UNDERSTAND THE CONCEPT
Reliability concerns performing without failure over a mission. Maintainability concerns restoration under defined conditions. Availability concerns readiness when needed. A system can fail relatively often yet show high availability if restoration is quick; the operating consequence of those failures can still be serious.
Under a simple steady-state repairable-system model, inherent availability is MTBF / (MTBF + MTTR), using consistent operating and active repair durations. Operational availability needs a broader agreed time accounting, including relevant waiting and support delays. Do not interchange the two measures.
Questions to take back to your team
- Which availability definition is being reported?
- Does downtime include logistics and administrative delays?
- Are mission reliability and readiness shown separately?
Further reading
Explore the primary references below. Requirements and applicability depend on your organization and jurisdiction.
