Time in Service (TIS), or flight hours, logged in maintenance records against an installed rotorcraft transmission is normally used as the “official” time on wing metric for the transmission’s component wear out inspection interval requirement and, in some instances, retirement change on life limited parts. This AIR addresses traditional methods of transmission TBO extensions and introduces rotorcraft transmission monitoring usage metrics that could be used to modify TIS inspections by tracking torque to determine both loads on life limited parts and component wear. This is a document of the SAE HM-1 Committee intended to be used as a technical information source and is not intended as a legal document or standard. This AIR does not provide detailed implementation steps, but does address general implementation, past experience, concerns and potential benefits.