Fault isolation and diagnosis is one of the key aircraft maintenance activities performedrnin Ethiopian Airlines. The main features of fault diagnosis in aircraft maintenancerninvolve multidisciplinary knowledge in aircraft functional systems and the indefiniternrelationship between .symptom and source or failure. In order 10 facilitate these activitiesrnthe experience and knowledge of aircraft technicians plays a significant role in quicklyrnsolving aircraft system failures without delaying flight schedules. However the airline isrnlosing significant amount of skilled and experienced technicians whose contribution tornthe fault diagnosis was invaluable.rnA knowledge based system is developed to .facilitate the fault isolation technique., inrnaircrafi maintenance using the experience and knowledge of skilled technicians alongrnwith the relevant mail1lenance documents and maintenance records. The domainrnknowledge modeling is performed using decision trees in such a way that a rule basedrninference can be implemented for knowledge representation. The prototype developedrnemploys the utilization of,/ac(s and come up with conclusions based on the backwardrnchaining inference. The rules in (he knowledge base are constructed Form analyzing thernrecords of the aircraft maintenance resume book along with (he available maintenancerndocumel1ls. A prolog programming language is used to demonstrate the prototype andrn(he result of the study has revealed that there is an accuracy of 86%. Adopting thernknowledge based system is supposed to retain the aircraft maintenance knowledge andrnmakes the airline stronger by itself rather than depending fully on human experts.rnThe knowledge based .system needs further works in updating its knowledge base whenrnnew facts are introduced besides of creating generalized pattern for identifying systemrnfaults.