Mean time to repair (MTTR)

The maintenance metric that drives efficiency

A practical guide to using MTTR and other metrics

What is MTTR?

Mean time to repair (MTTR) is a maintenance metric that measures the average time required to troubleshoot and repair failed equipment. It reflects how quickly an organization can respond to unplanned breakdowns and repair them.

MTTR calculates the period between the start of the incident and the moment the system returns to production. This takes into account the time to:

  1. Notify technicians
  2. Diagnose the issue
  3. Fix the issue
  4. Allow the equipment to cool down
  5. Reassemble, align, and calibrate the asset
  6. Set up, test, and start up the asset for production

This metric does not take into account lead time for parts.

How to calculate MTTR

The MTTR formula is calculated by dividing the total unplanned maintenance time spent on an asset by the total number of failures that asset experienced over a specific period. Mean time to repair is most commonly represented in hours.

The MTTR calculation assumes that:

  1. Tasks are performed sequentially
  2. Tasks are performed by appropriately trained personnel
MTTR equation

For example, if you have spent 50 hours on unplanned maintenance for an asset that has broken down eight times over the course of a year, the mean time to repair would be 6.25 hours.

What is considered world-class MTTR is dependent on several factors, like the type of asset, its criticality, and its age. However, a good rule of thumb is an MTTR of under five hours.

Learn more about maintenance KPIs and how to use them.

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How is MTTR used?

Mean time to repair is used as a baseline for increasing efficiency, finding ways to limit unplanned downtime, and boosting the bottom line. Because long repair times for mission-critical equipment mean product scrap, missed orders, and soured business relationships, MTTR helps organizations identify why maintenance may be taking longer than what is ideal and make more informed decisions to fix the underlying causes.

What does MTTR mean for maintenance?

Conducting an MTTR analysis can provide insight into the way your maintenance operation purchases equipment, schedules maintenance, and completes tasks. Ultimately, MTTR helps your organization wipe out any inefficiencies that are causing lost production and the lost money that comes with that.

Repair or replace decisions

MTTR can be used for making repair or replace decisions on aging assets. If an asset takes longer to repair as it ages, it may be more economical to replace it. MTTR can also be used to inform the purchasing and design process by predicting lifecycle costs of new systems.

Preventive maintenance scheduling

Tracking MTTR also helps to ensure your preventive maintenance program and PM tasks are as effective and efficient as possible. Although MTTR measures reactive maintenance, assets that take longer to repair may have PMs associated with them that aren’t working well. Mean time to repair is a gateway into the root cause of this problem and provides a path to a solution. See how to find a scheduled maintenance work order that could have led to a breakdown here.

For example, if MTTR is increasing, it might be because PMs aren’t standardized, leading to more equipment failure. A work order may tell a technician to lubricate a part, but it might not tell them which lubricant or how much. Adding this information to a work order will ensure work is done quickly and accurately, leading to less downtime. Learn how to create world-class standardized work orders here.

MRO inventory purchasing and planning

A longer than usual mean time to repair could be a sign that your parts strategy is not working. Stockouts and disorganized spares have a huge impact on delayed work. About 50% of all unscheduled downtime can be linked to a lack of spare parts, according to this report. Between 10% and 25% of a technician’s time is spent looking for hard-to-find parts.

If you are consistently seeing a longer MTTR on certain assets, parts of the plant, or a certain facility, it’s worth investigating if parts are the reason. Check to see if critical parts are chronically understocked, if they’re defective, or if they’re mislabeled. You can also check out this tool that will help you forecast exactly what parts you need for upcoming work (including reactive work!) so you’re never in this situation again.

Your business and MTTR

Mean time to repair is a tool for evaluating the quality of a facility’s maintenance practices and processes. It can also be used to investigate the value and performance of assets so an organization can make smarter decisions about asset management. MTTR is a starting point for assessing efficiency and eliminating redundancies, roadblocks, and confusion in maintenance so a business can avoid needless downtime and go back to what it does best — manufacturing and selling goods.

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