Discussion on Airworthiness Requirement of Widespread Fatigue Damage – Safe-life Methodology or Damage-tolerance Methodology

Regulatory action and research conducted by FAA and industries to preclude widespread fatigue damage occurring in transport airplane fleet is introduced, especially the milestones in the rulemaking course. This article gives an interpretation of the current airworthiness requirement relating to widespread fatigue damage and limit of validity based on analysis of the widespread fatigue damage characteristics. The conclusion is made that the methodology of the current airworthiness requirement is a methodology both safe-life and damage-tolerance since that MSD/MED cracks are difficult to detect.