Making sense of maintenance metrics: System availability

Welcome to our series of blog posts about maintenance metrics. This post outlines everything you need to know about system availability: What it is, how to calculate it, and why it’s important to your maintenance operation. Click here to see the rest of the series.

Table of contents

Explaining system availability

System availability is a metric used to measure the percentage of time an asset can be used for production. It calculates the probability that a system isn’t broken or down for preventive maintenance when it’s needed for production. System availability allows maintenance teams to determine how much of an impact they are having on uptime and production.

For example, let’s say you’re cooking the turkey for Thanksgiving and have 10 hours until dinner. You spend half an hour cleaning the oven and half an hour pre-heating it. The oven also breaks down for an hour. That means the oven was only available for eight hours. Thankfully, that’s all it takes to cook your turkey.

When you translate this example to a facility that relies on producing things, you can see how important system availability can be. If a piece of equipment isn’t available at the right times, it can mean more than just a late dinner — it can mean late orders, missed shipments, broken contracts, upset customers, and lost money. Maintenance can have a huge influence on system availability, from the way preventive maintenance is scheduled and carried out, to the response of the team when an asset breaks down unexpectedly.

Availability, reliability, and maintainability: What’s the difference?

Asset availability is impacted by several factors. Reliability and maintainability are two factors that are heavily influenced by maintenance. Understanding how reliability and maintainability affect availability is key to improving it at your facility.

What is reliability?

System reliability is the probability that an asset can perform without failure for a specific period of time and under normal operating conditions. A reliable piece of equipment performs like it’s supposed to every time you use it. Simply put, reliability is the absence of unplanned downtime. For example, think about your car — reliability is having it start every time you put the key in the ignition.

If a piece of equipment isn’t available at the right times…it can mean late orders, missed shipments, broken contracts, upset customers, and lost money.

Availability and reliability are often confused for one another, although they are very different. Reliability is impacted by unplanned downtime, whereas availability is impacted by all downtime, planned and unplanned, including breakdowns, inspections, equipment changes, and more. If an asset never fails, it is 100% reliable. However, that same asset may be down for one of every 10 hours during a routine inspection. In this scenario, the availability would be 90%.

What is maintainability?

Maintainability measures the ability to maintain or restore a piece of equipment to its functioning state. It calculates how easy it is to identify problems with a system and solve the problem. Because maintainability impacts the length of downtime for an asset, it also has a direct impact on availability.

The maintainability of an asset is commonly measured with mean time to repair (MTTR). A shorter MTTR means higher maintainability. Higher maintainability can be achieved with a variety of strategies, such as better training and knowledge transfer, maintenance checklists, improved troubleshooting, smarter inventory management, and a bigger focus on a modular design.

How to calculate system availability

There are two components to the system availability formula. The first is total uptime and the second is total downtime. Uptime is any time that asset is performing at a normal output. Downtime is any time the equipment is not available for production, including planned and unplanned downtime.

To calculate system availability for a certain period of time, divide an asset’s total amount of uptime by the sum of total uptime and total downtime.

Availability = uptime ÷ (uptime + downtime)

Here’s an example of the system availability formula in action: One of your top production assets ran for 100 hours last month. The asset broke down twice during the month, and it took one hour to repair each time. The asset was also shut down for eight hours in a month for routine inspections.

At the end of the month, you can see that there was 100 hours of uptime on the machine and 10 total hours of downtime on the machine. Therefore, the availability calculation looks like this:

Availability = 100 ÷ (100 + 10)
Availability = 100 ÷ 110
Availability = 0.909
Availability = 90.9%

If you’re looking to benchmark your operation against the best in the world, top-tier organizations achieve system availability of 90% or higher.

How to improve system availability

Every company wants its equipment to work as much as possible. After all, when equipment is running, money is being made. That’s why improving asset availability is so crucial to production facilities. Maintenance teams can play a huge role in increasing availability and ensuring the success of an organization.

Make good use of failure codes

Failure codes tell you everything about why an asset failed so you can quickly understand how to make it right. They impact availability by helping you reduce downtime. When unplanned downtime strikes, failure codes allow technicians to respond quickly, troubleshoot better, and get an asset up and running sooner. They also help you ensure breakdowns don’t become a problem in the first place. Failure codes help you collect a mountain of historical data, which allows you to identify the root cause of a breakdown, spot trends with troublesome work practices, and build a reliability-centred maintenance strategy. For example, if misaligned bearings cause consistent failure, you can make changes to your processes and tools to solve the problem.

Build maintenance SOPs and maintenance checklists

Standard operating procedures and maintenance checklists provide structure to your operation so work is done accurately and quickly. Availability is improved by increasing reliability and reducing maintenance time. Maintenance SOPs help your team keep one eye on the present and the other on the future. Breakdowns are fixed, but they’re also investigated so the root cause is dealt with. They also dictate how work orders are handled so resources are used efficiently on critical assets. Maintenance checklists guide technicians during repairs and PMs. Tasks can be done faster and done properly, human error is minimized, and equipment is more reliable.

When equipment is running, money is being made. That’s why improving asset availability is so crucial to production facilities.

Optimize your preventive maintenance

Preventive maintenance affects availability by helping to reduce failure and by taking equipment out of production for routine maintenance. Pinpointing which PMs should be done more or less often will make your operation more efficient and maximize availability. Start by looking at failure rates to optimize PM intervals. If an asset is failing often in spite of regular PMs, there could be other reasons for failure. Next, look at historical failure codes to determine if you can avoid breakdowns by introducing a new PM. Lastly, eliminate unnecessary PMs. If failure rates are low, revisit the frequency of PMs on that asset.

Levelling up with improved system availability

Improving system availability can have a ripple effect across your entire organization. It means maintenance resources are being used efficiently, production levels are as high as possible, and your company’s margins can be healthier than ever. There are several ways maintenance can influence system availability by targeting improved reliability and maintainability. Creating better processes and using all the tools at your disposal are the quickest ways the maintenance team can make a big impact on availability and help the business take a step forward.