The purpose of this SAE Aerospace Information Report (AIR) is to provide management, designers, and operators with information to assist them to decide what type of power train monitoring they desire. This document is to provide assistance in optimizing system complexity, performance and cost effectiveness. This document covers all power train elements from the point at which the gas generator energy is transferred to mechanical energy for propulsion purposes. The document covers engine power train components, their interfaces, transmissions, gearboxes, hanger bearings, shafting and associated rotating accessories, propellers and rotor systems as shown in Figure 1. This document addresses application for rotorcraft, turboprop, and propfan drive trains for both commercial and military aircraft.