Inherent Availability
Inherent availability is the theoretical availability of a repairable asset based on failure frequency and active corrective repair time, excluding planned maintenance and support delays.
What this term means in maintenance
Inherent availability is the theoretical availability of a repairable asset based on failure frequency and active corrective repair time, excluding planned maintenance and support delays.
Common formula
Inherent availability = MTBF ÷ (MTBF + MTTR)
Here MTTR normally means active corrective repair time.
Practical example
An asset has:
- MTBF: 400 hours
- MTTR: 10 hours
Inherent availability = 400 ÷ 410 = approximately 97.6%
What is excluded
Inherent availability normally excludes:
- Preventive maintenance
- Logistics delay
- Waiting for parts
- Administrative delay
Why it is used
It helps compare design reliability and maintainability.
Common mistake
Presenting inherent availability as actual plant availability ignores real operating and support delays.
How this term differs
Inherent Availability is the theoretical design-level availability based on failure frequency and active repair time. It is related to OEE Availability, Achieved Availability, and Operational Availability, but these terms describe different records, measures, roles, strategies, or decisions and should not be used interchangeably.
Related concepts
Related maintenance terms
Keep exploring connected CMMS, reliability, and maintenance planning terms.
Mean Time Between Failures
Mean Time Between Failures, or MTBF, is the average operating time between failures of a repairable asset during a defined period.
Mean Time to Repair
Mean Time to Repair, or MTTR, is the average time required to restore a repairable asset after failure.
Operational Availability
Operational availability is the proportion of total required time that an asset is ready for use under actual operating and support conditions.
Inherent Availability FAQs
- What is inherent availability?
Theoretical availability based on MTBF and active corrective repair time.
- What is the inherent-availability formula?
MTBF divided by MTBF plus MTTR.
- What is excluded?
Preventive maintenance, logistics, parts waiting, and administrative delay.