An upper attachment system for a trimmable horizontal stabiliser actuator (THSA) comprises: a housing 11 holding a yoke 2 and a ballscrew 3; a nut 4 coupled to the housing 11 and cooperating with the ballscrew 3 such that rotation of the ballscrew 3 relative to the nut4 results in linear motion of the ballscrew 3; a recess formed between the yoke 2 and the ballscrew 3 and arranged to receive, in use, an upper part 27 of a tie bar 29 of the secondary load path of the actuator; and a biasing mechanism 6, 7, 8 arranged such that, in use, when no axial load is applied to the tie bar 29, the yoke 2 and the ballscrew 3 are held by balanced forces from the biasing mechanism 6, 7, 8 in a position within the recess, and such that when, in use, an axial load is applied to the yoke 2 by the upper part 27 of the tie bar 29, the balanced forces from the biasing mechanism 7, 8, 9 are overcome and the axial load along with the biasing mechanism 7, 8, 9 results in linear motion of the ballscrew 3 in a first axial direction relative to the nut 4, wherein the linear motion moves the ballscrew 3 toward the yoke 2 and closes the recess around the upper part 27 of the tie bar 29.