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Why do equipment failures happen even when preventive maintenance is completed?

Completing a PM shows that a task was recorded as done; it does not prove the task addresses the actual failure mode or gives enough warning to act.

What to look for

Review the failure history, task instructions and findings for the affected asset. Check whether the PM is aimed at the failure mechanism, whether its interval is appropriate for the operating conditions, and whether abnormal findings generate work that is completed in time.

Practical next steps

• Compare failures with the PMs performed before them, not just the compliance percentage.
• Ask technicians whether instructions, access and tools allow a meaningful inspection.
• Evaluate whether condition monitoring, a redesigned task or another strategy addresses the failure more effectively.

Do not remove or change safety-critical, statutory or manufacturer-required tasks without the appropriate technical review and site approval.

Trace the failure back to the task

Choose a recent significant failure and reconstruct the sequence: when the last PM was performed, what the technician was instructed to inspect, what was found, whether follow-up work was created, and when that work was completed. Compare the task to the actual failure mechanism, operating duty and available lead time.

A completed lubrication task, for example, may not detect a developing alignment issue. A vibration finding may also be useful only if it is interpreted and acted on before the defect progresses. These are illustrative possibilities, not a diagnosis of a specific failure.

Questions to ask the team

• Can the task detect or prevent this failure mode, and what evidence supports that?
• Are instructions specific enough to produce an actionable finding?
• Do technicians have access, time, tools and a clear escalation path?
• Are defects corrected before the next interval, or do they remain in backlog?

Use the answers to propose a change and have the appropriate technical authority review it. Preserve applicable safety, regulatory and manufacturer requirements.

Related answer: Which maintenance metrics should a plant manager review?

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