MIL-STD-471A
10 Jan 1975
APPENDIX B
TEST METHODS AND DATA ANALYSIS
B.10 Scope.
B.10.1 Purpose -
This appendix contains test methods and criteria for
demonstrating the achievement of specified quantitative maintainability
requirements:
Some of the test methods included are identical to test
methods contained in previous versions of this Standard.
Table IA indicates
the correspondence of the test methods included in this Standard to those
included in past versions.
B.10.2 Application -
The following matrix (Fig. B-1) summarizes the major
characteristics of each test method as well as the quantitative requirements
which must be specified for each test method.
The data analysis method
included with each test method provides the decision criteria for acceptance
or rejection of the item being demonstrated.
B.10.3 Sample Size
- Each of the test plans contained in this appendix includes
an equation or other directions for determining a minimum sample size of mainte-
nance tasks.
Any departure from the minimum sample size requirement can affect
the statistical validity of the test procedures. Some of the test plans in
the appendix require a prior estimate of the variance of the distribution of
interest for the calculation of sample size.
Such prior estimates, subject to
government approval, can be obtained from data on similar equipment provided
similarities in maintainability design, skill levels of maintenance personnel,
test equipment,
manuals and the maintenance environment are considered in the
estimation process. Equations for predicting the variance when prior estimates
are not available are presented in DDC document AD-869396, Maintainability
Prediction and Demonstration Techniques, Vol. II, cited in para. B.10.6, which
can be used, provided the information needed for the prediction is available.
The 85th -
95th upper confidence bound on the predicted or estimated variance
shall be used to insure preservation of the desired risk values. Average observed
values of the variance have ranged from
B.10.4 Task Selection -
Selection of tasks to be sampled when employing fault
simulation will
be made in accordance with Appendix A of this standard. The
Procuring Activity shall have the option of surveillance over and/or participat-
ing in the random selection of tasks comprising the demonstration population
(Column 11 of Table I) down to and including the specific faults to be simulated.
This shall occur at a specific conference at a time established by the contractor,
consistent with the Maintainability Program Plan schedule.
In the event that
tasks so chosen can result in events detrimental to safety of personnel or
property, appropriate redesign action must take place; in the event that secondary
failures result, they will be documented and their impact on item maintainability
assessed.
A report of such findings shall be made to-the procuring activity.
Care must be exercised in selecting and sampling tasks to insure that a true
simple random sample is obtained when sequential tests are employed.
Departures
from simple random sampling, such as proportionate stratified sampling, can
effect the validity of the test procedures presented herein, however, this effect
is considered minimal for
are not sequential tests.
tests.
Supersedes page 26 of 27
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the sample sizes required by the test
Simple random sampling shall be used
March 1973
procedures which
for sequential
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