We don’t live in a perfect world. Imperfect humans build imperfect machines. An unavoidable result of this is that the systems and assets we operate fail from time to time. However, businesses can still function with these imperfect systems if, when we need them, they are properly functioning. This is called system availability. System availability is the probability a system is functioning when needed to, under normal operating conditions. When the system is alive and well, the organization can continue to produce output and meet orders. The availability equation is as follows:
Availability calculations do not include preventive maintenance downtime. To increase availability, we can either increase the average time interval between repairs (MTBF) or decrease the amount of time spent doing the repair (MTTR). Understanding how maintainability and reliability affect availability is key in maximizing it, however, we must do this in a cost-effective manner. It is not possible to keep pumping capital into improving availability and expect linear returns.
What is maintainability?
Maintainability is the ease in which something can be maintained or restored to its functioning state. It determines how easy it is to isolate bugs or problems within a system preform the repair. Maintenance can impact maintainability directly by shortening the MTTR. This could be achieved through training; knowledge transfers, creating standardized procedures and checklists in your CMMS, creating best practices for troubleshooting, having the right tools onsite and recoding repair history in your CMMS to review later. As many of these actions can be tracked in Maintenance Assistant CMMS, it can play a large part in improving maintainability. Maintainability is also one of the most commonly over looked design attributes that can make the difference between a five-minute swap out and a 1-week rebuild. Modern systems are designed with modular components so they can be swapped out quickly. A quick example of this is modern aircrafts compared to pre-jet age models. Older airplanes typically had the propeller engine house in the fuselage at the front of the aircraft. This made it difficult to repair due to the positioning and the location of the propellers engine. Modern aircraft have turbines hanging below the wings that can be swapped in and out in 8 hours if needed. This means the repair can be completed offline and the aircraft is back flying quickly with the replacement engine.
System reliability is the probability that the asset will be able to execute a failure-free operation for a managed period of time within normal operating conditions. When reliability gets out of control, it can lead to a domino effect that engulfs the organization.
For example, it can lead to increase in stock outs; costly emergency parts orders, missed PMs, collateral damage, manpower shortages and ultimately missed orders. Maintenance can impact reliability by increasing the time lag between repairs. This can be achieved by optimizing the preventive maintenance program on an asset or the system. The easiest way is to include steps to proactively perform inspections so issues are spotted before they turn into something more serious. The common way to measure reliability is MTBF, which refers to the average time the asset functions normally before it fails. Maintainability rates are easier to predict and generally more accurate but reliability has a bigger impact on availability. Long periods of improved reliability will lead to increased availability. Maintenance doesn’t impact availability directly; rather it indirectly impacts availability through maintainability and reliability.
Cost vs. availability
Understanding how properly functioning systems and assets contribute to the bottom line is crucial in recognizing how important asset availability is to an organization. Ask any CEO or accountant how they measure how effective their maintenance function is and they will say cost – how much are we paying our maintenance guys and how much are they spending on parts and materials to keeping our assets operating. Today’s environment calls for a more forward-looking approach. Rather than examine costs in the past, organizations need to be able to predict outcomes. Take the airline industry for example; airlines only make money when their aircraft are in the air. By improving reliability and maintainability, it will have a direct impact on availability going forward, and thus the profitability of the business.
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