More and more transport airplane designs are being affected by the requirements of Section 25.1309 of the Federal Aviation Regulations as their certification bases include Amendment 25-23. Although this regulation became effective in 1970 and Advisory Circular No. 25.1309-1 was published in 1982, misunderstandings still exist concerning its application and its effects on maintenance and operations. This paper attempts to clarify some of the more common misconceptions about numerical methods of analysis and to outline how the results of these analyses may affect airplane maintenance and operations. Maintenance effects are generally of the type which require that a particular inspection or test be accomplished within a specified time. Operational effects have been minor to date and have been limited to specifying a time allowed for airplane dispatch with certain equipment inoperative.