Unplanned downtime is the time an asset is out of service because it failed, as opposed to planned downtime, which is time the schedule took it out for a task. The distinction is the whole subject: a site with a lot of planned downtime and little unplanned has a schedule that runs; a site with the reverse has a queue of breakdowns. This page says what counts, how to measure it from work orders rather than from memory, what it costs against planned work, and what reducing downtime takes, in the order the moves pay.
What counts
An asset is in unplanned downtime from the moment it stops or is stopped because of a fault, to the moment it is handed back running. Waiting for a technician counts. Waiting for a part counts. Waiting for the line to be cleared counts. The repair itself counts. A planned task that overruns is planned downtime that overran, not unplanned. A reactive work order whose times are recorded honestly is the measurement; a whiteboard is not.
Measuring it from work orders
Each reactive work order records the reported time and the returned time; the difference is that failure's downtime. Sum by asset and by month, and split it into waiting for a technician, waiting for a part, and repairing, because each has a different fix. MTTR is the average of those differences. The equipment downtime calculation page on this site walks the arithmetic for one asset, and the maintenance log worksheet has the two time columns.
What it costs against planned work
This site's worked example puts a breakdown at 3.4 hours of a technician against 1.1 hours for the same work done as a planned job, $110.40 a breakdown at a $48 loaded rate, and 84 breakdowns a month across 180 assets, which is $9,273.60 a month before the value of what the line did not make. The lost output is usually the larger number and it is the site's to put in; the technician arithmetic is the floor.
Reducing downtime, in the order that pays
First, record it, because a site that does not know its downtime by asset cannot aim at it. Second, spares for the assets whose downtime is mostly waiting for a part. Third, findings on every work order so that the repeat failures show. Fourth, a preventive task or an inspection against each repeat failure, with an interval from the history. Fifth, a schedule that is actually done when due, because deferral is where unplanned downtime comes from. Training and new equipment are last, and rarely needed before the first five.
Questions people ask about unplanned downtime
Is unplanned downtime the same as breakdown time?
Breakdown is the event; unplanned downtime is the time it cost, including the waiting. Most of the reducible part is the waiting.
How do I separate waiting time from repair time?
Record three times on the work order: reported, started, returned. Reported to started is waiting; started to returned is repair plus any waiting for parts, which the technician notes.
What is a good unplanned downtime figure?
One that is falling on the assets you are working on. There is no benchmark that survives the difference between a bottling line and a hotel boiler.