This article is for production managers, maintenance managers and plant managers who watch two availability figures clash in every performance review.
- Maintenance and production do not measure the same availability.
- Changeovers, waiting and micro-stops are left out of maintenance availability.
- Both indicators can be configured to flatter the line.
- A single source of time-stamped, typed stops reconciles both views.
It is a familiar scene. Maintenance presents 98% availability. Production answers with an OEE whose availability rate is much lower. Both are right, and that is exactly the problem: they are not measuring the same thing.
Two availabilities, two definitions
For maintenance, availability measures the equipment’s ability to run. It is calculated from breakdowns: uptime divided by total time, or MTBF divided by the sum of MTBF and MTTR. A changeover, a material shortage or a missing operator are not breakdowns. They are left out of the calculation.
For production, the OEE availability rate compares run time with planned production time. Any unplanned stop brings it down, whatever the cause: breakdown, adjustment, changeover, missing parts, waiting for a quality check.
So a machine can be perfectly reliable in the maintenance sense and poorly available for production. The disagreement is not about wrong numbers. It is about a scope nobody ever spelled out.
Then there are micro-stops. In the most common OEE convention, they count against the performance rate rather than availability. Some plants put them under availability. Both approaches hold up, as long as micro-stops are counted somewhere, which is rarely the case.
What FreeMaint highlighted on the maintenance side
In Maintenance KPIs that lie (in French), FreeMaint takes apart three indicators every CMMS displays. Their finding fits in one sentence: “It’s their configuration that lies.”
- Inflated MTBF. When preventive and corrective work are mixed in the failure counter, the more preventive work you do, the better MTBF looks. In their example, the naive MTBF comes out at 159 hours, versus 1,752 hours when only real breakdowns are counted.
- Underestimated MTTR. It only counts repairing the equipment, not the downstream line waiting or reworking the batch. Their example shows 2 hours of MTTR for around 32 hours of actual downtime.
- Overstated availability. Short stops cleared without a work order do not show up. FreeMaint estimates that around 60% of line stops last less than 15 minutes. In their example, availability drops from 98.9% to about 97.8% once those stops are added back in.
Their conclusion applies to production too: the indicator is correct, it is the way it is built that misleads.
The same mechanism on the production side
OEE has its own ways of flattering a line.
- An overly generous ideal cycle time. If the theoretical rate is set below the machine’s real rate, the performance rate is automatically inflated. Slowdowns become invisible.
- “Planned” stops that are not really planned. Classified as a planned stop, a changeover or a cleaning is removed from planned production time. OEE goes up without the line making a single extra part.
- Good parts instead of first-pass good parts. Counting a reworked part as good wipes out the quality loss, even though the rework used machine time and labor.
In all three cases, the number still holds up in a meeting. It just no longer tells you where capacity is being lost.
Getting maintenance and production to agree
| Indicator | What it measures | What it misses | Reliable source |
|---|---|---|---|
| Maintenance availability | Equipment reliability against breakdowns | Changeovers, waiting time, micro-stops without a work order | Time-stamped stops, filtered on the “breakdown” type |
| MTBF | Average interval between two failures | Preventive work if mixed with corrective | Breakdowns only, preventive excluded |
| MTTR | Repair time | Line downtime and restart | Machine stop duration, not just the work order |
| OEE availability | Run time over planned production time | Stops reclassified as “planned” | All stops, with their cause |
Reconciliation rests on one simple rule: a single source of downtime events, shared by both departments. Every stop is detected automatically, time-stamped, then categorized: breakdown, changeover, waiting, adjustment, micro-stop. Maintenance calculates its MTBF on breakdowns. Production calculates its OEE on everything. One dataset, two readings, no more arguing about the number.
Where to start
- Write both definitions on one page. Formula, scope, what is excluded. Often it is the first time they have been put side by side.
- Pick a pilot line and measure every stop for two weeks. No duration threshold, no reclassification.
- Present the results together. A review where maintenance and production read the same downtime table changes the tone of the meeting.
Across equipped plants, TEEPTRAK sees an average gain of 10 to 15 OEE points and 30% fewer unplanned stops. The starting point is always the same: seeing every stop.
Further reading
- Maintenance KPIs that lie, FreeMaint: the three calculation errors in detail, with their fixes. FreeMaint also offers an MTBF and MTTR calculator (in French).
- OEE data reliability: common measurement errors and solutions
- Understanding and reducing machine downtime
FAQ
How do you calculate machine availability? On the maintenance side, divide uptime by total time, or MTBF by the sum of MTBF and MTTR. On the OEE side, divide run time by planned production time, after subtracting all unplanned stops.
Why is maintenance availability higher than OEE availability? Because it only counts breakdowns. Changeovers, waiting time and adjustments lower OEE availability but not maintenance availability.
Do micro-stops count toward availability? Depending on the convention used, they count toward availability or performance. What matters is that they are measured, which manual logging rarely allows.
0 Comments