Perspectives on Integrating Structural Health Monitoring Systems into Fixed-Wing Military Aircraft
|Publication Date:||1 September 2019|
This SAE Aerospace Information Report (AIR) is prepared for stakeholders seeking information about the evolution, integration, and approval of SHM technologies for military aircraft systems. The report provides this information in the form of (a) two military organizations' perspectives on requirements, and (b) general SHM challenges and industry perspectives. The report only provides information to generate awareness of perspectives for military aircraft and, hence, assists those who are involved in developing SHM systems understanding the broad range of regulations, requirements, and standards published by military organizations that are available in the public domain from the military organizations.
A wide range of engineering disciplines are required to evolve SHM systems and integrate matured technologies into military aircraft. The disciplines are required from stakeholders with varying experiences: aircraft manufacturers, system suppliers, regulatory agencies, academia, etc. The stakeholders' SHM activities will benefit from information highlighting the perspectives of key international military organizations in terms of their requirements and identified SHM challenges. Therefore, the main purposes of this report are:
• Generate multi-discipline awareness of a wide range of SHM disciplines including perspectives on military requirements and main SHM challenges.
• Provide context and information where appropriate on the evolution and integration of SHM into military aircraft and maintenance support systems.
Whilst this report presents the perspectives of military organizations and include examples of identified challenges, the following imperative explanatory notes should be considered:
• This report does not promote or endorse a technology or a system. The report only provides references to information to assist in validating, verifying, and certifying SHM systems, and integrating matured systems into military aircraft by imperative considerations of the relevant military regulations and standards.
• The report contents do not constitute a policy or regulatory requirements of any of the military organizations considered in this report. For each military organization, the applicable regulations, requirements, and standards are those published and updated by the organization. Therefore, the information in this report must only be considered as guidance information.
• The information of Section 3 is collated from public domain papers, standards, and MOD publications by authors who do not represent the UK MOD.
• Whilst the information in this report is applicable to rotorcraft, considerations should be made to the specific structures, operations, and environments of the rotorcraft, along with the vibratory loads induced on the airframe structures by rotors and transmissions. Also, considerations should be made to the fact that a large number of military helicopters have been fitted with Health and Usage Monitoring Systems (HUMS). Therefore, an SHM AIR dedicated to rotorcraft application is being prepared by the AISC-SHM committee; the rotorcraft AIR would include the military perspective of the U.S. Army.
Field of Application
The information contained in this document can assist in the following:
• Maturing SHM systems for military applications,
• Deriving from the identified challenges approaches to exploit SHM technologies, and
• Integrating matured SHM technologies into military aircraft and associated maintenance support systems.
NOTE: This SAE document is not a policy or a regulatory document; therefore, the reader of this report is not compelled to follow the information presented in the report.
An Overview of This Document
Section 2 of this report lists the applicable documents that contain detailed information about the regulations, standards, and requirements of military organizations. The section also lists key non-military publications that are widely accepted by various military organizations. The section collates relevant definitions followed by the references from which they are quoted. Those definitions without references are either: (a) definitions introduced for the purpose of this report, or (b) definitions believed to agree with the generally accepted understanding of the terms.
The military regulations, standards, and processes required for designing, approving, and maintaining aircraft structures can vary between nations and between the military operators of one nation. However, the wide range of manufacturers within the defense industry implements similar best practice approaches to develop aircraft products that comply with the varying regulations and standards across the military organizations. For example, the common practices for developing an aircraft product include most of the main development activities and processes shown in Figure 1, with minor variations in the names of the activities/processes
In other words, the perspectives of military operators are expected to show the following:
• Significant Differences: The military perspectives on the design and maintenance approaches can show significant differences between various military organizations; for example, some of these approaches are based on safe-life methodologies and others based on damage tolerance methodologies.
• Process Differences: Differences are expected in the details of the approval and certification processes, including variations in the interaction mechanisms between the military authorities and the developers, as well as differences in the names of the approval/certificati
• Insignificant Differences: Often, the above differences do not have any significant influence on the common development practices of aircraft products. The manufacturers within the defense industry implement similar best practice approaches to develop aircraft products; generally, the documents of these approaches call for or include parts similar to international standards such as ARP4754, ARP4761, DO-178, and DO-160.
Therefore, only in Section 3 of this document, the common development practices of aircraft products are briefly discussed based on such above international standards because the UK defense standards explicitly quote them as applicable documents. Section 3 also presents the UK military perspective by providing information derived through the following activities: (a) discussing the Damage Tolerance and Safe Life approaches used to design and maintain aircraft structures; the Safe Life approach is the standard approach in the UK, (b) reviewing the UK military regulations that govern the design and maintenance of structures, (c) summarizing regulations and processes required to overcome the threats to structural integrity, (d) discussing the evolution and acquisition phases of UK military aircraft products including SHM systems, (e) presenting the architectural ingredients and choices that can deliver required SHM intended functions, (f) establishing the requirements of SHM systems that are essential for compliance with airworthiness regulations and industry-accepted standards, (g) presenting the methods required to validate and verify aircraft products with interpretations and extensions specific to SHM systems, and (h) presenting the certification phases, their outputs, and associated approval forms of the UK Military Aviation Authority (MAA).
Section 4 presents two key documents that describe the U.S. Air Force perspective. By following the guidance of these documents, SHM systems can be matured, developed, and integrated into the U.S. Air Force aircraft and its support systems.
Section 5 highlights some of the main challenges facing SHM and presents general industrial perspectives indicating the progress made to address these challenges. Regarding the implementation of SHM NDI inspection tasks, two key aerospace documents (MIL-STD-1530 and A4A MSG-3) have added SHM to their contents.