This paper describes a numerical methodology coupling Navier-Stokes equations and structural modal equations for predicating 3D transonic wing flutter. A dual-time step implicit unfactored Gauss-Seidel iteration with Roe scheme are employed for the flow solver. A modal approach is used for the structural response. The flow and structural solvers are fully coupled vis successive iterations within each physical time step. The accuracy of the modal approach structure solver is validated with finite element solver ANSYS. The results indicate that the first five modes are sufficient to accurately model the wing structure response for present study. The computed flutter boundary of AGARD wing 445.6 for free stream Mach numbers ranging from 0.499 to 1.141 agrees well with the experiment.