Fault tolerant safe flight controller bank

This paper examines the issues of safety and certification as they apply to flight control system for commercial planes. Theoretical designs may guarantee stability but some stable trajectories should not be considered safe for human passengers. On the issue of certification, getting acceptance for a control structure may prove challenging if it is not possible to establish a priori the control algorithms that will be used in a particular situation. The approach presented here proposes control structures of reduced complexity that can be exhaustively tested and where the issue of safety can also be addressed. The reduced complexity is achieved by introducing a finite partition of the fault space and designing robust controllers that perform safely within each partition. The transition among controllers is determined by a fault isolation mechanism that uses to advantage the "over-instrumentation" in commercial planes. The concept has been tested with extensive simulations using a 6DOF nonlinear model for B747/200 as a rigid body. This paper presents results for the case of single faults on the control surface actuators. The results support the premises that the structure enables the examination of all possible errors in the fault isolation and that the testing of the controller supplies valuable data for the design of a fault isolation technique.