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Accelerometers are transducers, or sensors, that convert acceleration into an electrical signal that can be used for airframe, drive, and propulsion system vibration monitoring and analysis within vehicle health and usage monitoring systems. This document defines interface requirements for accelerometers and associated interfacing electronics for use in a helicopter Health and Usage Monitoring System (HUMS). The purpose is to standardize the accelerometer-to-electronics interface with the intent of increasing interchangeability among HUMS sensors/systems and reducing the cost of HUMS accelerometers. Although this interface was specified with an internally amplified piezoelectric accelerometer in mind for Airframe and Drive Train accelerometers, this does not preclude the use of piezoelectric accelerometer with remote charge amplifier or any other sensor technology that meets the requirements given in this specification.

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.