BIZOMAT MAKEOS · Maintenance
Repairable Asset Availability
What do operating and repair records show about availability?
Calculate observed availability and simple failure and repair averages for one repairable asset.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Operating time | h | Total actual operating hours over the observation window. |
| Corrective repair downtime | h | Total corrective downtime in the same window; declare whether waiting time is included. |
| Observed failures | failures | Consistently defined failure events for this one asset. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Operating time
- What it is
- The total hours the asset actually ran over the observation window, excluding stops for repairs and other non-operating time.
- Units and format
- Enter a number in h: hours. The form accepts 0 h or more. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 900 h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- More uptime raises availability and the MTBF estimate.
- Get it right
- Use operating hours, not calendar hours; idle time when not required is neither uptime nor downtime here.
What this means: Corrective repair downtime
- What it is
- The total hours the asset was out of action for corrective repairs in the same window.
- Units and format
- Enter a number in h: hours. The form accepts 0 h or more. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 100 h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- More downtime lowers availability and raises average downtime per failure.
- Get it right
- Decide and state whether waiting for parts or technicians is included, and apply it consistently.
What this means: Observed failures
- What it is
- The number of failure events recorded for this asset in the same window, counted to one consistent definition.
- Units and format
- Enter a number in failures: failures. The form accepts 0 failures to 1000000 failures. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5 failures as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- More failures lower MTBF and average repair time per failure; availability does not change.
- Get it right
- With 0 failures the tool does not estimate MTBF; it does not mean the asset never fails.
Method and formulas
- Observed availability = operating time / (operating time + corrective downtime).
- For a nonzero failure count: operating-time MTBF estimate = operating time / failures; average corrective downtime = downtime / failures.
- Example: 900 operating hours, 100 corrective hours and five failures gives 90% observed availability, 180 h MTBF and 20 h average corrective downtime.
Limitations
- A simple historical summary, not a reliability prediction or maintenance interval recommendation.
- Zero observed failures does not establish infinite MTBF; the tool leaves that estimate unreported.
- MTTR is a repair-time metric only when the recorded downtime contains repair time; logistics delays change the meaning.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- MTBF
- MTTR
- asset availability
- repair history
Who it is for
- Maintenance planners
- Reliability engineers
What you get
- Observed availability
- Operating-time MTBF estimate
- Average corrective downtime / failure
Interpreting the result
- Keep event definitions and observation windows consistent. Analyse failure causes before changing maintenance intervals.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed p. 2578 (maintenance context); this record-based KPI is an original extension. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Up and down: the two-state model
In Breakdowns and Buffers by the Numbers
What it covers: A repairable machine as a two-state Markov process: failure and repair rates from a stoppage log, steady-state availability, settling after a restart, and why stop definitions matter.
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