The High Redundancy Actuation (HRA) project investigates the use of a relatively high number of small actuation elements, assembled in series and parallel in order to form a single actuator which has intrinsic fault tolerance. Both passive and active methods of fault tolerant control are being considered for use with the HRA. In either approach, some form of health monitoring is required to indicate the requirement for reconfiguration in the latter case and the need for maintenance in the former. This paper presents a method of detecting faults in a HRA using an Interacting multiple-model (IMM) algorithm.