Appendix 3 to AMC 20-20A Guidelines for establishing instructions for continued airworthiness of structural repairs and modifications

1.         INTRODUCTION

With an SSID, CPCP,mandatory modifications and an LOVin place, an individual aircraft may still not meet the intended level of airworthiness for ageing aircraft structures. Repairs and modifications to aircraft structure also warrantinvestigation. It is recommended that for large transport aeroplanes, all repairs and modifications that affect the FCS should be assessed using some form of damage-tolerance-based evaluation. A regulatory requirement for damagetolerance was not applied to aeroplane design types certified before 1978, and even after this time, the implementation of DTE on repairs and modifications was not consistent. Therefore, the damagetolerance characteristics of repairs and modifications may vary widely and are largely unknown. In view of these concerns, it is necessary to perform an assessment of the repairs and modifications on certain aircraft in service to establish their damagetolerance characteristics. Further information on the background to the need for damage‑tolerance‑based inspection programmes for repairs is provided in Annex 6 to this Appendix.

Repairs and modifications to aeroplanes certified to JAR 25 Change 7 or 14 CFR 25 Amendment 45 or later must comply with the fatigue and damage tolerance requirements of their certification basis. In addition, points 26.307, 26.308, 26.309, 26.332 to 26.334 and 26.370 of Part-26 define additional requirements for certain repairs and modifications that must be addressed using the damage tolerance methodology.

In cases where a new DTE is performed by DAHs to comply with points 26.333 and 26.334 of Part-26 for existing changes or for new changes or repairs, according to CS 25.571 Amendment 18 or earlier amendments, the DTE and development of DTI should take into account the cracking scenarios that could reasonably be expected to occur in the remaining operational lifetime of the aeroplane into which the repair or modification can be incorporated.

2.         DEFINITIONS

See paragraph 4 of this AMC.

3.         ESTABLISHMENT OF A DAMAGE-TOLERANCE-BASED INSPECTION PROGRAMME FOR REPAIRS AFFECTING FCS

3.1       Overview of the TCH tasks for repairs that may affect the FCBS

(a)       Identify the affected aircraft model, models, aircraft serial numbers, and DSG stated as a number of flight cycles, flight hours, or both.

(b)      Identify the certification level.

(c)       Identify and develop a list of FCBS.

(d)      Submit the list of FCBS to EASA for approval, and make it available to operators and STCHs.

(e)      Review and update published repair data as necessary.

(f)       Submit any new or updated published repair data to EASA for approval (or approve the data in accordance with Subpart M of Part 21), and make it available to operators.

(g)       Develop REGs and submit them to EASA for approval, and make the approved REGs available to operators.

3.2.                  Certification level

In order to understand what data is required, the TCH should identify the amendment level of the original aircraft certification relative to CS 25.571. The amendment level is useful in identifying what DT data may be available and what standard should be used for developing new DT data. The two relevant aircraft groups are:

Group A     Aircraft certified to CAR 4b or 14 CFR § 25.571, prior to Amendment 25-45 or JAR 25 Change 7 or equivalent. These aircraft were not evaluated for damage tolerance as part of the original type certification. Unless previously accomplished, existing and future repairs to FCBS will need DT data to be developed.

Group B      Aircraft certified to JAR 25 Change 7 or 14 CFR § 25.571, Amendment 25-45 or later. These aircraft were evaluated for damage tolerance as part of the original type certification. As noted in the introduction, some of these repairs may not have repair data that includes appropriate DTI and the TCH and operators may need to identify and perform a DTE of these repairs and develop DTIs.

3.3.     Identifying fatigue-critical baseline structure (FCBS)

TC holders should identify and make available to operators a list of baseline structure that is susceptible to fatigue cracking that could contribute to a catastrophic failure. The term ‘baseline’ refers to the structure that is designed under the original type certificate or amended type certificate for that aircraft model (that is, the ‘as delivered aircraft model configuration’). Guidance for identifying this structure can be found in CS-25 AMC 25.571. This structure is referred to in this AMC as ‘fatigue-critical baseline structure.’ The purpose of requiring identification and listing of FCS is to provide operators with a tool that will help in evaluating existing and future repairs or modifications. In this context, FCS is any structure that is susceptible to fatigue that could contribute to a catastrophic failure, and should be subject to a DTE. The DTE would determine if DTIs need to be established for the repaired or modified structure. For the purpose of this AMC, structure that is modified after aircraft delivery from the TCH is not considered to be ‘baseline’ structure.

CS 25.571(a) states ‘An evaluation of the strength, detail design, and fabrication must show that catastrophic failure due to fatigue environmental and accidental damage,will be avoided throughout the operational life of the aeroplane. This evaluation must be conducted…for each part of the structure which could contribute to a catastrophic failure (such as wing, empennage, control surfaces, fuselage, engine mounts, and their related primary attachments)…’.When identifying FCBS, it is not sufficient to consider only that structure identified in the SSID or ALS. Some SSIDs or ALSs might only include supplemental inspections of the most highly stressed elements of the FCBS. An SSID or ALS often refers to this structure as a PSE. If repaired, other areas of structure not identified as a PSE in the SSID or ALS may require supplemental inspections. The term PSE has, at times, been interpreted narrowly by industry. The narrow application of the term PSE could incorrectly limit the scope of the structure that would be considered relative to fatigue if repairs or modifications exist or are madesubsequently. The relationship between PSE and FCS could vary significantly depending on the TCH’s working definition of PSE. In addition, there may be structure whose failure would be catastrophic, but due to low operational loads on the part, the part will not experience fatigue cracking. However, if the subject part is repaired or modified, the stresses in the part may be increased to a level where it is now susceptible to fatigue cracking. These types of parts should be considered as FCS.

TCHs should develop the list of FCBS and it should include the locations of the FCS and a diagram showing the extent of the FCS. TCHs should make the list available to STCHs and to operators.

Note: Typically, for the purposes of compliance with Part-26 related to FCS, it is not expected that composite structures will be identified as FCS; however, metallic repairs/changes to composites may be FCSs. If composite structures on a type design are found to be susceptible to fatigue cracking, this should be discussed with EASA under the CAW procedures. With the increase in the use of composites, EASA will monitor the adequacy of existing structural integrity programmes for composite structures, including repairs.

3.4.     Certification standard applied when performing a DTE

For Group A aircraft, the TCH should use the requirements of JAR 25.571 Change 7 or 14 CFR § 25.571, at Amendment 25-45, as a minimum standard. For Group B aircraft, the TCH should use the requirements that correspond to the original certification basis as a minimum standard. For each repair requiring a DTE, the DAH should apply not less than the minimum standard when developing new or revised DT data. The certification standard applied by the TCH in performing a DTE for repairs should be identified in the Part-26 compliance documentation submitted to EASA, and applicable Part-26 paragraphs clearly referenced in the approved documentation provided to the operator.

3.5.     Performing a DTE on a repair that affects FCBS

When performing a DTE on a repair that affects the FCBS, the DTE would apply to the affected FCBS and repair. This may consist of an individual analysis or the application of a DT-based process such as RAGs that would be used by an operator. The result of the DTE should lead to developing DTIs that address any adverse effects the repair may have on the FCBS. If the DTE results determine that DTIs are not required to ensure the continued airworthiness of the affected FCBS, the TCH should note that in the DTE documentation.

The term ‘adverse effects’ refers to a degradation in the fatigue life or inspectability of the affected FCBS. Degradation in fatigue life (earlier occurrence of critical fatigue cracking) may result from an increase in internal loading, while degradation of inspectability may result from physical changes made to the structure. The DTE should be performed within a time frame that ensures the continued airworthiness of the affected FCBS.

3.6.     Review of published repair data

Published repair data are generally applicable instructions for accomplishing repairs, such as those contained in SRMs and SBs. TCHs should review their existing repair data and identify each repair that affects the FCBS. For each such repair, unless previously accomplished, the TCH must perform a DTE and develop any necessary DTI for the affected FCBS and repair data. For some repairs, the results of the DTE will conclude that no new DTI will be required for the affected FCBS or repair. For these cases, the TCH should provide a means that informs the operator that a DTE was performed for the subject repair. This may be accomplished, for example, by providing a statement in a document, such as an SRM, stating that all repairs contained in this manual have had a DTE performed. This should preclude operators from questioning those repairs that do not have DTIs. TCHs should provide a list of their published repair data to operators and a statement that a DTE has been performed on this data. The following examples of published repair data developed by the TCH should be reviewed and included in this list:

(a)       SRMs,

(b)      SBs,

(c)       documents containing AD-mandated repairs, and

(d)      other documents available to operators (e.g. some sections of aircraft maintenance manuals and component maintenance manuals) that may contain approved repair data.

3.7.     Developing DT data for existing published repair data

3.7.1. SRMs

The TCH should review the repair data contained in each SRM and identify repairs that affect FCBS. For these repairs, the TCH will need to determine if the SRM needs revising to provide adequate DTI. In determining the extent to which an SRM may need to be revised for compliance, consider the following:

(a)       Whether the existing SRM contains an adequate description of DTIs for the specific model.

(b)       Whether normal maintenance procedures (e.g. the inspection threshold and/or existing normal maintenance inspections) are adequate to ensure the continued airworthiness (inspectability) is equal to the unrepaired surrounding structure.

(c)       Whether SRM Chapter 51 standard repairs have a DTE.

(d)       Whether all SRM-specific repairs affecting FCBS have had a DTE performed.

(e)       Whether there is any guidance on proximity of repairs.

(f)        Whether existing superseded repairs are addressed and how a DTE will be performed for repairs that are likely to be superseded in the future and how any DTI will be made available.

3.7.2. SBs

The TCH should review the repair data contained in its SBs (See Annex 4) and identify those repairs that affect FCBS. For those repairs, the TCH should then determine if a new DTE will need to be performed. This review may be done in conjunction with the review of SBs for modifications that affect FCBS.

3.7.3. ADs

The TCH should review ADs that provide maintenance instructions to repair FCBS and determine if the instructions include any necessary DT data. While maintenance instructions supporting ADs are typically contained in SBs, other means of documentation may be used.

3.7.4. Other forms of data transmission

In addition to SRMs, SBs, and documentation for ADs, the TCH should review any other documents (e.g. aircraft maintenance manuals and component maintenance manuals) that contain approved repair data. Individual repair data not contained in the above documents will be identified and DT data obtained through the REGs process.

3.8.     Developing DT data for future published repair data

Following the completion of the review and revision of existing published data, any subsequent repair data proposed for publication should also be subject to DTE and DTI provided.

3.9.     Approval of DT data developed for published repair data

For existing published repair data that requires new DT data for repairs affecting the FCBS, the TCH should submit the revised documentation to EASA for approval unless otherwise agreed in the compliance plan approved in accordance with point 26.301 of Part-26. For instance, it may be agreed that the data can be approved according to an existing or a modified process utilising the Part 21 DOA privileges for repair approval of the TCH. The DT data for future published repair data may be approved according to existing processes.

3.10.   Documentation of DT data developed for published repair data

TCHs should include the means used to document any new DTI developed for published repair data. For example, in lieu of revising individual SBs, the TCH may choose to establish a collector document that would contain new DTI developed and approved for specific repairs contained in various SBs.

3.11.   Existing repairs

TCHs should develop processes that will enable operators to identify and obtain DTI for existing repairs on their aircraft that affect FCBS. Collectively, these processes are referred to as the REGs and are addressed in subparagraph 3.13.

According to point 26.309 of Part-26, REGs are required for aircraft for which the TC was issued prior to 11 January 2008. Derivatives of aircraft for which the original TC was issued prior to 11 January 2008 where only part of the structure is certified to CS-25 Amdt 1 or later should have REGs that address the whole structure, due to the risk that subsequent repairs may have been implemented without adequate knowledge of the applicability of the certification basis to the various areas of the structure.

3.12.   Future repairs

Future repairs to FCS must have a DTE performed in accordance with Part 21 and the applicable certification basis. This includes blend-outs, trim-outs, etc., that are beyond published limits. For new repairs, the applicant may, in conjunction with an operator, use the three-stage approval process provided in Annex 1to this Appendix. This process involves incremental approval of certain engineering data to allow an operator to return its aircraft to service before all DT data is developed and approved. The applicant should document this process and the operator should reference it in their maintenance programme if it is intended to apply it.

3.13.   Repair evaluation guidelines

REGs provide instructions to the operator on how to survey aircraft, how to obtain DTI, and an implementation schedule that provides timelines for these actions. Effective REGs may require that certain DT data be developed by the TCH and made available to operators. Updated SRMs and SBs, together with the existing, expanded, or new RAG documents, form the core of the information that will need to be made available to the operator to support this process. In developing REGs the TCH will need to determine what DT data is currently available for repairs and what new DT data will need to be developed to support operator compliance. REGs should include:

(a)       a process for conducting surveys of affected aircraft that will enable identification and documentation of all existing reinforcing repairs that affect FCBS;

(b)      a process for obtaining DTI for repairs affecting FCBS that are identified during an aircraft survey; and

(c)       an implementation schedule that provides timelines for:

(1)       conducting aircraft surveys,

(2)       obtaining DTI, and

(3)       incorporating DTI into the operator’s maintenance programme.

3.13.1.Implementation schedule

(a)       Theschedule provided in this Section is applicable to REGs produced in compliance with point 26.309 of Part-26. In cases where REGs are deemed necessary, the TCH should propose a schedule for approval by EASA that takes into account the distribution of the fleet relative to ¾ DSG, the extent of the work involved, and the airworthiness risk. Aircraft fleets approaching orexceeding their DSGs should be given priority in the implementation schedule.

(b)       Survey schedule for EASA-approved REGs applicable to aircraft maintained under Part-M

The following basis for accomplishing the aircraft repair assessment survey is approved by EASA and may be used by operators maintaining aircraft according to the Part-M and Part-26 requirements:

The repair survey, the first step of the repair assessment, must be carried out at the earliest convenient opportunity (e.g. the next heavy maintenance check). In addition, the implementation of the surveys across the fleet must be achieved without exceeding the DSG or a period of 7 years following the approval by EASA of these REGs, whichever occurs later. By adhering to these timescales, the REGs are acceptable to EASA for use by operators needing to demonstrate compliance with point 26.370(a)(ii) of Part-26.

To ensure that the TCH can support the operators’ requests for data following the survey, operators should not defer the implementation of the programme across their fleet until the end of the allowed time period.

(c)       Obtaining DTIs and incorporation of DTIs into the maintenance programme must be completed as follows:

For existing, non-published repairs and deviations from published repairs identified in the survey, if the REGs direct operators to contact the TCH to obtain DTIs, the TCH should approve the DTIs within 12 months after identification, unless the TCH uses another process agreed by EASA. To facilitate this, the operator should provide the TCH with that request and the associated information within 3 months from the identification.

For repairs covered by the TCH’s published repair data, operators should obtain and incorporate into their maintenance programmes DTIs for existing repairs within 6 months after accomplishing the aeroplane survey. For non‑published repairs found during the survey, the incorporation should be completed no later than 6 months after the approval of the data (see Annex 2 to this Appendix for the DTI assessment process).

3.13.2.Developing a process for conducting surveys of affected aircraft

The TCH should develop a process for use by operators to conduct aircraft surveys. These aircraft surveys are conducted by operators to identify and document repairs and repairs to modifications that may be installed on their aircraft. Surveys are intended to help the operators determine which repairs may need a DTE in order to establish the need for DTI. Identification of repairs that need DTI should encompass only existing reinforcingrepairs i.e. those repairs that reinforce and restore the strength of the FCBS. This typically excludes maintenance actions such as blend-outs, plug rivets, trim-outs, etc. The process the TCH develops to conduct surveys should include:

(a)       a survey schedule;

(b)       areas and access provisions for the survey;

(c)       a procedure for repair data collection that includes:

(1)       repair dimensions,

(2)       repair material,

(3)       repair fastener type,

(4)       repair location,

(5)       repair proximity to other repairs,

(6)       repairs covered by published repair data, and

(7)       repairs requiring DTI;

(d)       a means to determine whether a repair affects FCBS or not.

3.13.3.Developing a process to obtain DT data for repairs

(a)       The TCH must develop a process that operators can use to obtain DTIs that address the adverse effects that repairs may have on FCBS. In developing this process, TCHs will need to identify all applicable DTIs they have developed that are available to operators.This may include updated SRMs and SBs, existing RAGs, expanded or new RAGs, and other sources of DTIs developed by the TCH. For certain repairs, the process may instruct the operators to obtain direct support from the TCH. In this case, the TCH evaluates the operator’s request and makes available the DTI for a specific repair or group of repairs, as needed. These may include operator or third‑party developed/approved repairs, and repairs that deviate from approved published repair data.

(b)       The process should state that existing repairs that already have DTIs developed and in place in the maintenance programme require no further action. For existing repairs identified during an individual aircraft survey that need DTIs established, the process may direct the operators to obtain the required DTIs from the following sources:

(1)       TCH-published service information such as DT-based SRMs, SBs, or other documents containing applicable DT data for repairs.

(2)       Existing approved RAG documents (developed for compliance with SFAR § 121.107).

(3)       Expanded or newly developed RAG documents. In order to expedite the process for an operator to obtain the necessary DTI to address the adverse affects that repairs may have on FCBS, the TCH may determine that the existing RAG document should be expanded to address other FCBS of the aircraft’s pressure boundary. In addition, for aircraft that do not currently have a RAG, the TCH may determine that in order to fully support operators in obtaining DTIs, a new RAG document may need to be developed. General guidance for developing this material can be found in Annex 2 below, which is similar to FAA AC 120-73, Damage Tolerance Assessment of Repairs to Pressurised Fuselages.

(4)       Procedures developed to enable operators to establish DTIs without having to contact the TCH for direct support. These procedures may be similar in concept to the RAG documents.

(5)       Direct support from the TCH for certain repairs. The operator directly solicits DTIs from a TCH for certain individual repairs as those repairs are identified during the survey.

3.14    Repairs to removable structural components

FCS may include structure on removable structural parts or assemblies that can be exchanged from one aircraft to another, such as door assemblies and flight control surfaces. In principle, the DT data development and implementation process also applies to repairs to FCS on removable components. During their life history, however, these parts may not have had their flight times recorded on an individual component level because they have been removed and reinstalled on different aircraft multiple times. These actions may make it impossible to determine the component’s age or total flight hours or total flight cycles. In these situations, guidance for developing and implementing DT data for existing and new repairs is provided in Annex 3to this Appendix. Additional guidance to assist in controlling and/or tracking certain maintenance requirements on removable structure components might be found in A4A Spec 120[10] ‘Removable Structural Components Industry Guidelines’.

3.15    Training

The complexity of the repair assessment and evaluation may require adequate training for proper implementation. In that case, it is necessary that each TCH consider providing training for all operators of the aircraft considered by this AMC

4.         MODIFICATIONS AND REPAIRS TO MODIFICATIONS(COMPLIANCE WITH POINTS 26.307,26.308 AND 26.332 TO 26.334 OF PART-26)

4.1.     TCH and STCH tasks — Modifications and repairs to modifications

The following is an overview of the TCH and STCH tasks necessary for modifications that affect FCBS. This overview also includes TCH and STCH tasks necessary for repairs that may affect any FCS of the subject modifications. These tasks are applicable to those modifications that have been developed by the TCH or STCH.

(a)       Establish a list of modifications that may affect FCBS. From that list establish a list of modifications that may contain FCS.

(b)      In consultation with operators, determine which aircraft have the modification(s) installed.

(c)       STCHs should obtain a list of FCBS from the TCH for the aircraft models identified above.

(d)      STCHs should identify:

—        modifications that affect FCBS, or

—        modifications that contain FCS.

(e)      Determine if DT data exists for the identified modifications.

(f)       Develop additional DT data, if necessary.

(g)       Establish an implementation schedule for DTI for modifications.

(h)      Review existing DT data for published repairs made to modifications that affect FCBS.

(i)        Develop additional DT data for published repairs made to modifications that affect FCBS.

(j)        Establish an implementation schedule for DTI for published repairs made to modifications.

(k)       Prepare documentation, submit it to EASA for approval, and make it available to operators.

4.2.     Specific modifications to be considered

The TCH should consider modifications and any STCs they own for modifications that fall into any of the categories listed in Annex 5to this Appendix. STCHs should do the same for their STC modifications. For modifications that are not developed by a TCH or STCH, the operator should consider whether the modification falls into any of the categories listed in Annex 5to this Appendix.

4.3.     Modifications and published repairs affecting those modificationsthat need DT data

Using the guidance provided in AMC 25.571 and the detailed knowledge of the modification and its effect on the FCBS, the TCH or STCH, or in certain cases the operator, should consider the following situations in determining what DT data needs to be developed.

4.3.1. Modifications that affect FCBS

Any modification identified in Annex 5 that is installed on FCBS should be evaluated regardless of the size or complexity of the modification. In addition, any modification which indirectly affects FCBS (e.g. modifications which change the fatigue loads environment, or affect the inspectability of the structure, etc.) must also have a DTE performed to assess its impact.

4.3.2. Modifications that contain new FCS

For any modification identified in Annex 5to this Appendix that affects FCBS, the TCH or STCH should identify any FCS of the modification. Any modification that contains new FCS should be evaluated regardless of the size or complexity of the modification. Examples of this type of modification may be a modification that adds new structural splices, or increases the operational loads causing existing structure to become fatigue critical. If a modification does not affect FCBS, then it can be assumed that this modification does not contain FCS.

4.3.3   Published repairs affecting modifications to FCS

Published repair data are generally applicable instructions for accomplishing repairs, such as those contained in SRMs and SBs. TCHs and STCHs should review their existing repair data and identify each repair that affects FCMS. The following examples of published repair data developed by the TCHs and STCHs should be reviewed and included in this list:

(a)       SRMs,

(b)       SBs,

(c)       documents containing AD-mandated repairs, and

(d)       other documents available to operators (e.g. some sections of aircraft maintenance manuals and component maintenance manuals) that may contain approved repair data.

4.4.     Reviewing existing DT data for modifications that affect FCBS

Based on the CS 25.571 certification amendment level and other existing rules, the modification’s approval documentation may already provide appropriate DT data.

The TCH or STCH should identify modifications that have existing approved DT data. Acceptable DT data contains a statement of DTE accomplishment and are approved. Confirmation that approved DT data exists should be provided to the operators.

Modifications that have been developed by a TCH may affect FCBS. These include design changes and in some cases STCs. These changes to type design also require review for appropriate DT data.

4.5.     Developing additional DT data for modifications that affect FCBS

DT data may be submitted for approval and published as follows:

(a)       STC modifications:Additional DT data for existing modifications may be approved as a change to an existing STC by the STCH and published, for example, as a supplement to the ALS. Alternatively, an application can be made to EASA in order for the data to be submitted to EASA in the form of a specific Part-26 compliance document, and the resulting approved DTI made available to operators.

(b)      TC holder modifications:Additional DT data for existing modifications may be published in the form of a revised ALS, an SSID and TCH service information.

Note: The TCH and STCH should submit data to EASA that describes and supports the means used to determine whether a modification affects FCBS, and the means used for establishing FCS of a modification.

(c)       Modifications not developed by a TCH or STCH: For modifications identified in Annex 5to this Appendix that affect FCBS and were not developed by a TCH or STCH, the operator is responsible for obtaining DT data for those modifications. Operators may establish agreements with DAHs for those existing individual modifications that do not have DT data or other procedures implemented. In cooperation with the operator, the DAH should establish DT data according to an implementation plan approved by the competent authority with respect to the maintenance programme. Part-26 and CS-26 provide critical timelines for this activity.

(d)      In cases where the threshold inspection of the DTI is likely to have been or soon will be exceeded by the fleet leaders, an implementation schedule will be needed.

Typically, the proposed grace period should not exceed 24 months.

The approval of the DT data will be according to a process agreed by EASA.

The process for operators to obtain the data and the implementation schedule should follow that given in paragraph 6.

4.6.     Developing additional DT data for published repairs that affect FCMS

For each such repair, unless previously accomplished, the TCH or other DAH must perform a DTE and develop any necessary DTI for the affected FCBS, and repair data. For some repairs, the results of the DTE will conclude that no new DTI will be required for the affected FCBS or repair. For these cases, the TCH or other DAH should provide a means that informs the operator that a DTE was performed for the subject repair. This may be accomplished, for example, by providing a statement in a document, such as an SRM, stating that ‘all the repairs contained in this manual have had a DTE performed’. This is intended to assist operators in showing compliance with point 26.370 of Part-26 and prevent them from questioning those repairs that do not have DTIs. TCHs and other DAHs should provide a list of their published repair data to operators, and a statement that a DTE has been performed on this data.

5.         DEVELOPMENT OF TCH AND STCH DOCUMENTATION AND EASA APPROVAL

TCH, STCHs, operators and the airworthiness authorities should work together to develop model-specific documentation with oversight provided by those authorities and assistance from the ARAC AAWG. It is anticipated that TCHs will utilise structural task groups (STGs) to support their development of model-specific documents. EASA will approve the TCH or STCH submissions of the REGs and any other associated documentation required by Part-26. In order to facilitate operators’ compliance with Part-26, the DAHs may find it helpful to consolidate their compliance data in as few documents as possible, or provide a guide to all the relevant DT data in a separate communication to operators.

6.         OPERATOR TASKS — REPAIRS, MODIFICATIONS AND REPAIRS TO MODIFICATIONSINSUPPORT OF COMPLIANCE WITH POINT 26.370 OF PART-26 AND CS 26.370

This paragraph provides guidance to operators for developing a means for addressing the adverse effects that repairs and modifications may have on FCS. The guidance supports operators that need to comply with point 26.370 of Part-26, and explains how operators can develop an implementation plan to obtain and implement all the applicable DT data for modifications and repairs when using CS 26.370 as a means of compliance. The plan will contain processes and timelines for operators to use, for obtaining and incorporating into their maintenance programme, DTIs that address the adverse effects of repairs and modifications.

Operators will need to determine how they will obtain the information necessary to develop the plan by considering the following conditions:

(a)       The operator processes ensure that DT data for repairs and modifications affecting FCBS have been developed and all the applicable DTIs have been incorporated into the operator’s maintenance programme. If an operator is able to demonstrate that these processes have been in place and followed throughout the operational life of the aircraft for all repairs and modifications affecting FCBS, then no further action is required for existing repairs and modifications

(b)       The TCH or STCH or other DAH exists and will make the DTIs available to the operator automatically or upon request according to points 26.333 and 36.334 of Part-26 respectively.

(c)       DTIs already exist and are available.

(d)       DTIs are not available from the TCH or STCH or other DAH;

(e)       DTIs are not available for modifications developed by organisations other than TCH or STC holders (e.g. major changes approved under FAA Form 337, accepted under the EU‑USA bilateral agreement, but that were approved before 14 CFR Part-26 became applicable).

Figure A3-1 below outlines an overview of developing a means of compliance for modifications to be addressed by STCHs/TCHs and operators in order to comply with points 26.306 to 26.309, 26.332 to 26.334 and 26.370 of Part-26.

6.1.     Contents of the maintenance programme

(a)       The operator’s maintenance programme should contain or refer to an implementation plan that ensures that:

(1)       all new repairs and modifications that affect FCBS will have DT data and DTI or other procedures implemented;

(2)       all existing repairs and modifications to FCBS have been or will be evaluated for damage tolerance and have DTI or other procedures implemented. In the context of this implementation plan, there should be a process that:

(i)        reviews operator processes to determine if DT data for repairs and modifications affecting FCBS have been developed and incorporated into the operator’s maintenance programme for the operational life of the aircraft. If an operator is able to demonstrate that these processes ensure that DT data is developed for all repairs and modifications affecting FCBS, then no further action is required for existing repairs and modifications.

(ii)       identifies or surveys existing repairs (using the applicable REGs or survey parameters from Annex 2 to this Appendix) and modifications that affect FCBS and obtain and implement DTI for those repairs and modifications. This should include an implementation schedule that provides timing for incorporation of the DT data into the operator’s maintenance programme, within the timeframe given in the applicable TCH or STCH’s approved documentation.

(b)      Figure A3-2 below outlines one possible means that an operator can use to develop an implementation plan for aircraft in their fleet.

Figure A3-2: Operator’s maintenance programme approval process

6.1.1.  Implementation plan for repairs

Except as described in CS 26.370, the maintenance programme should include a repair survey schedule to identify repairs that may need DT data developed. The TCH’s REGs may be used as a basis for this plan. (See Paragraph 3.13 above and Annex 2 for further information)

6.1.2. Implementation plan and actions for modifications

(a)       Points 26.307, 26.308, 26.333 and 26.334 of Part-26 require DAHs to develop DTI for existing modifications (design changes) within a certain timescale. CS 26.370 provides means of compliance to operators on how to revise the maintenance programme by including an implementation plan to show how approved DTI data will be obtained and used to address the potential adverse effects of repairs and modifications to FCS and submit it for approval to the competent authority. To show compliance with CS 26.370, operators are first requested to develop a list of modifications affecting FCBS through a review of the aircraft records. The operator will need to show to their competent authority that the aircraft records are a reliable means for identifying modifications that affect FCBS. The aircraft records, in conjunction with data provided by the DAH, may also be sufficient to help identify whether DTI exists for all modifications. However, for some older aircraft, a review of records alone may not always be adequate to identify all the modifications that have an adverse effect on FCBS, or be sufficient to establish whether a DTE has been accomplished and DTI is complete, without requesting such information from the DAH. Physical inspection of the aircraft may help establish the scope of the modification if it is unclear from the records. Finally, the aircraft survey for repairs may also identify modifications affecting FCS, which should then be evaluated and DTI obtained as necessary in accordance with CS 26.370(h).

(b)                   To support identification of modifications that need to be addressed, operators should — concurrently with the TCH and STCHs’ tasks — identify the TCH or STC or other approval holder-developed modifications that exist in their aircraft fleets.To support compliance with point 26.370 of Part-26 as envisaged in CS 26.370, operators should perform the following tasks:

(1)       From the review of records, compile a listing of all TCH and STCH‑developed modifications that are currently installed on their fleet.

(2)       Delete from the listing those modifications that do not affect FCBS. Documents from the TCH may be used to identify the FCBS.

Note: In order to ensure timely compliance with point 26.370 of Part‑26, operators should begin developing the list of modifications that affect FCBS, for each affected aircraft in the fleet, as soon as the TCHs make their FCBS listing available.

(3)       The modifications that affect FCBSmust be reviewed to determine whether:

(i)        DT data already exists in the maintenance programme, or is available and is complete; or

(ii)       DT data needs to be developed.

(4)       For DT data that is complete, the operator should incorporate it into the maintenance programme and implement it according to the schedule provided in 6.1.3 or as otherwise agreed by the competent authority. Note: Complete DTI for STCs approved after 1 September 2003 should be available to operators not later than 30 months after the date of applicability of point 26.370 of Part-26 following approval by EASA unless the STCH no longer exists.

(5)       For DT data that is not available or is incomplete 30 months after the date of applicability of point 26.370 of Part-26, the operator should ensure that the plan developed according to CS 26.370 will address each affected modification.

(6)       Where DT data is not available or is incomplete, the operator should notify both the STCH or a third party that DT data for the modification is required.

(7)       Establish whether the STCH or a third party will provide the data.

Note: For modifications addressed by point 26.334 of Part-26 (for change approvals issued before 1 September 2003), the DAH does not need to develop the DT data until requested by an operator and has 24 months from that date to submit the data for approval. It is therefore envisaged that DTI for these modifications will be addressed in accordance with paragraph (8) and the timescales of  26.370 (h). Whatever the approval date of the change, the operator is responsible for obtaining the DTI from the approval holder once it becomes available. It is therefore recommended that the operator contacts the approval holder or a third party as soon as possible after identifying a modification that affects FCBS to establish when the DTI will become available.

(8)       For those modifications where the DTI will not be incorporated into the maintenance programme within 36 months from the date of applicability of point 26.370(a)(ii) of Part-26, the operator’s DT data implementation plan should contain the following information:

(i)        a description of the modification;

(ii)       the affected aircraft and the affected FCS;

(iii)      the DSG of the affected aircraft;

(iv)      a list of the FCS introduced by the modification (if it exists);

(v)       the CS 25.571 certification level for determining the DT data;

(vi)      a plan for obtaining DT data for each modification (e.g. reliance on the existing STCH or a formal contract with a Part 21‑Subpart J-approved third party) to produce DT data within a specified compliance time in accordance with CS 26.370;

(vii)     a DT data implementation schedule for incorporating the DT data into the maintenance programme once it is received;

(viii)    a means of ensuring that the aircraft will not be operated beyond the time limit established for obtaining DT data.

(9)       For modifications that are found during the aircraft survey for repairs, the operator should ensure that DT data is obtained and submitted to EASA for approval. Once approved, the operator should incorporate the DTIs into its maintenance programme no later than 12 months from the date when the modification was identified.

6.1.3. Implementation of DTI

Operators should accomplish the first inspection of a change according to the approved DTI implementation schedule. If the age of the modification is unknown, the operator should use the aircraft age in total flight cycles or total flight hours, as applicable. Where there is any doubt about the applicability of the programme data or the timescales provided in the DAH documentation, EASA should be consulted by the operators and competent authorities concerned.

7.         ROLE OF THE COMPETENT AUTHORITY

The competent authority’s role is to verify that the AMP is in compliance with point 26.370 of Part-26 and ensure that their aircraft continuing airworthiness monitoring survey programme takes into account the risks associated with potential non-compliance of operators’ or owners’ AMPs with the requirements of point 26.370 of Part-26. (Ref. Part-M requirements for the Competent Authority (M.B.301 and 303)).

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