Work out system availability instantly with clear inputs, formula shown and shareable results.
Inherent availability of a component is MTBF/(MTBF+MTTR). Components in series multiply, so a chain of five components at 99.67% each gives only 98.35%. Operational availability further deducts planned maintenance, and multiplying its complement by 8760 gives expected annual downtime hours.
Availability
A_component = MTBF / (MTBF + MTTR); A_series = A^n
Operational
A_operational = A_series x (8760 - planned downtime) / 8760
Availabilities multiply. Ten components at 99% each give 90.4% system availability, which is why simplification is often more effective than improving individual items.
Halving MTTR usually gives the same availability gain as doubling MTBF, and is far cheaper to achieve through spares, access design and trained crews.