H - Evident

If the failure consequence is evident, select Yes. If it is hidden, select No. A hidden failure does not become apparent to the operating crew under normal circumstances if the failure mode occurs on its own.

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1 - On-condition task

This task entails checking for potential failures so that action can be taken to prevent the functional failure or to avoid the consequences of the functional failure. On-condition tasks are so called because the items that are inspected are left in service on the condition that they continue to meet specified performance standards.

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H4 - Failure finding

This task involves checking a hidden function at regular intervals to find out whether it has failed. The intervals are calculated based on the required availability of the asset and the reliability of the protected function. This strategy applies when the failure effect is hidden.

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S - Safety

There is an unacceptable risk that the effects of the failure mode could kill or injure someone.

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2 - Scheduled restoration

The scheduled task restores the capability of an asset at or before a specified interval (age limit), regardless of its condition at the time, to a level that provides a tolerable probability of survival to the end of another specified interval.

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H5 - Multiple failure

A multiple failure occurs if a protected function fails while its protective device or protective system is in a failed state. This option applies when the failure effect is hidden.

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E - Environmental

There is an unacceptable risk that the effects of this failure mode could breach a known environmental standard or regulation.

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3 - Scheduled discard

The scheduled task entails discarding an asset at or before a specified age limit, regardless of its condition at the time.

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S4 - Combination of tasks

If a failure mode or a multiple failure could affect safety or the environment and no scheduled task on its own reduces the risk of failure to an appropriate level, a combination of tasks (usually from two different task categories, such as an on-condition task and a scheduled discard task), might be needed. This strategy applies to safety and environmental consequences.

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O - Operational

The failure mode has a direct adverse effect on the operational capability of the asset (output, product quality, customer service, military capability, or operating costs in addition to the cost of repair). A non-operational failure does not adversely affect safety, the environment, or operations, but repair or replacement is required for any item(s) that may be affected by the failure.

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Frequency

Frequency with which the recommended action needs to be performed. When failure mode optimization requires Isograph Availability Workbench, this attribute is mapped to the inspection task’s Interval property in AWB.

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Recommended strategy

• Do the on-condition task: Condition-based maintenance entails checking for potential failures so that action can be taken to prevent the functional failure or to avoid the consequences of the functional failure. On-condition tasks are so called because the items that are inspected are left in service on the condition that they continue to meet specified performance standards. • Do the scheduled restoration task: Scheduled restoration entails restoring the initial capability of an existing asset at or before a specified age limit, regardless of its apparent condition at the time. • Do the scheduled discard task: Scheduled discard or replacement tasks entail discarding an asset at or before a specified age limit, regardless of its condition at the time. • Do a combination of tasks: If a failure mode could affect safety or the environment and no scheduled task on its own reduces the risk of failure to an appropriate level, a combination of tasks (usually from two different task categories, such as an on-condition task and a scheduled discard task), might be needed. This strategy applies to safety and environmental consequences. • Do the failure-finding task: Failure-finding maintenance involves checking a hidden function at regular intervals to find out whether it has failed. Intervals are calculated based on the required availability of the asset and the reliability of the protected function. • Redesign is compulsory or desirable: Modification or redesign is any one-time change to the equipment, training, maintenance or operating procedures, etc. • No scheduled maintenance: No scheduled maintenance means assets are left in service until a functional failure occurs, at which point they are repaired or replaced. • Review existing maintenance is available for secondary action plans only. This strategy alerts the analysis team to review an asset’s existing maintenance program to identify items that are no longer required. • Not analyzed: Not anlayzed means that an action type has not been determined.

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