3. RMA Application Rationale: Availability

The probability a repairable item will perform its intended function at a given point in time (or over a specified period of time). In other words, availability is the probability of an item’s mission readiness, an uptime state with the likelihood of a recoverable downtime state. Its value is in the interval [0, 1], and cannot be less than zero and cannot be greater than one. Note: It is availability and not reliability that addresses downtime (e.g., time for maintenance, repair, and replacement activities). It is important to determine if the management question or system requirement is limited to reliability (only uptime) or if it pertains to availability (uptime with recoverable downtime in the near term). 

There are many types of Availability, Point availability (A(t)), Average availability Steady State availability (A(∞)), Inherent availability (A_i), Operational availability (A_o), and Data availability (A_d), and each can be assessed using demonstrated (descriptive - based on actual achieved performance) or predictive (inferential - based solely on the failure distribution (reliability math model) and the repair distribution (maintainability math model)) measures of performance. However each has its own considerations and value to the metric consumer.

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