AMC 20-20B Continuing structural integrity programme

• ED Decision 2020/023/R found in: EAR for AMC for Airworthiness of Products, Parts and Appliances (AMC-20) (Amendment 21)
• ED Decision 2021/007/R found in: EAR for AMC for Airworthiness of Products, Parts and Appliances (AMC-20) (Amendment 22)
• ED Decision 2021/007/R found in: EAR for AMC for Airworthiness of Products, Parts and Appliances (AMC-20) (Amendment 23)

Damage tolerance (DT) is the attribute of the structure that permits it to retain its required residual strength without detrimental structural deformation for a period of use after the structure has sustained a given level of fatigue, corrosion, and accidental or discrete source damage. Design a pproval h older (DAH) is the holder of any design approval, including type certificate, supplemental type certificate or earlier equivalent, or repair approval. Damage tolerance data is the combination of DTE documentation and DTI. Damage tolerance evaluation (DTE) is a process that leads to the determination of the maintenance actions necessary to detect or preclude fatigue cracking that could contribute to a catastrophic failure. When applied to repairs and changes, a DTE includes the evaluation of the repair or change and the fatigue-critical structure affected by the repair or change. Damage tolerance inspection (DTI) is a documented inspection requirement or other maintenance action developed by holders of design approvals or third parties as a result of a damage tolerance evaluation. A DTI includes the areas to be inspected, the inspection method, the inspection procedures (including the sequential inspection steps and acceptance and rejection criteria), the inspection threshold and any repetitive intervals associated with those inspections. DTIs may also specify maintenance actions such as replacement, repair or modification. Design s ervice g oal (DSG) is the period of time (in flight cycles or flight hours, or both ) established at design and/or certification during which the aeroplane structure is expected to be reasonably free from significant cracking. Existing design changes or repairs are changes and repairs which are to be approved before the date of entry into force of this rule. Fatigue-critical alteration structure (FCAS) is equivalent to fatigue-critical modified structure. Fatigue-critical baseline structure (FCBS) is the baseline structure of an aeroplane that is classified by the type certificate holder as a fatigue-critical structure. Fatigue-critical modified structure (FCMS) means any fatigue-critical structure of an aeroplane introduced or affected by a change to its type design and that is not already listed as part of the fatigue-critical baseline structure. Fatigue - c ritical s tructure (FCS) is a structure of an aeroplane that is susceptible to fatigue cracking that could lead to a catastrophic failure of the aircraft. For the purposes of this AMC, FCS refers to the same class of structure that would need to be assessed for compliance with JAR 25.571 Change 7 or 14CFR § 25.571(a) at Amendment 25-45, or late r. The term ‘ FCS ’ may refer to fatigue - critical baseline structure, fatigue critical modified structure, or both. Inspection start point (ISP) is the point in time when special inspections of the fleet are initiated due to a specific probability of having an MSD/MED condition. Future design changes and repairs are changes and repairs which are to be approved on or after the date of entry into force of this rule. Limit of validity (LOV) (of the engineering data that supports the structural maintenance programme) means, in the context of the engineering data that supports the structural maintenance programme, a period of time, stated as a number of total accumulated flight cycles or flight hours or both, during which it is demonstrated that widespread fatigue damage will not occur in the aeroplane . Multiple -e lement d amage (MED) is a source of widespread fatigue damage characterised by the simultaneous presence of fatigue cracks in similar adjacent structural elements. Multiple -s ite d amage (MSD) is a source of widespread fatigue damage characterised by the simultaneous presence of fatigue cracks in the same structural element. and ( e) Assess the damage tolerance of structural repairs. Subsequent to these five major elements being identified, it was recognised that an additional factor in the Aloha accident was widespread fatigue cracking. Regulatory and i ndustry experts agreed that, as the transport aircraft fleet continues to age, eventually w idespread f atigue d amage (WFD) is inevitable. Structures Task Groups sponsored by the Task Force were assigned the task of developing these elements into usable programmes. The Task Force was later re established as the AAWG of the ARAC. Although there was JAA membership and European o perators and i ndustry representatives participated in the AAWG, recommendations for action focussed on FAA operational rules which are not applicable in Europe. It was therefore decided to establish the EAAWG on this subject to implement a geing a ircraft activities in Europe , not only for the initial ‘ AATF eleven ’ aeroplanes, but also other old aircraft and more recently certified ones. EAAWG recommendations followed, leading to the development of guidance material for TCHs and operators, and proposals to develop Sub-part M of JAR OPS. The subsequent establishment of the Agency and new EU regulations led to the current format of Part-M for continuing airworthiness, the associated maintenance programme requirements and to the inclusion of ageing aircraft structures programmes in AMC Part M (M.A.302). AMC 20-20 supported this process and set out means by which TCHs and operators could develop and implement ageing aircraft structures programmes. This AMC supports DAH and operator compliance with the requirements introduced by Commission Implementing Regulation (EU) 2020/1159 on ageing aeroplane structures, amending Regulation (EU) 2015/640 (Part-26), and the associated CS-26 specifications. The Regulation includes requirements for specific DAHs to perform damage tolerance and other evaluations of existing airframe structure, develop certain data and ICA if they have not already done so, and make it available to operators. Furthermore, operators, in addition to implementing these new ICA as envisaged under Part-M, are required by Part-26 to ensure that approved damage-tolerance-based inspections are obtained and implemented on all repairs and modifications affecting the FCS on aeroplanes certified for 30 passengers or more or for 7 500 lb or more payload. Points 26.300 through 26.370 of Part-26 provide requirements for a complete retroactively applicable continuing structural integrity programme for specific categories of large aeroplanes. The principal means of compliance with those regulations may be found in CS-26, which, in turn, refers to this AMC. 4. DEFINITIONS AND ACRONYMS ( a) For the purposes of this AMC, the following definitions apply: Airworthiness limitation section (ALS) means a section in the instructions for continued airworthiness, as required by points 21.A.61, 21.A.107 and 21.A.120A of Annex I (Part 21) to Regulation (EU) No 748/2012 , which contains airworthiness limitations that set out each mandatory replacement time, inspection interval and related inspection procedure. Baseline structure refers to the structure that is designed under the type certificate for that aeroplane model (that is, the ‘as delivered aeroplane model configuration’). Corrosion prevention and control programme (CPCP) is a document reflecting a systematic approach to prevent and to control corrosion in an aeroplane’s primary structure, consisting of basic corrosion tasks, including inspections, areas subject to those tasks, defined corrosion levels and compliance times (implementation thresholds and repeat intervals). A baseline CPCP is established by the type certificate holder, which can be adapted by operators to create a CPCP in their maintenance programme specific to their operations. AMC 20-20 A Continuing s tructural i ntegrity p rogramme ED Decision 2020/023/R 1. PURPOSE ( a) This a cceptable m eans of c ompliance ( AMC) provides guidance to type certificate holders (TCHs), supplemental type certificate holders (STCHs) , repair approval holders, maintenance organisations, operators and competent authorities for developing continuing structural integrity programme s to ensure safe operation of ageing aircraft throughout their operational li v e s . This AMC is primarily aimed at large aeroplanes ; h owever, this material is also applicable to other aircraft types for operators and TCHs wishing to develop robust continuing structural integrity programmes . (b) It is particularly important for the TCHs of ageing aircraft to ensure that their continuing structural integrity programmes remain valid throughout the operational life of the aircraft. ( c) The means of compliance described in this document provides guidance to supplement the engineering and operational judgement that must form the basis of any compliance findings relative to continuing structural integrity programmes. ( d) Like all acceptable means of compliance material, this AMC is not in itself mandatory, and does not constitute a requirement. It describes an acceptable means, but not the only means, for showing compliance with the requirements. While these guidelines are not mandatory, they are derived from extensive industry experience in determining compliance with the relevant requirements. (e) This AMC also supports compliance with the ageing structural integrity requirements in Annex I (Part-26) to Regulation (EU) 2015/640 , as introduced by Regulation (EU) 2020/1159 (ref. points 26.300 through 26.370 and the associated CS-26 paragraphs) including limits of validity (LOVs), WFD evaluation, damage tolerance for repairs and modifications, and processes for ensuring the continued validity of the continuing structural integrity programme. 2. RELATED REGULATIONS AND DOCUMENTS ( a) Implementing Rules and Certification Specifications : P oint 21 . A.61 Instructions for continued airworthiness P oint 21 .A.120 Instructions for continued airworthiness Points 26.300 through 26.334 applicable to DAHs P oint 21 .A.433 Repair design Point 26.370 Rules applicable to operators P oint M.A.302 Maintenance programme CS 25.571 Damage tolerance and fatigue evaluation of structure CS 25.1529 Instructions for continued airworthiness CS 26.300 through 26.370 Means of compliance for Part-26 ageing aeroplane structures requirements ( b) EASA AMC and FAA Advisory Circulars AMC 25.571 Damage tolerance and fatigue evaluation of structure AC 91-81 Management Programs for Airplanes with Demonstrated Risk of Catastrophic Failure Due to Fatigue, 29 April 2008, FAA AC 91-56 B Continuing Structural Integrity for Airplanes , 7 March 2008, FAA AC 120 - 73 Damage Tolerance Assessment of Repairs to Pressurised Fuselages, FAA , 14 December 2000 AC120-93 Damage Tolerance Inspections for Repairs and Alterations AC120-104 Establishing and Implementing Limit of Validity to Prevent Widespread Fatigue Damage AC 25.1529-1 A Instructions for C ontinued A irworthiness of Structural R epairs on Transport Airplanes, FAA , 20 November 2007 (c) Related d ocuments ‘ Recommendations for Regulatory Action to Prevent Widespread Fatigue Damage in the Commercial Aeroplane Fleet ’ , Revision A, dated June 29, 1999 [A report of the Airworthiness Assurance Working Group for the Aviation Rulemaking Advisory Committee Transport Aircraft and Engine Issues] . AAWG Final Report on Continued Airworthiness of Structural Repairs, Dec 1996. ATA report 51-93-01 structural maintenance programme guidelines for continuing airworthiness , May 1993. AAWG Report on Structures Task Group Guidelines, Rev 1 June 1996 . AAWG Report: Recommendations concerning ARAC taskings FR Doc 04-10816 Re f. : Multiple -s ite d amage (MSD) is a source of widespread fatigue damage characterised by the simultaneous presence of fatigue cracks in the same structural element. Primary s tructure is structure that carries flight, ground, crash or pressurisation loads. Published repair data are instructions for accomplishing repairs which are published for general use in structural repair manuals and service bulletins (or equivalent types of documents). Repair assessment guidelines (RAGs) provide a process to establish damage tolerance inspections for repairs on the fuselage pressure boundary structure. Repair a ssessment p rogramme (RAP) is a programme to incorporate damage tolerance-based inspections for repairs to the fuselage pressure boundary structure (fuselage skin, door skin, and bulkhead webs) into the operator’s maintenance and/or inspection programme. Repair e valuation g uidelines (REG s ) are established by the type certificate holder and guide operators to establish damage tolerance inspections for repairs that affect fatigue-critical structure to ensure the continued structural integrity of all relevant repairs . Structural modification point (SMP) is the point in time when a structural area must be modified to preclude WFD. Widespread f atigue d amage (WFD) means the simultaneous presence of cracks at multiple locations in the structure of an aeroplane that are of such size and number that the structure will no longer meet the fail-safe strength or residual strength used for the certification of that structure . (b) The following list defines the acronyms that are used throughout this AMC: | AAWG | Airworthiness Assurance Working Group | | --- | --- | | AC | advisory circular | | AD | airworthiness directive | | ALS | airworthiness limitations section | | AMC | acceptable means of compliance | | ARAC | Aviation Rulemaking Advisory Committee | | BZI | baseline zonal inspection | | CAW | continuing airworthiness | | CPCP | corrosion prevention and control programme | | CS | certification specification | | DAH | design approval holder | | DSD | discrete source damage | | DSG | design service goal | | DT | damage tolerance | | DTE | damage tolerance evaluation | | DTI | damage tolerance inspection | | EAAWG | European Ageing Aircraft Working Group | | EASA | European Union Aviation Safety Agency | | ESG | extended service goal | | FAA | Federal Aviation Administration | | FAR | Federal Aviation Regulation | | FCBS | fatigue-critical baseline structure | | FCS | fatigue-critical structure | | ICA | instructions for continued airworthiness | | ISP | inspection start point | | JAA | Joint Aviation Authorities | | JAR | joint aviation regulation | | LOV | limit of validity | | MED | multiple-element damage | | MRB | Maintenance Review Board | | MSD | multiple-site damage | | MTOM | maximum take-off mass | | MSG | Maintenance Steering Group | | NAA | national aviation authority | | NDI | non-destructive inspection | | NTSB | National Transportation Safety Board | | PSE | principal structural element | | RAP | repairs assessment programme | | REGs | repair evaluation guidelines | | SB | service bulletin | | SMP | structural modification point | | SRM | structural repair manual | | SSID | supplemental structural inspection document | | SSIP | supplemental structural inspection programme | | STG | structural task group | | STCH | supplemental type certificate holder | | TCH | type certificate holder | | WFD | widespread fatigue damage | AAWG Report on Structures Task Group Guidelines, Rev 1 June 1996 . AAWG Report: Recommendations concerning ARAC taskings FR Doc 04-10816 Re f. : Aging Airplane safety final ru le. 14 CFR 121.370a and 129.16 . Federal Aviation Administration 14 CFR Parts 26, 121, and 129 [Docket No FAA 2005-21693; Amendment Nos 26–1, 121–337, 129–44] Damage Tolerance Data for Repairs and Alterations Final Rule. Federal Aviation Administration 14 CFR Parts 25, 26, 121, and 129 [Docket No FAA 2006-24281; Amendment Nos 25–132, 26–5, 121–351, 129–48] Aging Airplane Program: Widespread Fatigue Damage Final Rule. 3. BACKGROUND Service experience has shown there is a need to have continu ally updated knowledge on the structural integrity of aircraft, especially as they become older , to ensure they continue to meet the level of safety intended by the certification requirements. The continued structural integrity of aircraft is of concern because factors such as fatigue cracking and corrosion are time dependent, and our knowledge about them can best be assessed based on real-time operational experience and the use of the most modern tools of analysis and testing. In April 1988, a high-cycle transport aeroplane en-route from Hilo to Honolulu, Hawaii, suffered major structural damage to its pressurised fuselage during flight. This accident was attributed in part to the age of the aeroplane involved. The economic benefit of operating certain older technology aeroplanes resulted in the operation of many such aeroplanes beyond their previously expected retirement age. Because of the problems revealed by the accident in Hawaii and the continued operation of older aircraft, both the competent authorities and industry generally agreed that increased attention needed to be focused on the ageing fleet and on maintaining its continued operational safety. In June 1988, the FAA sponsored a conference on ageing aircraft. As a result of that conference, an ageing aircraft task force was established in August 1988 as a sub-group of the FAA ’ s Research, Engineering, and Development Advisory Committee, representing the interests of the aircraft operators, aircraft manufacturers, regulatory authorities, and other aviation representatives. The task force, then known as the Airworthiness Assurance Task Force (AATF), set forth five major elements of a programme for keeping the ageing fleet safe. For each aeroplane model in the ageing transport fleet , these elements consisted of the following: (a) Select service bulletins describing modifications and inspections necessary to maintain structural integrity; ( b) Develop inspection and prevention programmes to address corrosion; ( c) Develop generic structural maintenance programme guidelines for ageing aeroplanes; ( d) Review and update the s upplemental s tructural i nspection d ocuments (SSID s ) which describe inspection programmes to detect fatigue cracking; and ( e) Assess the damage tolerance of structural repairs. | RAP | repairs assessment programme | | REGs | repair evaluation guidelines | | SB | service bulletin | | SMP | structural modification point | | SRM | structural repair manual | | SSID | supplemental structural inspection document | | SSIP | supplemental structural inspection programme | | STG | structural task group | | STCH | supplemental type certificate holder | | TCH | type certificate holder | | WFD | widespread fatigue damage | Baseline structure refers to the structure that is designed under the type certificate for that aeroplane model (that is, the ‘as delivered aeroplane model configuration’). Corrosion prevention and control programme (CPCP) is a document reflecting a systematic approach to prevent and to control corrosion in an aeroplane’s primary structure, consisting of basic corrosion tasks, including inspections, areas subject to those tasks, defined corrosion levels and compliance times (implementation thresholds and repeat intervals). A baseline CPCP is established by the type certificate holder, which can be adapted by operators to create a CPCP in their maintenance programme specific to their operations. Damage tolerance (DT) is the attribute of the structure that permits it to retain its required residual strength without detrimental structural deformation for a period of use after the structure has sustained a given level of fatigue, corrosion, and accidental or discrete source damage. Design a pproval h older (DAH) is the holder of any design approval, including type certificate, supplemental type certificate or earlier equivalent, or repair approval. Damage tolerance data is the combination of DTE documentation and DTI. Damage tolerance evaluation (DTE) is a process that leads to the determination of the maintenance actions necessary to detect or preclude fatigue cracking that could contribute to a catastrophic failure. When applied to repairs and changes, a DTE includes the evaluation of the repair or change and the fatigue-critical structure affected by the repair or change. Damage tolerance inspection (DTI) is a documented inspection requirement or other maintenance action developed by holders of design approvals or third parties as a result of a damage tolerance evaluation. A DTI includes the areas to be inspected, the inspection method, the inspection procedures (including the sequential inspection steps and acceptance and rejection criteria), the inspection threshold and any repetitive intervals associated with those inspections. DTIs may also specify maintenance actions such as replacement, repair or modification. Design s ervice g oal (DSG) is the period of time (in flight cycles or flight hours, or both ) established at design and/or certification during which the aeroplane structure is expected to be reasonably free from significant cracking. Existing design changes or repairs are changes and repairs which are to be approved before the date of entry into force of this rule. Fatigue-critical alteration structure (FCAS) is equivalent to fatigue-critical modified structure. Fatigue-critical baseline structure (FCBS) is the baseline structure of an aeroplane that is classified by the type certificate holder as a fatigue-critical structure. Fatigue-critical modified structure (FCMS) means any fatigue-critical structure of an aeroplane introduced or affected by a change to its type design and that is not already listed as part of the fatigue-critical baseline structure. Fatigue - c ritical s tructure (FCS) is a structure of an aeroplane that is susceptible to fatigue cracking that could lead to a catastrophic failure of the aircraft. For the purposes of this AMC, FCS refers to the same class of structure that would need to be assessed for compliance with JAR 25.571 Change 7 or 14CFR § 25.571(a) at Amendment 25-45, or late r. The term ‘ FCS ’ may refer to fatigue - critical baseline structure, fatigue critical modified structure, or both. Inspection start point (ISP) is the point in time when special inspections of the fleet are initiated due to a specific probability of having an MSD/MED condition. Future design changes and repairs are changes and repairs which are to be approved on or after the date of entry into force of this rule. AMC 20-20 B Continuing s tructural i ntegrity p rogramme ED Decision 2021/007/R 1. PURPOSE ( a) This a cceptable m eans of c ompliance ( AMC) provides guidance to type certificate holders (TCHs), supplemental type certificate holders (STCHs) , repair approval holders, maintenance organisations, operators and competent authorities for developing continuing structural integrity programme s to ensure safe operation of ageing aircraft throughout their operational li v e s . This AMC is primarily aimed at large aeroplanes ; h owever, this material is also applicable to other aircraft types for operators and TCHs wishing to develop robust continuing structural integrity programmes . (b) It is particularly important for the TCHs of ageing aircraft to ensure that their continuing structural integrity programmes remain valid throughout the operational life of the aircraft. ( c) The means of compliance described in this document provides guidance to supplement the engineering and operational judgement that must form the basis of any compliance findings relative to continuing structural integrity programmes. ( d) Like all acceptable means of compliance material, this AMC is not in itself mandatory, and does not constitute a requirement. It describes an acceptable means, but not the only means, for showing compliance with the requirements. While these guidelines are not mandatory, they are derived from extensive industry experience in determining compliance with the relevant requirements. (e) This AMC also supports compliance with the ageing structural integrity requirements in Annex I (Part-26) to Regulation (EU) 2015/640 , as introduced by Regulation (EU) 2020/1159 (ref. points 26.300 through 26.370 and the associated CS-26 paragraphs) including limits of validity (LOVs), WFD evaluation, damage tolerance for repairs and modifications, and processes for ensuring the continued validity of the continuing structural integrity programme. (f) This AMC also supports compliance with the ageing structural integrity requirements in point 21.A.65 of Part 21 as well as compliance with the certification basis established in accordance with points 21.A.101(h) and 21.A.433(a)(5) of Part 21. 2. RELATED REGULATIONS AND DOCUMENTS ( a) Implementing Rules and Certification Specifications : P oint 21 . A.61 Instructions for continued airworthiness Point 21.A.65 Continuing structural integrity for aeroplane structures Point 21.A.101 Type-certification basis, operational suitability data certification basis and environmental protection requirements for a major change to a type-certificate P oint 21 .A.120 Instructions for continued airworthiness Points 26.300 through 26.334 applicable to DAHs P oint 21 .A.433 Repair design Point 26.370 Rules applicable to operators P oint M.A.302 Maintenance programme CS 25.571 Damage tolerance and fatigue evaluation of structure CS 25.1529 Instructions for continued airworthiness CS 26.300 through 26.370 Means of compliance for Part-26 ageing aeroplane structures requirements ( b) EASA AMC and FAA Advisory Circulars AMC 25.571 Damage tolerance and fatigue evaluation of structure AMC1 21.A.65 Continuing structural integrity programme for aeroplane structures AMC1 21.A.101(h) Type-certification basis for changes to large aeroplanes subject to point 26.300 of Part-26 AMC1 21.A.433(a)(5) Requirements for the approval of repairs to large aeroplanes subject to point 26.302 of Part-26 AC 91-81 Management Programs for Airplanes with Demonstrated Risk of Catastrophic Failure Due to Fatigue, 29 April 2008, FAA AC 91-56 B Continuing Structural Integrity for Airplanes , 7 March 2008, FAA AC 120 - 73 Damage Tolerance Assessment of Repairs to Pressurised Fuselages, FAA , 14 December 2000 AC120-93 Damage Tolerance Inspections for Repairs and Alterations and ( e) Assess the damage tolerance of structural repairs. Subsequent to these five major elements being identified, it was recognised that an additional factor in the Aloha accident was widespread fatigue cracking. Regulatory and i ndustry experts agreed that, as the transport aircraft fleet continues to age, eventually w idespread f atigue d amage (WFD) is inevitable. Structures Task Groups sponsored by the Task Force were assigned the task of developing these elements into usable programmes. The Task Force was later re established as the AAWG of the ARAC. Although there was JAA membership and European o perators and i ndustry representatives participated in the AAWG, recommendations for action focussed on FAA operational rules which are not applicable in Europe. It was therefore decided to establish the EAAWG on this subject to implement a geing a ircraft activities in Europe , not only for the initial ‘ AATF eleven ’ aeroplanes, but also other old aircraft and more recently certified ones. EAAWG recommendations followed, leading to the development of guidance material for TCHs and operators, and proposals to develop Sub-part M of JAR OPS. The subsequent establishment of the Agency and new EU regulations led to the current format of Part-M for continuing airworthiness, the associated maintenance programme requirements and to the inclusion of ageing aircraft structures programmes in AMC Part M (M.A.302). AMC 20-20 supported this process and set out means by which TCHs and operators could develop and implement ageing aircraft structures programmes. This AMC supports DAH and operator compliance with the requirements introduced by Commission Implementing Regulation (EU) 2020/1159 on ageing aeroplane structures, amending Regulation (EU) 2015/640 (Part-26), and the associated CS-26 specifications. The Regulation includes requirements for specific DAHs to perform damage tolerance and other evaluations of existing airframe structure, develop certain data and ICA if they have not already done so, and make it available to operators. Furthermore, operators, in addition to implementing these new ICA as envisaged under Part-M, are required by Part-26 to ensure that approved damage-tolerance-based inspections are obtained and implemented on all repairs and modifications affecting the FCS on aeroplanes certified for 30 passengers or more or for 7 500 lb or more payload. Points 26.300 through 26.370 of Part-26 provide the requirements for a complete retroactively applicable continuing structural integrity programme for specific categories of large aeroplanes. The principal means of compliance with those re quirements may be found in CS-26, which, in turn, refers to this AMC. Additionally, this AMC supports (R)TCH compliance with the requirements introduced by Commission Delegated Regulation (EU) 2021/699 of 21 December 2020 on continuing structural integrity of large aeroplanes, amending Annex I (Part 21) to Commission Regulation (EU) No748/2012 . 4. DEFINITIONS AND ACRONYMS ( a) For the purposes of this AMC, the following definitions apply: Airworthiness limitation section (ALS) means a section in the instructions for continued airworthiness, as required by points 21.A.61, 21.A.107 and 21.A.120A of Annex I (Part 21) to Regulation (EU) No 748/2012 , which contains airworthiness limitations that set out each mandatory replacement time, inspection interval and related inspection procedure. Baseline structure refers to the structure that is designed under the type certificate for that aeroplane model (that is, the ‘as delivered aeroplane model configuration’). AC 120 - 73 Damage Tolerance Assessment of Repairs to Pressurised Fuselages, FAA , 14 December 2000 AC120-93 Damage Tolerance Inspections for Repairs and Alterations AC120-104 Establishing and Implementing Limit of Validity to Prevent Widespread Fatigue Damage AC 25.1529-1 A Instructions for C ontinued A irworthiness of Structural R epairs on Transport Airplanes, FAA , 20 November 2007 (c) Related d ocuments ‘ Recommendations for Regulatory Action to Prevent Widespread Fatigue Damage in the Commercial Aeroplane Fleet ’ , Revision A, dated June 29, 1999 [A report of the Airworthiness Assurance Working Group for the Aviation Rulemaking Advisory Committee Transport Aircraft and Engine Issues] . AAWG Final Report on Continued Airworthiness of Structural Repairs, Dec 1996. ATA report 51-93-01 structural maintenance programme guidelines for continuing airworthiness , May 1993. AAWG Report on Structures Task Group Guidelines, Rev 1 June 1996 . AAWG Report: Recommendations concerning ARAC taskings FR Doc 04-10816 Re f. : Aging Airplane safety final ru le. 14 CFR 121.370a and 129.16 . Federal Aviation Administration 14 CFR Parts 26, 121, and 129 [Docket No FAA 2005-21693; Amendment Nos 26–1, 121–337, 129–44] Damage Tolerance Data for Repairs and Alterations Final Rule. Federal Aviation Administration 14 CFR Parts 25, 26, 121, and 129 [Docket No FAA 2006-24281; Amendment Nos 25–132, 26–5, 121–351, 129–48] Aging Airplane Program: Widespread Fatigue Damage Final Rule. 3. BACKGROUND Service experience has shown there is a need to have continu ally updated knowledge on the structural integrity of aircraft, especially as they become older , to ensure they continue to meet the level of safety intended by the certification requirements. The continued structural integrity of aircraft is of concern because factors such as fatigue cracking and corrosion are time dependent, and our knowledge about them can best be assessed based on real-time operational experience and the use of the most modern tools of analysis and testing. In April 1988, a high-cycle transport aeroplane en-route from Hilo to Honolulu, Hawaii, suffered major structural damage to its pressurised fuselage during flight. This accident was attributed in part to the age of the aeroplane involved. The economic benefit of operating certain older technology aeroplanes resulted in the operation of many such aeroplanes beyond their previously expected retirement age. Because of the problems revealed by the accident in Hawaii and the continued operation of older aircraft, both the competent authorities and industry generally agreed that increased attention needed to be focused on the ageing fleet and on maintaining its continued operational safety. In June 1988, the FAA sponsored a conference on ageing aircraft. As a result of that conference, an ageing aircraft task force was established in August 1988 as a sub-group of the FAA ’ s Research, Engineering, and Development Advisory Committee, representing the interests of the aircraft operators, aircraft manufacturers, regulatory authorities, and other aviation representatives. The task force, then known as the Airworthiness Assurance Task Force (AATF), set forth five major elements of a programme for keeping the ageing fleet safe. For each aeroplane model in the ageing transport fleet , these elements consisted of the following: (a) Select service bulletins describing modifications and inspections necessary to maintain structural integrity; ( b) Develop inspection and prevention programmes to address corrosion; ( c) Develop generic structural maintenance programme guidelines for ageing aeroplanes; ( d) Review and update the s upplemental s tructural i nspection d ocuments (SSID s ) which describe inspection programmes to detect fatigue cracking; and ( e) Assess the damage tolerance of structural repairs. Future design changes and repairs are changes and repairs which are to be approved on or after the date of entry into force of this rule. Limit of validity (LOV) (of the engineering data that supports the structural maintenance programme) means, in the context of the engineering data that supports the structural maintenance programme, a period of time, stated as a number of total accumulated flight cycles or flight hours or both, during which it is demonstrated that widespread fatigue damage will not occur in the aeroplane . Multiple -e lement d amage (MED) is a source of widespread fatigue damage characterised by the simultaneous presence of fatigue cracks in similar adjacent structural elements. Multiple -s ite d amage (MSD) is a source of widespread fatigue damage characterised by the simultaneous presence of fatigue cracks in the same structural element. Primary s tructure is structure that carries flight, ground, crash or pressurisation loads. Published repair data are instructions for accomplishing repairs which are published for general use in structural repair manuals and service bulletins (or equivalent types of documents). Repair assessment guidelines (RAGs) provide a process to establish damage tolerance inspections for repairs on the fuselage pressure boundary structure. Repair a ssessment p rogramme (RAP) is a programme to incorporate damage tolerance-based inspections for repairs to the fuselage pressure boundary structure (fuselage skin, door skin, and bulkhead webs) into the operator’s maintenance and/or inspection programme. Repair e valuation g uidelines (REG s ) are established by the type certificate holder and guide operators to establish damage tolerance inspections for repairs that affect fatigue-critical structure to ensure the continued structural integrity of all relevant repairs . Structural modification point (SMP) is the point in time when a structural area must be modified to preclude WFD. Widespread f atigue d amage (WFD) means the simultaneous presence of cracks at multiple locations in the structure of an aeroplane that are of such size and number that the structure will no longer meet the fail-safe strength or residual strength used for the certification of that structure . (b) The following list defines the acronyms that are used throughout this AMC: | AAWG | Airworthiness Assurance Working Group | | --- | --- | | AC | advisory circular | | AD | airworthiness directive | | ALS | airworthiness limitations section | | AMC | acceptable means of compliance | | ARAC | Aviation Rulemaking Advisory Committee | | BZI | baseline zonal inspection | | CAW | continuing airworthiness | | CPCP | corrosion prevention and control programme | | CS | certification specification | | DAH | design approval holder | | DSD | discrete source damage | | DSG | design service goal | | DT | damage tolerance | | DTE | damage tolerance evaluation | | DTI | damage tolerance inspection | | EAAWG | European Ageing Aircraft Working Group | | EASA | European Union Aviation Safety Agency | | ESG | extended service goal | | FAA | Federal Aviation Administration | | FAR | Federal Aviation Regulation | | FCBS | fatigue-critical baseline structure | | FCS | fatigue-critical structure | | ICA | instructions for continued airworthiness | | ISP | inspection start point | | JAA | Joint Aviation Authorities | | JAR | joint aviation regulation | | LOV | limit of validity | | MED | multiple-element damage | | MRB | Maintenance Review Board | | MSD | multiple-site damage | | MTOM | maximum take-off mass | | MSG | Maintenance Steering Group | | NAA | national aviation authority | | NDI | non-destructive inspection | | NTSB | National Transportation Safety Board | | PSE | principal structural element | | RAP | repairs assessment programme | | REGs | repair evaluation guidelines | | SB | service bulletin | | SMP | structural modification point | | SRM | structural repair manual | | RAP | repairs assessment programme | | REGs | repair evaluation guidelines | | SB | service bulletin | | SMP | structural modification point | | SRM | structural repair manual | | SSID | supplemental structural inspection document | | SSIP | supplemental structural inspection programme | | STG | structural task group | | STCH | supplemental type certificate holder | | TCH | type certificate holder | | WFD | widespread fatigue damage | Future design changes and repairs are changes and repairs which are to be approved on or after the date of entry into force of this rule. Limit of validity (LOV) (of the engineering data that supports the structural maintenance programme) means, in the context of the engineering data that supports the structural maintenance programme, a period of time , stated as a number of total accumulated flight cycles or flight hours or both, during which it is demonstrated that widespread fatigue damage will not occur in the aeroplane . Multiple -e lement d amage (MED) is a source of widespread fatigue damage characterised by the simultaneous presence of fatigue cracks in similar adjacent structural elements. Multiple -s ite d amage (MSD) is a source of widespread fatigue damage characterised by the simultaneous presence of fatigue cracks in the same structural element. Primary s tructure is structure that carries flight, ground, crash or pressurisation loads. Published repair data are instructions for accomplishing repairs which are published for general use in structural repair manuals and service bulletins (or equivalent types of documents). Repair assessment guidelines (RAGs) provide a process to establish damage tolerance inspections for repairs on the fuselage pressure boundary structure. Repair a ssessment p rogramme (RAP) is a programme to incorporate damage tolerance-based inspections for repairs to the fuselage pressure boundary structure (fuselage skin, door skin, and bulkhead webs) into the operator’s maintenance and/or inspection programme. Repair e valuation g uidelines (REG s ) are established by the type certificate holder and guide operators to establish damage tolerance inspections for repairs that affect fatigue-critical structure to ensure the continued structural integrity of all relevant repairs . Structural modification point (SMP) is the point in time when a structural area must be modified to preclude WFD. Widespread f atigue d amage (WFD) means the simultaneous presence of cracks at multiple locations in the structure of an aeroplane that are of such size and number that the structure will no longer meet the fail-safe strength or residual strength used for the certification of that structure . ( b) The following list defines the acronyms that are used throughout this AMC: | AAWG | Airworthiness Assurance Working Group | | --- | --- | | AC | advisory circular | | AD | airworthiness directive | | ALS | airworthiness limitations section | | AMC | acceptable means of compliance | | ARAC | Aviation Rulemaking Advisory Committee | | BZI | baseline zonal inspection | | CAW | continuing airworthiness | | CPCP | corrosion prevention and control programme | | CS | certification specification | | DAH | design approval holder | | DSD | discrete source damage | | DSG | design service goal | | DT | damage tolerance | | DTE | damage tolerance evaluation | | DTI | damage tolerance inspection | | EAAWG | European Ageing Aircraft Working Group | | EASA | European Union Aviation Safety Agency | | ESG | extended service goal | | FAA | Federal Aviation Administration | | FAR | Federal Aviation Regulation | | FCBS | fatigue-critical baseline structure | | FCS | fatigue-critical structure | | ICA | instructions for continued airworthiness | | ISP | inspection start point | | JAA | Joint Aviation Authorities | | JAR | joint aviation regulation | | LOV | limit of validity | | MED | multiple-element damage | | MRB | Maintenance Review Board | | MSD | multiple-site damage | | MTOM | maximum take-off mass | | MSG | Maintenance Steering Group | | NAA | national aviation authority | | NDI | non-destructive inspection | | NTSB | National Transportation Safety Board | | PSE | principal structural element | | RAP | repairs assessment programme | | REGs | repair evaluation guidelines | | SB | service bulletin | | SMP | structural modification point | | SRM | structural repair manual | AC 120 - 73 Damage Tolerance Assessment of Repairs to Pressurised Fuselages, FAA , 14 December 2000 AC120-93 Damage Tolerance Inspections for Repairs and Alterations AC120-104 Establishing and Implementing Limit of Validity to Prevent Widespread Fatigue Damage AC 25.1529-1 A Instructions for C ontinued A irworthiness of Structural R epairs on Transport Airplanes, FAA , 20 November 2007 ( c) Related d ocuments ‘ Recommendations for Regulatory Action to Prevent Widespread Fatigue Damage in the Commercial Aeroplane Fleet ’ , Revision A, dated June 29, 1999 [A report of the Airworthiness Assurance Working Group for the Aviation Rulemaking Advisory Committee Transport Aircraft and Engine Issues] . AAWG Final Report on Continued Airworthiness of Structural Repairs, Dec 1996. ATA report 51-93-01 structural maintenance programme guidelines for continuing airworthiness , May 1993. AAWG Report on Structures Task Group Guidelines, Rev 1 June 1996 . AAWG Report: Recommendations concerning ARAC taskings FR Doc 04-10816 Re f. : Aging Airplane safety final ru le. 14 CFR 121.370a and 129.16 . Federal Aviation Administration 14 CFR Parts 26, 121, and 129 [Docket No FAA 2005-21693; Amendment Nos 26–1, 121–337, 129–44] Damage Tolerance Data for Repairs and Alterations Final Rule. Federal Aviation Administration 14 CFR Parts 25, 26, 121, and 129 [Docket No FAA 2006-24281; Amendment Nos 25–132, 26–5, 121–351, 129–48] Aging Airplane Program: Widespread Fatigue Damage Final Rule. 3. BACKGROUND Service experience has shown there is a need to have continu ally updated knowledge on the structural integrity of aircraft, especially as they become older , to ensure they continue to meet the level of safety intended by the certification requirements. The continued structural integrity of aircraft is of concern because factors such as fatigue cracking and corrosion are time dependent, and our knowledge about them can best be assessed based on real-time operational experience and the use of the most modern tools of analysis and testing. In April 1988, a high-cycle transport aeroplane en -route from Hilo to Honolulu, Hawaii, suffered major structural damage to its pressurised fuselage during flight. This accident was attributed in part to the age of the aeroplane involved. The economic benefit of operating certain older technology aeroplanes resulted in the operation of many such aeroplanes beyond their previously expected retirement age. Because of the problems revealed by the accident in Hawaii and the continued operation of older aircraft, both the competent authorities and industry generally agreed that increased attention needed to be focused on the ageing fleet and on maintaining its continued operational safety. In June 1988, the FAA sponsored a conference on ageing aircraft. As a result of that conference, an ageing aircraft task force was established in August 1988 as a sub-group of the FAA ’ s Research, Engineering, and Development Advisory Committee, representing the interests of the aircraft operators, aircraft manufacturers, regulatory authorities, and other aviation representatives. The task force, then known as the Airworthiness Assurance Task Force (AATF), set forth five major elements of a programme for keeping the ageing fleet safe. For each aeroplane model in the ageing transport fleet , these elements consisted of the following: ( a) Select service bulletins describing modifications and inspections necessary to maintain structural integrity; ( b) Develop inspection and prevention programmes to address corrosion; ( c) Develop generic structural maintenance programme guidelines for ageing aeroplanes; ( d) Review and update the s upplemental s tructural i nspection d ocuments (SSID s ) which describe inspection programmes to detect fatigue cracking; and ( e) Assess the damage tolerance of structural repairs. Baseline structure refers to the structure that is designed under the type certificate for that aeroplane model (that is, the ‘as delivered aeroplane model configuration’). Corrosion prevention and control programme (CPCP) is a document reflecting a systematic approach to prevent and to control corrosion in an aeroplane’s primary structure, consisting of basic corrosion tasks, including inspections, areas subject to those tasks, defined corrosion levels and compliance times (implementation thresholds and repeat intervals). A baseline CPCP is established by the type certificate holder, which can be adapted by operators to create a CPCP in their maintenance programme specific to their operations. Damage tolerance (DT) is the attribute of the structure that permits it to retain its required residual strength without detrimental structural deformation for a period of use after the structure has sustained a given level of fatigue, corrosion, and accidental or discrete source damage. Design a pproval h older (DAH) is the holder of any design approval, including type certificate, supplemental type certificate or earlier equivalent, or repair approval. Damage tolerance data is the combination of DTE documentation and DTI. Damage tolerance evaluation (DTE) is a process that leads to the determination of the maintenance actions necessary to detect or preclude fatigue cracking that could contribute to a catastrophic failure. When applied to repairs and changes, a DTE includes the evaluation of the repair or change and the fatigue-critical structure affected by the repair or change. Damage tolerance inspection (DTI) is a documented inspection requirement or other maintenance action developed by holders of design approvals or third parties as a result of a damage tolerance evaluation. A DTI includes the areas to be inspected, the inspection method, the inspection procedures (including the sequential inspection steps and acceptance and rejection criteria), the inspection threshold and any repetitive intervals associated with those inspections. DTIs may also specify maintenance actions such as replacement, repair or modification. Design s ervice g oal (DSG) is the period of time (in flight cycles or flight hours, or both ) established at design and/or certification during which the aeroplane structure is expected to be reasonably free from significant cracking. Existing design changes or repairs are changes and repairs which are to be approved before the date of entry into force of this rule. Fatigue-critical alteration structure (FCAS) is equivalent to fatigue-critical modified structure. Fatigue-critical baseline structure (FCBS) is the baseline structure of an aeroplane that is classified by the type certificate holder as a fatigue-critical structure. Fatigue-critical modified structure (FCMS) means any fatigue-critical structure of an aeroplane introduced or affected by a change to its type design and that is not already listed as part of the fatigue-critical baseline structure. Fatigue - c ritical s tructure (FCS) is a structure of an aeroplane that is susceptible to fatigue cracking that could lead to a catastrophic failure of the aircraft. For the purposes of this AMC, FCS refers to the same class of structure that would need to be assessed for compliance with JAR 25.571 Change 7 or 14CFR § 25.571(a) at Amendment 25-45, or late r. The term ‘ FCS ’ may refer to fatigue - critical baseline structure, fatigue critical modified structure, or both. Inspection start point (ISP) is the point in time when special inspections of the fleet are initiated due to a specific probability of having an MSD/MED condition. Future design changes and repairs are changes and repairs which are to be approved on or after the date of entry into force of this rule. AMC 20-20 B Continuing s tructural i ntegrity p rogramme ED Decision 2021/007/R 1. PURPOSE ( a) This a cceptable m eans of c ompliance ( AMC) provides guidance to type certificate holders (TCHs), supplemental type certificate holders (STCHs) , repair approval holders, maintenance organisations, operators and competent authorities for developing continuing structural integrity programme s to ensure safe operation of ageing aircraft throughout their operational li v e s . This AMC is primarily aimed at large aeroplanes ; h owever, this material is also applicable to other aircraft types for operators and TCHs wishing to develop robust continuing structural integrity programmes . (b) It is particularly important for the TCHs of ageing aircraft to ensure that their continuing structural integrity programmes remain valid throughout the operational life of the aircraft. ( c) The means of compliance described in this document provides guidance to supplement the engineering and operational judgement that must form the basis of any compliance findings relative to continuing structural integrity programmes. ( d) Like all acceptable means of compliance material, this AMC is not in itself mandatory, and does not constitute a requirement. It describes an acceptable means, but not the only means, for showing compliance with the requirements. While these guidelines are not mandatory, they are derived from extensive industry experience in determining compliance with the relevant requirements. (e) This AMC also supports compliance with the ageing structural integrity requirements in Annex I (Part-26) to Regulation (EU) 2015/640 , as introduced by Regulation (EU) 2020/1159 (ref. points 26.300 through 26.370 and the associated CS-26 paragraphs) including limits of validity (LOVs), WFD evaluation, damage tolerance for repairs and modifications, and processes for ensuring the continued validity of the continuing structural integrity programme. (f) This AMC also supports compliance with the ageing structural integrity requirements in point 21.A.65 of Part 21 as well as compliance with the certification basis established in accordance with points 21.A.101(h) and 21.A.433(a)(5) of Part 21. 2. RELATED REGULATIONS AND DOCUMENTS ( a) Implementing Rules and Certification Specifications : P oint 21 . A. 61 Instructions for continued airworthiness Point 21.A. 65 Continuing structural integrity for aeroplane structures Point 21.A. 101 Type-certification basis, operational suitability data certification basis and environmental protection requirements for a major change to a type-certificate P oint 21 .A. 120 Instructions for continued airworthiness Points 26.300 through 26.334 applicable to DAHs P oint 21 .A. 433 Repair design Point 26.370 Rules applicable to operators P oint M.A.302 Maintenance programme CS 25.571 Damage tolerance and fatigue evaluation of structure CS 25.1529 Instructions for continued airworthiness CS 26.300 through 26.370 Means of compliance for Part-26 ageing aeroplane structures requirements ( b) EASA AMC and FAA Advisory Circulars AMC 25.571 Damage tolerance and fatigue evaluation of structure AMC1 21.A. 65 Continuing structural integrity programme for aeroplane structures AMC1 21.A.101(h) Type-certification basis for changes to large aeroplanes subject to point 26.300 of Part-26 AMC1 21.A.433(a)(5) Requirements for the approval of repairs to large aeroplanes subject to point 26.302 of Part-26 AC 91-81 Management Programs for Airplanes with Demonstrated Risk of Catastrophic Failure Due to Fatigue, 29 April 2008, FAA AC 91-56 B Continuing Structural Integrity for Airplanes , 7 March 2008, FAA AC 120 - 73 Damage Tolerance Assessment of Repairs to Pressurised Fuselages, FAA , 14 December 2000 AC120-93 Damage Tolerance Inspections for Repairs and Alterations and ( e) Assess the damage tolerance of structural repairs. Subsequent to these five major elements being identified, it was recognised that an additional factor in the Aloha accident was widespread fatigue cracking. Regulatory and i ndustry experts agreed that, as the transport aircraft fleet continues to age, eventually w idespread f atigue d amage (WFD) is inevitable. Structures Task Groups sponsored by the Task Force were assigned the task of developing these elements into usable programmes. The Task Force was later re established as the AAWG of the ARAC. Although there was JAA membership and European o perators and i ndustry representatives participated in the AAWG, recommendations for action focussed on FAA operational rules which are not applicable in Europe. It was therefore decided to establish the EAAWG on this subject to implement a geing a ircraft activities in Europe , not only for the initial ‘ AATF eleven ’ aeroplanes, but also other old aircraft and more recently certified ones. EAAWG recommendations followed, leading to the development of guidance material for TCHs and operators, and proposals to develop Sub-part M of JAR OPS. The subsequent establishment of the Agency and new EU regulations led to the current format of Part-M for continuing airworthiness, the associated maintenance programme requirements and to the inclusion of ageing aircraft structures programmes in AMC Part M (M.A.302). AMC 20-20 supported this process and set out means by which TCHs and operators could develop and implement ageing aircraft structures programmes. This AMC supports DAH and operator compliance with the requirements introduced by Commission Implementing Regulation (EU) 2020/1159 on ageing aeroplane structures, amending Regulation (EU) 2015/640 (Part-26), and the associated CS-26 specifications. The Regulation includes requirements for specific DAHs to perform damage tolerance and other evaluations of existing airframe structure, develop certain data and ICA if they have not already done so, and make it available to operators. Furthermore, operators, in addition to implementing these new ICA as envisaged under Part-M, are required by Part-26 to ensure that approved damage-tolerance-based inspections are obtained and implemented on all repairs and modifications affecting the FCS on aeroplanes certified for 30 passengers or more or for 7 500 lb or more payload. Points 26.300 through 26.370 of Part-26 provide the requirements for a complete retroactively applicable continuing structural integrity programme for specific categories of large aeroplanes. The principal means of compliance with those re quirements may be found in CS-26, which, in turn, refers to this AMC. Additionally, this AMC supports (R)TCH compliance with the requirements introduced by Commission Delegated Regulation (EU) 2021/699 of 21 December 2020 on continuing structural integrity of large aeroplanes, amending Annex I (Part 21) to Commission Regulation (EU) No748/2012 . 4. DEFINITIONS AND ACRONYMS ( a) For the purposes of this AMC, the following definitions apply: Airworthiness limitation section (ALS) means a section in the instructions for continued airworthiness, as required by points 21.A.61, 21.A.107 and 21.A.120A of Annex I (Part 21) to Regulation (EU) No 748/2012 , which contains airworthiness limitations that set out each mandatory replacement time, inspection interval and related inspection procedure. Baseline structure refers to the structure that is designed under the type certificate for that aeroplane model (that is, the ‘as delivered aeroplane model configuration’).