Abstract: The reliablity design advisory expert system ( RDAES) is becoming a design tool urgentlyneeded by designers, but only a few have been developed at home or abroad. The r esear chanddevelopment work done by the aut hors gives a new approach to establish this kind of expert system.The new concept of importance level, adapt ability , and loss level are suggested and applied to the inference machine in this paper . The expert system' s features, main functions and resear chresults of the RDAES prototype for an airer aft landing gear extending / retracting system are introduced.The results of cases application indicate that the development of RDAES is successful;the thinking, concepts and approaches adopt ed are correct, and have won high praise from the relateddesign groups.

Key words: expertsystem, importancelevel, adaptabioity, losslevel.