The USAF initiated the Aircraft Structural Integrity Program (ASIP) over 40 years ago because of catastrophic, unanticipated, in-flight fatigue failures of in-service aircraft. In essence, ASIP is the management tool for the USAF to safely manage the fleet from initial operating capability through the design service goal and beyond. Since ASIP's inception, the USAF has not had a single catastrophic structural failure. The primary analysis tool to determine the fatigue life of a structural component in ASIP is linear elastic fracture mechanics (LEFM). In this effort, nine LEFM parameters were identified that affect the fatigue life: initial flaw assumption, boundary correction factor, load interaction models, crack growth rate data, stress intensity factor, threshold stress intensity factor, yield stress, and critical stress intensity factor.