The growing body of technology relative to maintenance monitoring provides substantial evidence that on-condition maintenance will be a reality in the foreseeable future. The Military Airlift Command's MADAR (Malfunction Detection, Analysis, and Recording) System is emerging as the “missing link” which has heretofore retarded progress toward attainment of this increasingly-important goal. The key issue is real time response. Monitoring-system reliability, accuracy, and repeatibility are all of little consequence if the system output is not timely enough to assist the maintenance function. Recent use of communications links by some airlines to transmit recorded data to a centrally-based computer has reduced the time span between data generation and its availability for use. Nevertheless, the response time is still estimated to be somewhere between 5 and 24 hr. The best response time (5 hr) exceeds the time available for turnaround maintenance by a factor of five, and is ten times longer than the time allotted for enroute maintenance. Thus the most efficient of the “recorder-type” AIDS finds value chiefly in the domain of longterm trend analysis. Placing the data-processing and decision-making functions aboard the aircraft effectively reduces the response time to zero. The real-time awareness of aircraft condition thereby afforded expands the AIDS domain to include short-term maintenance situations, a capability essential to realization of true on-condition maintenance.