The Experimental Advanced Design Advisor (XAIDA) is a system for the development of computer-based maintenance training. XAIDA acquires knowledge of a device from a subject matter expert and applies common maintenance-training procedures to generate interactive training from the description. XAIDA provides maintenance training in four areas: the physical characteristics of a device, its theory of operation, operating and maintenance procedures, and troubleshooting. XAIDA relies on an instructional device known as a transaction shell, an instructional procedure applicable to particular instructional objectives of a specific type. XAIDA employs a different transaction shell for each of the four above-mentioned areas, and each shell employs a knowledge structure appropriate to the shell. Semantic networks represent physical characteristics and procedures; causal reasoning schemes represent theory of operation; and fault trees represent troubleshooting. Each shell provides a browser that is used to present knowledge to the student and a practice environment that promotes skill acquisition under the guidance of an intelligent tutoring system. Subject-matter experts create device descriptions using a WYSIWYG knowledge acquisition system that makes for extremely efficient development. This paper describes each shell in detail, summarizes the research that has been done, and describes where XAIDA stands in relation to other knowledge-based authoring tools. (http://aied.inf.ed.ac.uk/members99/archive/vol_10/hsieh/full.html)