Maintenance management explained: breakdown, preventive, corrective, routine, predictive maintenance and TPM, a worked MTBF, MTTR and availability example, the bathtub curve and group replacement.
Updated 11 min read
Maintenance is the set of activities needed to keep plant, machinery, equipment, buildings and other facilities in good working condition. Maintenance management is the planning, organising, directing and controlling of those activities so that equipment is available, safe and reliable at the lowest total cost. In plain words, it means keeping machines fit, safe and ready for use, instead of waiting for them to fail.
The topic matters because production depends on machines. When a key machine stops, output is lost, workers sit idle, orders are delayed and customers complain. Good maintenance keeps production continuous, extends the life of costly equipment, protects workers and, over time, saves more money than it costs.
Every machine wears with use. Bearings wear, belts stretch, lubricants break down and electrical contacts loosen. Without a system, these small problems grow into sudden breakdowns. Maintenance management is needed because it:
keeps production continuous and delivery promises reliable;
reduces downtime, the time a machine is not available for productive use;
protects the large investment in plant and machinery;
improves product quality, since worn machines produce more defects;
improves safety for workers and property;
lowers total cost by replacing emergency repairs with planned work.
The basic idea is simple: it is usually cheaper to look after a machine than to rescue it. In a continuous or mass-production line, one stopped machine can halt the whole line, so maintenance is directly linked to production continuity.
Correct operation, lubrication, cleaning, correct loading and timely replacement of parts help equipment last longer and give better value for the investment.
Breakdown (reactive or run-to-failure) maintenance means repairing a machine only after it has failed. For example, a photocopier is used until it jams and stops, and only then is a technician called.
Advantages
No planning or scheduled maintenance cost in advance.
Few maintenance staff needed when failures are rare.
Suitable for cheap, non-critical items with standby units.
Disadvantages
Sudden stoppages and loss of production.
Repairs are often more expensive and need overtime.
Idle labour, delayed orders and unhappy customers.
Higher safety risk, since failures can be violent.
Large stocks of spare parts may be needed "just in case".
Preventive (planned) maintenance means inspecting, servicing and replacing parts at fixed intervals, based on time or usage, before failure occurs. For example, a bus operator changes engine oil every 10,000 km and replaces brake pads on a schedule.
Advantages
Fewer breakdowns and less unplanned downtime.
Maintenance can be done at convenient times, such as weekends.
Longer machine life and better product quality.
Safer operation and better planning of spares and labour.
Disadvantages
Regular cost even when the machine is running well.
Parts may be replaced while they still have useful life.
Needs records, schedules and trained staff.
Poorly done servicing can itself introduce faults.
Preventive maintenance is especially important for costly equipment, critical machines, production lines and any machine whose breakdown causes heavy loss.
Corrective maintenance goes beyond repairing a failure: it removes the root cause of repeated trouble, often by modifying or redesigning the equipment. If a conveyor belt keeps slipping, the firm may realign or redesign the drive instead of tightening the belt again and again.
Routine maintenance covers small regular tasks such as cleaning, lubrication, tightening, inspection and minor adjustments, done daily or at short intervals, often by operators themselves. Many major failures begin as small ignored issues, so routine care is very valuable.
Predictive maintenance monitors the actual condition of equipment and acts when warning signs appear. Tools include vibration analysis, temperature (thermal imaging) checks, oil analysis, ultrasonic testing and sensor readings. The rule is: maintain when the condition says so, not merely by the calendar and not only after failure. It avoids both surprise failures and unnecessary part replacement, but it needs instruments and skilled analysts.
TPM, developed in Japan and described by Seiichi Nakajima, makes maintenance everyone's job. Operators perform basic care (autonomous maintenance), while specialists handle planned and improvement work. TPM aims for zero breakdowns, zero defects and zero accidents, and it measures performance with Overall Equipment Effectiveness (OEE).
Worked example: reliability, availability and choosing a policy#
Suppose a packaging machine is scheduled to run 480 hours a month. Under a breakdown-only policy it fails 6 times a month, and the repairs take 24 hours in total. Each failure costs ₹40,000 in repair, scrap and lost output.
Step 1: Operating (up) time.
Uptime=480−24=456 hours
Step 2: Mean time between failures (MTBF).
MTBF=Number of failuresUptime=6456=76 hours
Step 3: Mean time to repair (MTTR).
MTTR=Number of failuresTotal repair time=624=4 hours
Step 4: Availability.
A=MTBF+MTTRMTBF=76+476=0.95=95%
Step 5: Monthly cost of the breakdown policy.
6×40,000=₹2,40,000
Step 6: Monthly cost of a preventive policy. A preventive programme costing ₹60,000 a month (planned servicing, lubrication and part changes) is expected to cut failures to 2 a month.
2×40,000+60,000=80,000+60,000=₹1,40,000
Step 7: Decision. The preventive policy saves 2,40,000−1,40,000=₹1,00,000 a month, so it should be adopted. The general rule is: choose preventive maintenance when the preventive cost is less than the failure cost it avoids. Here ₹60,000 is spent to avoid 4 failures worth ₹1,60,000.
Monthly cost of the two maintenance policies in the worked example.
Extension: OEE. If the machine's availability is 95 per cent, it runs at 90 per cent of its rated speed, and 98 per cent of its output is good, then
OEE=0.95×0.90×0.98=0.838≈83.8%
OEE shows that downtime is only one of three losses; speed losses and quality losses matter too.
Failure rate is high at first because of manufacturing defects, poor installation or initial weakness. It falls quickly as these faults are found. Burn-in testing, careful commissioning and warranties deal with this stage.
As the machine ages, wear and tear raise the failure rate again. At this point major overhaul or replacement is considered, so maintenance and replacement decisions go together.
The bathtub curve: failure rate is high early, low during useful life, and rises again in the wear-out stage.
Some items do not deteriorate gradually but fail suddenly, such as bulbs, fuses and small electronic parts. For large numbers of identical, low-cost items, a firm may use group replacement: replace all of them together at fixed intervals, and replace individual failures in between. Replacing items in a group is cheaper per item, because labour and access costs are shared, than replacing each one when it fails. The best group-replacement interval is the one with the lowest average cost per period. Items that deteriorate gradually, such as vehicles, are replaced when their average annual cost, including rising running costs, is at its minimum.
Good records include machine history cards, service dates, breakdown dates, repair costs, spare parts used, maintenance schedules and downtime data. They help managers identify problem machines, plan future work, control cost and make replacement decisions. Without records, maintenance becomes irregular and reactive.
A maintenance schedule is a timetable showing which machine will be serviced, when, what work is needed and who will do it. It turns preventive maintenance from an intention into a routine and is coordinated with the production schedule so that servicing does not clash with urgent orders.
If a machine fails and the spare is missing, downtime and production loss grow. Maintenance planning therefore identifies critical spares, keeps essential stock and coordinates with purchase and stores, linking maintenance with inventory management.
Manufacturing: lathes, presses, boilers, conveyors, packaging lines, compressors and furnaces.
Services: aircraft in airlines, lifts and air-conditioning in hotels and malls, medical equipment in hospitals, ATMs in banks, servers in IT firms, and buses in transport undertakings. In services, a breakdown is often seen directly by the customer, which makes maintenance even more visible.
Conditions for effective maintenance management#
Support from top management and an adequate budget
Clear maintenance policy for each class of equipment
Trained and motivated maintenance staff and operators
Accurate records and a working schedule
Availability of tools and critical spare parts
Coordination with production, stores and purchase
Regular review of downtime, cost and failure data
What is the difference between preventive and predictive maintenance?#
Preventive maintenance is done at fixed time or usage intervals whatever the machine's condition. Predictive maintenance is done when monitoring, such as vibration or oil analysis, shows that the machine is actually deteriorating.
Is breakdown maintenance ever the right choice?#
Yes. For cheap, non-critical items, or where a standby unit exists, the cost of planned servicing can exceed the cost of an occasional failure, so running to failure is sensible.
How is corrective maintenance different from breakdown maintenance?#
Breakdown maintenance restores a failed machine. Corrective maintenance removes the root cause of repeated failures, often by modifying the equipment, so the fault does not return.
How do you calculate availability of a machine?#
Availability equals MTBF divided by the sum of MTBF and MTTR. With an MTBF of 76 hours and an MTTR of 4 hours, availability is 76 out of 80, or 95 per cent.
Group replacement means replacing all similar low-cost items, such as street lights or bulbs, at once at fixed intervals, while replacing individual failures in between. It saves labour and access cost per item.
Worn or faulty equipment can cause accidents, fires and electrical hazards. Regular checks and timely replacement of faulty parts correct unsafe conditions early.
