MODIA (Method of Designing Instructional Alternatives) was developed to help the Air Force manage resources for formal training by systematically and explicitly relating quantitative requirements for training resources to the details of course design and course operation during the planning stage. This report describes MODCOM (MODIA Cost Model), a FORTRAN-programmed computer model for estimating the investment and operating costs associated with alternative training course designs; a separate appendix describes the program. The model uses instructional policy data input to the User Interface (UI), resource requirements generated by the Resource Utilization Model (RUM), and cost and manning factors supplied by the planner or, in some cases, stored in the program, to project total course costs for up to five years. Options are available as to which costs should be included and how they should be computed. The basic equation parameters of all estimating relationships have been completely generalized in order that the model may accommodate a wide range of alternatives; e.g., number of entrants, course duration, grade structure of the instructor force, the levels of staff and base support, pay and allowance factors, and the types of courseware and hardware used. The five outputs of MODCOM are: (1) graduates by student type; (2) student and staff man-years; (3) courseware, hardware, and facility characteristics and requirements; (4) total course costs by functional element; and (5) total course costs by program and appropriation. (Author/DAG)