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Maintenance (technical)

  (Redirected from Repair)
Mechanical repair
Field repair of aircraft engine (1915-1916)

The technical meaning of maintenance involves functional checks, servicing, repairing or replacing of necessary devices, equipment, machinery, building infrastructure, and supporting utilities in industrial, business, governmental, and residential installations.[1][2] Over time, this has come to often include both planned (scheduled) and preventive maintenance as cost-effective practices to keep equipment ready. Together, these functions are referred to as Maintenance, repair and overhaul (MRO). MRO is also used for Maintenance, repair and operations.[3]



Road repair

Over time, the terminology of maintenance and MRO has begun to become standardized. The United States Department of Defense uses the following definitions:[4]

  • Any activity—such as tests, measurements, replacements, adjustments, and repairs—intended to retain or restore a functional unit in or to a specified state in which the unit can perform its required functions.[4]
  • All action taken to retain material in a serviceable condition or to restore it to serviceability. It includes inspections, testing, servicing, classification as to serviceability, repair, rebuilding, and reclamation.[4]
  • All supply and repair action taken to keep a force in condition to carry out its mission.[4]
  • The routine recurring work required to keep a facility (plant, building, structure, ground facility, utility system, or other real property) in such condition that it may be continuously used, at its original or designed capacity and efficiency for its intended purpose.[4]

Maintenance is strictly connected to the utilization stage of the product or technical system, in which the concept of maintainability must be included. In this scenario, maintainability is considered as the ability of an item, under stated conditions of use, to be retained in or restored to a state in which it can perform its required functions, using prescribed procedures and resources.[5][6]

In some domains like aircraft maintenance, terms maintenance, repair and overhaul[7] also include inspection, rebuilding, alteration and the supply of spare parts, accessories, raw materials, adhesives, sealants, coatings and consumables for aircraft maintenance at the utilization stage. In international civil aviation maintenance means:

  • The performance of tasks required to ensure the continuing airworthiness of an aircraft, including any one or combination of overhaul, inspection, replacement, defect rectification, and the embodiment of a modification or a repair.[8]

This definition covers all activities for which aviation regulations require issuance of a maintenance release document (aircraft certificate of return to service - CRS).


The basic types of maintenance falling under MRO include:[9]

  • Preventive maintenance, also known as PM
  • Corrective maintenance where equipment is repaired or replaced after wear, malfunction or break down.
  • Predictive maintenance, which uses sensor data to monitor a system, then continuously evaluates it against historical trends to predict failure before it occurs.[10]

Architectural conservation employs MRO to preserve, rehabilitate, restore, or reconstruct historical structures with stone, brick, glass, metal, and wood which match the original constituent materials where possible, or with suitable polymer technologies when not.[11]

Preventive maintenanceEdit

C-130J Hercules preventive cleaning at Keesler Air Force Base, Mississippi after a period of operation over the Gulf of Mexico (salt and moisture which lead to active corrosion require regular cleaning)

Preventive maintenance is "a routine for periodically inspecting" with the goal of "noticing small problems and fixing them before major ones develop."[12] Ideally, "nothing breaks down."[13]

The New York Times gave an example of "machinery that is not lubricated on schedule" that functions "until a bearing burns out." Preventive maintenance contracts are generally a fixed cost, whereas improper maintenance introduces a variable cost: replacement of major equipment.[12]

Other terms and abbreviations related to PM are:

  • scheduled maintenance[14]
  • planned maintenance,[15] which may include scheduled downtime for equipment replacement
  • planned preventive maintenance (PPM) is another name for PM[16]

Planned preventive maintenance (PPM), more commonly referred to as simply planned maintenance (PM) or scheduled maintenance, is any variety of scheduled maintenance to an object or item of equipment. Specifically, planned maintenance is a scheduled service visit carried out by a competent and suitable agent, to ensure that an item of equipment is operating correctly and to therefore avoid any unscheduled breakdown and downtime.[17]

  • breakdown maintenance:[16] fixing things only when they break. This is also known as "a reactive maintenance strategy"[18] and may involve "consequential damage."[19]

Planned maintenanceEdit

Along with condition-based maintenance, planned maintenance comprises preventive maintenance, in which the maintenance event is preplanned, and all future maintenance is preprogrammed. Planned maintenance is created for every item separately according to manufacturers recommendation or legislation. Plans can be date-based, based on equipment running hours, or on the distance travelled by the vehicle. A good example of a planned maintenance program is car maintenance, where time and distance determine fluid change requirements. A good example of condition-based maintenance is the oil pressure warning light that provides notification that you should stop the vehicle because engine lubrication has stopped and failure will occur.

Planned maintenance has some advantages over condition-based maintenance (CBM), such as:

  • easier planning of maintenance and ordering spares,
  • costs are distributed more evenly,
  • no initial costs for instruments used for supervision of equipment.

Disadvantages are:

  • less reliable than equipment with fault reporting associated with CBM
  • more expensive due to more frequent parts change
  • requires training investment and ongoing labor costs

Parts that have scheduled maintenance at fixed intervals, usually due to wearout or a fixed shelf life, are sometimes known as time-change interval, or TCI items.

Predictive replacementEdit

Predictive replacement is the replacement of an item that is still functioning properly.[20] Usually it's a tax-benefit based[citation needed] replacement policy whereby expensive equipment or batches of individually inexpensive supply items are removed and donated on a predicted/fixed shelf life schedule. These items are given to tax-exempt institutions.[21][citation needed]

Preventive maintenance (interim)Edit

Preventive maintenance or preventative[22] maintenance (PM) has the following meanings:

  • The care and servicing by personnel for the purpose of maintaining equipment in satisfactory operating condition by providing for systematic inspection, detection, and correction of incipient failures either before they occur or before they develop into major defects.
  • The work carried out on equipment in order to avoid its breakdown or malfunction. It is a regular and routine action taken on equipment in order to prevent its breakdown.[23]
  • Maintenance, including tests, measurements, adjustments, parts replacement, and cleaning, performed specifically to prevent faults from occurring.


The main goal behind PM is for the equipment to make it from one planned service to the next planned service without any failures caused by fatigue, neglect, or normal wear (preventable items). This may be by preventing the failure before it actually occurs which Planned Maintenance and Condition Based Maintenance help to achieve. It is designed to preserve and restore equipment reliability by replacing worn components before they actually fail. Maintenance activities include partial or complete overhauls at specified periods, oil changes, lubrication, minor adjustments, and so on. In addition, workers can record equipment deterioration so they know to replace or repair worn parts before they cause system failure. The ideal machine maintenance program would prevent any unnecessary and costly repairs.

Machine maintenance for various equipment and facilities is quite nuanced. For instance, maintaining certain equipment may include a "preventive maintenance checklist" which includes small checks which can significantly extend service life. Furthermore, other considerations such as weather and equipment are taken into account; for instance, in the case of HVAC systems, maintenance is often performed before the hottest time of the year.

Condition-based maintenanceEdit

Condition-based maintenance (CBM), shortly described, is maintenance when need arises. Albeit chronologically much older, It is considered one section or practice inside the broader and newer predictive maintenance field, where new AI technologies and connectivity abilities are put to action and where the acronym CBM is more often used to describe 'condition Based Monitoring' rather than the maintenance itself. CBM maintenance is performed after one or more indicators show that equipment is going to fail or that equipment performance is deteriorating.

This concept is applicable to mission-critical systems that incorporate active redundancy and fault reporting. It is also applicable to non-mission critical systems that lack redundancy and fault reporting.

Condition-based maintenance was introduced to try to maintain the correct equipment at the right time. CBM is based on using real-time data to prioritize and optimize maintenance resources. Observing the state of the system is known as condition monitoring. Such a system will determine the equipment's health, and act only when maintenance is actually necessary. Developments in recent years have allowed extensive instrumentation of equipment, and together with better tools for analyzing condition data, the maintenance personnel of today is more than ever able to decide what is the right time to perform maintenance on some piece of equipment. Ideally, condition-based maintenance will allow the maintenance personnel to do only the right things, minimizing spare parts cost, system downtime and time spent on maintenance.


Despite its usefulness, there are several challenges to the use of CBM. First and most important of all, the initial cost of CBM can be high. It requires improved instrumentation of the equipment. Often the cost of sufficient instruments can be quite large, especially on equipment that is already installed. Wireless systems have reduced the initial cost. Therefore, it is important for the installer to decide the importance of the investment before adding CBM to all equipment. A result of this cost is that the first generation of CBM in the oil and gas industry has only focused on vibration in heavy rotating equipment.

Secondly, introducing CBM will invoke a major change in how maintenance is performed, and potentially to the whole maintenance organization in a company. Organizational changes are in general difficult.

Also, the technical side of it is not always as simple. Even if some types of equipment can easily be observed by measuring simple values as vibration (displacement or acceleration), temperature or pressure, it is not trivial to turn this measured data into actionable knowledge about the health of the equipment.

Value potentialEdit

As systems get more costly, and instrumentation and information systems tend to become cheaper and more reliable, CBM becomes an important tool for running a plant or factory in an optimal manner. Better operations will lead to lower production cost and lower use of resources. And lower use of resources may be one of the most important differentiators in a future where environmental issues become more important by the day.

A more down to earth scenario where value can be created is by monitoring the health of your car motor. Rather than changing parts at predefined intervals, the car itself can tell you when something needs to be changed based on cheap and simple instrumentation.

It is Department of Defense policy that condition-based maintenance (CBM) be "implemented to improve maintenance agility and responsiveness, increase operational availability, and reduce life cycle total ownership costs".[24]

Advantages and disadvantagesEdit

CBM has some advantages over planned maintenance:

  • Improved system reliability
  • Decreased maintenance costs
  • Decreased number of maintenance operations causes a reduction of human error influences

Its disadvantages are:

  • High installation costs, for minor equipment items often more than the value of the equipment
  • Unpredictable maintenance periods cause costs to be divided unequally
  • Increased number of parts (the CBM installation itself) that need maintenance and checking

Today, due to its costs, CBM is not used for less important parts of machinery despite obvious advantages. However it can be found everywhere where increased reliability and safety is required, and in future will be applied even more widely.[25][26]


Corrective maintenance is a type of maintenance used for equipment after equipment break down or malfunction is often most expensive – not only can worn equipment damage other parts and cause multiple damage, but consequential repair and replacement costs and loss of revenues due to down time during overhaul can be significant. Rebuilding and resurfacing of equipment and infrastructure damaged by erosion and corrosion as part of corrective or preventive maintenance programmes involves conventional processes such as welding and metal flame spraying, as well as engineered solutions with thermoset polymeric materials.[27]


More recently, advances in sensing and computing technology have given rise to predictive maintenance. This maintenance strategy uses sensors to monitor key parameters within a machine or system, and uses this data in conjunction with analysed historical trends to continuously evaluate the system health and predict a breakdown before it happens.[10] This strategy allows maintenance to be performed more efficiently, since more up-to-date data is obtained about how close the product is to failure.[28]


The marine transportation,[29] offshore structures,[30] industrial plant and facility management industries depend on maintenance, repair and overhaul (MRO) including scheduled or preventive paint maintenance programmes to maintain and restore coatings applied to steel in environments subject to attack from erosion, corrosion and environmental pollution.[30]

See alsoEdit

  • Repair, in medicine, according to the ICD-10-PCS, in the Medical and Surgical Section 0, root operation Q, means restoring, to the extent possible, a body part to its normal anatomic structure and function. This definition, repair, is used only when the method used to accomplish the repair is not one of the other root operations. Examples would be colostomy takedown, herniorrhaphy of a hernia, and the surgical suture of a laceration.


  1. ^ "Defense Logistics Agency". Retrieved 5 August 2016.
  2. ^ "European Federation of National Maintenance Societies". Retrieved 5 August 2016. All actions which have the objective of retaining or restoring an item in or to a state in which it can perform its required function. The actions include the combination of all technical and corresponding administrative, managerial, and supervision actions.
  3. ^ "MRO - Definition". RF System Lab.
  4. ^ a b c d e Federal Standard 1037C and from MIL-STD-188 and from the Department of Defense Dictionary of Military and Associated Terms
  5. ^ "AAP-6 - Glossary of terms and definitions". NATO Standardization Agency. North Atlantic Treaty Organization: 158.
  6. ^ "Commercial Electrical Contractor and Domestic Electrician Leeds". 247 Electrical Services Leeds. Retrieved 2017-01-26.
  7. ^ United States Code of Federal Regulations Title 14, Part 43 - Maintenance, Preventive Maintenance, Rebuilding, and Alteration
  8. ^ Airworthiness Manual, Doc 9760 (3 ed.). Montreal (Canada): International Civil Aviation Organization. 2014. p. 375. ISBN 978-92-9249-454-4. The Airworthiness Manual (Doc 9760) contains a consolidation of airworthiness-related information previously found in other ICAO documents ... provides guidance to States on how to meet their airworthiness responsibilities under the Convention on International Civil Aviation. This third edition is presented based on States' roles and responsibilities, thus as State of Registry, State of the Operator, State of Design and State of Manufacture. It also describes the interface between different States and their related responsibilities. It has been updated to incorporate changes to Annex 8 to the Chicago Convention — Airworthiness of Aircraft, and to Annex 6 — Operation of Aircraft
  9. ^ "Types of Maintenance". Retrieved 6 March 2019.
  10. ^ a b Garcia, Mari Cruz; Sanz-Bobi, Miguel A.; Del Pico, Javier (August 2006), "SIMAP: Intelligent System for Predictive Maintenance: Application to the health condition monitoring of a windturbine gearbox", Computers in Industry, 57 (6): 552–568, doi:10.1016/j.compind.2006.02.011
  11. ^ Horie, Charles Velson (2010). Materials for Conservation: Organic Consolidants, Adhesives and Coatings (2nd ed.). Butterworth-Heinemann. ISBN 978-0-75-066905-4.
  12. ^ a b Micharl Decourcy Hinds (February 17, 1985). "Preventive Maintenance: A Checklist". The New York Times.
  13. ^ Erik Sandberg-Diment (August 14, 1984). "Personal computers preventive maintenance for an aging computer".
  14. ^ "CPOL: System Maintenance and Downtime Announcements". Retrieved March 21, 2019. ... out of service from 6:00-7:00am Eastern for regularly scheduled maintenance.
  15. ^ "Dodge City Radar Planned Maintenance". (National Weather Service). ... will be down for approximately five days
  16. ^ a b "The development of a cost benefit analysis method for monitoring the condition of batch" (PDF).
  17. ^ Wood, Brian (2003). Building care. Wiley-Blackwell. ISBN 978-0-632-06049-8. Retrieved 2011-04-22.
  18. ^ "What is PPM Maintenance?".
  19. ^ e.g. from leaks that could have been prevented
  20. ^ "Spacewalking Astronauts Swap Out Space Station's Batteries". The New York Times. March 22, 2019. Retrieved March 22, 2019.
  21. ^ such as universities and local schools, which write government-acceptible receipts
  22. ^ Ben Zimmer (April 18, 2010). "Wellness". The New York Times. Complaints about preventative go back to the late 18th century ... ("Oxford English Dictionary dates preventive to 1626 and preventative to 1655) ..preventive has won"
  23. ^ Bamiro, O.A.; Nzediegwu, D.; Oladejo, K.A.; Rahaman, A.; Adebayo, A. (2011). Mastery of Technology for Junior School Certificate Examination. Ibadan: Evans Brothers (Nigeria Publishers) Limited.
  24. ^ CBM Policy Memorandum.
  25. ^ Liu, Jie; Wang, Golnaraghi (2010). "An enhanced diagnostic scheme for bearing condition monitoring". IEEE Transactions on Instrumentation and Measurement. 59 (2): 309–321. doi:10.1109/tim.2009.2023814.
  26. ^ Jardine, A.K.S.; Lin, Banjevic (2006). "A review on machinery diagnostics and prognostics implementing condition-based maintenance". Mechanical Systems and Signal Processing. 20 (7): 1483–1510. doi:10.1016/j.ymssp.2005.09.012.
  27. ^ Industrial Polymer Applications: Essential Chemistry and Technology (1st ed.). United Kingdom: Royal Society of Chemistry. 2016. ISBN 978-1782628149.
  28. ^ Kaiser, Kevin A.; Gebraeel, Nagi Z. (12 May 2009), "Predictive Maintenance Management Using Sensor-Based Degradation Models", IEEE Transactions on Systems, Man, and Cybernetics - Part A: Systems and Humans, 39 (4): 840–849, doi:10.1109/TSMCA.2009.2016429
  29. ^ Berendsen, A. M.; Springer (2013). Marine Painting Manual (1st ed.). ISBN 978-90-481-8244-2.
  30. ^ a b ISO 12944-9:2018 – Paints and Varnishes – Corrosion Protection of Steel Structures by Protective Paint Systems – Part 9: Protective Paint Systems and Laboratory Performance Test Methods for Offshore and Related Structures

  This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C" (in support of MIL-STD-188).


  • Maintenance Planning, Coordination & Scheduling, by Don Nyman & Joel Levitt Maintenance ISBN 978-0831134181

Further readingEdit