Diagnosis of the air distribution system of the JAS39 Gripen environmental control system

Traditionally supervision has been achieved using limit checking and hardware redundancy, but these methods have proven insufficient. The availability of information from all parts of the aircraft and the computing capacity available in the Gripen today enables the implementation of sophisticated supervision methods, for instance model based diagnosis. The purpose of this thesis was to investigate which faults in the distribution part of the Environmental Control System (ECS) could be detected with the sensors available today, using model based diagnosis, and to clarify where new ones could be useful in order to design an improved diagnosis system. No measurement data from a real ECS could be obtained, so the real system had to be replaced by an Easy5-model. Therefore the diagnosis system developed in this thesis is not directly applicable on a real ECS. With the sensors available, 8 of the 9 faults important to detect, can be detected. The last important fault can be detected if one new pressure is installed. Acknowledgements This work has been carried out in cooperation with Saab AB. I would like to thank my two supervisors, Erik Frisk, LiTH, and Birgitta Lantto, Saab AB, for all their help and guidance. I would also like to thank the two groups GDGT and GDGM at Saab, for all pleasant coffeebreaks. A special thanks to Per Nilsson and Mikael Holmberg for making me feel so welcome at the office. Linköping, February 2001 Johan Karlsson