Ultrahigh reliability estimates for systems exhibiting globally time-dependent failure processes

A long-standing conjecture, that application of the instantaneous coverage technique to the time-dependent failure rate case also provides conservative reliability estimates, is resolved negatively. In particular, two examples are provided which show that even monotonic failure rates can lead to overly optimistic estimates. An alternative extension of the instantaneous coverage technique, consistent with the constant-rate approach, is then offered. The novel approach is shown to provide conservative estimates in the time-dependent case, provided fault-handling and recovery time distributions can be described by step functions.<>