are not free. Paying for these warranties raises some of the contextual problems identified above. Assuming funding can be arranged, there are real analytic and implementation problems. One key problem is identifying a reasonable set of incentives or penalties for keeping or not keeping the promises made. Also, it is difficult to enforce these warranties because of the many factors that are not under the control of the developer and producer of the weapon system. These factors include the behavior of the user, the environment of use, the operational support system, and the specific counterforces used against the system. It is difficult to prove that a system has not met performance requirements.

Discussion of the Blischke and Camm Papers

Allen Beckett agreed that reliability estimation is extremely challenging. How does one estimate the reliability of an engine that has been overhauled? What are its failure modes? How does one develop a spares budget for a system in development? Beckett acknowledged that collecting relevant data is necessary and that there are promising modeling approaches. But the key is to understand the operational issues so the models will represent all of the complexities.

The related issue of surveillance testing was raised by Rob Easterling. The objectives of such testing are to find and fix reliability problems, and then update the estimate of system reliability. For defense systems, surveillance testing poses some difficult problems. First, in the case of complicated defense systems, it is unlikely that a large number of replications for surveillance testing will be available. Second, there are a multitude of environments and missions with potentially different reliabilities and failure modes for a given system. The fundamental complication, however, is that it is difficult to quantify the goals of surveillance testing. For example, what is the tolerable probability of failing to detect a fault leading to a reduction in reliability of more than 10 percent in 2 years of testing? It may be that surveillance test plans cannot be driven solely by statistical arguments.

However, statistical constructs should be part of the decision process regarding surveillance testing. Like a warranty, surveillance testing should be considered a type of insurance policy, whereby some amount of protection is being purchased for the price of additional testing. The general point is that, regardless of how a surveillance test plan and the associated decision rule based on the test results are derived—whether through eco-



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