Building a better maintenance schedule starts with understanding your assets and your resources, and how you can effectively bring the two together. This article looks at two core principles of PM scheduling, fixed and floating schedules, to help you better organize preventive maintenance.
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Many everyday activities can be considered maintenance, from brushing your teeth to washing dishes. Most of these tasks are so routine, you barely think about how often you do them. Teeth are brushed at the same time every day and the dishwasher is run when it’s full.
The same ideas guide preventive maintenance scheduling. Tasks are scheduled at certain intervals because it’s what’s best for the asset. But “what’s best” for assets can differ. Understanding the difference allows you to coordinate PMs more effectively, build an efficient maintenance schedule, reduce the risk of downtime, effectively manage backlog, and control costs.
What are fixed and floating PM schedules?
Fixed PM scheduling is when regular maintenance is scheduled at a certain time or usage interval based on the target start date of the previous work.
For example, maintenance may be set up for a truck every 1,000 miles. A work order is triggered every 1,000 miles, regardless of when maintenance was last completed. That means that even if the previous PM was late (let’s say it was done at 1,400 miles), the next PM would still be triggered at 2,000 miles. Fixed PMs can also be time-based. If that same truck is scheduled for maintenance every 10 days, a work order is sent out on the tenth day, whether the last PM was done on time, five days late, or not at all.
Building a better maintenance schedule starts with understanding your assets, your resources, and how to effectively bring the two together.
Floating PM scheduling is when preventive maintenance is scheduled based on the completion of the previous PM, the past usage of an asset, and the condition of the asset.
For example, a motor needs to be inspected after every 100 hours of operation. This maintenance might take place in a week or a month, depending on the production schedule. The next round of maintenance also changes if the motor is used differently. Maybe the motor is inspected after 120 hours of operation because a PM is done late. In this situation, the next work order for this PM would be triggered at 220 hours under a floating maintenance schedule.
When to use fixed PM scheduling
Fixed preventive maintenance scheduling doesn’t work for every asset, nor does it work in every situation. There are a few scenarios when a fixed PM schedule works best and helps a facility use its resources efficiently while reducing downtime.
Maximizing labour and parts
Fixed PMs can help spread out tasks evenly for organizations with a large number of PMs. This makes it easier to plan labour and resources. Predictable tasks mean that the right number of staff and inventory (not too much and not too little) can be planned for a shift, day or week well in advance.
Creating effective schedules
If your facility has PMs that require shorter intervals, like daily or weekly, a fixed schedule is the easiest path to an effective schedule. It ensures that these tasks are completed consistently and on time, which is especially important when they’re done on heavily used, production-critical assets.
Effectively managing warranties
Equipment manufacturers often recommend using a fixed PM schedule and can revoke warranties if these recommended schedules aren’t followed. While you shouldn’t completely base your maintenance schedule on warranties, it can be a factor, which makes sticking to a fixed schedule a good idea.
Meeting compliance regulations
Fixed PMs are generally more useful when certain assets or facilities are the focus of regulatory compliance or audits. Because a fixed schedule shows a predictable pattern, it is often seen as reliable proof that a facility is meeting certain regulatory benchmarks and is consistently giving attention to the necessary assets.
When to use floating PM scheduling
A floating PM schedule can be a more complex way to plan preventive maintenance and requires certain circumstances to work successfully. Certain assets and situations call for floating PMs more than others.
Increasing schedule flexibility
A floating schedule offers more flexibility for organizations with PMs that are spread over a long period of time and when those PMs can be late with minimal risk of failure or safety hazards. This flexibility allows the maintenance team to push PMs in favour of emergencies that have a huge impact on production.
Assessing risk and prioritizing tasks
Floating PMs are great for low-priority, routine preventive maintenance tasks that need to be completed on a regular basis, but won’t affect the reliability or safety of equipment. In this situation, floating PMs allow the maintenance team to assess risk and prioritize tasks that matter most without an obligation to keep up with a strict schedule.
Coordinating maintenance and production schedules
A common use of floating schedules is for assets that are in high demand for production or service, but have a high degree of reliability and will not negatively impact safety or uptime if maintenance is late. The flexibility allows in a floating schedule means that unnecessary downtime can be reduced and uptime can be maximized.
How to use maintenance metrics to improve PM schedules
Asset type, asset history, and organizational processes determine whether you choose fixed or floating PMs for a piece of equipment. The next step is to set the frequency of these tasks. Maintenance metrics provide data to help you make this decision and optimize your schedule.
Mean time between failures
Mean time between failures (MTBF) helps establish how reliable an asset is and gets you closer to figuring out how long you have before that asset fails. This information can be used to shift PMs around and maximize time and resources without gambling with the health of equipment.
For example, an asset’s MTBF may be 150 hours, but a preventive maintenance work order is created for the asset every 100 hours. It’s apparent that the asset can be inspected less often, say every 125 hours. Having this information allows you to use time, labour, parts, and costs where they’re needed more.
Preventive maintenance compliance
Preventive maintenance compliance (PM compliance) measures how successful your team is at completing preventive maintenance tasks. Keeping track of PM compliance for critical assets is one way to ensure time is being spent on the most important jobs and that you’re not spreading the maintenance team too thin.
Tasks are scheduled at certain intervals because it’s what is best for the asset. But “what’s best” for assets can differ. Understanding the difference allows you to coordinate PMs more effectively.
For example, your facility’s PM compliance on a critical piece of equipment might be 60%, which is very low. There are many potential reasons why PM compliance is low, but the most likely cause is a jam-packed schedule and not enough technicians to complete every task. In this situation, you can consider placing more technicians on these shifts or moving non-essential PMs to another day.
Maintenance cost as a percentage of replacement asset value
Maintenance cost as a percentage of replacement value (MPRAV) is one way to calculate if the value of an asset is worth the number of maintenance resources being given to it. A culture of total productive maintenance and better maintenance processes can reduce MPRAV and have an indirect, but huge, impact on PM scheduling.
For example, one of your assets might break down a lot. You’re spending more time (and money) on PMs to reduce the frequency of failure. This puts a strain on the maintenance schedule. Calculating MPRAV helps you visualize these inefficiencies and find alternatives, like investing in new equipment, higher-quality parts, and better training. This leads to fewer breakdowns and less frequent PMs, leaving more time and money for other assets and PMs.
The bottom line on preventive maintenance scheduling
Every facility has unique assets, production schedules, and maintenance teams. That’s why every facility will schedule its PMs a little differently. However, there are some tried and true methods for structuring and optimizing a PM schedule. This includes using fixed and floating schedules and metrics to bolster PM scheduling. When maintenance operations can apply these concepts to their schedule, it empowers them to cut costs, eliminate inefficiencies, use labour more effectively, and increase uptime.