A full order model of an aeroelastic aircraft has too many parameters to yield satisfactory estimates. In this paper, using simulated data, rigid body and aeroelastic derivatives are estimated in longitudinal axis for single elastic mode. The proposed approach uses an integrated model structure. It emphasizes the use of estimation techniques that have the capability to accurately determine modal characteristics in those flight test situations where the measured data is dominated by elastic effects. Output error method in time domain is applied to the simulated flight data to identify the aircraft derivatives.