Wear debris monitoring is the most effective technique available for detecting impending failure of oil-wetted components. The majority of the gas turbines operated in a flight environment utilize magnetic chip collector (mag plug) inspections to detect the onset of oil-wetted component failures. However, successful chip collector usage depends upon timely inspection and the subsequent disposition of recovered debris. Shortcomings in these critical maintenance actions, and/or wear modes which result in product failure between scheduled inspection intervals, compromise the effectiveness of this method of wear debris monitoring.The General Electric GE90 engine utilizes the Quantitative Debris Monitor (QDM ®), developed by Vickers, Tedeco Division. The QDM system - the first and only advanced, remote-indicating lube debris monitor qualified for commercial flight service - continuously monitors the lube oil for the presence of wear debris. The system is capable of counting individual debris particles and distinguishing their size relative to a preset “target” threshold. These advanced features permit “on-condition” maintenance, and distinguish QDM from mag plugs and electric chip detectors, which may be subject to costly “nuisance” debris indications.Performance and qualification requirements were developed in cooperation with General Electric and its French partner, SNECMA. The QDM system was qualified to customer specifications and released as standard equipment on initial GE90 entry into service. Field experience since service release has confirmed the system's ability to reliably and accurately indicate impending oil-wetted component failure well in advance of the loss of functionality.