often excludes diagnosis or logistics delays depending on definition.
- A wide gap between MDT and MTTR for the same events usually points to diagnosis, spare-parts, or scheduling delays rather than repair skill.
- Both measures require a consistent definition of what counts as the start and end of the event to be comparable.
How is Mean Down Time calculated?
Mean Down Time measures the full average duration an asset is stopped for a given set of events, from the moment it stops to the moment production actually resumes, potentially including time spent diagnosing the fault, waiting for spare parts or personnel, performing the repair itself, and restarting.
What influences Mean Down Time?
MTTR specifically measures repair time (the active work of fixing the fault) and, depending on how an organization defines it, may or may not include diagnosis and waiting time. Mean Down Time typically captures the full elapsed stop duration including those surrounding activities, which is why MDT figures are often higher than MTTR figures for the same set of events, and comparing the two can reveal where delay actually occurs.
FAQ
Frequently asked questions
How is the average downtime duration per failure determined?
Mean Down Time (MDT): the average full duration of a downtime event, from stop to resume, across a set of observed events, which can include diagnosis and waiting time in addition to the repair itself, distinguishing it from MTTR.
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