maintainability in engineering maintainability is the ease with which a product can be maintained in order to correct defects or their cause repair or replace faulty or wornout components without having to replace still working parts prevent unexpected working condition maximize a products useful life maximize efficiency reliability and safety meet new requirements make future maintenance easier or cope with a changed environment in some cases maintainability involves a system of continuous improvement learning from the past in order to improve the ability to maintain systems or improve reliability of systems based on maintenance experience in telecommunication and several other engineering fields the term maintainability has the following meanings a characteristic of design and installation expressed as the probability that an item will be retained in or restored to a specified condition within a given period of time when the maintenance is performed in accordance with prescribed procedures and resources the ease with which maintenance of a functional unit can be performed in accordance with prescribed requirements software engineering in software engineering these activities are known as software maintenance cf isoiec 9126 closely related concepts in the software engineering domain are evolvability modifiability technical debt and code smells the maintainability index is calculated with certain formulae from linesofcode measures mccabe measures and halstead complexity measures the measurement and track maintainability are intended to help reduce or reverse a systems tendency toward code entropy or degraded integrity and to indicate when it becomes cheaper andor less risky to rewrite the code than it is to change it this article incorporatespublic domain material from the general services administration document federal standard 1037c in support of milstd188 list of system quality attributes maintenance repair and operations mro supportability disambiguation serviceability disambiguation software sizing blanchard s b maintainability a key to effective serviceability and maintenance management john wiley sons inc newyork 1995 ebeling c e an introduction to reliability and maintainability engineering mcgrawhill companies inc boston 1997 patton j d maintainability and maintenance management instrument society of america research triangle park north carolina 19 calculation field testing and history of maintainability index mi with references measurement of maintainability index mi original sei technical report defining the maintainability index p231 