Failure mode tests that called out the failure modes we changed must be updated to now test for both failure modes. Testing for both failure modes ensures that the original detection percentage will remain the same. Having reconciled this split in failure modes with our original tests, we can now focus on building prognostic tests.

Prognostic tests identify impending failure. This only differs from standard diagnostic tests in regards to "when." As a result, one only need be concerned with two aspects of the Prognostic test:

• When is the test used
• What failures does the test cover

First, the test must be used prior to diagnostic tests (in our strategy) if we wish see the true impact of prognostics. This is accomplished by adding a test prerequisite from diagnostic tests to each respective prognostic test equivalent. This will ensure that if applicable, the prognostic test will have a chance to detect and/or isolate failure ahead of the diagnostic tests. Any benefits will be clearly identified in the fault groups that result.

Second, the failures that the test covers should be typically confined to those additional failure modes that were added to account for the capabilities of trend analysis and prediction. Although there may be unusual circumstances where a trend is only examined when another unrelated failure occurs, it is certainly not the norm.

Having accounting for both the capabilities of trend analysis (by adding failure modes) and the prognostic decision-making itself (by adding tests), eXpress now has the information necessary to accurately assess the benefits of prognostics. Keeping prognostic tests in their own test set also allows simple trade-off studies and reporting.