A system and method of activating protection means (1) in order to protect the physical integrity of an occupant of an aircraft (10) during an accident is provided. The protection means (1) are activated when, firstly the acceleration of said aircraft (10) along a particular axis (X, Y, Z) of the coordinate system of the aircraft (10) is greater than a first variable threshold, and secondly when the speed variation of the aircraft along said particular axis (X, Y, Z) is greater than a second variable threshold. The first variable threshold and the second variable threshold each vary as a function of the stage of flight of the aircraft (10) in such a manner as to be minimized during predetermined accident-prone stages of flight.