In the paper, dynamic simulation of landing impact of a large transport aircraft, based on a non-linear dynamical model that allows for touchdown analysis of an aircraft 3D landing is presented. The aircraft model is shaped as a multibody system with variable kinematical structure. The model includes discontinuous dynamics of the main landing gear shock absorber, tire dynamics and wheel spin-up effect. The aerodynamic loads are considered, too. Because of its great influence on an aircraft ground dynamical behavior and landing gear subparts loads determination, dynamical model of the main gear shock absorber is presented in more details. Based on the developed model, the touchdown impacts of a transport aircraft for different 3D flight-landing parameters (one gear landing cases) are simulated with the focus on the main gear shock absorbers loads determination.