Patent ID: 8359851

Claim:
A trim actuator actuating system for a hydraulically actuatable trimmable horizontal stabilizer actuator (THSA) of an aircraft, the system comprising: at least one hydraulic linear actuator; a first hydraulic power supply system; and an autonomous second hydraulic power supply system; wherein the at least one hydraulic linear actuator is coupled to the first power supply system, which applies hydraulic power to the hydraulic linear actuator during normal operation, and the at least one hydraulic linear actuator has hydraulic power applied to it by the second power supply system during malfunction operation, in which the first power supply system has at least partially broken down, wherein the at least one hydraulic linear actuator is implemented as a piston cylinder unit having a piston rod and a cylinder, and the linear actuator comprises a mechanical lock, which is configured to fix the piston rod in relation to the cylinder in the last position set before a breakdown in the event of a breakdown of both the first and the second power supply systems, wherein the mechanical lock comprises at least one first form fitting element that is situated around an outer circumference in an area of the exit of the piston rod on the cylinder and a plurality of second form fitting elements that move jointly with the piston rod upon an actuation of the linear actuator and past the first form fitting element, wherein the at least one first form fitting element is engageable in a form fitting way with one of the plurality of second form fitting elements at discrete positions in a longitudinal direction of the piston rod by which the piston rod is fixed in relation to the cylinder; wherein the lock comprises an immersion tube that is connected to the piston rod at an end outside the cylinder and encloses the piston rod concentrically at an interval, the interval being dimensioned in such a way that the cylinder plunges into the interval upon an actuation of the linear actuator; wherein the plurality of second form fitting elements is formed by a plurality of grooves that are incorporated into an inner circumference of the immersion tube.