4.3.1 R/M Considerations in System
From a system effectiveness viewpoint, reliability and
maintainability jointly provide system availability and dependability.
Increased reliability directly contributes to system uptime, while improved
maintainability reduces downtime. If reliability and maintainability are not
jointly considered and continually reviewed, serious consequences may result.
With military equipment, failures or excessive downtime can jeopardize a
mission and possibly cause a loss of lives. Excessive repair time and failures
also impose burdens on logistic support and maintenance activities, causing
high costs for repair parts and personnel training, expenditure of many
manhours for actual repair and service, obligation of facilities and equipment
to test and service, and to movement and storage of repair parts.
From the cost viewpoint, reliability and maintainability must be
evaluated over the system life cycle, rather than merely from the standpoint
of initial acquisition. An effective design approach to reliability and
maintainability can reduce the cost of upkeep.
Both reliability and maintainability are important
considerations for the user of the system, although maintainability is
probably more important from the point of view of most users. Although
frequent system failures may be an annoyance, if each failure can be repaired
in a very short time so that the system has a high availability, and the
maintenance costs are reasonable, then the poor reliability may be acceptable.
For example, if failures occur on the average of every fifteen minutes but can
be repaired in a microsecond, at acceptable cost, the user will not be too
concerned. On the other hand, if repair of a failure takes hours or days, the
user has a nonavailable weapon system which may have a significant effect on
the operational commanderís readiness