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Reliability and maintainability program and plan |
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|  MIL-G-24477(SHIPS)
3.1.2.1 Reliability and maintainability program and plan. The contractor shall
develop, submit for review/maintain and implement a reliability and maintainability program
and plan using MIL-STD-785 (see 6.2) and MIL-STD-470 (see 6.2) as guides. Where a program
plan and report for similar equipment was previously submitted by the contractor, the
contractor need only propose any changes considered appropriate because of dissimilar items
and current intended use.
3.1.2.1.1 The reliability and maintainability program and plan shall cover as a mini-
mum control, monitoring, and conformance to 3.1.2.2 through 3.1.2.5.
3.1.2.2 The diesel generator set design shall be based on a life expectancy of 125,000
hours of operation with no limitations as to the number of starts and stops. This includes
100,000 hours at rated load, 20,000 hours between 50 percent and 100 percent rated load, and
5000 hours below 50 percent rated load. The time between overhauls shall be not less than
10,000 hours.
3.1.2.3 The design shall be such that parts which are not classified as onboard repair
parts need not be repaired or replaced except during overhaul periods or where damage is
incurred due to external causes unrelated to the design.
3.1.2.4 The design shall be such as to minimize the need for replacement of parts
which are in the onboard repair parts category between overhaul periods. Such features shall
be predicated on the following:
(a) Generator sets are installed and operated in accordance with the
instructions contained in the technical manual.
(b) Planned maintenance actions are accomplished by ships force in
accordance with the manufacturer's recommendations as developed from
the maintenance engineering analysis (MEA) conducted in accordance with
MIL-M-24365.
(c) Recommended inspections and repair actions during overhaul are accomplished
in accordance with instructions and tasks developed from the MEA and when
necessary, complementing information contained in the technical manuals.
(d) Generator sets are expected to operate for 10,000 hours between overhaul
periods.
(e) The loads involved during operation between overhaul periods will be as
specified in 3.1.2.2.
3.1.2.5 Reliability prediction. The reliability prediction of the generator set
shall be based on the failure rate of parts, and the information specified in 3.1.2.1
through 3.1.2.4. The design and application of parts shall be such that the Mean-Time-
Between Failure (MTBF) of the generator set is at least 1000 hours and the mean-time-to-
repair (MTTR) is no more than 24 hours. The MTBF shall be predicted using the design
prediction procedure of MIL-STD-756 and using the failure rate sources specified therein.
For parts where no failure rate is available, a failure rate shall be estimated and the
basis for the estimate stated in the calculations. The derating factors used for each part
and the stress levels at which each part is operating shall be stated in reliability calcula-
tions. The stress levels shall be those as determined from test insofar as practicable.
In those instances where test data is not available, design date shall be used.
3.1.2.6 A failure is defined as occurring when the collective or individual unit
performance degrades to the point where the performance requirements of this specification
cannot be met or wherein personnel safety is jeopardized.
3.1.2.7 The maintainability of the complete generator set shall be predicted in
accordance with procedure IV of MIL-HDBK-472. The failure rates used shall be those which
have been determined in the reliability predictions. The maintainability prediction shall
take into consideration all design changes made during the engineering design phase.
3.1.2.8 Failure modes and effects analysis. The contractor shall conduct before the
design tests a failure modes and effects analysis (FMEA). Prior to conducting the FMEA, the
contractor shall prepare an FMEA selection report to describe the depth of the analysis.
The content of the report shall be as specified in the contract or order and shall be
submitted for contracting agency review. The analysis shall include as a minimum the
critical subsystems, the accessories, controls, and parts delivered under the contract whose
failure would cause the system to fail. The FMEA shall include the identification and
tabulation of all ways (or modes) in which any part can fail and the effect of each failure
mode on the next higher assembly and the next higher assembly and the system as a whole,
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