Trimmable horizontal stabiliser actuator secondary load path detector

1 . A secondary load path assembly comprising:

a secondary load path comprising:

a plate;

a secondary nut; and

a transfer plate secured to the plate and configured to connect the plate and the secondary nut in load transfer engagement, the transfer plate having an opening therethrough (therethrough, an axis defined through the opening, and the secondary nut protruding axially through the opening; wherein, in a state in which load is not transmitted via the secondary load path, a clearance is provided between the secondary nut and the opening;

a locking unit configured to lock the secondary nut to the transfer plate when load is to be transmitted through the secondary path, the locking unit comprising a lock arranged to axially move to a lock position in which it is located in the clearance between the secondary nut and the opening to lock the secondary nut to the transfer plate; and

means for indicating when the lock is in the lock position, wherein the means for indicating when the lock is in the lock position comprises a switch arranged to be activated by the lock in the lock position and a ball located between the lock and the switch the lock and the ball being configured such that as the lock moves into the lock position it pushes against the ball to engage with and activate the switch.

2 . The assembly of claim 1 , wherein the locking unit is mounted to the transfer plate.

3 . The assembly of claim 1 , wherein the locking unit further comprises:

a lock spring arranged to bias the lock towards the opening in the transfer plate such that when the secondary nut moves relative to the transfer plate to close the clearance on one side of the opening, a gap (G) is formed between the secondary nut and an opposite side of the opening and the lock moves axially under the bias of the lock spring into the gap (G) to secure the secondary nut against movement in the opening relative to the transfer plate.

4 . The assembly of claim 1 , wherein the lock includes a lock body and a locking end,

wherein the locking end being configured to fit within the gap (G) in the lock position and the lock body having a recess formed therein to receive the ball, such that when the lock is not in the lock position, the ball is located in the recess and does not activate the switch and when the lock is in the lock position, the ball is not located in the recess and is pushed by the lock body against, and to activate the switch.

5 . The assembly of claim 1 , wherein the lock is formed to receive a tool to cause axial movement of the lock away from the transfer plate to verify correct functioning of the lock.

6 . The assembly of claim 1 , wherein the lock is formed to receive a tool to cause axial movement of the lock away from the transfer plate to verify correct functioning of the lock; and

wherein rotation of the lock by a tool causes the lock to move against the bias of the spring such that the ball is not located in the recess and the switch is activated to verify correct functioning of the lock.

7 . The assembly of claim 1 , further comprising:

a maintenance cap to cover the locking unit.

8 . The assembly of claim 7 , wherein the maintenance cap is removably fitted over the lock unit by means of screw fasteners.

9 . The assembly of claim 2 , wherein the locking unit is secured to the transfer plate by screw fasteners.

10 . A force transmitting shaft assembly having a primary load transfer path and a secondary load transfer path assembly as claimed in claim 1 .

11 . A trimmable horizontal stabiliser actuator (THSA), comprising:

a force transmitting shaft assembly as claimed in claim 10 .

12 . The THSA of claim 11 , wherein the plate is a failsafe plate secured to an aircraft having the THSA.