This article describes the findings of research for some recent transport airplane's accidents related to fatigue cracks. One is a B747SR's accident due to crack initiating at the fastener holes (to say Multiple-Site Damage). The other describes the crash of UAL's DC10-10 (N1819U), in Sioux City, Iowa, U. S. A., on July 19, 1989, which experienced a catastrophic failure of the No. 2 tail-mounted engine during cruise flight. The third explains the in flight separation of the No. 2 engine and engine pylon from B747-100F, shortly after departure from Anchorage International Airport, Anchorage, Alaska, on March 31, 1993. As a result of investigation for B747-100F's accident, National Transportation Safety Board made some important recommendations (One is to amend the design load requirements of Title 14 Code of Federal Regulations Part 25 to consider multiple axis loads encountered during severe turbulence) to the Federal Aviation Administration. Also, current aging airplane service data have identified that there are more cracked airplanes with increasing fleet edge, and possibly several fatigue cracks in some of the cracked airplanes. Especialy, MSD helped focus the attention of the aeronautical field on the problems of operating an aging transport airplanes. Therefore, FAA proposed to rivise the Advisory Circular No. 25·571-1A (Damage tolerance and fatigue evaluation of structure) on 3/5/1986. This article describes one operator's viewpoint on the means to maintain the safety of aircraft structures in consideration of the revised structural fatigue evaluation standards.
