Reliability Engineering


Training & Seminars




Norcan Reliability Engineering


Reliability Centred Maintenance 

Stanley Nowlan and Howard F. Heap

Provides the first full discussion of reliability-centered maintenance as a logical discipline for the development of scheduled-maintenance programs:

The objective of such programs is to realize the inherent reliability capabilities of the equipment for which they are designed, and to do so at minimum cost. Each scheduled-maintenance task in an RCM program is generated for an identifiable and explicit reason.
The consequences of each failure possibility are evaluated, and the failures are then classified according to the severity of their consequences.

Then for all significant items —those whose failure involves operating safety or has major economic consequences—proposed tasks are evaluated according to specific criteria of applicability and effectiveness. The resulting scheduled-maintenance program thus includes all the tasks necessary to protect safety and operating reliability, and only the tasks that will accomplish this objective.

Up to this point the only document describing the use of decision diagrams for developing maintenance programs has been MSG-2, the predecessor of PCM analysis. MSG-2 was concerned primarily with the development of prior-to-service programs and did not cover the use of operating information to modify the maintenance program after the equipment enters service or the role of product improvement in equipment development.

The chief focus was on the identification of a set of tasKS that would eliminate the cost of unnecessary maintenance without compromising safety or operating capability. There was no mention of the problem of establishing task intervals, of consolidating the tasks into work packages, or of making decisions where the necessary information is unavailable. The treatment of structure programs was sketchy, and zonal and other general inspection programs were not discussed at all.

A Maintenance Philosophy

An operator's maintenance program has four objectives:

  • To ensure realization of the inherent safety and reliability levels of the equipment
  • To restore safety and reliability to their inherent levels when deterioration has occurred
  • To obtain the information necessary for design improvement of those items whose inherent reliability proves inadequate
  • To accomplish these goals at a minimum total cost, including maintenance costs and the costs of residual failures
  • widely accepted as a world-wide specification for organizations seeking to demonstrate a high level of professionalism in managing their physical assets

Reliability-centered maintenance is based on the following precepts:

A failure is an unsatisfactory condition. There are two types of failures: functional failures, usually reported by operating crews, and potential failures, usually discovered by maintenance crews.

The consequences of a functional failure determine the priority of maintenance effort. These consequences fall into four categories:

Safety consequences, involving possible loss of the equipment and its occupants

Operational consequences, which involve an indirect economic loss as well as the direct cost of repair

Nonoperational consequences, which involve only the direct cost of repair

Hidden-failure consequences, which involve exposure to a possible multiple failure as a result of the undetected failure of a hidden function

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Reliability Centred Maintenance - Stanley Nowlan and Howard F. Heap



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