SAE ARP 5120 provides recommended best practices, procedures, and technology to guide the physical and functional development, integration, verification, and validation of highly reliable Engine Health Management System (EHMS) for gas turbine engines, including aircraft engines and Auxiliary Power Units (APUs). This ARP also serves as a concise reference of considerations, approaches, activities, and requirements for producing the end-to-end engine health monitoring system comprised of both on and off-board subsystems for the sensing, acquisition, analysis, detection, and data handling functions of an EHMS. These functions and related maintenance activities promote engine safety. These functions may also be used to effect continued operation or return to service decisions when demonstrated as compliant with the applicable airworthiness requirements defined by the responsible Aviation Authority. Where practical, this document delineates between military and commercial practices.