(b) Identification of repairs that affect FCBS.
(2) A process operators can use to determine how to obtain DTI for those repairs identified in the survey that affect FCBS.
(3) An implementation schedule for existing repairs that provides timelines for the following:
(a) An operator conducting the airplane survey(s);
(b) TC Holder making the DTI for repairs available to operators (if the operator obtains DTI from the TC Holder); and
(c) Operator incorporating into the airplane maintenance program the DTI for repairs that affect FCBS identified in the airplane survey.
Figure 1, below, shows the process for producing a Compliance Document for repairs that affect FCBS.
Identify Airplane Info FCBS list Compliance Doc
• Airplane info
• FCBS list (or reference to doc.)
• DTI for Published Repair Data (or reference to doc.)
• Repair Evaluation Guidelines ID, review, update Published Repair Data Develop expanded or new RAG document (if necessary) REG
• Survey process
• Process to obtain DTI
• Implementation schedule ACO Operator Compliance Plan
• Airplane info
• Milestones / means of compliance for o List of FCBS o DT Data for Published Repair Data o REG Means to address repairs that affect FCBS PMI Approval = Compliance with AASR TCH December 20, 2010 December 30, 2009 90 days from effective date of rule.
180 days from eff. date of rule
June 30, 2009 STG Activity STG Activity § 26.43(c) § 26.43(d) § 26.43(f) § 26.49 TC Holder Tasks for Repairs
Figure 1 - TC Holder Tasks for Repairs
202. Applicability. The airplane make, model, model variations or serial numbers, gross weights, certification amendment level, and design service goal (DSG) should be identified in the Compliance Document. For each model of airplane, the TC Holder will identify the DSG and work with the operators (see paragraphs 105d and 201a of this AC) to identify the information operators will need for compliance with parts 121 and 129. The established DSG for a particular airplane type should be representative of the airplane, considering the probable variation of the number of flight hours per cycle that could exist in the fleet.
203. Certification Level. In order to understand what data are required, the TC Holder should identify the amendment level of the original certification relative to § 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 airplane groups are:
a. Group A - Airplanes certified to CAR 4b or § 25.571, prior to Amendment 25-45.
These airplanes were not evaluated for damage tolerance as part of the original type certification. Therefore, the requirements of the AASFR are beyond the scope of the original certification amendment level. Unless previously accomplished, existing and future repairs to FCBS will need DT Data developed.
b. Group B - Airplanes certified to § 25.571, Amendment 25-45 or later. These airplanes were evaluated for damage tolerance as part of the original type certification. Repairs to these airplanes will need to meet their certification level. Some of these repairs may not have repair data that includes DTI and the TC Holder and operators may need to identify and perform a DTE of these repairs and develop DTI.
204. Identifying Fatigue Critical Baseline Structure (FCBS). TC Holders must identify and make available 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 airplane model (that is, the as delivered airplane model configuration). Guidance for identifying this structure can be found in AC 25.571-1C, Damage Tolerance and Fatigue Evaluation of Structure, dated April 29, 1998, or current revision. This structure is referred to as “fatigue critical baseline structure.” The purpose of requiring identification and listing of fatigue critical structure (FCS) under the Design Approval Holder DT Data Rule is to provide operators with a tool that will help in evaluating existing and future repairs or alterations. In this context, fatigue critical structure is any structure that is susceptible to fatigue that could contribute to a catastrophic failure, and should be subject to a damage tolerance evaluation (DTE). The DTE would determine if DTIs need to be established for the repaired or altered structure. For the purpose of this AC, structure that is altered after airplane delivery from the TC Holder is not considered to be “baseline” structure.
a. The intent of the AASFR is to address the same structure that is required to be evaluated for damage tolerance for original type design compliance with § 25.571. Section 25.571(a) states “An evaluation of the strength, detail design, and fabrication must show that catastrophic failure due to fatigue…will be avoided throughout the operational life of the airplane. 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 supplemental structural inspection document (SSID) or airworthiness limitation section (ALS). Some SSIDs or ALSs might only include supplemental inspections of the most highly stressed elements of the FCBS. A SSID and ALS often refer to this structure as a Principal Structural Element (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 applied 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 alterations exist or are subsequently made. The relationship between PSE and FCS could vary significantly depending on the TC Holder’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 altered, 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.
b. TC Holders must develop the list of FCBS (§ 26.43(b)) and include the locations of FCS and a diagram showing the extent of FCS, and submit it to the FAA Oversight Office for review and approval by the date specified in § 26.43(f)(1). Upon approval, the TC Holders must make the list available to STC Holders and to operators. While the list will be submitted to the FAA before the Compliance Document submittal, the list or a reference to the list should also be included in the Compliance Document.
205. Certification Standard Applied When Performing a DTE. When developing DT Data, the certification level of the affected airplane determines the standard for performing the DTE. For Group A airplanes, as identified in paragraph 203 of this AC, the TC Holder should use the requirements of § 25.571, at Amendment 25-45, as a minimum standard. For Group B airplanes, the TC Holder should use the requirements that correspond to the original certification level as a minimum standard. For each repair requiring a DTE, the TC Holder must apply the minimum standard when developing the new DT Data required by § 26.43(c). The TC Holder may use the guidance included in AC 25.571-1C, as revised, or the revision level of that AC which is consistent with the certification amendment level. The certification standard applied by the TC Holder in performing a DTE for repairs should be provided in the modelspecific Compliance Document.
206. Performing a DTE on a Repair That Affects FCBS.
a. When performing a DTE on a repair that affects 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 Repair Assessment Guidelines that would be used by an operator.
The results of the DTE should lead to developing DTI 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 TC Holder should note that in the DTE documentation.
b. The term ‘‘adverse effects’’ refers to a degradation in the fatigue life or inspectability of the affected FCBS. Degradation in fatigue life may result from an increase in loading, while degradation of inspectability may result from physical changes made to the structure. The
DTE would be performed within a time frame that ensures the continued airworthiness of affected FCBS.
207. Review of Published Repair Data. Published repair data are generally applicable instructions for accomplishing repairs, such as those contained in structural repair manuals (SRMs) and service bulletins (SBs). These data are approved for general application to a particular airplane model or airplane configuration. TC Holders publish repair data in SRMs, SBs, or equivalent types of documents. Since operators use these data for most repairs, providing DTI in these documents would enable them to comply with the AASFR for most existing and future repairs. Section 26.43(c), Existing and future published repair data, requires the TC Holder to review its repair data and identify each repair that affects FCBS. For each such repair, unless previously accomplished, the TC Holder must perform a DTE and develop any necessary DTI for the affected FCBS and repair data. This DTI will provide operators a means for addressing these repairs for compliance with the AASFR. 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 TC Holder should provide a means that informs the operator 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.
To support TC Holder compliance with § 26.43(c), the TC Holder should include a list of its published repair data in the Compliance Document and a statement that a DTE has been performed on this data. The following examples of published repair data developed by the TC Holder must be reviewed and included in this list:
a. SRMs,
b. SBs,
c. Documents containing AD mandated repairs, and
d. Other documents available to operators (for example, airplane maintenance manuals and component maintenance manuals) containing approved repair data.
208. Developing DT Data for Existing Published Repair Data. As described in paragraph 207, above, the TC Holder must perform a DTE for all repairs specified in its existing published repair data that affect FCBS. To accomplish this, the TC Holder will need to review its published repair data and identify repair data that would affect FCBS. Once those repairs are identified, the TC Holder will need to determine if new DT Data will need to be developed for the FCBS affected by the repair and for the repair itself. In the Compliance Plan, the TC Holder should describe the process used to ensure a DTE will be performed for repairs contained in existing published repair data that affect FCBS. In the Compliance Document, the TC Holder should include the new DTI developed for published repair data or make reference to those published repair documents that are new or have been updated to include DTI for compliance with § 26.43(c).
a. SRMs. The TC Holder should review the repair data contained in each SRM and identify repairs that affect FCBS. For these repairs, the TC Holder will need to determine if
the SRM needs revising to comply with § 26.43(c). In determining the extent to which an SRM may need to be revised for compliance, consider the following:
(1) Whether the existing SRM contains an adequate description of DTIs for the specific model.
(2) Whether normal maintenance procedures (for example, the inspection threshold and/or existing normal maintenance inspections) are adequate to ensure the continued airworthiness (inspectability) equal to the unrepaired surrounding structure.
(3) Whether SRM Chapter 51 standard repairs have a DTE.
(4) Whether all SRM specific repairs affecting FCBS have had a DTE performed.
(5) Whether there is any guidance on proximity of repairs.
(6) Whether superseded repairs are addressed and how a DTE is performed for future superseded repairs and how any DTI will be made available.
b. SBs. The TC Holder should review the repair data contained in its SBs and identify those repairs that affect FCBS. For those repairs, the TC Holder should then determine if a new DTE will need to be performed for compliance with § 26.43(c). The compliance plan described in paragraph 108 of this AC should include the description of the process the TC Holder will use to determine which SBs would require development of new DT Data.
This review may be done in conjunction with the review of SBs for alterations that affect FCBS that is described in Chapter 3 of this AC.
NOTE: Alterations and repairs to alterations are addressed in Chapter 3 of this AC.
c. ADs. The TC Holder should review ADs that provide maintenance instructions to repair FCBS and determine if the instructions include any necessary DT Data. While the maintenance instructions supporting ADs are typically contained in SBs, other means of documentation may be used.
d. Other Forms of Data Transmittal. In addition to SRMs, SBs, and documentation for ADs, the TC Holder should review any other documents (for example, airplane maintenance manuals and component maintenance manuals) that contain repair data.
209. Developing DT Data for Future Published Repair Data. Section 26.43(c) requires TC Holders to perform a DTE and develop DTIs for all future repair data that affect FCBS.
Future repair data refers to data published after the effective date of § 26.43.
210. Submittal of DT Data Developed For Existing Published Repair Data. For existing published repair data described in paragraph 208 of this AC that require new DT Data for repairs affecting FCBS, the TC Holder must submit the new DT Data to the FAA Oversight Office for approval by June 30, 2009 (§ 26.43). The DT Data for future published repair data
may be approved by an FAA Designee as coordinated with and authorized by the FAA Oversight Office.
211. Submittal of DT Data Developed For Future Published Repair Data. The TC Holder must submit the DT Data to the FAA Oversight Office for approval. The DT Data for future published repair data may be approved by a FAA Designee, as coordinated with and authorized by the FAA Oversight Office. Repair data without DT Data will not be approved by the FAA.
212. Documentation of DT Data Developed for Published Repair Data. In the compliance plan, the TC Holder should include the means used to document any new DTIs developed for published repair data as required by § 26.43(c) (see paragraph 208 of this AC).
The Compliance Document should include the new DTI or reference documents containing the DTIs. For example, in lieu of revising individual SBs, the TC Holder may choose to establish a collector document that would contain new DTIs developed and approved for specific repairs contained in various SBs. Documents containing DTIs developed for compliance with the Design Approval Holder DT Data Rule would be made available to operators upon FAA approval.
213. Existing Repairs. TC Holders will be required to develop processes that will enable operators to identify and obtain DTI for existing repairs on their airplanes that affect FCBS.
Collectively, these processes are referred to as the Repair Evaluation Guidelines and are addressed in paragraph 216 of this AC. These processes should be included in the Compliance Document or in a separate document and will provide operators a means for addressing existing repairs installed on their airplanes.
214. Future Repairs. Whether or not a DTE is already required by the airplane certification level or other FAA-approved program, all new repairs installed on or after the effective date of §§ 26.43, 26.45, and 26.47, that affect FCBS must have a DTE performed. This includes blendouts, trim-outs, etc. that are beyond published TC Holder limits. For new repairs, the TC Holder may, in conjunction with an operator, use the three stage approval process provided in Appendix 5 of this AC. This process involves incremental approval of certain engineering data to allow an operator to return its airplane to service before all the DT Data are developed and approved. The TC Holder should include this process in the Compliance Document if it intends to apply it. The operator would then include this same process in its OIP as a means for addressing new repairs that adversely affect FCBS.
215. Expanded or New Repair Assessment Guidelines.
a. In order to expedite the process for an operator to obtain DTIs necessary to address the adverse affects repairs may have on FCBS, the TC Holder may determine that the existing Repair Assessment Guidelines (RAGs) document should be expanded to address other FCBS of the airplane pressure boundary. In addition, for airplanes that do not currently have a RAG, the TC Holder may determine that in order to fully support operators in obtaining DTIs, a new RAG document may need to be developed.
b. General guidance for developing this material can be found in AC 120-73, Damage Tolerance Assessment of Repairs to Pressurized Fuselages. The RAGs or any other
streamlined process developed to enable operators to obtain DTIs without having to go directly to the TC Holder will support the TC Holder’s development of the Regulatory Evaluation Guidelines (REGs) addressed in the following paragraph. As part of the REGs, the TC Holder will be required to develop a process that operators can use to determine how they may obtain DTI for a particular repair to support compliance with the AASFR. For certain airplane models a RAG will be a key component of that process.
216. Repair Evaluation Guidelines. The REGs provide instructions to the operator on how to survey airplanes, how to obtain DTIs, and an implementation schedule that provides timelines for these actions. To assist the operators in obtaining DTIs for various repairs, § 26.43(e) requires the TC Holder to develop REGs for operators’ use and submit them to the FAA Oversight Office for approval by June 30, 2009. Effective REGs may require that certain DT Data be developed by the TC Holder 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 the REGs the TC Holder will need to determine what DT Data are currently available for repairs and what new DT Data will need to be developed to support operator compliance.
The REGs may be submitted as part of the Compliance Document under a section titled “Repair Evaluation Guidelines” or as a separate document referenced in that section. The REGs should include:
a. A process for conducting surveys of affected airplanes that will enable identification and documentation of all existing repairs that affect FCBS;
b. A process for obtaining DTIs for repairs affecting FCBS that are identified during an airplane survey; and
c. An implementation schedule that provides timelines for:
(1) Conducting airplane surveys,
(2) Obtaining DTIs, and
(3) Incorporating DTIs into the operator’s maintenance program.
Paragraphs 217 through 219 of this AC describe the elements listed above in paragraphs 216(a), 216(b), and 216(c).
217. Implementation Schedule. The implementation schedule described in this paragraph represents an acceptable timeline for conducting airplane surveys. Any deviation to the timeline should be justified and presented to the FAA Oversight Office for approval. To support the operator in developing an OIP for its particular fleet of airplanes, the TC Holder should include the information contained in this section in the Compliance Document. Appendix 6 of this AC defines a process that may be used to establish timelines for assessing repairs and developing required maintenance actions. This process includes the airplane repair survey, identifying and dispositioning repairs requiring immediate action, and developing damage tolerance inspections.
The timing allowance for any given airplane depends on the age of the airplane on December 18,
2009. An example of establishing the timeline for when an airplane survey should be conducted can be found in Appendix 8 of this AC.
a. The implementation schedule for airplane surveys takes into account the percentage of time in hours, cycles, or both, in relation to an airplane’s design service goal (DSG). The TC Holder should identify the established DSG for a particular airplane type that is representative of the airplane, considering the probable variation of the number of flight hours per cycle that could exist in the fleet. The TC Holder should include in it compliance plan a description of the methodology used to establish the DSG. The following three processes can be used to schedule airplane surveys.
(1) Airplanes less than 75 percent of DSG on December 18, 2009. Operators complete a survey at the first heavy maintenance check (time limit equivalent to a “D-check”) after an individual airplane reaches 75 percent of the DSG, not to exceed the DSG.
NOTE: A heavy maintenance check (D-check or equivalent airplane inspection) is an airplane maintenance visit where the major structural inspections are performed.
In some cases, this may be a formal D-check or, in the case of a Maintenance Steering Group (MSG)-2 or -3 based maintenance program, the D-check equivalent may be the “C-check” multiple that contains the majority of the major structural inspections, such as a “C-4” which is sometimes called a heavy maintenance visit.
(2) Airplanes between 75 percent of the DSG and the DSG on December 18, 2009. Operators complete a survey of individual airplanes at or before the next heavy maintenance check (equivalent to a D-check) after December 20, 2010, not to exceed the DSG or 6 years, whichever occurs later.
(3) Airplanes Beyond the DSG on December 18, 2009. Operators complete a survey of individual airplanes at or before the next heavy maintenance check (equivalent to a D-check) after December 20, 2010, not to exceed 6 years.
NOTE: Operators should not defer the implementation of the program until the end of the D-check time period. For example, if an operator has 30 airplanes over DSG on December 18, 2009, and is operating on a 6-year D-check equivalent, the operator should inspect approximately 5 airplanes each year until all of the airplanes are inducted into the program. The highest time airplanes should be inspected first (for example, using the above example of 30 affected airplanes, the 10 highest time airplanes should be surveyed in the first two years).
b. Data Submissions for Repairs Identified During the Survey.
(1) The TC Holder is required to submit DT Data to the FAA Oversight Office for approval within certain time frames. These time frames take into consideration whether the data is for existing published repairs and existing non-published repairs. The operator has a specified time frame for obtaining and incorporating the DTI into its maintenance program based on the TC Holder’s DTE.
(a) For existing published repairs, the TC Holder must submit the data by June 30, 2009.
(b) For existing, non-published repairs and deviations to published repairs identified in the survey, if the REGs direct operators to contact the TC Holder to obtain DTIs, the TC Holder should submit the DT Data to the FAA Oversight Office within 12 months after identification.
(c) For repairs covered by TC Holder published repair data, operators should obtain and incorporate into their maintenance program DTIs for existing repairs within 6 months after accomplishing the airplane survey. For non-published, repairs found during the survey, incorporation should be completed no later then 6 months after FAA approval of the data (see Appendix 6 of this AC for the DTI assessment process).
(2) The DT Data for repairs identified in an airplane survey may be approved by a FAA Designee, as coordinated with and authorized by the FAA Oversight Office. The same timelines for data approval apply.
218. Developing a Process for Conducting Surveys of Affected Airplanes. The TC Holder should develop a process for use by operators to conduct airplane surveys. These airplane surveys are conducted by operators to identify and document repairs and repairs to alterations that may be installed on their airplanes. The survey is intended to help the operators determine which repairs may need a DTE in order to establish the need for DTIs. Identification of repairs that need DTIs should encompass only existing repairs that reinforce (for example, restore strength) the FCBS. This typically excludes maintenance actions such as blend-outs, plug rivets, trim-outs, etc. The process the TC Holder develops to conduct surveys should include:
a. A survey schedule based on the DSG (see paragraph 217(a) of this AC).
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 DTIs.
d. A means to determine whether or not a repair affects FCBS.
219. Developing a Process to Obtain DT Data for Repairs.
a. The TC Holder must develop a process that operators can use to obtain DTIs that address the adverse effects repairs may have on FCBS. In developing this process, TC Holders 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 TC Holder. For certain repairs, the process may instruct the operators to obtain direct support from the TC Holder. In this case, the TC Holder evaluates the operator’s request and makes available 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. This process will be the key element of the REGs described in paragraph 216 of this AC.
b. The process should state that existing repairs that already have DTIs developed and in place in the maintenance program require no further action. For existing repairs identified during an individual airplane survey that need DTIs established, the process may direct the operators to obtain the required DTIs from the following sources:
(1) TC Holder published service information such as DT-based SRMs, SBs, or other documents containing applicable DT Data for repairs.
(2) Existing FAA-approved RAG documents (developed for compliance with § 121.107).
(3) Expanded or newly developed RAG documents.
(4) Procedures developed to enable operators to establish DTIs without having to contact the TC Holder for direct support. These procedures may be similar in concept to the RAG documents.
(5) Direct support from the TC Holder for certain repairs. The operator directly solicits DTIs from a TC Holder for certain individual repairs as those repairs are identified during the survey.
220. Repairs to Alterations. See Chapter 3 of this AC.
221. Repairs to Removable Structural Components. Fatigue critical structure (FCS) may include structure on removable structural parts or assemblies that can be exchanged from one airplane 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 of removal and reinstallation on different airplanes 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 Appendix 7 of this AC.
222. FAA Oversight Office Approval. The FAA Oversight Office responsible for the affected airplane’s TC or STC will approve the TC or STC Holder submissions whether submitted as separate documents or consolidated in a Compliance Document. This approval process also includes any documents referenced from a Compliance Document. Any subsequent revisions to the submissions, either separate documents or a Compliance Document, or to DTIs for repairs must be submitted to the FAA Oversight Office for review and approval. The DT Data submitted by TC or STC Holders may be approved by a FAA Designee, as coordinated with and authorized by the FAA Oversight Office.
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