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  • «:4 DEFENCE SCIENCES TECHNOLOGY

    VX^ ^0^

    DEF STAN 00-970 Requirements for the Design and Airwortliiness of Composite Aircraft Structure

    Paul J. Callus

    DSTO-TN-0498

    DISTRIBUTION STATEMENT A Approved for Public Release

    Distribution Unlimited

    20030905 034

  • *

    DEFENCE SCIENCES. TECHNOLOGY

    DEF STAN 00-970 Requirements for the Design and Airworthiness of Composite Aircraft Structure

    Paul J. Callus

    Air Vehicles Division Platforms Sciences Laboratory

    DSTO-TN-0498

    ABSTRACT

    One of the impediments to the introduction of composite structure into Australian Defence Force (ADF) aircraft is the difficulty in identifying those airworthiness requirements specific to these materials. The ADF uses a comparative approach where tenderers propose their own certification basis. This is assessed against the ADF comparative certification basis to ensure that all relevant issues are covered in adequate depth. The ADF comparative certification basis is DEF STAN 00-970 [2] supplemented with AAP 7001.054 [1]. This basis was reviewed. Those requirements relevant to the airworthiness of composite structure were identified and are presented in this report. The requirements for any specific composite part will likely be a sub-set of these and must be developed on a case-by-case basis.

    RELEASE LIMITATION

    Approved for public release

    fOd'H-MS2

  • Publisljed hy

    DSTO Platforms Sciences Laboratory 506 Lorimer St Fisliermans Bend, Victoria 3207 Australia

    Telephone: (03) 9626 7000 Fax: (03)9626 7999

    © Commonwealth of Australia 2003 AR-012'787 June 2003

    APPROVED FOR PUBLIC RELEASE

  • DEF STAN 00-970 Requirements for the Design and Airworthiness of Composite Aircraft

    Structure

    Executive Summary (U)

    The Australian Defence Force (ADF) maintains a keen interest in the application of composite materials to aircraft structures. The reduced weight and improved resistance to fatigue and corrosion degradation offer the potential to improve aircraft performance while reducing through-life-support costs. Many current aircraft contain significant quantities of monoUthic and bonded composite material. This appears likely to increase in future acquisitions. In addition the ADF has a long history of using bonded composite repairs to support its fleet. Despite this background, virtually all of the composite structure within ADF aircraft, particularly primary structure, has been certified outside of Australia.

    One reason for this is the difficulty in identifying the specific set of airworthiness design requirements against which the composite structure will be certified. Currently there is no documentation that does this.

    The ADF airworthiness policy (Australian Air Publication 7001.054 [1]) states that contractors should submit their proposed certification basis and this wiU be assessed by the Commonwealth against a comparative basis. The ADF comparative basis is the UK Ministiy of Defence's DEF STAN 00-970 [2], supplemented with AAP 7001.054 to account for specific ADF requirements. These documents focus on traditional metallic aircraft stiucture, so their layout and treatment of issues is not optimised for composites.

    DEF STAN 00-970 and AAP 7001.054 were reviewed and, in this report, the requirements and guidance considered relevtmt to composite structure are collated and re-arranged into a more logical format for composites. This is the first time that the airworthiness requirements relevant to composite stiucture have been identified and extiacted from the ADF comparative airworthiness standards.

    The certification requirements for any specific composite part must be developed on a case-by-case basis. The requirements identified in this report cover aU possible composite stiuctures, from a non-structural part to an entire aircraft. The requirements for any specific part will likely form a sub-set of these.

  • Contents

    1. INTRODUCTION 1

    2. AIRWORTHINESS CERTIFICATION FOR ADF AIRCRAFT 1 2.1 Contractor proposes certification basis 2 2.2 Acceptance of certification basis 2 2.3 Contractor proposes means of demonstrating compliance 2 2.4 Acceptance of means of demonstrating compliance 4 2.5 Contractor to demonstrate compliance 4 2.6 ADF acceptance 4

    3. FORMAT OF THE COMPARATIVE CERTIFICATION BASIS FOR COMPOSITE STRUCTURE 4

    4. AIRWORTHINESS REQUIREMENTS FOR COMPOSITE AIRCRAFT STRUCTURE 6

    5. APPLICATION 52

    6. DISCUSSION 52

    7. ACKNOWLEDGMENTS 53

    8. REFERENCES 53

    APPENDIX A: SELECTED SUMMARY OF DEF STAN 00-970/1 (AL14) 55

    APPENDIX B: COMPARATIVE BASIS FORMATTED IN ORDER OF DEF STAN 00-970/1 (AL14) CHAPTER 87

    APPENDIX C: STRUCTURE OF DEF STAN 00-970/2 91

  • DSTO-TN-0498

    1. Introduction

    The Australian Defence Force (ADF) maintains a keen interest in the application of composite materials to aircraft structures. The reduced weight and improved resistance to fatigue and corrosion degradation offer the potential to improve aircraft performance while reducing through-life-support costs. Many military aircraft currently in production contain significant quantities of monolithic and bonded composite material. The use of composites appears hkely to increase in future generations of aircraft. In addition, the ADF has a long history of using bonded composite repairs to support its fleet. Despite this backgrotmd, virtually all of the composite structure within ADF aircraft, particularly primary structure, has been certified outside of AustraUa.

    A contributing factor to the lack of composites certification is the difficulty in identifying the airworthiness requirements that must be met by composite structure. To address this situation the comparative airworthiness design requirements for ADF aircraft were reviewed and those sections considered relevant to composites have been extracted and collated in a format that is logical for composites.

    2. Airworthiness Certification for ADF Aircraft

    Significant effort and expense is required to certify metallic or composite aircraft structure. It is therefore strongly recommended that the certification issues be addressed as early as possible in any project. Policy regarding the application of airworthiness design standards within the ADF, i.e. airworthiness certification, is given in AAP 7001.054 [1]. The ADF has adopted a comparative approach where, for any acquisition or major upgrade, tenderers propose their own certification basis. In this context the term certification basis describes the complete set of airworthiness design requirements and so includes the effects of updates, improvements, special conditions or directives to standards. This proposed certification basis is assessed, by the Technical Airworthiness Regulator (TAR) or their nominated Centre of Expertise, against the ADF comparative certification basis. Any differences between the ADF and the tenderer are resolved by negotiation. The Directorate General Technical Airworthiness (DGTA) is the ADF TAR.

    The ADF comparative certification basis is the UK Ministry of Defence (MoD) Standard DBF STAN 00-970 [2], supplemented by Sections 2 to 4 of AAP 7001.054 to address known deficiencies in DBF STAN 00-970 when it is appHed to ihe ADF. AAP 7001.054 states that DBF STAN 00-970 was chosen as the comparative standard because it is an accessible, comprehensive, military airworthiness standard and not because it has been judged any more, or less, safe or complete than other military or civil standards.

  • DSTO-TN-0498

    Sections 2.1 to 2.6 below provide a summary of the airworthiness certification process

    within the ADF.

    2.1 Contractor proposes certification basis

    The ADF comparative certification basis is DBF STAN 00-970 supplemented with AAP 7001.054. Contractors may choose to use this as their certification basis, or propose their own. While this non-prescriptive approach permits innovative solutions, and these types of solutions are encouraged, it is the responsibility of the contractor to convince the TAR that their approach provides an equivalent level of safety to the comparative basis. In addition, the more significant the deviation from the comparative basis then the greater the time required by the TAR to review the proposal.

    The preferred approach is that the contractor submits their certification basis in the form of a Certification Basis Description (CBD). This provides the TAR with sufficient information to determine whether the certification basis will produce an airworthy structure. The CBD will eventually includes details of the certification requirement, verification method, conditions, verification agency and verification evidence documents, but at the initial submission it will only contain the certification requirements. An excerpt from a sample CBD is shown in Table 1.

    Tlie contractor shall decide the level of detail provided in the CBD. It shall be sufficiently detailed to demonstrate that all issues have been covered, but not so detailed that it loses its effectiveness as a management tool. Ref. [1] stated that an adequately detailed CBD for an aircraft that was certified to FAR 25 would normally be achieved by numbering every section of FAR 25 (e.g. 25.1309) on a separate line of the CBD. This equates to the third order headings in the comparative certification basis shown in Table 2 or each of the items in the summary Table 3.

    2.2 Acceptance