Most equipment does not wear out by the calendar. A forklift used on two shifts needs service twice as often as one used on one shift, and a standby generator that rarely runs still needs monthly checks because batteries and fuel degrade with time. Getting the trigger right is what separates a schedule that prevents breakdowns from one that wastes labour.
This guide explains the three triggers, how to build a schedule step by step, and works through a schedule for generators, forklifts and chillers. It ends with the KPIs that show whether the schedule works, common mistakes and an FAQ.
Which trigger should you use: date, running hours or meter reading?
The right trigger is the one that tracks wear. Manufacturers' manuals usually state intervals in the unit that matters, so start there.
| Trigger | How it works | Best for | Watch out for |
|---|---|---|---|
| Calendar date | Service every set number of days, weeks or months | Assets that age with time whether used or not: fire systems, standby generators, building systems, statutory inspections | Over-servicing assets that sit idle, and under-servicing heavily used ones |
| Running hours | Service after a set number of operating hours, read from an hour meter | Engines, compressors, forklifts, production machines | Hour meters must be read regularly, or the trigger never fires |
| Meter reading | Service after a set count: kilometres, cycles, units produced | Vehicles, presses, packaging lines, lifts | Odometer or counter readings need a reliable source, often telematics or the production system |
| Whichever comes first | Two triggers combined, such as every 500 hours or 6 months | Most engines and vehicles, where oil and filters degrade with time as well as use | Both counters must be tracked, and the schedule resets from the actual service date |
In the Gulf, heat and dust shorten many intervals. Air filters on generators and vehicles working outdoors in summer often need changing well before the manufacturer's standard interval, and chillers and air-handling units run far more hours than in cooler climates. Treat the manual as a maximum, and shorten intervals where inspection records show faster wear.
Some maintenance is required by regulation rather than chosen. Fire alarm and fire protection systems, lifts, and cooling towers have inspection regimes set by the local authorities, and those dates sit in the same schedule as everything else. In Dubai, for example, the Municipality's Legionella guideline requires cooling towers to be cleaned and disinfected at least every six months by an approved contractor, with monthly bacteria counts and quarterly Legionella tests.
How do you build a preventive maintenance schedule?
- List every asset. Give each one an ID, location, make, model, serial number and installation date. If an asset is not in the register, it will not be in the schedule.
- Rank assets by criticality. Ask what happens if it fails: production stops, safety risk, customer impact, or nothing much. Spend preventive effort on the top two groups; low-criticality items can run to failure.
- Take tasks and intervals from the manual. Record each service level separately, for example a 250-hour check, a 500-hour service and a 2,000-hour overhaul, each with its own task list.
- Choose the trigger and lead time. Set whether the work order is created a set number of days, or hours, before the service is due, so parts can be ordered and downtime planned.
- Attach parts, labour and tools. List the filters, oils and belts each service uses, the estimated hours and the skills needed. This makes spare-part demand predictable.
- Assign responsibility. In-house technician, team or external contractor, with the contract reference where the service is outsourced.
- Generate work orders and record completion. When the work is closed, record the date, the hour or meter reading, the parts used and the findings. The next due date should be calculated from what actually happened, not from the original plan.
- Review every quarter. Compare breakdowns against the schedule. Repeated failures between services mean the interval is too long or a task is missing.
Step 7 is where most schedules drift. If technicians do the work but nobody records the reading, the system keeps raising work orders on the old cycle, and the team learns to ignore them.
What does a real schedule look like? A worked example
A food distributor's warehouse in Sharjah has two 500 kVA standby generators, six diesel forklifts and two air-cooled chillers serving the cold rooms. This is its schedule:
| Asset | Service | Trigger | Interval | Est. hours per service |
|---|---|---|---|---|
| Generators GEN-01, GEN-02 | Inspection and load test | Date | Monthly | 1.5 |
| Generators GEN-01, GEN-02 | Oil, filters, coolant check | Hours or date, whichever first | 250 hours or 12 months | 4 |
| Forklifts FL-01 to FL-06 | Standard service | Running hours | Every 250 hours | 2 |
| Chillers CH-01, CH-02 | Coil cleaning, refrigerant and electrical checks | Date | Quarterly | 6 |
| Chillers CH-01, CH-02 | Major service | Date | Annually, before summer | 12 |
The forklifts show why the trigger matters. FL-01 to FL-03 work two shifts, about 364 hours a month, so each needs a service roughly every three weeks, or about 17 a year. FL-04 to FL-06 work about 130 hours a month and need a service only every two months, about 6 a year.
| Approach | Services a year (6 forklifts) | Result |
|---|---|---|
| Monthly calendar schedule | 72 | Busy trucks serviced every 364 hours instead of 250; quiet trucks serviced twice as often as needed |
| Running-hours schedule | 69 | Every truck serviced at 250 hours, for about the same labour |
The labour is almost the same, but the hours-based schedule puts it where the wear is. For the generators, the 12-month limit fires before 250 hours because standby units run only a few hours a month in testing, which is exactly why the "whichever first" rule exists.
The chiller major service is fixed in March, before cold-room loads peak in summer. In total, the schedule needs about 254 technician hours a year, which the maintenance supervisor can plan around.
How do you know the schedule is working?
Five numbers, reviewed monthly, tell you whether preventive maintenance is preventing anything.
| KPI | Formula | What it tells you |
|---|---|---|
| PM compliance | Preventive work orders completed on time ÷ preventive work orders due | Whether the plan is being followed. Below about 90%, the schedule exists on paper only |
| Planned maintenance share | Planned labour hours ÷ total maintenance labour hours | How much time goes on planned work rather than firefighting. Many teams aim for 80% or more |
| Mean time between failures (MTBF) | Operating hours ÷ number of breakdowns, per asset | Whether breakdowns are becoming less frequent |
| Mean time to repair (MTTR) | Total repair hours ÷ number of repairs | Whether repairs are fast, which often depends on spare parts being in stock |
| Maintenance cost per asset | Labour, parts and contractor cost per asset per year | Which assets cost more to keep than to replace |
In the Sharjah example, suppose forklift FL-02 had four breakdowns last year in 4,368 operating hours, an MTBF of 1,092 hours. After moving to the hours-based schedule, it has one breakdown in the next six months of about 2,180 hours. MTBF more than doubles, and the improvement is visible in the data rather than claimed.
Read the KPIs together. High PM compliance with no improvement in MTBF means the tasks are wrong, not the timing. Low compliance with rising breakdowns means the team needs time or parts before it needs a better schedule.
What are the most common preventive maintenance mistakes?
| Mistake | What happens | Fix |
|---|---|---|
| Every asset on a monthly calendar schedule | Heavily used assets are under-serviced, idle ones over-serviced | Use running hours or meter readings where the manual does |
| Hour and meter readings not recorded | Usage-based triggers never fire, or fire late | Record a reading at every service, and weekly for critical assets |
| Next due date counted from the plan, not the actual service | Late services push the following one too close, or early ones create gaps | Reset the counter from the actual completion date or reading |
| No parts listed on the task | Technicians arrive and wait for filters | Attach parts to each service level and reserve them when the work order is created |
| Work orders closed with no findings | No history to show why an asset keeps failing | Require a short findings note and any follow-up work order |
| Contractor services kept outside the system | Statutory inspections are missed, and costs are invisible | Schedule contractor visits as work orders with the contract reference |
Checklist before you switch the schedule on
What does HYP see at maintenance teams?
At manufacturers, distributors and facility operators across the Gulf, our implementation team often finds the maintenance plan in a wall chart or a spreadsheet of monthly dates. It works until the supervisor goes on leave, or until the fleet grows past what one person can track. Breakdowns are logged in a separate notebook, if at all, so nobody can tell whether the plan is preventing them.
The first improvement is usually not a new schedule. It is recording a meter or hour reading on every work order. Within a few months, the history shows which assets are serviced too often, which too rarely, and which fail no matter what, and the schedule can be adjusted from evidence.
In HYP, preventive plans can be set by date, running hours or meter reading for each asset, and generate work orders with their parts and labour ahead of the due date. Completed work orders update the asset history and the next due date. See how it works on our Maintenance Management page.
Related reading: a schedule only works if the parts are on the shelf. See Spare Parts Inventory: How Maintenance Teams Avoid Stock-Outs Without Overstocking.