A six-degree-ofreedom piecewise simulation of aircraft motion is developed in SIMULINK. Using a mathematical model of fixed-wing aircraft, the simulation is used to observe the longitudinal and lateral-directional motions of the aircraft following a pilot input. The mathematical model is in state-space form and uses aircraft stability and control derivatives calculated from the aircraft geometric and aerodynamic characteristics. The simulation takes into account the changed speed and altitude due to pilot input and demonstrates the non-linearity of the aircraft motion due to change in speed and altitude. The results from the simulation are compared with the known results to validate the mathematical model used. The simulation is carried out for a number of airspeed and altitude combinations to examine the effect of changing speed and altitude on the aircraft dynamic response.