In reliability, one is concerned with designing an item to last
as long as possible without failure; in maintainability, the emphasis is on
designing an item so that a failure can be repaired as quickly as possible.
The combination of high reliability and high maintainability results in high
system availability; the theory of which is developed in Section 5.7.
Maintainability, then, is a measure of the ease and rapidity
with which a system or equipment can be restored to operational status
following a failure. It is a function of the equipment design and
installation, personnel availability in the required skill levels, adequacy of
maintenance procedures and test equipment, and the physical environment under
which maintenance is performed.
As with reliability, maintainability parameters are also
probabilistic and are analyzed by the use of continuous and discrete random
variables, probabilistic parameters, and statistical distributions. An example
of a discrete maintainability parameter is the number of maintenance actions
completed in some time t, whereas an example of a continuous maintainability
parameter is the time to complete a maintenance