This PhD dissertation deals with Fault-Tolerant Flight Control System as applied to Bell-205 Helicopter which was a platform for earlier research on design of control laws using modern robust control techniques. Earlier research was focusing on control law design, simulation, and flight testing. This thesis has applied the general concept in Fault- Tolerant Control on the vehicle and built Fault Detection, Isolation, and Accommodation (FDIA) for the sensors using actual Flight Test Data (FTD) and the results was validated against other FTD data sets and found quite satisfactory. In an additional step, the FDIA was integrated with an H∞ controller and checked against various faults and the resultant FTFCS was tested. The -synthesis was used in the analysis & design of an FTFCS and this integration has indicated better performance and stability margins over H∞. Finally, the insight thinking about the implication of faults on controllers and overall system integrity has led to mathematical formulation of a novel FTFCS scheme which is adaptive in nature and based on manipulation of Algebraic Riccati Equations. The simulation results is not part of the thesis.