F2A is an aero-hydro-servo-elastic tool developed based on AQWA by Yang Yang, a postdoctoral research associate in Liverpool John Moores University for performing fully coupled analysis of floating offshore wind turbines (FOWT). The aero-servo-elastic simulation capabilities are fully implemented within the user_force64.dll which is a built-in DLL of AQWA for external force calculation. For a coupled analysis of a floating offshore wind turbine subjected to wind, wave and current loadings, the aerodynamic loads acting on the rotor, the elastic responses of the blades and tower, and the servo-control are examined through the DLL, considering the influence from the platform motions. The platform position, velocity and acceleration at each degree of freedom are passed into the DLL to update the kinematics of the upper structures. Before being passed into DLL, these terms are transformed from the inertial coordinate system to the local coordinate system of the platform.