METHOD OF CALCULATION
It involves counting the number of each part type and multiplying with the generic failure rate of each part. On summing up the product, we obtain the failure rate of each functional circuit.
The information needed to apply the method is:
(1) Generic failure rate
(2) Part Quality level
(3) Equipment Environment
The equipment failure rate is obtained by looking up a generic failure rate in Table - 4.1, multiplying it by quality factor, and then summing it with failure rate obtained by other components. The general mathematical expression for equipment failure rate with this method is:
Above equation is applied, when the entire equipment is being used in one environment. If the equipment comprises several units operating in different environments, (such as avionics systems with units in airborne inhabited or uninhabited environment), then this equation should be applied to the period of the equipment in each environment. These "environment equipment" failure rates should be added to determine total .the same values that are used in part stress analysis. Microcircuits have an additional multiplying factor, πL, which accounts for maturity of the manufacturing process. For devices that are in production for two years or more, there is no need to apply learning factor. For those in production less than two years, λg should be multiplied by learning factor πL