Three Dimensions for #availability Inherent, Achieved & Operational Availability.
Mohamed Hafez, MBA, Master Mechanical Engineering, ,CRL,LSSGB, MLA II, CAT-II VA,TapRoot Team Leader.
Rotating Equipment Lead @ SASREF | Reliability Expert in Mechanical Engineering |Master of Business Administration l.
Three Dimensions for #availability which are Inherent, Achieved & Operational Availability.
#Availability is Probability that the system will be available when required.
1.Inherent availability is the steady state availability, considering only the corrective downtime of the system and assuming no external factors influence its performance.
****these internal characteristics.
MTBF: Mean Time Between Failure which reflects the average time a system operates before failure occurrence.
MTTR: Mean Time to Repair which defined the average time required to repair the system
Inherent Av. gives initial information about system reliability and base for the further availability metrics.
2.Achieved Availability (Aa):
in addition to internal product characteristics preventive maintenance downtimes are also included.
Both corrective and preventive maintenance actions are considered.
MTBM (Mean Time Between Maintenance) is used for calculating Achieved Availability. MTBM consider the system downtime during preventive maintenance activities and failure caused repair time. Simply explanation is average duration between one to another maintenance activity.
Mct and Mpt is used for calculation of Achieved Availability.
Mcmt is the average time required to perform repair action when the system fails.
Mpmt is the average time required to perform preventive maintenance action on the product in defined period.
MTBPM = Mean Time Between Preventive Maintenance
Mpmt = Mean Preventive Maintenance Time
Mcmt = Mean Corrective Maintenance Time
Achieved Availability offers a more realistic information about product performance by incorporating planned maintenance activities that contribute to its overall uptime.:
3. Operational Availability (Ao):
Operational Availability is a real-world metric that takes into consideration both planned, unplanned downtime and logistic delays providing a comprehensive view of a system's actual operational performance. This metric includes all actual source of downtime, such as administrative downtime, logistic delay, etc.
#Operational Availability is the ratio of the system uptime to total time.
Inherent, Achieved, and Operational Availability are interconnected metrics that provide different perspectives on a system's reliability and performance.
High Inherent Availability ensures the reliability of product/system.
Achieved Availability guides maintenance planning, reducing unplanned downtime.
Operational Availability provides a real-world assessment considering the all possible downtime of the product/system and help companies understand product availability characteristic. Each of this metrics should be evaluated by manufacturers to produce more competitive products.
References
MIL-HDBK-338 Rev. B - Electronic Reliability Design Handbook
James V. JONES, Integrated Logistic Support Handbook
DOD Guide for Achieve Reliability, Availability and Maintainability