How Much Maintenance is Enough, and How Much is Too Much?

One of the prime reasons for pursuing asset performance management (APM) is to optimize the availability and reliability of your assets while minimizing risk and costs. It is the primary reason companies decide to move beyond reactive maintenance. There always seems to be the delicate balance between not enough maintenance and too much maintenance. Either way, unexpected failures can not only lead to lost productivity and unexpected costs, they can result in far worse consequences, including being in the spotlight in national or international news.

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When maintenance activities become part of the news

Before the fatal Germanwings Barcelona to Dusseldorf flight crash in the French Alps last week was determined to be a deliberate act, the speculation was that some type of failure incapacitated the crew and caused the accident. The big question was ‘how could that be?’ given the plane had undergone a significant preventative maintenance (PM) procedure just the day before. In this case it turns out maintenance was not the issue, but for the first two days it was the prime suspect.

In a situation just the day before at the Sugarloaf Ski Resort in Carrabassett Valley, Maine, a mechanical failure of the gearbox of a ski lift failed, disabling the braking system and resulting in seven injured riders with three hospitalized. Approximately 220 riders had to be evacuated off the lift. Just a day earlier the lift had undergone routine PM and had a daily inspection prior to use. That lift had passed an annual state inspection and dynamic load test in the last year and regularly had PM at weekly, monthly and yearly intervals, yet it still failed catastrophically. Stories like this seem to occur regularly and the reputation damage—even if short-term, such as in the German Wings accident, where maintenance was not the issue—can still have an impact.

Why too much maintenance is just as bad as not enough

One of the objectives of a good PM or predictive maintenance (PdM) program is to prevent failures by performing routine inspections and preventative repairs. Yet companies report that equipment that has been operating well, when taken offline for PM, can fail soon after return-to-service for a variety of reasons. A classic study done by on the Australian Defense Forces determined that PM activities can induce failures for a variety of reasons: 

• Defective replacement parts introducing a mechanism not re-sent before PM.
• Incorrect procedures introducing anomalies that result in failures.
• Effectiveness issues such that maintenance procedure may not complete properly, such as seals seating or gaskets not sealing.
• Damage during maintenance may occur that goes undetected introducing a failure mechanism.
• Extended maintenance activity introducing lack-of-use cases where equipment operates best when in continuous service.
• Human error—i.e. people just executing the wrong activity.

There is also the fact that, particularly after significant rebuild activities, that the classic infant mortality bathtub curve also know as the P-F curve applies once again, so failures may seem to increase as a result of maintenance.

The solution lies in optimizing the maintenance interval

The goal of APM is to achieve operational excellence with you assets. This means maintaining at just the right interval. Classic PM programs, whether calendar or usage based typically either over- or under-maintain equipment.

The way to achieve this is to utilize both condition based maintenance (CBM) and reliability-centered maintenance (RCM) approaches on those critical assets, such as with the gearbox on the Sugarloaf ski lift. While not every asset demands the rigor of RCM, those assets whose failure can lead to injury or the loss of life really need the type of critical assessment that RCM provides to achieve a proper level of operational risk management (ORM).

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