[en] When calculating the impact-force of an aircraft striking a building the deformation of this building is not taken in account. To which extent the elastic displacements of a structure influence the impact on plates and on spherical shells is investigated in this paper. The aircraft is idealized by a linear mass-spring-dashpot-combination, which can suffer elastic as well as plastic deformation. This 'aircraft' normally strikes a spherical shell at the apex. The time-dependent reactions of the shell as a function of the unknown impact load (F)t are expanded in terms of the normal modes, which are Legendre functions. The continuity condition at the impact point leads to an integral-equation for F(t), which may be solved by Laplace transformation. (Auth.)