In the environment of procuring various high-tech weapon systems, maintenance budget grew at an annual rate of 6.5 percent for last fourteen years(2008-2021). The rate is much higher than the growth rate of the other operating & support budget, 3.9 percent. In particular, aircraft maintenance budget were increasing more steeply with 7.0 percent because more new aircraft are procured and maintenance policy is highly regulated and safety critical. This study aims to develop maintenance cost estimating relationships for creating analytic application on Air Force fighter aircraft individually. Utilizing the budget documentations and information systems related to maintenance, 8 fighter aircraft operated from 1988 to 2019 are analyzed. Thirty regression models created for each aircraft by combining various variables and data periods are compared using Diebold-Mariano test with two criteria of R² and MAPE. Maintenance cost estimation of an individual aircraft is important for setting budgets and for deciding when to replace aging systems. In addition, results from this study provide insight on when to start using actual O&S costs as a baseline for estimates in lieu of an analogous aircraft that has no sufficient cost data.