Secondary load path detection

A nut arrangement for a screw actuator, comprising:

• a primary nut for providing a primary load path;
• a secondary nut for providing a secondary load path;
• a flexible coupling to link the primary nut to the secondary nut during normal operation when the primary load path is active, wherein the flexible coupling provides a bias that allows relative axial movement between the primary and secondary nuts;
• and
• a sensor to detect relative axial movement between the primary and secondary nuts,
• wherein the sensor is used as part of a wear detection arrangement to monitor a change in backlash between the primary and secondary nuts;
• wherein an interface ring is provided to link the secondary nut to the primary nut and the interface ring is seated with respect to the primary or secondary nut by the flexible coupling;
• wherein the interface ring is coupled to the secondary nut with a mechanism which allows the interface ring and the secondary nut to be displaced with respect to each other to test the flexible coupling;
• and
• wherein the mechanism comprises a mount provided on the interface ring for a bolt, a flange provided on the secondary nut and a bolt, the bolt having a tail end portion which extends through the flange of the secondary nut and into the mount, and wherein a spring is provided towards a head end portion of the bolt to bias the head end portion of the bolt away from the flange.