Wars, especially modern ones that involve huge masses of people, one of the many consequences - often tragic - have the ability to uproot brilliant minds from the most disparate sectors and confront them with issues that probably would never have attracted their attention. This is what happened in 1943 to Conrad Hal Waddington. Evolutionary biologist, paleontologist, geneticist, embryologist, philosopher, poet and painter, Waddington was not particularly interested in aviation but with the outbreak of the Second World War he found himself enlisted in the Royal Air Force (RAF).

Aged forty, when he became scientific advisor to the Commander-in-Chief of the Coastal Command, Waddington was already an established scientist but fighting the German submarine threat more effectively seemed to have little relevance to his studies on epigenetics. Waddington and his colleagues developed a series of surprising recommendations that challenged the conventional military wisdom of the time in terms of attack tactics but what we remember him for here was his observation concerning the fact that of the 40 B-24 "Liberators" of the Coastal Command only half were flying in search of German U-boats while the other 50% was systematically grounded largely undergoing maintenance or waiting for it, whether planned or unplanned.

Adopting the methods that had already challenged his established beliefs, Waddington applied statistics and observed that scheduled preventive maintenance at very intense cycles was harmful, increasing the frequency of failures after the interventions. As with surgery, maintenance had to be performed no more than necessary otherwise risking reducing safety and reliability. The proposed solution was to increase the time interval between scheduled maintenance cycles and to eliminate all preventive maintenance activities that could not be proven effective. 


Maintenance and reliability

In the 1960s, at United Airlines the aeronautical engineer Stanley Nowlan and the mathematician Howard Heap rediscovered these principles independently - Waddington's results remained classified until 1973. This phenomenon was later nicknamed the "Waddington Effect" and led to the first development in condition-based monitoring while laying the foundations for predictive maintenance. Reliability Centred Maintenance was formalised for the first time by Tom Matteson and by the afore-mentioned Nowlan and Heap to describe a process used to determine the requirements for optimal maintenance in the aeronautical field and then extended to other areas to establish safe minimum maintenance levels and to ensure that the systems continue to do what is required of them. Among the paradigm changes inspired by RCM, some concerned the fact that the vast majority of failures are not necessarily linked to the age of the asset and that efforts should be aimed at identifying the causes of failures rather than the life expectancy of the components.

As we have seen, the techniques that allow us to design, build and manage systems with the aim of maximising production time saw the first applications in areas where operational continuity was a safety requirement (aerospace, chemical, nuclear, power industries).

The objectives of reducing costs - in terms of maintenance costs and production stoppages - are the second driver that has stimulated the study of techniques to increase the reliability and maintainability of systems.

Today, the use of extremely precise and finely calibrated digital instruments and the ability to predict mechanical component failures has significantly improved analytical capabilities.

Benefits of predictive maintenance

The benefits that can derive from the application of predictive maintenance are:

  • Reduction of stops due to failure
  • Reduction of repair times
  • Reduction of faults caused by a previous fault
  • Optimal use of components according to their useful life
  • Limitation of qualitative drifts (quality maintenance)
  • Optimisation of spare parts

Another aspect should also be considered; the absence of damage (from scheduled downtime to the serious accident, passing through the fault), permitted by predictive maintenance, reduces the risk profile to the point that many insurance companies promote the adoption of predictive maintenance protocols with discounts on premiums.


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