Abstract: The method of using Kane's equation to develop the dynamic equations of a flexible aircraft system including landing gear mechanisms is investigated in this paper. Two kinds of mathematical models of runway surface are given. Then, the numerical simulation method is discussed for simulating the attitude, velocities, accelerations and dynamic loads of a flexible aircraft during take-off and landing, taktng into accounf of the effect of inertial forces and moments of large landing gear parts on the motion of the system. As a simple example, the symmetric take-off and landing of KC-135 aircraft on the runway No. 12 is simulated. The numerical results are only for reference.