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Assessing Criticality

Ask two people in your plant which is the most critical item of equipment, and the chances are that they will give different answers. How can we conduct an objective and rational assessment of criticality that will be acceptable to all personnel and will provide an optimal prioritization of maintenance actions?

A practical and effective method for criticality assessment ensures that your maintenance and engineering efforts are focused in the correct areas.

What is Equipment Criticality?

An aircraft is a complex machine that can fail in many different ways. We might be justified in considering any failure mode as critical if it can cause the aircraft to crash. So we agree that all the following failure modes are critical:

  • Failure of all engines
  • Wing falls off
  • Both pilots fall unconscious
  • Aircraft hit by meteorite

If asked to rank these in order of criticality, most people would rank ‘Aircraft hit by meteorite’ as least critical. Why should this be 0 when the consequences of failure (total loss of aircraft) is just as severe as the others?

Obviously, the low probability of failure is the distinguishing factor here. We instinctively know that that the chances of an aircraft being hit by a meteorite are tiny compere even to the small chance of an engine failure. Hence it is clear that in assessing criticality, the consequences of failure, and the probability of failure (or failure rate) are the two prime factors.