Advisory Circular
U.S. Department of Transportation Federal Aviation Administration
Subject: DAMAGE TOLERANCE
INSPECTIONS FOR REPAIRS AND
ALTERATIONS
Date: 11/20/07 Initiated by: ANM-100 AC No: 120-93
This advisory circular (AC) provides guidance material for Type Certificate (TC) Holders, Supplemental Type Certificate (STC) Holders, and operators to comply with requirements in the Aging Airplane Safety Act to ensure the airworthiness of aging airplane parts and components.
The Aging Airplane Safety Rule that supports the Act specifies incorporating damage tolerancebased inspections into an operator’s continuous airworthiness maintenance program. These inspections will help ensure the integrity of fatigue critical structure on transport category airplanes operated in air transportation. This guidance will provide persons who have developed repairs and alterations with a means to develop damage tolerance data to be used to determine damage tolerance inspections for repairs and alterations that affect fatigue critical structure. This AC will give guidance on developing compliance documents, schedules and plans that will assist in developing and incorporating damage tolerance inspections into maintenance programs of certain transport category airplanes with respect to repairs and alterations.
Signed by John J. Hickey Signed by Carol E. Giles for
John J. Hickey James J. Ballough Director, Aircraft Certification Service Director, Flight Standards Service
CONTENTS
Paragraph Page Chapter 1. OVERVIEW
100. Purpose 6
101. Applicability 6
102. Damage Tolerance 7
103. TC and STC Holder Information 8
104. TC and STC Holder Data Submittal 9
105. Compliance Documents 9
106. TC Holder Tasks - Repairs 11
107. TC and STC Holder Tasks – Alterations and Repairs to Alterations 11
108. Compliance Plans 12
109. Operator Tasks – Repairs, Alterations and Repairs to Alterations 13
110. Airplane Models Not Requiring Additional DT Data. 14
111. – 199. [Reserved] 14
Chapter 2. TYPE CERTIFICATE (TC) HOLDER TASKS FOR REPAIRS
200. General Information About This Chapter 15
201. Compliance Document Contents 15 Figure 1 - TC Holder Tasks for Repairs 17
202. Applicability 18
203. Certification Level 18
204. Identifying Fatigue Critical Baseline Structure (FCBS) 18
205. Certification Standard Applied in Performing a DTE 19
206. Performing a DTE on Repairs That Affect FCBS 19
207. Review of Published Repair Data 20
208. Developing DT Data for Existing Published Repair Data 20
209. Developing DT Data for Future Published Repair Data 21
210. Submittal of DT Data Developed For Existing Published Repair Data 21
211. Submittal of DT Data Developed For Future Published Repair Data 22
212. Documentation of DT Data Developed for Published Repair Data 22
213. Existing Repairs 22
214. Future Repairs 22
215. Expanded or New Repair Assessment Guidelines 22
216. Repair Evaluation Guidelines 23
217. Implementation Schedule 23
218. Developing a Process for Conducting Surveys of Affected Airplanes 25
219. Developing a Process to Obtain DT Data for Repairs 26
220. Repairs to Alterations 26
221. Repairs to Removable Structural Components 26
222. FAA Oversight Office Approval 26
223. – 299. [Reserved] 27
CONTENTS
P a r a g r a p h P a g e
Chapter 3. TC AND STC HOLDER TASKS FOR ALTERATIONS AND
REPAIRS TO ALTERATIONS
300. General Information About This Chapter 28
301. Contents of Compliance Document 28 Figure 2 - TC and STC Holder Tasks for Alterations and Repairs to Alterations 30
302. Applicability 31
303. Certification Amendment Level 31
304. Obtaining the List of FCBS 31
305. Identifying Alterations That Affect FCBS 31
306. Identifying FCAS 32
307. List of Alterations 32
308. Description of Alteration 32
309. Certification Standard Applied in Performing a DTE 32
310. Performing a DTE on Alterations That Affect FCBS 33
311. Reviewing Existing DT Data for Alterations That Affect FCBS 33
312. Developing DT Data for Alterations 34
313. Timelines for Developing Data For Alterations 34
314. Developing DT Data for Repairs Affecting FCAS 34
315. Timelines for Developing DT Data For Repairs Affecting FCAS 35
316. FAA Oversight Office Approval 35
317. – 399. [Reserved] 36
Chapter 4. OPERATOR TASKS FOR REPAIRS AND ALTERATIONS
400. General Information About This Chapter 37
401. Developing an Operator Implementation Plan 37
402. Contents of an OIP 37
403. Repairs 38
404. Schedule for Implementing DTI for Existing Repairs 39
405. Implementing DTI For Repairs 39 406 Alterations 40
407. Schedule for Developing and Incorporating DTI for Alterations 41
408. Implementing DTIs for Alterations 41
409. Existing Responsibilities 42
410. FAA Principal Maintenance Inspector Approval of OIP 42
411. Maintenance Program Changes 43
412. – 499. [Reserved] 43
CONTENTS
P a r a g r a p h P a g e
Chapter 5. ADMINISTRATIVE REQUIREMENTS.
500. AC Availability – How Do I Get a Copy of the Publications Referred To In This AC?
501. Who Do I Submit Comments To About This AC? 44
502. – 599. [RESERVED]. 44
CONTENTS
P a r a g r a p h P a g e
LIST OF APPENDICES
1 Regulatory And Guidance Material Related To This AC A1-1
1. Title 14 of the Code of Federal Regulations (14 CFR) A1-1
2. Advisory Circulars A1-1
3. FAA Policy Statement A1-1
4. FAA Orders A1-2
5. Other Documents Referred to in this AC A1-2
2 Definitions A2-1
3 Acronyms Used In This AC A3-1
4 Background A4-1
5 Approval Process For New Repairs A5-1
6 Assessment Of Existing Repairs A6-1
1. Airplane Repair Survey A6-1
2. Identification and Disposition of Repairs Requiring Immediate Action A6-1
3. Damage Tolerance Inspection Development A6-1
7 Repairs And Alterations To Removable Structural Components A7-1
8 Program Implementation Examples A8-1
9 List of Significant Alterations That May Adversely Affect Critical Structure
A9-1
CHAPTER 1. OVERVIEW
100. Purpose.
a. This AC is directed to Type Certificate (TC) and Supplemental Type Certificate (STC) Holders and operators of transport category airplanes. It provides guidance material for developing and incorporating a means for addressing the adverse effects that repairs, alterations and modifications may have on fatigue critical structure. This AC supports TC and STC Holder compliance with Title 14 Code of Federal Regulations (14 CFR) 26.43, Holders of type certificates – Repairs; 14 CFR 26.45, Holders of type certificates – Alterations and repairs to alterations; and 14 CFR 26.47, Holders and applicants of Supplemental type certificates – Alterations and repairs to alterations. These regulations are established in the Design Approval Holder Damage Tolerance Data Rule. These regulations require TC Holders and STC Holders to develop certain information needed to support operator compliance with 14 CFR 121.1109 and 14 CFR 129.109, the Aging Airplane Safety Final Rule (AASFR) with respect to repairs and alterations. This AC provides guidance for TC and STC Holders to address new and existing repairs and alterations that affect fatigue critical structure (FCS) of the original, as delivered, baseline airplane structural configuration, that is, fatigue critical baseline structure (FCBS). It also provides guidance for repairs that affect FCS of an alteration, referred to in this AC as fatigue critical alteration structure (FCAS).
b. This AC also provides guidance for operators of transport category airplanes to comply with the requirements of the AASFR. Sections 121.1109 and 129.109 require operators’ maintenance programs to include a means for addressing the adverse effects repairs, alterations and modifications may have on FCS. To facilitate operator compliance, this AC provides guidance for developing an Operator Implementation Plan (OIP). The OIP will contain the means for addressing the adverse effects of repairs and alterations. Principal Maintenance Inspector (PMI) approval of the OIP constitutes compliance with §§ 121.1109 and 129.109. It should be noted that operators are not required to perform any actions for baseline structure. This is because, for affected airplanes certificated prior to Amendment 25-45, baseline structure is addressed by the Supplemental Structural Inspection Programs (SSIP) mandated by airworthiness directives. The type certification process for airplanes certificated at Amendment 25-45 or later required that damage tolerance-based inspections be established for baseline structure.
c. For the purposes of this AC, the term “alteration” is considered to be synonymous with the term ‘‘modification.’’ An alteration is a design change that is made to an airplane;
however, various segments of industry have also defined these changes as ‘‘modifications.’’ In this AC an alteration is all-inclusive of any design change.
101. Applicability.
a. The guidance provided in this AC is primarily applicable to TC Holders, STC Holders, and operators of transport category, turbine powered airplane models with a type certificate issued after January 1, 1958, that, as a result of original type certification or later increase in capacity, have —
(1) A maximum type certificated passenger seating capacity of 30 or more; or 6
(2) A maximum payload capacity of 7,500 pounds or more.
The guidance provided in this AC may be used by persons other than TC or STC Holders (for example, third party engineering firms), in support of developing Damage Tolerance (DT) Data on behalf of operators.
b. Like all AC material, this AC is not, in itself, mandatory, and does not constitute a regulation. It describes an acceptable means, but not the only means, for showing compliance with the requirements for transport category airplanes. The Federal Aviation Administration (FAA) will consider other methods of showing compliance that an applicant may elect to present. While these guidelines are not mandatory, we derived them from extensive FAA and industry experience in showing compliance with the relevant regulations. On the other hand, if we become aware of circumstances that convince us that following this AC would not result in compliance with the applicable regulations, we will not be bound by the terms of this AC. We may require additional substantiation or design changes as a basis for finding compliance.
c. This material does not change, create any additional, authorize changes in, or permit deviations from, regulatory requirements.
d. Terms in this AC, such as “shall” or “must” are used only in the sense of ensuring applicability of this particular method of compliance when the acceptable method of compliance described herein is used.
102. Damage Tolerance.
a. Amendment 25-45 to 14 CFR part 25 introduced the use of damage tolerance principles.
This approach requires evaluating the structure to determine its crack growth and residual strength characteristics. The evaluation supplies the information necessary to develop a maintenance plan for continued airworthiness. In this AC, a Damage Tolerance Evaluation (DTE) refers to a process that includes analysis and/or tests and service data that lead to the development of a multiple or a single means for determining maintenance actions necessary to detect fatigue cracking that could contribute to a catastrophic failure. Consistent with the guidance provided by this AC, a DTE could entail anything from a rigorous analysis methodology for use by a structures analyst to generic guidelines for operator use. If the DTE concludes that damage tolerance-based supplemental structural inspections are not necessary for a repair or alteration that affects fatigue critical structure, the DTE would provide a summary of those results. In some cases, the DTE may conclude that a repair or alteration, or the FCBS affected by a repair or alteration, needs to be replaced or modified.
The DTE documentation will identify the evaluated FCS, the basic assumptions applied in a DTE, and the results of a DTE, which are usually Damage Tolerance Inspections (DTIs). In this AC DTIs are inspections or other maintenance actions developed as a result of a DTE.
If the results of the DTE indicate that DTIs are not necessary for a repair or alteration that affects fatigue critical structure, then the DTIs should provide a summary of those results.
The DTIs developed as a result of a DTE must comply with the damage tolerance requirement of § 25.571 at Amendment 25-45, or later.
b. Damage Tolerance Inspections (DTIs) are comprised of the following items that may result from a DTE:
• Where to inspect.
• How to inspect.
• How often to repeat the inspection.
• A time limit when the repair needs to be replaced (if necessary).
• If the DTE concludes that DT-based supplemental structural inspections are not necessary, the DTI documentation should include a statement that the normal zonal inspection program is sufficient.
c. For some airplane models, the requirements of the Aging Airplane Safety Final Rule (AASFR) are beyond the scope of the original certification level. For these airplane models, certain information may exist in various FAA-approved documents, such as Supplemental Structural Inspection Documents (SSIDs), repair assessment guideline (RAG) documents, airworthiness limitation sections (ALSs), structural repair manuals (SRMs), service bulletins (SBs), and airworthiness directives (ADs). As stated in the Aging Airplane Safety Interim Final Rule (AASIFR), which was issued on December 6, 2002, FAA-approved SSIDs or RAGs are an acceptable means of compliance with §§ 121.1109(c)(1) and 129.109(b)(1) for the areas covered by those documents. While the methodologies used by TC Holders to develop SSIDs vary, the FAA-approved SSIDs are developed to address fatigue damage in baseline structure.
103. TC and STC Holder Information.
Sections 26.43, 26.45, and 26.47 require, among other things, that the TC and STC Holders develop certain information that will provide the means for operators to address the adverse effects of repairs and alterations. This information must be submitted to the FAA Oversight Office for approval. The information submitted for approval should include the following:
• List of Fatigue Critical Structure:
o FCBS (TC Holder),
o FCAS (TC and STC Holder).
• Updated published repair data (TC Holder).
• Repair Evaluation Guidelines (TC Holders) that include:
o A process operators can use to conduct airplane surveys to enable identification of repairs that affect FCBS.
o A process operators can use to determine how to obtain DTI for those repairs that affect FCBS that are identified in the survey.
o An implementation schedule that provides timelines of airplane surveys and incorporating necessary DTIs into an operator’s maintenance program.
• DTIs for alterations that affect FCBS. The DTIs would apply to affected FCBS and any FCAS (TC and STC Holders).
• DTIs for TC or STC Holder repairs they developed for these alterations.
• DTIs for all future repairs and alterations.
104. TC and STC Holder Data Submittal.
a. For repairs, TC Holders must submit the list of FCBS and the list of published repair data separately. However, we recommend that this information also be included or referenced in a Compliance Document that should also contain the Repair Evaluation Guidelines.
b. For alterations, TC Holders must submit the list of FCAS and any DTI required for their alteration data separately. This includes any DTI required for repair data developed for those alterations. We recommend that this information also be included or referenced in a Compliance Document.
c. For alterations, STC Holders must submit a list of FCAS for their STCs. The STC Holders should include DTIs required for their alterations into a Compliance Document.
The list of FCAS may be included in or referenced in that Compliance Document.
105. Compliance Documents.
a. In order for operators to incorporate means to address repairs and alterations as required by the AASFR, operators should use the information identified in paragraph 103 of this AC to develop an Operator Implementation Plan (OIP). The OIP would be approved by the operators’ PMI and be incorporated into their continuous airworthiness maintenance program (CAMP). This AC recommends that TC and STC Holders develop a Compliance Document that contains or references the information operators will need to develop their OIP. As discussed in paragraph 103 and chapters 2 and 3 of this AC, there are certain data that should be included in the Compliance Document which will support FAA review and approval and operators development of their OIP.
b. In developing a Compliance Document, the TC and STC Holders should use the guidance material in this AC to identify the information operators will need to support their development of an OIP. This AC recommends that sections be developed within the Compliance Document that address airplane applicability, lists of fatigue critical baseline structure (FCBS) and fatigue critical alterations structure (FCAS), Damage Tolerance Evaluations (DTEs), and Damage Tolerance Inspections (DTIs). A TC Holder’s Compliance Document should also include a section that addresses the elements of its 9
Repair Evaluation Guidelines (REGs). While this AC recommends that the information comprising the REGs be submitted to the FAA as part of the Compliance Document, the TC Holder may submit the REGs information in a separate document for approval and reference that document in the REGs section of the Compliance Document.
c. TC Holders may incorporate the compliance documentation for both repairs (see paragraph 201 of this AC) and alterations (see paragraph 301 of this AC) into a single Compliance Document, or develop a separate Compliance Document for each.
d. TC Holders, STC Holders, operators and civil aviation airworthiness authorities should work together to develop model-specific Compliance Documents with oversight provided by those authorities and assistance from the Aviation Rulemaking Advisory Committee’s (ARAC) Airworthiness Assurance Working Group (AAWG). We anticipate that TC Holders will utilize structural task groups (STG) to support their development of modelspecific Compliance Documents. The assistance provided by the AAWG is in accordance with an FAA tasking to ARAC (69 FR 26641, May 13, 2004).
(1) The goal of this tasking was the development of guidance material for repairs and alterations affecting FCS. This AC contains the guidance developed by ARAC in accordance with the FAA tasking. In previous aging airplane program development activities, ARAC’s AAWG formed model-specific STGs to develop programs for those models. Task 4 of the FAA’s tasking to ARAC addresses the model-specific STGs by requiring ARAC’s AAWG to oversee the STG activity to ensure uniform application of this AC guidance material. Where necessary, an STG for this activity should be formed and tasked to develop the model-specific Compliance Document. We anticipate that both repairs and alterations can be addressed in the same STG meetings. This joint effort between the TC Holder and operators will help to ensure that operators will have access to the DTIs required for any installed repairs and alterations developed by the TC Holder that affect FCBS. In accordance with the tasking, the AAWG will “Oversee the Structural Task Group (STG) activities that will be coordinated for each applicable airplane model by the respective TC Holders and part 121 and 129 operators. These STG activities will involve developing model-specific approaches that support compliance with §§ 121.1109 and 129.109 under the guidance material supplied in Task 1 of the FAA tasking to ARAC.”
(2) In addition to the STG meetings chaired by the TC Holder, it may be beneficial for certain STC Holders to establish an STG for their alteration(s). This would allow the STC Holder to coordinate the development of DT Data for the STC Holder’s alteration with affected operators.
e. TC and STC Holders should submit the data required by §§ 26.43, 26.45, and 26.47, and the Compliance Document recommended by this AC to the FAA Oversight Office for approval and make the approved Compliance Document available to operators. Note that certain data required by §§ 26.43, 26.45, and 26.47 may be submitted as part of the Compliance Document submittal. The primary reason for separate submittals is due to different submittal dates required by the part 26 rules. The Compliance Document is the last document submitted and can serve as an all inclusive document that supports operators in developing their OIPs for compliance with the AASFR. Data submitted earlier, such as
the list of FCBS, which must be made available to the operators before the Compliance Document is submitted, may also be included in the Compliance Document. As a minimum, data that must be made available to the operators should be referenced in the Compliance Document.
106. TC Holder Tasks - Repairs. The following is an overview of the tasks for repairs that may affect FCBS. These tasks are further developed in Chapter 2 of this AC. These tasks are necessary to support a TC Holder’s timely compliance with § 26.43 and an operator’s compliance with §§ 121.1109 and 129.109.
a. Identify the affected airplane model, models, airplane serial numbers, and design service goal stated as a number of flight cycles, flight hours, or both.
b. Identify the certification level.
c. Identify and develop a list of the FCBS.
d. Submit the list of FCBS to the FAA Oversight Office for approval, and make it available to operators.
e. Review and update published repair data as necessary.
f. Submit any new or updated published repair data to the FAA Oversight Office for approval, and make it available to operators.
g. Revise existing Repair Assessment Guidelines (RAGs) or develop new RAGs, as determined necessary, and submit them to the FAA Oversight Office for approval, and make them available to operators.
h. Develop Repair Evaluation Guidelines (REGs), and submit them to the FAA Oversight Office for approval, and make the approved REGs available to operators. We anticipate that the REGs will be submitted as part of the Compliance Document.
i. Prepare a Compliance Document that contains or references the REGs and any other information necessary to support operators in developing their OIPs.
j. Submit the Compliance Document to the FAA Oversight Office for approval, and make it available to operators.
107. TC and STC Holder Tasks – Alterations and Repairs to Alterations. The following is an overview of the TC and STC Holder tasks necessary for alterations that affect FCBS. This overview also includes TC and STC Holder tasks necessary for repairs that may affect any FCS of the subject alterations. These tasks are applicable to those alterations that have been developed by the TC or STC Holder and are further developed in Chapter 3 of this AC.
These tasks are necessary to support TC Holder compliance with § 26.45, STC Holder compliance with § 26.47, and operator compliance with §§ 121.1109 and 129.109.
a. Establish a list of alterations that may affect FCBS. From that list establish a list of alterations that may contain FCS.
b. In consultation with operators, determine which airplanes have those alteration(s) installed.
c. STC Holders should obtain a list of FCBS from the TC Holder for the airplane models identified in paragraph 101, above.
d. STC Holders should identify:
• Alterations that affect FCBS, or
• Alterations that contain FCS.
e. Determine if DT Data exist for the identified alterations.
f. Develop additional DT Data, if necessary.
g. Establish an implementation schedule for alterations.
h. Review existing DT Data for repairs made to alterations that affect FCBS.
i. Develop additional DT Data for repairs made to alterations that affect FCBS.
j. Establish an implementation schedule for repairs made to alterations.
k. Prepare a Compliance Document, submit it to the FAA Oversight Office for approval, and make it available to operators.
108. Compliance Plans. TC and STC Holders are required by § 26.49 to submit a Compliance Plan to the FAA Oversight Office. This plan will detail the TC or STC Holder’s means of compliance with §§ 26.43, 26.45, and 26.47. Specific details of the acceptable contents of a Compliance Plan and procedures for submission to the FAA are described in AC 26-1, Part 26, Continued Airworthiness and Safety Improvements, which may include:
a. A project schedule identifying all major milestones, including but not limited to a:
(1) Schedule for submitting the list of FCBS or FCAS as applicable,
(2) Schedule for submitting a list of published repair data,
(3) Schedule for submitting updated published repair or alteration data as applicable,
(4) Schedule for submitting REGs, and
(5) Schedule for establishing the Structures Task Group (if applicable).