This paper is concerned with the designing of simultaneous flight control deflections for aircraft system identification. The elevator, ailerons and rudder are excited with harmonically related multisine signals. The optimal deflections are designed when there is no information about the stability and control derivatives and when this information is available. The inclusion of the system dynamics in the inputs design phase is done with the D-optimality criterion. Both sets of optimal flight surface deflections are used as excitations of a nonlinear aircraft model which is identified through the maximum likelihood estimation method. Parameters accuracy for those maneuvers (designed with and without a-priori knowledge) is presented and compared.