Abstract: This paper studies a sensor fault tolerant system for an aircraft in a Microwave Landing System (MLS) environment. The objective of the fault tolerant system is to detect failures in navigation aid instruments and on-board sensors and to provide reliable estimates for the aircraft states in the possible presence of these sensor malfunctions. A failure detection and isloation (FDI) algorithm is used to detect and isolate the navigation aid instrument failures. The nonlinear filtering techaique using separated-bias estimation is used to generate the state estimation of the aircraft. State estimates are used by an automatic guidance and control system to land the aircraft along a prescribed path.

Key words: landing, fault tolerant navigation, extended Kalman filtering, separated-bias es-timation