MNT.2:4 - Solution
Start from the required function and a failure account sufficient to distinguish policy alternatives. Identify the loss of function, credible mechanisms and consequences. When one policy covers several mechanisms, check each mechanism that could justify a different task. Retain uncertainty where it matters rather than inventing a lifetime distribution from sparse events.
Construct the plausible task alternatives. The following distinctions help select a task; they are not a ladder of maturity.
| Task family | What can make it useful | What can defeat it |
|---|---|---|
| Corrective or deliberate run-to-failure | Failure is detectable and its consequence, recovery demand and collateral effects are acceptable for the use. | A hidden protection loss, unacceptable exposure or unavailable recovery capability makes waiting untenable. |
| Age- or usage-based action | Failure behaviour and restoration effectiveness support acting before a relevant age or usage condition. | Calendar age is a weak predictor, or replacement repeatedly introduces faults. |
| Condition-based action | An observable condition changes early enough to support a useful response. | The relevant failure is not detected, the alarm is unreliable, or response lead time exceeds the usable warning. |
| Failure-finding | A task reveals loss of a function that normal operation does not expose, such as a standby protective function. | The test misses the relevant failure or creates unacceptable exposure without adequate controls. |
| Opportunity-based combination | Shared access or downtime makes coordinated tasks worthwhile. | Bundling consumes useful life, creates interference or overcommits the outage. |
For each credible alternative, explain what performing the task changes. Include imperfect repair, task-induced defects and residual failure modes when material. If no acceptable maintenance action addresses a serious failure, return the specific redesign, redundancy or changed-use question to engineering or operation. Adding inspections that cannot reveal or alter the failure is not a substitute.
For condition-based work, reason across the complete response. The usable interval between detectable degradation and unacceptable functioning must accommodate detection delay, interpretation, obtaining support, access and the selected intervention, with uncertainty appropriate to the consequence. This is an applicability question, not a universal formula for a safe interval. A local detection threshold or interval needs the equipment and operating evidence that supports it.
Compare alternatives using the receiving use’s relevant values: loss of service, exposure, labour, material, disturbance, environmental effects and uncertainty. Use comparable operating horizons and state deliberately accepted trade-offs. Existing adequate evidence may already settle the choice. Select further investigation only when an attainable answer could change it enough to justify acquisition, interpretation, delay and displaced work.
State the chosen policy in actionable terms. Name the applicable population or configuration, task, trigger or interval basis, relevant support assumptions, response to an out-of-scope condition and the evidence or changed use that would reopen it. Where an operative requirement fixes a task, preserve its current force. A separate merits appraisal may support a request to the authorized rule holder; it does not authorize unilateral relaxation.