Unplanned Downtime
Unplanned downtime is the period when equipment is unexpectedly unavailable during time it was required or scheduled to operate.
What this term means in maintenance
Unplanned downtime is the period when equipment is unexpectedly unavailable during time it was required or scheduled to operate.
Causes of unplanned downtime
Possible causes include:
- Equipment breakdown
- Utility failure
- Material shortage
- Quality hold
- Control-system fault
- Operator issue
- Safety event
- Process instability
Not every unplanned stop is caused by maintenance.
Basic calculation
Total unplanned downtime = Number of unplanned stops × Average stop duration
Unplanned downtime percentage = Unplanned downtime ÷ Scheduled time × 100
Practical example
A line has four unplanned stops averaging 45 minutes.
Total unplanned downtime = 4 × 45 = 180 minutes
Maintenance use
Maintenance teams should review:
- Affected asset
- Failure mode
- Cause
- Stop frequency
- Stop duration
- Repair time
- Repeat occurrence
- Production consequence
Common mistake
Combining all unplanned downtime under “breakdown” hides utility, material, quality, process, and operating causes.
Related concepts
Related maintenance terms
Keep exploring connected CMMS, reliability, and maintenance planning terms.
Equipment Downtime
Equipment downtime is the period when an asset is required or scheduled to operate but is unavailable or unable to perform its intended function.
Breakdown Maintenance
Breakdown maintenance is repair work performed after an asset has failed and can no longer perform its required function.
Emergency Work Percentage
Emergency Work Percentage is the share of total maintenance work or labor hours consumed by jobs requiring immediate response.
Glossary FAQs
- What is unplanned downtime?
It is unexpected equipment unavailability during time the asset was required or scheduled to operate.
- Is all unplanned downtime caused by breakdowns?
No. Utilities, materials, quality, process, control, and operating issues may also cause it.
- How is unplanned downtime percentage calculated?
Divide unplanned downtime by scheduled time and multiply by 100.