We develop an object-oriented simulation that models the airdrop mission of the newest U.S. transport aircraft, the C-17 Globemaster III. The simulation, written in MODSIM III, is based on three basic object types: a C-17, a wake vortex, and a paratrooper. The aircraft object provides the required aerodynamic constants for simulating the wake vortices generated off each wing tip; the vortex object includes velocity field and decay models as well as a position algorithm; and, the paratrooper object implements a 6-degree of freedom trajectory model. After considering two validation scenarios, we generate vortex encounter information for various formations and wind conditions, and quantify the associated risk of paratrooper/vortex encounters in a potential encounter rate. Time over the DZ is a primary concern in any airdrop operation, and the results of this analysis form a tool that allows the ground commander to assess the risk involved in decreasing that time. We also present a 3D visualization of the simulation output that may be used for mission planning and prototyping of new aircraft formations or tactics.