Widespread Fatigue Damage Evaluation for Multiple Elements Based on Probabilistic Approach

In order to obtain a Type Certificate for civil transport category aircraft the Applicant must to comply with some design rules - airworthiness requirements. Among those, the one associated with structural fatigue (§25.571), whose main objective is related to prevent a catastrophic event, from structural damage, during the operational life of the aircraft. That section requires special attention for Widespread Fatigue Damage (WFD). For that, the design approval holder (DAH) must establish a Limit of Validity (LOV) of the engineering data that supports the structural maintenance program. Up to the LOV, DAH must demonstrate that the aircraft will be free from WFD. A Widespread Fatigue condition can be originated from: Multiple Site Damage, Multiple Element Damage or a combination of both. The objective of this work is to propose a probabilistic approach to define maintenance actions to prevent widespread fatigue damage condition from Multiple Element Damage up to the LOV.