The Strategy of Widespread Fatigue Damage in FMP System

As is known,widespread fatigue damage ( WFD) is a common phenomenon of aging aircraft being a negative impact on safety and reliability. The current FAR 25. 571( b) requires that"An LOV ( Limit of Validity) must be established,during which it is demonstrated that widespread fatigue damage will not occur in the aircraft structures". The FAA issued AC 91-82A in August 2011 providing guidance on developing and implementing a Fatigue Management Program ( FMP) system to address in-service issues for metallic fatigue critical structures. This action brings new challenges to aircraft manufacturers in China. This paper introduces the problem of widespread fatigue damage including the MSD( multiple site damage) and MED( multiple element damage) and the differences between them and the steps to establish the LOV / ELOV( Extended limit of validity) . Authors in this paper is also proposing some management indicators to control WFD during the design phase and maintenance. Developing and implementing the management indicators to address WFD which are involved in the FMP system may provide guidance on the estimation and management to address WFD for present and future aircraft. Finally,some suggestions are put forward to provide the theoretical basis for large civil aircraft design and airworthiness.