This paper presents a new active approach in order to design a modelbased fault tolerant control (FTC) systemfor three phase induction motors (IMs) subjected tomechanical faults caused by stator and rotor failures. In this approach, a nominal controller achieves control objectives in fault free case. Themain part of this approach is related to design a fault/state observer for simultaneous estimation of additive faults which model the mechanical faults and axial fluxes in any operating conditions. For trade off between robustness and performance in the presence of uncertainties and faults, this fault/state observer design problem is reduced to a well known mixed H-2/H infinity optimisation problem by using polytopic linear parameter varying approach. The FTC system consists of a nominal controller together with an observer which provides auxiliary inputs using the estimation of additive faults in order to compensate their undesirable effects on IM performance. The simulation results are shown to illustrate the effectiveness of the proposed approach to compensate the mechanical faults in IM.