The technical meaning of maintenance involves operational and functional checks, servicing, repairing or replacing of necessary devices, equipment, machinery, building infrastructure, and supporting utilities in industrial, business, governmental, and residential installations. Over time, this has come to often include both scheduled and preventive maintenance as cost-effective practices to keep equipment ready for operation at the utilization stage of a system lifecycle.
The marine transportation, offshore structures, 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.
Over time, the terminology of maintenance and MRO has begun to become standardized. The United States Department of Defense uses the following definitions:
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.
In some domains like aircraft maintenance, terms maintenance, repair and overhaul 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:
This definition covers all activities for which aviation regulations require issuance of a maintenance release document (aircraft certificate of return to service - CRS).
Over time, corrective maintenance gave way to preventive maintenance. New technologies are continuing to expand the scope of the field. The basic types of maintenance falling under MRO include:
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.
Preventive maintenance is maintenance performed with the intent of avoiding failures, safety violations, unnecessary production costs and losses, and to conserve original materials of fabrication. The effectiveness of a preventive maintenance schedule depends on the RCM analysis which it was based on, and the ground rules used for cost efficacy.
Corrective maintenance of 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.
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. 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.
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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.
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