MNT.3:4 - Solution
State the functioning question and the failure claim that would change the decision. Separate a complete loss, degraded contribution and loss of a protective function. Define the event sufficiently for another reader to distinguish it from an inspection finding or preventive removal.
Recover available evidence at its actual scope. For a physical component, this can include operating conditions, measurements, photographs, inspection returns, installation and removal facts, applicable configuration and the sequence of earlier work. Preserve when and how observations were obtained. An occurrence reconstructed from an operator’s report has a different evidential limit from a directly inspected fracture surface.
Build the smallest useful causal account. Connect the required function to the observed departure, candidate mechanism, local effect, System effect and consequence. A short table can keep alternatives visible:
| Candidate explanation | Observation it explains | Evidence that could change the maintenance choice |
|---|---|---|
| Bearing damage | A supported bearing-related signal or physical finding | The specialist interpretation and applicable component inspection. |
| Alignment or installation problem | A change associated with installation or operating load | Existing alignment and installation records, or a justified discriminating check. |
| Measurement or operating-context change | A discontinuity matching sensor, speed or load change | Comparable measurement conditions and instrument information. |
These are example hypotheses, not a diagnostic rule for all pumps. Include a different mechanism when the actual evidence makes it consequential.
Distinguish what is supported, what remains plausible and what is contradicted. Do not turn a possibility into a cause by placing it in a fault-tree box. Where several explanations support the same immediate recommendation, return that recommendation’s evidential basis and leave the stronger causal claim unresolved. Where the alternatives require different actions, identify the smallest attainable observation that could discriminate them.
For population claims, recover the denominator and observation process. Operating hours, starts, cycles, calendar exposure and units under observation answer different questions. A unit still operating at the end of observation has a known survival interval, not a known eventual lifetime. A preventive removal ends or changes that component’s exposure; an overhaul may not restore it to an as-new state. Treat those distinctions explicitly before fitting or comparing a failure model.
When selecting an investigation, compare its obtainable contribution with the whole burden. Include the effect of delay, disturbance, specimen preservation and specialist interpretation. A low-value inquiry can stop while an adequate maintenance answer remains available. If a claim has high consequence, use the applicable evidence and assurance rules for that claim; more records alone do not establish it.
Return a failure account whose uncertainty changes action where necessary. Preserve evidence needed by a real later decision in the maintenance history. State a reopen condition, such as recurrence under a supposedly corrected condition or a newly inspected part contradicting the diagnosis.