Reliability Terms
1. Active Repair Time – That portion of the downtime during which one or more maintainers are working on the equipment or system to affect a repair. This time includes preparation time, fault-correction time, and final checkout time for the equipment system, and perhaps other downtime subdivisions, as required in special cases.
2. Achievable Availability -- The probability that a system is operating satisfactorily at any point after the start of operation, when operated under stated conditions when the times considered are operating time, active repair time, logistic time, administrative time, and preventive maintenance time.
3. Administrative Time – That portion of the downtime not included under active repair and logistic downtime, but required to make decisions about maintenance crews, etc.
4. Availability – The percent of time that equipment is mechanically able to perform its required function.
5. Corrective Maintenance – Maintenance activities required to place equipment back into its required operating state.
6. Design Adequacy – The probability that a system will successfully accomplish its mission, given that it is operating within design specifications, and accomplish all the design-to objectives.
7. Downtime – The total time during which the system is not in acceptable operating condition. Downtime can be subdivided into a number of categories such as active repair time, logistic time, and administrative time.
8. Failure – The loss of equipments ability to perform its required function. Does not require the equipment to be inoperable.
9. Failure Effects – The physical manifestations of the loss of required function. Includes such items as equipment downtime, loss of quality, injuries, damage to other equipment and surroundings, and environmental impacts.
10. Free Time – Time during which operational use of the system is not required, but for which the system is operationally ready.
11. Intrinsic Availability – The probability that a system is operating satisfactorily at any point after the start of operation, when operated under stated conditions when the only times considered are operating time, and active repair time.
12. Logistic Time – That portion of the downtime during which repair is delayed solely because of the necessity for waiting for a replacement part or other subdivision of the equipment or system, for acquisition of required tools, additional maintenance personnel, diagnostic equipment, etc.
13. Maintainability – The probability that, when maintenance action is initiated under stated conditions, a failed system will be returned to operating condition after a specified downtime.
14. MTBF – Mean Time Between Failures. Applicable to repairable systems.
15. MTTF – Mean Time To Failure. Applicable to non-repairable systems.
16. MTTR – Mean Time To Repair. The average time it takes to perform corrective maintenance on a system.
17. Operational Availability -- The probability that a system is operating satisfactorily at any point after the start of operation, during normal plant operations.
18. Reliability (R) – The probability that a system will perform satisfactorily for a given period of time under stated conditions.
19. Repairability -- The probability that a failed system will be returned to operable condition within a specified repair time. Ease of access to critical components improves repairability.
20. Storage Time – Time during which the system is assumed to be in operable condition, but is not required for use.
21. Unreliability (Q) – The complement of Reliability.