[en] A simplified derivation of the reaction-time history in the case of an aircraft impacting a nuclear power plant is given. The equation of motion for the rigid part of the aircraft is obtained by considering it as a variable system of particles losing mass. The equation of motion for the crushing region is obtained by the methods of continuum mechanics. It is shown that the reaction is not affected by the manner in which the velocity distribution in the crushing region of the aircraft decreases to zero at the rigid wall of the nuclear power plant structure. (Auth.)