Whether these defects become a fault or not is a function of the system affected, the service conditions at the defect location within the aircraft, available alternative redundancies, the function of other cables in an affected bundle, and the age of the insulation. An analysis is needed which quantifies the risk of these insulation defects through consideration of these factors. Aircraft safety is based on the reliability of consequence-limiting systems and equipment. PRA is an analytical technique for integrating diverse aspects of design and operation in order to assess the risk of a particular aircraft and to develop an information base for analyzing aircraft specific and generic issues. PRA involves developing a set of possible casualty sequences and determining their outcomes.
System models consist of event trees and fault trees.
Casualty Defined as any undesirable single or combination of faulted critical aircraft systems or equipment where the only ultimate result is a crash. Event trees Depict initiating events and combinations of system successes and failures. Event tree development consists of identification of initiating events and systems that respond to each initiating event. Separate event trees are constructed for each initiating event or class of initiating events. An event sequence is a subset of the event tree that consists of or follows one configuration or combination of failures.