An aircraft structural deformation sensor system comprises a deformation sensor arrangement comprising one or more transceiver(s), each transceiver matched to at least one corresponding transponder and configured to be attached to a support component. The deformation sensing arrangement is configured such that one or more range values between the at least one transceiver and the at least one corresponding transponder is determinable by the transceiver. A deformation controller is configured to process the one or more range values from the transceiver(s) and compute a deformation state of the deformable component relative to the support component.