TABLE OF CONTENTS Risk management is a very important aspect of maintaining safety at an acceptable level in service. Figure 6.1 describes a control process that is based on changes in inspection approaches and periods.
The major inspections are selected by type and approach so that the lower bound value, LB, is not violated and the interval is selected so that the upper bound, UB, is not exceeded. So when service data are used to update knowledge and reduce uncertainty, inspection methods and periods can be used as the means of a control process to maintain safety in service.
The probability of an unsafe state (or unsafe flight) is the "measure of safety" that is the basis for the design to explicit safety constraints. Figure 6.1 illustrates the concept, and the probability of an unsafe state during the flight just before the inspection at time T is,
where the first term of the right-hand side of Eq. (6.1) describes the effect of damage, and can be written as,
where j represents damage size regions 3, 4, 5.
The second term describes "degradation" in properties without measurable mechanical damage sizes. The third term deals with accidental damage during operation, and can be written as,
The letter k refers to the kth flight after the last major inspection. The following sub-events are involved,
U T: Acceptable integrity at T;
Y k: Accidental damage inflicted on flight k
