Three Types of Maintenance

It's a matter of fact that every physical system (from light bulbs to aircraft engines) degrades over time and requires servicing to keep operating. Subject to the nature of the system, one of 3 few different maintenance strategies will be used to service the asset. These three different types are as follows:

• Reactive Maintenance
• Preventive Maintenance
• Predictive Maintenance

Reactive Maintenance

Reactive Maintenance is the most basic maintenance strategy that a company could implement. It consists of waiting for a system to fail or break to then replace its components. As illustrated below, the system's condition degrades over time, but no action is taken until the system totally fails. This creates downtime and requires maintenance / repair activities to put the machine back into operation, let alone back to a healthy state. Often, Reactive Maintenance is employed because the state of the asset is simply not being monitored.

Reactive Maintenance is a strategy that is best suited for inexpensive and easily disposable products/consumables where downtime does not have a high impact on business operations or customer satistifaction. And it goes without saying that allowing an asset to run to failure is never a suitable option where failure would endager life.

The perfect use case for a reactive maintenance strategy is a light bulb that gets replaced after it fails. Such a product is cheap, disposable, easy and quick to replace, and the downtime does not normally impact any business operation. A counter-example would be an aircraft engine, where a failure is unacceptable as it puts at risk the lives life of hundreds of people. For this type of product, it is essential to implement a Preventive, or even better, a Predictive Maintenance strategy.

Preventive Maintenance

Preventive (or preventative) Maintenance is a strategy that consists of organising technical diagnosis and maintenance activities on a fixed, pre-defined schedule. As the name suggests, this strategy is an attempt to prevent the system from failing.

The frequency at which the machine should be inspected is generally defined using the Mean Time Between Failure (MTBF) of the system in combination with other readily available reliability data. Typically, intercepting an asset for servicing would need to occur at a cadence of less cycles/hours than stated in the MTBF. This would ensure more than half of failues be intercepted. But the other side of that decision would also be true - a significant prortion of service interventions would be uneccesary. So it's clear that because this pre-defined schedule does not take into account the real-time condition of the system, Preventative Maintenances generates unnecessary maintenance cost and does not fully protect the system from failures, as depicted in the below illustration.

Preventative Maintenance is a strategy that is best suited for expensive, and often, safety critical systems, where failures can cause low safety conditions, high repair costs, and downtime that significantly impacts business operations and customer satisfaction. Some examples include aircraft systems such as engines or landing gear, train systems, elevators, and even cars - passing an MOT on a yearly basis is indeed a Preventative Maintenance strategy. These systems are all safety critical and therefore need to be examined on a regular basis.

However, the clear downside of Preventive Maintenance is the unnecessary inspection costs that come with it. Indeed, conducting regular inspection and diagnosis , pre-defined schedule is very expensive.The simple example of a car's MOT speaks to everyone. While most cars are in a roadworthy condition, they still have to pass their MOT a yearly basis. However, this is clearly a neccesary part of car ownership, and the MOT cost is relatively low given the risk of failure due to a critical malfunction.

But now think about what the inspection cost could be for an entire aircraft. Every year, companies spend many millions on Preventative Maintenance, where maintenance may not have been neccessary. This cost constitutes lost business through downtime, reputation loss through customer dissatisfaction, and labour costs associated with inspecting equipment. This is where Predictive Maintenance comes in - to provide data driven insights that can inform maintenance decision, spreading out maintenance costs over more manageable timeframes than those offered by a Preventive Maintenance Strategy.

Predictive Maintenance

Unlike the 2 previous types of maintenance, Pedictive Maintenance consists of monitoring the real-life condition of a system, with the ultimate goal of determining its Remaining Useful Life (RUL) - that is, how long can the system operate before failing.

Knowing the RUL of a system gives the ability to organise maintenance in an optimal time before that system fails, thus avoiding unneccessary inspection tasks. On top of that, Predictive Maintenance offers a robustness that no other maintenance strategy can - it can detect and avoid more types of failures. Instead of simply running maintenance on a predefined schedule, Predictive Maintenance can detect an anomaly that would be missed during the inspection stage of a Preventive Maintenance check. Naturally, Preventative Maintenance is bound to a routine set of sub checks. Predictive maintenance checks the system health in a holistic manner observing the system as a whole, which often allows it to identify a much broader range of issues.

Predictive Maintenance: Driving Operations Through Data

Maintenance strategies are essential for ensuring the reliable and cost-effective operation of physical systems and assets. While Reactive Maintenance provides a basic approach suitable for inexpensive and disposable items, Preventive Maintenance schedules regular inspections to prevent failures in critical systems like aircraft engines. However, Predictive Maintenance represents the pinacle of Industry 4.0 - utilising data-driven monitoring to optimise maintenance timing and avoid unnecessary costs. By tracking real-time system condition and estimating Remaining Useful Life, Predictive Maintenance allows companies to stay ahead of failures, minimise downtime, and stretch maintenance cost. As technology continues advancing, the insights provided by Predictive Maintenance will become increasingly invaluable for organisations seeking to extend asset lifetimes, enhance safety, and elevate their maintenance programs to new heights of efficiency and effectiveness.