A REPORT OF THE AIRWORTHINESS ASSURANCE WORKING GROUP RECOMMENDATIONS FOR REGULATORY ACTION TO PREVENT WIDESPREAD FATIGUE DAMAGE IN THE COMMERCIAL AIRPLANE FLEET FINAL REPORT March 11, 1999 Revision A June 29, 1999 SIGNED BY Jack McGuire Jim Foucault Co-Chairperson, AAWG Co-Chairperson, AAWG Boeing Commercial Airplanes United Parcel Service A REPORT OF THE AAWG RECOMMENDATIONS FOR REGULATORY ACTION TO PREVENT WIDESPREAD FATIGUE DAMAGE IN THE COMMERCIAL AIRPLANE FLEET REVISION PAGE LTR DATE CHANGE PAGES PAGES PAGES APPROVED ADDED DELETED CHANGED BY - 3-11-99 Initial Release - - - - A 6-29-99 TAEIG Requested Change 0 0 1, 2, 10, AWH 128 June 29, 1999 PAGE 2 A REPORT OF THE AAWG RECOMMENDATIONS FOR REGULATORY ACTION TO PREVENT WIDESPREAD FATIGUE DAMAGE IN THE COMMERCIAL AIRPLANE FLEET TABLE OF CONTENTS REVISION PAGE....................................................................................................2 TABLE OF CONTENTS..........................................................................................3 LIST OF ABBREVIATIONS.....................................................................................6 REFERENCES.......................................................................................................7 1.0 EXECUTIVE SUMMARY..............................................................................8 1.1 CONCLUSIONS.......................................................................................8 1.2 RECOMMENDATIONS ..........................................................................10 2.0 AVIATION RULEMAKING ADVISORY COMMITTEE TASKING...............11 3.0 AIRWORTHINESS ASSURANCE WORKING GROUP.............................13 4.0 BACKGROUND .........................................................................................14 4.1 AFFIRMATION 1993 ARAC RECOMMENDATIONS.............................15 4.1.1 1993 ARAC Recommendations.......................................................15 4.1.2 1999 Adjustments to the 1993 Recommendations..........................16 4.2 ADVISORY CIRCULAR 91-56A.............................................................19 4.2.1 Text Changes..................................................................................20 4.2.2 Interpretation of Text .......................................................................21 4.2.3 Additional ATA/AIA Comments........................................................22 4.3 DEFINITIONS.........................................................................................22 4.4 MONITORING PERIOD..........................................................................25 4.5 PROPRIETARY DATA ISSUES.............................................................31 5.0 TECHNICAL ISSUES.................................................................................32 5.1 AUTHORITIES REVIEW TEAM ISSUES AND ACTION.......................32 5.2 AREAS SUSCEPTIBLE TO MSD/MED.................................................34 5.3 DSD COMBINED WITH MSD................................................................44 5.3.1 Background.....................................................................................44 5.3.2 Technical Approach.........................................................................44 5.3.3 Analytical Procedure........................................................................46 5.3.4 Environmental and Accidental Damage...........................................47 5.4 CERTIFICATION STANDARDS.............................................................49 5.4.1 Fail-Safe Analysis Damage Sizes....................................................51 5.4.2 Damage Tolerance Analysis Damage Sizes ...................................51 5.4.3 Survey of Certification Damage Size...............................................51 5.4.4 Safety Enhancements .....................................................................53 5.4.5 Conclusions..........................................................................................53 5.5 MANAGEMENT OF MSD/MED IN THE FLEET.....................................55 5.6 SUPPLEMENTAL TYPE CERTIFICATES.............................................56 5.6.1 Background.....................................................................................56 5.6.2 Discussion.......................................................................................56 5.6.3 Recommendations...........................................................................57 5.6.4 Compliance Time for STC WFD Assessment..................................58 5.6.5 Summary.........................................................................................58 5.7 COMBINATION OF MSD/MED SCENARIOS ........................................59 6.0 TECHNOLOGY READINESS ....................................................................60 6.1 1998 ASSESSMENT OF TECHNOLOGY AVAILABLE..........................60 6.1.1 1993 Recommendations..................................................................60 June 29, 1999 PAGE 3 A REPORT OF THE AAWG RECOMMENDATIONS FOR REGULATORY ACTION TO PREVENT WIDESPREAD FATIGUE DAMAGE IN THE COMMERCIAL AIRPLANE FLEET 6.1.2 1998 Status.....................................................................................61 6.1.3 Future Research..............................................................................62 6.1.4 Research Proposal..........................................................................63 6.1.5 Residual Strength............................................................................64 6.2 1998 AND NEAR FUTURE INDUSTRY NDI CAPABILITIES.................65 6.2.1 NDI Round-Robin............................................................................65 6.2.2 NDI Round-Robin Results...............................................................69 6.3 NDI Improvements with Regard to the Challenge of MSD......................74 7.0 AIRPLANE SPECIFIC EVIDENCE OF MSD/MED.....................................76 7.1 HEALTH OF FLEET WITH REGARD TO WIDESPREAD FATIGUE DAMAGE SOURCES.............................................................................76 7.1.1 Background -- The Communication Process Today........................76 7.1.2 Additional Operator Actions.............................................................77 7.1.3 Additional OEM Actions...................................................................78 7.1.4 OEM/Operator Improved Communication Improvements................78 7.1.5 Role of the STG...............................................................................78 7.2 VALUE OF SERVICE DIFFICULTY REPORTS.....................................79 7.2.1 Evaluation Process..........................................................................79 7.2.2 Results and Conclusions.................................................................79 7.3 AIRPLANE SPECIFIC EVIDENCE OF MSD/MED.................................80 7.3.1 Evaluation Process..........................................................................80 7.3.2 Results and Conclusions.................................................................80 7.3.3 Airplane Specific Instances Of MED / MSD.....................................81 8.0 OVERVIEW OF OEM METHODOLOGIES................................................83 8.1 AIRBUS INDUSTRIE..............................................................................83 8.1.1 Probabilistic Assessment of Structure Susceptible to MSD/MED....83 8.1.2 Calculation Procedure.....................................................................83 8.1.3 Monitoring Period............................................................................85 8.2 BOEING COMMERCIAL AIRPLANES...................................................87 8.2.1 Initiation / Threshold Determination.................................................87 8.2.2 Crack Growth...................................................................................89 8.2.3 Residual Strength............................................................................89 8.2.4 Inspection Programs........................................................................90 8.3 LOCKHEED-MARTIN AERONAUTICAL SYSTEMS..............................90 8.3.1 Crack Growth...................................................................................91 8.3.2 Residual Strength............................................................................92 8.3.3 Inspection Programs........................................................................92 8.4 OVERVIEW OF DELTA AIR LINES METHODOLOGY..........................92 8.4.1 Initiation...........................................................................................93 8.4.2 Crack Growth...................................................................................93 8.4.3 Residual Strength............................................................................94 8.4.4 Inspection Threshold/Interval Determination...................................94 8.5 ROUND ROBIN EXERCISES.................................................................95 8.5.1 Round-Robin Exercise Number 1.........................................................95 8.5.2 Round-Robin Exercise Number 2.........................................................96 8.5.3 Scatter Factors And Mean Life Tendencies For MSD Crack Initiation.........................................................................................102 June 29, 1999 PAGE 4 A REPORT OF THE AAWG RECOMMENDATIONS FOR REGULATORY ACTION TO PREVENT WIDESPREAD FATIGUE DAMAGE IN THE COMMERCIAL AIRPLANE FLEET 9.0 AIRPLANE SPECIFIC TIMETABLE RECOMMENDATIONS FOR COMPLETION OF AUDIT...........................................................................106 9.1 AIRPLANE FLEETS AT RISK ..............................................................106 9.2 LEAD TIME ISSUES FOR TERMINATING ACTIONS..........................109 9.2.1 Introduction....................................................................................109 9.2.2 Discussion.....................................................................................109 9.2.3 Structures Task Group Process.....................................................110 9.2.4 Summary.......................................................................................111 10.0 REGULATORY OPTIONS AND ANALYSIS ............................................112 10.1 REGULATORY OPTIONS....................................................................112 10.2 RELATIVE MERITS OF EACH OPTION..............................................112 10.3 RANKING OF APPLICABLE OPTIONS...............................................121 10.3.1 Short Term Actions........................................................................121 10.3.2 Long Term Actions ........................................................................121 10.4 PROPOSAL FOR RULEMAKING.........................................................122 10.4.1 Long Term Remedies....................................................................122 10.4.2 Short Term Remedies for Airworthiness Concerns........................123 10.4.3 Proposed 121 Rule Details............................................................123 10.4.4 FAR 25.1529 Rule Revision Details..............................................123 10.4.5 Proposed Use of Airworthiness Directives.....................................124 10.5 AAWG PROPOSAL FOR RULEMAKING.............................................124 10.6 ADVANTAGES AND DISADVANTAGES.............................................125 11.0 CONCLUSIONS.......................................................................................126 12.0 RECOMMENDATIONS............................................................................128 APPENDICES.....................................................................................................129 Appendix A ARAC TASKING STATEMENT..................................................129 Appendix B ARAC WORKING GROUP ACTIVITY REPORTS.....................132 Appendix C MEETING VENUES...................................................................138 Appendix D ATTENDANCE ROSTERS........................................................139 Appendix E SUPPLEMENTAL TYPE CERTIFICATES.................................140 Appendix F NDI DATABASE.........................................................................156 Appendix G PROPOSED ARAC TASKING STATEMENT FOR FOLLOW-ON TASKING...................................................................................161 June 29, 1999 PAGE 5 A REPORT OF THE AAWG RECOMMENDATIONS FOR REGULATORY ACTION TO PREVENT WIDESPREAD FATIGUE DAMAGE IN THE COMMERCIAL AIRPLANE FLEET LIST OF ABBREVIATIONS The following abbreviations are used throughout this report AATF Airworthiness Assurance Task Force AAWG Airworthiness Assurance Working Group AC Advisory Circular (FAR) ACJ Advisory Circular (JAR) AD Airworthiness Directive AECMA Association des Entreprises de Construction Mécanique et Aeronautique AIA Aerospace Industries Association of America ALI Airworthiness Limitation Instructions ARAC Aviation Rulemaking Advisory Committee ART Authorities Review Team ATA Air Transport Association of America CAA-UK Civil Aviation Authority - United Kingdom CTOA Crack Tip Opening Angle DGAC Direction Générale de l’Aviation Civile DSG Design Service Goal EIFS Equivalent Initial Flaw Size ESG Extended Service Goal FAA Federal Aviation Administration FAR Federal Aviation Regulation GARTEUR Group for Aeronautical Research and Technology in Europe HMV Heavy Maintenance Visit IATA International Air Transport Association ICWFD Industry Committee on Widespread Fatigue Damage JAA Joint Aviation Authorities JAR Joint Aviation Requirement MED Multiple Element Damage MSD Multiple Site Damage NAARP National Aging Aircraft Research Program NDI Non Destructive Inspection NP None Planned at this time NPRM Notice of Proposed Rulemaking NTSB National Transportation Safety Board OEM Original Equipment Manufacturer PMI Principal Maintenance Inspector (FAA) POD Probability of Detection RS Residual Strength SAETG Structural Audit Evaluation Task Group SB Service Bulletin SDR Service Difficulty Report (FAA) SFAR Special Federal Aviation Regulation SIA Structural Integrity Audit SIF Stress Intensity Factors SMAAC Structural Maintenance of Aging Aircraft SSIP Supplemental Structural Inspection Program STC Supplemental Type Certificate STG Structures Task Group TAEIG Transport Airplane and Engines Issues Group TARC Technical Advisory Regulatory Committee TC Type Certification TOGAA Technical Oversight Group RE: Aging Aircraft WFD Widespread Fatigue Damage June 29, 1999 PAGE 6 A REPORT OF THE AAWG RECOMMENDATIONS FOR REGULATORY ACTION TO PREVENT WIDESPREAD FATIGUE DAMAGE IN THE COMMERCIAL AIRPLANE FLEET REFERENCES [1] NTSB Report No. NTSB/AAR - 89/03, RE: 1988 Aloha Airlines 737 Accident. [2] A Report of the AATF on Fatigue Testing and/or Teardown Issues, February 1991, Available from the ATA. [3] Ronald Wickens et.al, ‘Structural Fatigue Evaluation for Aging Airplanes’, final report of the Airworthiness Assurance Working Group, page 43-24 (October 1993) [4] Anon., Continuing structural integrity program for large transport category airplanes, FAA Advisory Circular No. 91-56A, Federal Aviation Administration, U.S. Department of Transport (April 1998) [5] Anon., ‘Equipment, systems and installations’, Federal Aviation Regulations Part 25 - Airworthiness Standards: Transport Category Airplanes, Change 10, Section 25.1309, Federal Aviation Administration, Department of Transportation, Washington D.C. (March 1997) [6] Anon., ‘Equipment, systems and installations’, Joint Aviation Requirements JAR-25 - Large Aeroplanes, Change 14, Paragraph JAR 25.1309, Section (b), Joint Aviation Authorities, Hoofddorp, The Netherlands (May 1994) [7] Anon., ‘Engines’, Federal Aviation Regulations Part 25 - Airworthiness Standards: Transport Category Airplanes, Change 12, Section 25.903, Federal Aviation Administration, Department of Transportation, Washington D.C. (March1998) [8] Anon., ‘Turbine engine installations’, Joint Aviation Requirements JAR-25 - Large Aeroplanes, Change 14, Paragraph JAR 25.903, Section (d), Joint Aviation Authorities, Hoofddorp, The Netherlands (May 1994) [9] Anon., ‘Damage-tolerance and fatigue evaluation of structure’, Federal Aviation Regulations Part 25 - Airworthiness Standards: Transport Category Airplanes, Change 11, Section 25.571, Federal Aviation Administration, Department of Transportation, Washington D.C. (August 1997) [10] Anon., ‘Damage-tolerance and fatigue evaluation of structure’, Joint Aviation Requirements JAR-25 - Large Aeroplanes, Change 14, Paragraph JAR 25.571, Section (e), Joint Aviation Authorities, Hoofddorp, The Netherlands (May 1994) [11] Anon., ‘Design considerations for minimizing hazards caused by uncontained turbine engine and auxiliary power unit rotor failure’, Advisory Circular No. 20- 128A, Federal Aviation Administration, Department of Transportation, Washington D.C. (March 1997) June 29, 1999 PAGE 7 A REPORT OF THE AAWG RECOMMENDATIONS FOR REGULATORY ACTION TO PREVENT WIDESPREAD FATIGUE DAMAGE IN THE COMMERCIAL AIRPLANE FLEET 1.0 EXECUTIVE SUMMARY In August 1997, the FAA and JAA issued a Tasking Statement through the Aviation Rulemaking Advisory Committee (ARAC). This Tasking Statement requesting that a non-advocate group be formed to examine whether or not rule- making should be initiated that would require audits of airplane structure to preclude the occurrence of widespread fatigue damage in the commercial airplane fleet. This report represents the work product of that Tasking Statement. The Tasking was assigned to the Airworthiness Assurance Working Group (AAWG) in September 1997. This report is the culmination of 18 months of effort. In the process of the work, several conclusions and recommendations were reached. These results are presented below. 1.1 CONCLUSIONS • With respect to the 1993 AAWG Report entitled ‘Structural Fatigue Evaluation for Aging Airplanes’ • That the conclusions and recommendations of the 1993 AAWG Report are still generally applicable. • That AC 91-56A, released in April 1998 by the FAA has many inconsistencies in use of terminology and should be corrected. • That the list of structure susceptible to MSD/MED from the 1993 AAWG Report has been validated and expanded to include additional examples from industry experience. • That interaction of discrete source damage and MSD/MED need not be considered as assessment of total risk is within acceptable limits. • That because of the instances of MSD/MED in the fleet and the continued reliance on surveillance types of inspections to discover such damage, rules and advisory material should be developed that would provide specific programs to preclude WFD in the fleet. • With respect to maintenance programs: • That an effective aging airplane program including a Mandatory Modification Program, Corrosion Prevention and Control Program, Repair Assessment Program, and a structural supplemental inspection program (SSID or ALI) is a necessary prerequisite for an effective program for MSD/MED. • That as long as there is an effective corrosion prevention and control program, interaction of MSD/MED with environmental degradation is minimized. June 29, 1999 PAGE 8 A REPORT OF THE AAWG RECOMMENDATIONS FOR REGULATORY ACTION TO PREVENT WIDESPREAD FATIGUE DAMAGE IN THE COMMERCIAL AIRPLANE FLEET • That the use of a “Monitoring Period” for the management of potential multiple site damage and multiple element damage (MSD/MED) scenarios in the fleet is possible if MSD/MED cracking is detectable before the structure loses its required residual strength. • That any program established to correct MSD or MED in the fleet needs careful consideration for the necessary lead times to develop resources to implement fleet action. • That there is no universally acceptable or required damage size used for certification compliance. • With respect to research programs: • That additional research into the residual strength behavior of structure with MSD/MED should be conducted to supplement existing database. • That the highest potential to achieve the necessary improvements of flaw detectability is seen in the field of semi-automated eddy current systems. • With respect to the Fleet Health and MSD: • That every pre-amendment 45 commercial jet type airplane has had instances of MSD/MED in either test or service. • That normal inspections (e.g. maintenance programs plus aging airplane programs) conducted by the airlines using procedures developed by the manufacturer have found numerous instances of MSD/MED in the fleet since 1988. • That the value of SDRs in determining the health of the fleet with respect to MSD/MED occurrence is limited. • With respect to Analytical Assessment of MSD/MED: • Sufficient technology exists to complete the audit in a conservative manner. • That most OEMs have voluntary WFD audit programs in progress. • That damage scenarios involving combinations of MSD and MED must be considered if there is a possibility of interaction. • That the AAWG participating manufacturers have developed different but viable means of calculating the necessary parameters to characterize MSD/MED and define appropriate maintenance actions whether it be a monitoring period or structure modification/replacement. • That the analysis procedures used to characterize MSD/MED scenarios on airplanes needs careful correlation with test and service evidence. June 29, 1999 PAGE 9 A REPORT OF THE AAWG RECOMMENDATIONS FOR REGULATORY ACTION TO PREVENT WIDESPREAD FATIGUE DAMAGE IN THE COMMERCIAL AIRPLANE FLEET 1.2 RECOMMENDATIONS The following recommendations are made as a result of this study: • That the FAA review and make changes to AC 91-56A as delineated in section 4.2.1 and 4.2.2 of this report. These changes are intended to remove ambiguous use of terminology and provide additional guidance for entities performing the structural Audit • That the FAA fund research detailed in Section 6.0, In addition: • Every effort should be made to make data from tests conducted in all research programs available at the earliest possible time before formal reports are issued. • Tests currently funded, involving lead crack link-up, should be accomplished as soon as possible to support the first round of audits due in three years. • That the FAA issue a subsequent tasking to ARAC to develop necessary new and/or revised certification and operational rules with advisory material to make mandatory audit requirements for MSD/MED for all transport category airplanes. This recommendation includes the development of rules and advisory material as detailed in Section 10.0. • Existing Transport Category Airplanes - A FAA 121 (New) Rule and/or Part 39 (Amended) • New Certification Programs • FAA 25.1529 rule revision • FAA 121 (New) Rule for Operator Compliance • FAA AC for Both 121 (New) and 25.1529 (Revised) Rule • That WFD audits for nearly all pre-amendment 45 commercial jet airplanes should be completed and OEM documents published by December 31, 2001, with some exceptions. On other commercial jet transports, audits should be completed before the high time airplane reaches their respective design service goals. • That a SSIP or equivalent program and Repair Assessment Program for Post Amendment 45/Pre Amendment 54 airplane be developed and implemented. • That any rule published as a result of the subsequent tasking become effective one year after final rule publication. • That the analysis of STCs to primary structure be held to the same audit requirements (criteria and schedule) as OEM Structure. June 29, 1999 PAGE 10