As implied, verification, demonstration and evaluation is accomplished by performance of maintenance tasks at a specified maintenance level. Generation of the specific maintenance tasks during each maintainability test phase can take several forms as indicated below. The means by which the tasks are generated should be considered, planned for and documented in the maintainability test plan.
Actual operation of the item in the specified test, operational and maintenance environment is always the preferred method of maintenance tasks generation (i.e., maintenance is performed as a result of naturally occurring failures). This can only be done, however, provided that assurances can be given that a sufficient number of failures or maintenance tasks will occur during the test period to satisfy any minimum sample requirements for the test method employed. This method of maintenance task generation must therefore be considered early in the development stages to make sure that a sufficient number of test or operational hours are planned, both through tests dedicated for maintainability and other forms of testing, to make this approach feasible. Close coordination with the entire development team is required for this approach to maximize all test time planned.
In lieu of the naturally occurring failure approach to
maintenance task generation is the fault or failure simulation approach. This
approach is to introduce failures by way of faulty parts, deliberate
misalignment, open leads, shorted parts, etc. As part of this approach, a
maintenance task sampling plan, as described in Section 3.5.2 , must be prepared. When this is done as part of demonstration testing, the actual task selection should not be made by the test team until immediately prior to the demonstration.