7.5.5.4 __Dependent Failure
Probabilities__

Up to this point, it has been assumed that the failure of an
operative redundant element has no effect on the failure rates of the
remaining elements. Dependent failures might occur, for example, with a system
having two elements in parallel where both elements share the full load.

An example of conditional or dependent events is illustrated by
Figure 7.5-18. Assume elements A and B are both fully energized, and normally
share or carry half the load, L/2. If either A or B fails, the survivor must
carry the full load, L. Hence, the probability that one fails is dependent on
the state of the other, if failure probability is related to load or stress.
The system is operating satisfactorily at time t if either A or B or both are
operating successfully.