Secure blocking system comprising: i) two parts, a cylindrical shaft and an element, moving in translation relative to one another, one of the two parts being inserted into the other, ii) a means for blocking the translational movement, in which an immobilising element is arranged, said immobilising element being of the tube type, said blocking means being a blocking cylinder, iii) the immobilising tube being associated with a viscoelastic fluid located between the blocking cylinder and the immobilising tube, such that the translational movement is blocked when the viscoelastic fluid exerts a pressure on the walls of the immobilising tube and such that the translational movement is made possible during an emergency unlocking operation when the viscoelastic fluid is no longer subjected to pressure, iv) the blocking cylinder comprising an axial bore, configured to allow the cylindrical shaft to slide therethrough and comprising areas of different diameters, the diameter of the central portion of the bore being configured such that it fits a sealed ring-shaped chamber between the outer surface of the cylindrical shaft and the inner surface of the bore in which the viscoelastic fluid is located, characterised in that: v) said secure blocking system comprises a hydraulic fluid intake configured to bring a hydraulic fluid to the intersection between the surface of the cylindrical shaft and an inner surface of the immobilising tube arranged in the ring-shaped chamber so as to be in contact with the surface of the cylindrical shaft, the viscoelastic fluid being located between the tube and the inner surface of the bore, such that, in the presence of hydraulic fluid, the cylindrical shaft is free to move in translation, vi) the hydraulic fluid intake exerts sufficient pressure to deform the tube in the direction of the blocking cylinder, thanks to the compressing properties of the viscoelastic fluid. i) two parts, a cylindrical shaft and an element, moving in translation relative to one another, one of the two parts being inserted into the other, ii) a means for blocking the translational movement, in which an immobilising element is arranged, said immobilising element being of the tube type, said blocking means being a blocking cylinder, iii) the immobilising tube being associated with a viscoelastic fluid located between the blocking cylinder and the immobilising tube, such that the translational movement is blocked when the viscoelastic fluid exerts a pressure on the walls of the immobilising tube and such that the translational movement is made possible during an emergency unlocking operation when the viscoelastic fluid is no longer subjected to pressure, iv) the blocking cylinder comprising an axial bore, configured to allow the cylindrical shaft to slide therethrough and comprising areas of different diameters, the diameter of the central portion of the bore being configured such that it fits a sealed ring-shaped chamber between the outer surface of the cylindrical shaft and the inner surface of the bore in which the viscoelastic fluid is located, v) said secure blocking system comprises a hydraulic fluid intake configured to bring a hydraulic fluid to the intersection between the surface of the cylindrical shaft and an inner surface of the immobilising tube arranged in the ring-shaped chamber so as to be in contact with the surface of the cylindrical shaft, the viscoelastic fluid being located between the tube and the inner surface of the bore, such that, in the presence of hydraulic fluid, the cylindrical shaft is free to move in translation, vi) the hydraulic fluid intake exerts sufficient pressure to deform the tube in the direction of the blocking cylinder, thanks to the compressing properties of the viscoelastic fluid.