Maintenance Philosophy is the mix of strategies that ensure an item works as expected when needed. Definition Maintenance is a form of risk management that is required if and only if an item fails to satisfy the minimum level of specification performance when the items or system is required. Maintenance is optional and may not be required if the partially failed item still satisfies the minimum level of specification performance or if the item is not required for a span of time. Maintenance takes place in four phases. Failure Detection Fault isolation Corrective action Operational verification An item is said to be degraded when faults exist but normal operation can continue. Automatic recovery is used to avoid the need for maintenance. Automatic recovery from failure is required for systems and resources that cannot be accessed during deployment, such as rockets, missiles, satellites, submersibles, and items that are buried or encapsulated. There are multiple approaches. Custom items designed specifically for ultra high reliability Redundant items with reconfiguration features that automatically bypass failure Lot testing to reduce manufacturing defects Redundant items increase failure rate and reduce reliability if recovery is not automatic. Failure Detection Failure Detection involves two different maintenance strategies that interact with life-cycle cost and availability. Conditional Periodic Conditional Conditional maintenance relies on indicators that tell users when an item is failed. System is totally failed and cannot operate as expected System will function as expected but is degraded This requires automatic fault detection and reporting. Condition Based Maintenance (CBM) requires clearly observable or audible notification that is suitable for unsophisticated and untrained users, which includes the following. Colored indicator (red or yellow light) Display showing the phrase failed or degraded next to the item name Gage with clearly defined green, yellow, and red bands for normal versus faulted Audible indications, such as a buzzer, bell, or synthesized voice Recovery maintenance actions begin after notification occurs. Items are said to be instrumented when notification takes place automatically upon failure. There are two approaches. End-To-End (ETE) Self-reporting devices ETE testing involves an automated process that periodically injects something into the item, then the outputs are examined to determine if they satisfy the level of performance required by the specification. This may be intrusive, and could interfere with normal operation briefly. Self-reporting devices include automatic built-in-test (BIT) features that are less intrusive. Items without the kinds of notifications suitable for CBM have