10.3.1.2 __Reliability
Prediction of Dormant Products__

In the past, analysis techniques for determining reliability
estimates for dormant or storage conditions relied on simple rules of thumb such as:
“the failure rate will be reduced by a ten to one factor”, or “the expected
failure rate is zero.” A more realistic estimate, based on part count failure
results, can be calculated by applying the conversion factors shown for the
example in Table 10.3-5. The factors convert operating failure rates by part
type to dormant conditions for seven scenarios.

These conversion factors were
determined using data from various military contracts and algorithms from both
MIL-HDBK-217F and RADC-TR-85-91, “Impact of Nonoperating Periods on Equipment
Reliability” (Ref.
[34]). Average values for operating and dormant failure rates were
developed for each scenario. For example, to convert the reliability of an
operating airborne receiver to a ground nonoperating condition, determine the
number of components by type, then multiply each by the respective operating
failure rate obtained from handbook data, field data, or vendor estimates. The
total operating failure rate for each type is then converted using the
conversion factors of Table 10.3-5. The dormant estimate of reliability for
the example receiver is determined by summing the part
results.