In 1984 the Navy implemented the Aircraft Service Period Adjustment Program (ASPA) which was designed to induct aircraft into Standard Depot Level Maintenance (SDLM) only after they fail to meet certain criteria during an inspection. This thesis used regression analysis to explore the relationship between time F-14A aircraft serve in tour and the direct costs of the corresponding SDLM. Almost every year of ASPA, the average direct labor and material costs of F- 14A SDLM have increased, rising from $763,571 in 1985 to a high of $1.68 million in 1993. However, this analysis shows that only a weak correlation exists between the number of months an aircraft spends in tour and the direct costs of SDLM. A multiple regression model including additional variables such as aircraft age, tour number, whether a modification was performed concurrently, and work standard was found to explain 57 percent of the variation in the direct costs of SDLM. The effect of time in tour was insignificant.