Definition
Availability is the proportion of time an asset is in a condition to perform its required function, whether or not it is actually being used at that moment. It combines reliability (how often failures occur) and maintainability (how quickly the asset is restored), commonly expressed as uptime divided by total time (uptime plus downtime).
Key facts
- Measures the fraction of time an asset is capable of functioning, combining both failure frequency and repair speed.
- Commonly calculated as uptime / (uptime + downtime), though the specific downtime included (planned, unplanned, or both) must be defined.
- Improving availability can come from either increasing reliability (fewer failures) or improving maintainability (faster restoration): the two levers are distinct.
- One of the three factors multiplied together in OEE, alongside performance and quality.
What does Availability reveal about failures?
Availability measures the proportion of scheduled or total time an asset is actually capable of performing its function: a combined outcome of how rarely it fails (reliability) and how quickly it is restored when it does (maintainability), rather than either factor alone.
How do teams use Availability in failure analysis?
Reliability measures the probability of not failing over a period; maintainability measures how easily an asset can be restored once it does fail; availability combines both into one measure of usable time. Two assets with identical reliability can have very different availability if one is much faster to repair.
FAQ
Frequently asked questions
What does the availability of an asset mean?
It means the proportion of time the asset is capable of performing its required function, combining both how rarely it fails and how quickly it is restored when it does, commonly calculated as uptime divided by total time.
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