A Process for Utilizing Aerospace Propulsion Health Management Systems for Airworthiness Credit
ARP5987A
The process detailed within this document is generic and applies to the entire end-to-end health management capability, covering both on-board and on-ground elements, in both commercial and military applications throughout their lifecycle. This ARP addresses a gap in guidance related to usage of ground-based health management equipment for airworthiness credit, ensuring a level of integrity commensurate with the potential aircraft-level consequences of the relevant failure conditions. The practical application of this standardized process is detailed in the form of a checklist.
The on-board elements described here are typically the source of the data acquisition used for off-board analysis. The on-board aspects relating to airworthiness and/or safety of flight, e.g., pilot notification, are addressed by existing guidance and policy documents. If a proposed health management capability for airworthiness credit involves modification of the on-board systems, the substantiation of those changes should be based on the applicable type certification guidance. This document does not prescribe hardware or software assurance levels, nor does it answer the question “how much mitigation and evidence are enough?” The criticality level and mitigation methods will be determined between the applicant and the regulator.
There are cases where this process is applicable but may not be appropriate due to historical precedents. For example, there is a historical precedent for using an off-board health management solution to achieve compliance with Extended-Range Twin-Engine Operations Performance Standards (ETOPS) (refer to FAA AC 120-42A).
In order to provide some detailed guidance utilizing the process and checklist, some high-level examples of previous successful cases of maintenance credit applications for airworthiness credit are included. Refer to ARP5120 for additional examples of practical mitigating measures applicable to health management systems. At this point, it is incumbent on the applicant to explain any differences in terminology between the health management system they are seeking credit for and the appropriate regulatory references. For example, the system name often uses interchangeable terms such as “Engine Health Monitoring,” “Equipment Health Management,” “Prognostic Health Management,” “Powerplant Health Management,” etc.
Rationale:
This document was originally written to provide a process to achieve a maintenance credit using aerospace propulsion health management systems in a consistent way. The objective of the SAE Aerospace Recommended Practice (ARP) was to help applicants prepare the materials needed for regulators to carry out assessments of the merits of a maintenance credit application with a view to provide approval.
This document reflects the fact that regulatory approval has been provided to multiple engine and aircraft original equipment manufacturers (OEMs), allowing the use of propulsion health management functionality in the mitigation of Airworthiness Directives, extending inspection and maintenance intervals and more accurate determination of component life consumption, resulting in increased propulsion system availability.
Since its first publication in December 2018, this ARP has been widely discussed by both Industry and regulators. This revision includes updates to ensure the use of consistent terms and make connections to related external activities. The term “airworthiness credit” is introduced to better address new as well as existing designs (to which the term “maintenance credit” is still applicable). Lessons learned from individuals who have used the original document as the basis for applying for airworthiness credit are also included.
The SAE HM-1 committee is working on an equivalent vehicle-level document which covers this same process, together with examples of its application across an aircraft.
Related Topics:
Aircraft propulsion systems
Airworthiness
Also known as: SAE ARP 5987
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