Enclosure (4) to COMDTINST 4105.7
2
Failure of component/equipment causes total loss/severe degradation of
secondary mission.
3
Failure of component/equipment cause severe degradation of primary mission.
4
Failure of component/equipment causes total loss of mobility/ severe
degradation of mobility or total loss of primary mission. Loss of this equipment
results in a safety hazard to the platform or crew.
Complexity of Equipment/System is defined as:
The complexity of a system/equipment is a subjective indication of the "intricate nature" of the
equipment or system to the missions and operations of the unit. It describes the level of intricacy
as having many complicated interrelating parts or interfacing sub-components. Complexity of a
system/equipment can further be defined as the various levels of difficulty that may be
encountered in order to resolve casualties or analyze information.
Reliability, Maintainability, and Availability are defined as:
Reliability can be defined as the probability that a system or product will perform in a
satisfactory manner for a given period of time when used under specified operating conditions.
This definition stresses the elements of probability, satisfactory performance, time, and specified
operating conditions. In addition, Reliability is frequently defined in terms of mean time
between failure (MTBF), mean time between maintenance (MTBM), and mean time to repair
(MTTR). MTBF and MTBM may be calculated and expressed as:
MTBF = number of failures
MTBM = _______1_____
1 /mtbm∑ + 1/mtbmΩ
total operating hours
mtbm∑ = mean or average interval of unscheduled (corrective) maintenance.
mtbmΩ = mean or average interval of scheduled (preventative) maintenance.
These calculations are generally provided by the Original Equipment Manufacturer
(OEM) in the salient characteristics portion of the Technical Publication.
Maintainability, like reliability, is an inherent characteristic of system or product design. It
pertains to the frequency, ease, accuracy, safety, and economy in the performance of
maintenance actions. Maintainability can also be defined as a characteristic in the design that
can be expressed in terms requirements or estimations based on both preventative maintenance
(scheduled) requirements and corrective (unscheduled) maintenance requirements.
Availability, or the measure of the degree a system is in the operable and committable state, at
the start of a mission, when the mission is called for at an unknown random point in time.
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