An aircraft control surface skew and/or loss detection system including: an aircraft wing structure having a fixed part and at least two control surface elements (116,118,120,122) wherein the at least two control surface elements (116,118,120,122) are configured to be moveable relative to the fixed part, a cable operably connected to each of the at least two control surface elements (116,118,120,122) such that a tensile force is applied to the cable upon skew and/or loss of one of the control surface elements (116,118,120,122), and a sensor assembly having a first part and a second part, wherein one of the first and second parts has a first sensor and a second sensor (138,139) and wherein the cable is coupled to the other of the first and second part such that skew and/or loss of one of the control surface elements (116,118,120,122) causes movement of the second part relative to the first part, wherein: the first and second sensors (138,139) are configured to detect a first relative position of the first and second parts indicative of the wing structure supporting a load whilst in flight, characterized in that the first and second sensors are configured to detect a second relative position of the first and second parts indicative of the wing structure being supported whilst on the ground, and in that the first sensor is configured to detect when the first and second parts are within a first range of relative positions, and the second sensor is configured to detect when the first and second parts are within a second range of relative positions. an aircraft wing structure having a fixed part and at least two control surface elements (116,118,120,122) wherein the at least two control surface elements (116,118,120,122) are configured to be moveable relative to the fixed part, a cable operably connected to each of the at least two control surface elements (116,118,120,122) such that a tensile force is applied to the cable upon skew and/or loss of one of the control surface elements (116,118,120,122), and a sensor assembly having a first part and a second part, wherein one of the first and second parts has a first sensor and a second sensor (138,139) and wherein the cable is coupled to the other of the first and second part such that skew and/or loss of one of the control surface elements (116,118,120,122) causes movement of the second part relative to the first part, wherein: the first and second sensors (138,139) are configured to detect a first relative position of the first and second parts indicative of the wing structure supporting a load whilst in flight, characterized in that the first and second sensors are configured to detect a second relative position of the first and second parts indicative of the wing structure being supported whilst on the ground, and in that the first sensor is configured to detect when the first and second parts are within a first range of relative positions, and the second sensor is configured to detect when the first and second parts are within a second range of relative positions. the first and second sensors (138,139) are configured to detect a first relative position of the first and second parts indicative of the wing structure supporting a load whilst in flight, characterized in that the first and second sensors are configured to detect a second relative position of the first and second parts indicative of the wing structure being supported whilst on the ground, and in that the first sensor is configured to detect when the first and second parts are within a first range of relative positions, and the second sensor is configured to detect when the first and second parts are within a second range of relative positions.