Availability
A = MTBF / (MTBF + MTTR) - the fraction of calendar time the equipment is capable of operating.
Availability
99.701%
Number of 9s
2.52 -
Formula, assumptions, and limits
Targets: main propulsion A ≥ 0.995 (two 9s); steering gear ≥ 0.998; auxiliary ≥ 0.97. Nines notation: 99.9 % = 3 nines. Ship's Class may require spare-in-redundancy if A below threshold.
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| Mean Time Between Failures | h | maintenance records | |
| Mean Time To Repair | h | maintenance records | |
| Availability | - | result |