SAE ARP5120

Description / Abstract: ARP5120 provides recommended best practices, procedures, and technology to guide the physical and functional design, development, integration, verification, and validation of highly reliable Engine Health Management (EHM) systems for aircraft engines and Auxiliary Power Units (APUs). This SAE Aerospace Recommended Practice (ARP) also serves as a concise reference of considerations, approaches, activities, and requirements for producing the end-to-end engine health management system comprised of both on and off-board subsystems for the sensing, acquisition, analysis, detection, and data handling functions for EHM. 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.

Purpose The purpose of this ARP is to provide guidelines for the physical and functional integration of an EHM system with other aircraft systems and subsystems that can be used by the flight crew and/or maintenance staff. This includes guidelines for the development, support, and usage of ground station systems as part of EHM in an operational environment for processing engine data and supporting the customer and Original Equipment Manufacturer (OEM) in logistics management.

This ARP supplements ARP1587 by providing additional guidance on best practices for general gas turbine engine monitoring with typical commercial and military systems.

Introduction

EHM is a term that has been adopted to cover the overall system aspects associated with both the engine’s health and usage. From hardware to software and from diagnostics through prognostics, the principal functions of EHM are to assess the engine condition. Assessing engine condition is accomplished by gathering: event data to perform diagnostics; data for trending and performance analysis; and data to assess life usage of life limited parts (LLPs). EHM adds value by providing real time or near real time information on the functional and physical condition of a gas turbine via an Engine monitoring system (EMS). This information is used to alert operators to conditions that could impact safe operation, schedule inspections/repairs, and targeted troubleshooting to improve functional performance, forecast spares requirements, and manage warranties.

A basic concept of EHM is that data gathering and analysis be derived as much as possible through existing systems. Actual implementation of an EHM varies across customers/operators and the OEMs where an EHM system can be either fully or partially integrated into an aircraft or be dedicated to a propulsion system itself. Initial design should make use of engine variables which are primarily sensed for other purposes (e.g., engine control or flight deck display) before consideration of any additional parameters incorporated specifically for EHM. Integrating an EHM system within a platform’s existing systems is dependent on several influencing factors including communication networks, signal interferences, power requirements, etc.

The capabilities and technologies required to support EHM continue to be developed, becoming progressively more sophisticated to meet the increasing requirements for data acquisition, storage, transfer, processing, analytics and user interface both on and off-board. This ARP describes the recommended practices for EHM throughout the engine life-cycle including:

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  Conception

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  Design and Development (Specification, Hardware and Software Build, Verification and Validation)

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  Training and Entry into Service (EIS)

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  Sustaining Support (Maintenance, Error Correction, Systems Enhancements, De-Commissioning)

ARP4754 provides foundational guidance for designing and developing EHM system support hardware and software installed on the air vehicle. In addition, other available documents, such as RTCA DO-178, which provides guidance to the development of EHM software, and RTCA DO-248, which provides supporting guidance to RTCA DO-178. However, RTCA DO-178 does not specifically address the unique characteristics of ground based EHM software. As of the issuance of this document, there are activities underway within SAE to address this aspect. This ARP identifies, as applicable, additional or alternative development guidance for onboard hardware and software systems as well as off-board systems. This ARP also provides guidance for the development of the supporting infrastructure required for these ground-based functions. The guidance of this ARP applies to an EHM system implemented on a new platform or for retrofit on a legacy application.

When applying the guidelines of this ARP it should be noted that engine monitoring systems may be physically or functionally integrated with the engine control system and may also affect safety or be used to effect continued operation or return to service. For any decision to apply the guidelines of this ARP, the decisions shall be subject to the Type Investigation of the product in which they will be incorporated and must show compliance with the applicable airworthiness requirements as defined by the responsible Aviation Authority. This is not limited to but includes the application of software levels consistent with the criticality of the performed functions. For instance, Low Cycle Fatigue (LCF) cycle counters for safety critical parts would be included in the Type Investigation but most trend monitors and devices providing information for economically based maintenance decisions would not.