Useful checklists for maintainability demonstration plans, procedures, and reports

In maintainability demonstration, checklists play a very important role. The checklist for maintainability demonstration plans and procedures should cover items such as follows [2, 5]:

  • Purpose and scope: This is a statement of general test objectives and a general description of the test to be conducted.
  • Test facilities: This is information such as a description of the test item's configuration, a general description of test facility, identification of the test location, test area security measures, and test safety features.
  • Test requirements: These requirements include items such as the method of generating a candidate fault list, the method of selecting and applying faults from the candidate list, the levels of maintenance to be demonstrated, a list and schedule of test reports to be issued, and support material requirements.
  • Test participation: Decisions to be made regarding test participation are the test team members, their assignments, and test decisionmaking authority.
  • Test monitoring: This is the method of monitoring and recording test results.
  • Test schedule: This should include these items: the starting date, the finish date, and the test program review schedule.
  • Test conditions: Two components of these conditions are the modes of equipment/system operation during testing and a description of the environmental conditions under which the test to be conducted.
  • Test ground rules: Under this should be a list of items to which the rules apply. These items include maintenance time limits, maintenance inspection, maintenance due to secondary failures, instrumentation failures, and technical manual usage and adequacy.
  • Testability demonstration considerations: The components of these considerations include the method of selecting and simulating candidate faults, the built-in test requirements to be demonstrated, the repair levels for which requirements will be demonstrated, and acceptable levels of ambiguity at each repair level.
  • Reference documents: The checklist should also detail all applicable reference documents.

The maintainability demonstration reports checklist include items related to test results, such as maintenance tasks planned, maintenance tasks selected, measured repair times, data analysis calculation, the documentation used during maintenance, the selection method, application of the accept/reject criteria, a discussion of deficiencies highlighted during testing, and qualifications of the personnel conducting tasks.

Maintainability test approaches

All maintainability tests are not formal accept/reject demonstration tests. There are many points in the product/system life cycle and in related maintainability program tasks that need test data, both prior to and after the formal decision to accept or reject. Test data may be necessary for administrative and logistic control for updating corrective actions or modifications, to make decisions regarding maintainability design needs, or for evaluating life cycle maintenance support.

The maintainability test approaches that can provide this type of data fall into six categories, as shown in Fig. 10.2 [2].

All the six test categories of maintainability test approaches shown in Fig. 10.2 are described below.

• Dynamic tests: These tests simulate typical operation or uses of system/equipment so that each and every item involved can be checked. The tests involve a continuous input signal and analysis of the corresponding output signals for determining whether system/ equipment needs are fully satisfied. Furthermore, dynamic tests also provide additional information on matters such as integration rates, phase characteristics, and frequency responses.

Categories of maintainability test approaches

Figure 10.2 Categories of maintainability test approaches.

  • Static tests: These tests are simple and straightforward to conduct and provide quite useful information on the transient behavior of the item being tested. A series of intermittent, sequenced input signals feed into the item, and, for measuring its operation, the test monitors all output response signals. Furthermore, it is added that static tests generally establish a confidence factor but their application does not go beyond that.
  • Functional tests: These tests closely simulate normal operating conditions for establishing the product's state of readiness for conducting its proposed mission effectively. The tests can proceed on a system-wide level or focus on items such as replaceable subassemblies. Finally, it is to be noted that functional tests are conducted and required at each point of the evaluation for the product.
  • Closed-loop tests: These tests generate information for application in evaluating design effectiveness, tolerance adequacy, performance, and other key issues. In these tests, the stimulus is adjusted continuously according to the performance of the system/equipment under the test conditions. Closed-loop tests are very useful in situations when a high degree of accuracy is required as well as when test points radiate performance-degrading noise levels. However, it is to be noted that closed-loop circuits or paths in system or equipment design are quite difficult to maintain, and failures in the loop are quite difficult to diagnose.
  • Open-loop tests: These tests represent a refinement of dynamic and static tests, and they do not provide intelligence feedback to the item being tested, that is, the stimulus is not adjusted. Openloop tests generally provide better maintenance-related information than closed-loop tests because they make a direct observation of the system transfer function without the modifying feedback's influence. This approach is also cheaper and simpler than closed-loop testing and is probably the most appropriate type of testing for maintenance purposes because it eliminates the possibility of test instability.
  • Marginal tests: The objective of applying these tests is to isolate potential problems through the abnormal operating conditions' simulation. These tests supply unrelated stimulus to the system/ equipment under conditions such as extreme heat, vibrations, and lowered power supply voltages. Furthermore, these tests provide greatest value as part of fault prediction, where they highlight various incipient failures resulting from abnormal operating conditions and environments.
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