Abstract: An actuator comprises a rack arranged to be driven for movement by a rotatable pinion the rack having at least a first region having a first pitch circle diameter and a second region having a second, different, pitch circle diameter, and movable support means for supporting the rack for movement.

Abstract: A failsafe arrangement comprising a first mounting member and a second mounting member which is angularly moveable relative to the first mounting member. The first and second mounting members define first and second surfaces respectively which define therebetween a channel, the first and second surfaces being shaped such that the channel is of non-uniform width. At least one wedge member is disposed within the channel, the or each wedge member being carried by a drive member and being arranged such that, in use, when the drive member and the second mounting member move at substantially the same angular speed, the wedge member does not impair movement of the second mounting member relative to the first mounting member, relative angular movement of the drive member and the second mounting member causing the wedge member to cooperate with the first and second surfaces to apply a braking force so as to impede relative angular movement of the first and second mounting members.