Device for mechanically blocking a linear movement between two structures (1, 2), this device comprising a first element secured to one of said structures, and a second element (5, 20) secured to or bearing against the other of said two structures, said first and second elements cooperating linearly with one another by means of a double coaxial screw-and-nut pair, characterised: • in that the double screw-nut pair consists of: ■ a first screw-nut pair consisting of a so-called reversible screw and a nut cooperating without stress or almost without stress with said reversible screw; ■ a second screw-nut pair consisting of a so-called irreversible screw and a nut cooperating with said irreversible screw, the cooperation between these two elements having a determined clearance; one of the elements of the first pair being secured to one of the elements of the second pair, such that the rotation of one inherent to the relative linear movement of said first element with respect to the second element, rotates the other; • and in that the device comprises at least one elastic means, capable of acting on one of the constituent elements of the mentioned above screw-nut pairs, so as to: ■ maintain the screw-and-nut clearance of said second pair when the stress is less than a threshold fixed by construction, said stress corresponding to a rotational speed of one of the elements of the pair; and ■ cause the blocking of the cooperation of the elements of the second irreversible screw-and-nut pair beyond said stress threshold. • in that the double screw-nut pair consists of: ■ a first screw-nut pair consisting of a so-called reversible screw and a nut cooperating without stress or almost without stress with said reversible screw; ■ a second screw-nut pair consisting of a so-called irreversible screw and a nut cooperating with said irreversible screw, the cooperation between these two elements having a determined clearance; one of the elements of the first pair being secured to one of the elements of the second pair, such that the rotation of one inherent to the relative linear movement of said first element with respect to the second element, rotates the other; ■ a first screw-nut pair consisting of a so-called reversible screw and a nut cooperating without stress or almost without stress with said reversible screw; ■ a second screw-nut pair consisting of a so-called irreversible screw and a nut cooperating with said irreversible screw, the cooperation between these two elements having a determined clearance; • and in that the device comprises at least one elastic means, capable of acting on one of the constituent elements of the mentioned above screw-nut pairs, so as to: ■ maintain the screw-and-nut clearance of said second pair when the stress is less than a threshold fixed by construction, said stress corresponding to a rotational speed of one of the elements of the pair; and ■ cause the blocking of the cooperation of the elements of the second irreversible screw-and-nut pair beyond said stress threshold. ■ maintain the screw-and-nut clearance of said second pair when the stress is less than a threshold fixed by construction, said stress corresponding to a rotational speed of one of the elements of the pair; and ■ cause the blocking of the cooperation of the elements of the second irreversible screw-and-nut pair beyond said stress threshold.