Equipment downtime analysis is used to evaluate the expected time that a piece of equipment is not available (i.e., it is down) due to maintenance or a supply backlog. This value is the sum of elapsed maintenance time, awaiting parts time, and awaiting maintenance time. It is a primary measure of merit that considers reliability, maintainability, support system attributes, and operational environment. The results of this analysis may be used to calculate other equipment measures of merit, such as mission capable rate and equipment availability. The results of the analysis indicate those areas driving non-availability of the equipment and are used to evaluate alternative design and support concepts based on total system downtime.
Equipment downtime is derived by using the reliability and maintainability parameters and support parameters. Downtime (DT) is the sum of elapsed maintenance time (EMT), awaiting parts (AWP) time, and awaiting maintenance (AWM) time, and can be expressed as:
DT = EMT + AWP + AWM (Equation 5)
where: This parameter indicates repair time for corrective (unscheduled) maintenance. EMT is a function of failure rate, maintenance action rate, maintenance action to failure ratio, and mean time to repair. It can also include administrative and logistics delay.
AWP time combines mean operating hours between demands, not repairable this station (NRTS) rate, and expected available inventory to determine the expected length of time a part is not available due to stockout conditions.
AWM time is the expected length of time the equipment cannot be worked on due to any other considerations such as unavailable personnel, administrative delays, logistics delays other than spare parts (e.g., support equipment), and weather delay. This is usually derived from field data.
Equipment downtime analysis is typically performed at the total system level to provide the operator with information that can be used for: (1) alternative design or support system concept comparisons, (2) operations or mission planning, and (3) readiness capability assessment. Individual subsystems and lower indenture equipment items can also be evaluated using this analysis approach to identify the effects of individual equipment modifications or high-driver contributors to overall system downtime.
Equipment downtime analysis may be used any time during the program or product life cycle. The depth of this analysis increases as the system is more completely defined and parametrically described in the later phases of a program. Early use of downtime analysis will provide criteria to influence design for supportability, while later use will point out corrective actions that can be taken through changes in the design or support system.
Equipment downtime analysis results in a figure of merit called "equipment downtime," measured in hours, days or other time cycle appropriate for the equipment evaluated. It can be used to identify areas driving system non-availability, to compare alternate design or support system concepts, and as input to other equipment capability measures.