Appendix 8 A8-9 The substantiation data will include—
• A pictorial definition of each airplane model.
• A list of structure susceptible to WFD.
• The engineering data and analyses used to determine the WFD behavior of structure.
• ISPs and structural modification points (SMP).
For each affected model, AAC proposes to use the AC 120-104 guidance (as revised) for establishing the LOV and developing substantiation data. The proposed MOC for identifying and establishing maintenance actions are further described in section V1 of this compliance plan.
a. Candidate LOV [§ 26.21(b)(1)]—Identify the LOV that is likely to be proposed for compliance with § 26.21.
[At the beginning of the compliance process, you may have an LOV that is a likely candidate for a specific airplane model. This candidate LOV may or may not be the LOV you finally submit to the FAA for approval. Although the rule does not require that the compliance plan include a candidate LOV, you may elect to include that information in your compliance plan. The candidate LOV should be based on highlevel technical considerations such as the age and service experience of the fleet as well as results of previously accomplished fatigue tests and analyses. It may also be based on economic considerations.] Example: Candidate LOVs
• AAC1-P2: 35,000 flight cycles and 100,000 flight hours.
• AAC1-C: 30,000 flight cycles and 80,000 flight hours.
b. WFD-Susceptible Structure [§ 26.21(b)(1)]—Describe how you will determine WFD-susceptible structure and identify that structure.
[You must identify WFD-susceptible structure. Accomplishing this will require screening of all structural components—both baseline structure and structural modifications and replacements mandated by AD. The list of WFD-susceptible structure will be a subset of the list of fatigue-critical structure developed for § 26.43.]
Appendix 8 A8-10 Example: AAC will use the guidance in AC 120-104, Appendix 5 (as revised) to identify structure susceptible to WFD. AAC will use the list of fatigue-critical structure identified for § 26.43 as part of this process. Additionally, AAC will identify WFD-susceptible structure based on structural details and elements that are repeated over large areas and operated at the same stress levels [structure susceptible to multiple site damage (MSD) or multiple element damage (MED)]. AAC will cull out AD-mandated modifications, replacements, and baseline structure that do not need to be evaluated. The method for culling out structure will be identified in each model’s compliance documents. AAC will obtain FAA concurrence of this method early in the compliance process.
For the WFD-susceptible structure section of the AAC1-P2-WFD and AAC1-C-WFD documents, AAC will include the following information—
• Method for screening structure (including modifications and replacements mandated by AD) susceptible to WFD.
• Identification of structure susceptible to WFD. AAC will identify susceptible structure by:
1. Including sketches of the structure with dimensions and details to describe the structure and identify its location.
2. Summarizing the WFD-susceptible structure in a tabular format by—
• Assigning an identifier to the affected fatigue-critical structure.
• Describing the structure, parts, or element included in that structure.
• Identifying which airplanes or models this information applies to and the location where WFD would most likely occur.
See Section VI of this compliance plan, Maintenance Actions and Service Information, for further information on identifying structural details that must be inspected, modified, or replaced to support the LOV.
The following is an example of the format that AAC will use for identifying WFD-susceptible structure.
Appendix 8 A8-11 Fatigue-Critical Structure Part Name or Description Applicability Location Part No. 1 Wing – Fuselage Attachment AAC1-all Section 44, Zone xxxx Part No. 2 Part No. 3 Fuselage Skin Lap Joint xxxx modified per AD xxxxxxxx AAC1-all AD X modifies SN 1 – 250 Zone yyyy or Body Station xx – yy Part No. 4a Aft Pressure Dome – Lap Splice AAC1-all Section 48, Zone aaaa Part No. 4b Aft Pressure Dome – Y Chord AAC1-all Section 48, Zone bbbb Part No. N – NN Main Deck Cargo Door Frames … AAC1-C Section 43, Body Station xx – yy
c. WFD Evaluation of Susceptible Structure [§ 26.21(b)(1)]—Describe how you will evaluate structure for WFD susceptibility and determine the average behavior of WFD for that structure, as applicable.
[The DAH must establish an LOV that corresponds to the period of time, stated as a number of total accumulated flight cycles or flight hours or both, during which it is demonstrated that widespread fatigue damage (WSD) will not occur in the airplane.
This demonstration must include an evaluation of airplane structural configurations and be supported by test evidence and analysis at a minimum and, if available, service experience, or service experience and teardown inspection results, of hightime airplanes of similar structural design, accounting for differences in operating conditions and procedures.
You must evaluate each susceptible structure to some degree. For some structures, you may have data such as fatigue tests, analysis, and service experience that demonstrates that WFD will not occur before an airplane reaches its LOV. If that is the case, you may not have to go through the process of quantifying the WFD average behavior for that structure. For other structures, for which you do not have sufficient data, you will have to do an evaluation.] Example: AAC will establish an LOV based on AC 120-104 guidance (as revised). AAC’s Document AAC1-26-LOV describes that method, including the engineering data AAC will use to evaluate susceptible structure and quantify the WFD(average behavior) of that structure.
Appendix 8 A8-12 Engineering Data Laboratory Fatigue Tests. AAC conducted a full-scale fatigue test on the Model AAC1-P1 produced from 1967 to 1970. The fuselage, empennage, landing gear, and wing structure were tested. AAC has also conducted component-level testing of certain structural elements and testing of the fuselage for Model AAC1-P2. To support certification of Model AAC1-C to the damage tolerance requirements of § 25.571, Amendment 25-54, AAC had also previously conducted additional testing and teardown of some portions of the original test article and the Model AAC1-P2 fuselage produced from 1981 to 1982 AAC will use all that data now to determine the WFD average behavior for each susceptible structure, as necessary. AAC will provide document AAC1-26-TPR, which describes the test procedures and results.
Service Experience. AAC reviewed the in-service history of Model AAC1 structure (all three models) susceptible to WFD. This review included the evaluation of both positive and negative findings, and consideration of loads, mission profiles, environmental factors, and fleet operational statistics. AAC has conducted teardown inspections of certain WFD-susceptible structure on a high-time Model AAC1-P2 airplane. Some inspections included fractographic examination of the structure. AAC combined the service history results with test and analysis data to determine the WFD behavior of structure.
Analysis of Engineering Data AAC used an analysis approach, based on test and service experience, to determine fatigue, crack growth rates, and residual strengths of structures and to develop the Model AAC1 continued airworthiness structure inspection/maintenance requirements. AAC used AC 25.571-1 and AC 91-56 (as revised) as guidance for developing damage-tolerance inspections. AAC's crack growth analysis method is based on linear elastic fracture mechanics using tools such as NASGRO or AFGROW software to determine the time (measured in flight cycles or flight hours) between a detectable crack size and the critical crack size for each structure evaluated. AAC will use this information, as well as the guidance in AC 120-104 (as revised), to evaluate structure susceptible to WFD to determine if additional maintenance actions are required in order for airplanes to reach the LOV. The operating loads and loads spectra for these evaluations are defined in documents AAC1-P2-Loads and AAC1-C-Loads for the passenger and cargo airplanes respectively.
AAC will conduct additional fatigue and crack growth analyses to fully determine the WFD behavior of the structure. AAC will use existing and proposed fatigue test results as well as service experience (both positive and negative findings) to make this determination. The data will be contained in AAC1-26-TPR. AAC will also use statistical analyses to further evaluate the WFD behavior of the WFD susceptible structure.
Appendix 8 A8-13 Safety Factors AAC will apply safety factors to the analyses results to account for any uncertainties in the analyses and scatter in the data. The safety factors will also reflect AAC’s confidence level in the engineering data used. AAC will be using extensive service experience in conjunction with fatigue tests. Early in the compliance process, AAC will obtain responsible Aircraft Certification Service office concurrence with the safety factors before applying them to the analyses results.
AAC will apply appropriate safety factors to the analysis to determine what the WFD average behavior is for a structural component for the airplane model fleet. Based on the results of this task, AAC will identify ISPs and SMPs for the airplane model fleet.
Comparison of WFD-Susceptible Structure to a Candidate LOV Based on the data available, AAC will determine the time period representing the WFD average behavior for each structure susceptible to WFD and compare it to the candidate LOV. It may be found that maintenance actions are required before the airplane reaches the candidate LOV in order to preclude WFD. When AAC determines that maintenance actions are required, it will—
(1) Assess MSD/MED inspection reliability and practicality in relation to detectable size of cracks and probability of detection.
(2) Determine when inspections should start.
(3) Determine inspection intervals.
(4) Determine when modifications or replacements should occur. This process will determine the maintenance actions necessary for affected airplanes to reach the LOV. AAC will follow AC 120-104 guidance (as revised) for setting ISPs and SMPs.
d. Finalizing LOV for Compliance [§ 26.21(b)(1)]—Identify factors for consideration in finalizing the LOV.
[The LOV may be based on factors such as economics or input from operators in addition to the technical considerations. The DAH should identify those factors being considered.] Example: Once all susceptible structures have been evaluated and compared to the candidate LOV, AAC will determine where in the life of the airplane to establish the LOV it will submit for compliance. AAC will hold meetings—referred to as “Structures Task Group (STG) Meetings”— with industry and the authorities to discuss its findings, conclusions, and proposals for compliance with § 26.21. AAC will provide the FAA with the meeting schedule early in the compliance process.
Appendix 8 A8-14 VI. Maintenance Actions and Service Information [§ 26.21(b)(2)].
Describe the proposed method for identifying and developing WFD maintenance actions, if any.
[If the DAH establishes an LOV that relies on maintenance actions, those maintenance actions must be identified. Service information, which is typically issued in service bulletins, includes a description of the maintenance actions and the procedures for accomplishing them. Some of the maintenance actions required for the LOV may have already been published in a service bulletin and mandated by AD as of January 14, 2011.
If an inspection previously mandated by an AD to address WFD will be used to support the LOV, it should be identified as necessary to meet the LOV. For the rest, ADs will need to be issued.] Example: AAC will use the AC 120-104 guidance (as revised), in conjunction with results from an evaluation of the WFD-susceptible structure, to determine whether maintenance actions (inspections, modifications, and replacements) are required in order for affected airplanes to reach the LOV. If maintenance actions are required, AAC will identify them in documents AAC1-P2-WFD and AAC1-C-WFD. This will include identifying—
• All WFD maintenance actions.
o The structure to be inspected, modified, or replaced. For example, if the aft pressure dome is identified as WFD-susceptible structure (reference Appendix 5, Figure 5-7), AAC will identify the structural details of the outer ring splice and the web splices so that maintenance action can be performed properly.
o The method of inspection, modification, or replacement.
o The ISP (the point in time at which to begin inspections) and/or the SMP (the point in time to begin the modification).
o The repeat interval.
• All WFD maintenance actions for which service information has been issued, but ADs have not been issued.
• All WFD maintenance actions for which service information has not been issued and a proposed binding schedule for providing the necessary service information to the FAA for those actions in a timely manner so that ADs can be issued.
Appendix 8 A8-15 VII. Airworthiness Limitations Section (ALS) [§ 26.21(b)(3) and (4)].
Describe the MOC for revising or creating an ALS in the airplane’s Instructions for Continued Airworthiness (ICA), as applicable.
[If an ALS does not exist for the airplane model being considered, the DAH must establish one. When you submit the LOV for compliance with (b)(4), the FAA will be reviewing and approving the revision or creation of the ALS in addition to the LOV, and all substantiation data.] Example: AAC has an ALS in the Instructions for Continued Airworthiness (ICA) for Model AAC1-C, as required by part 25, Amendment 25-54 or later. The ALS includes reference to the fuselage structure inspections contained in the supplemental structural inspection document (AAC1-C-SSID) mandated by AD 98-xy-zz. AAC will develop an ALS for Model AAC1-P2, which was originally certified before Amendment 25-54 and therefore does not have an ALS. AAC will also reference in the ALS the supplemental structural inspection document AAC1-P2-SSID mandated by AD 88-xx-yy. The ALS for each model will contain a section that will include the FAA-approved LOV.
In service bulletins, AAC will define the WFD maintenance actions needed to support the LOV.
Although not required, AAC will revise the ALS for each model to include a reference to those maintenance actions when they are available to be included.
VIII. Certification Compliance Matrix.
Providing a certification compliance matrix would be one way to streamline the review process. Such a matrix would include each regulation number (paragraph by paragraph), what it requires, an MOC description, and the name of the compliance document.
Example: [The following example shows only a few of the paragraphs from § 26.21 that a DAH would include in its certification compliance matrix.]
Appendix 8 A8-16 Table 2
Certification Compliance Matrix
26.21—Limit of Validity (LOV) Regulation Requirement Means of Compliance (MOC) Description Compliance Document
26.21(a) Applicability. Except as provided in paragraph (g) of this section, this section applies to transport category, turbine-powered airplanes with a maximum takeoff gross weight greater than 75,000 pounds and a type certificate issued after January 1, 1958, regardless of whether the maximum takeoff gross weight is a result of an original type certificate or a later design change. This section also applies to transport category, turbine-powered airplanes with a type certificate issued after January 1, 1958, if a design change approval for which application is made after January 14, 2011, has the effect of reducing the maximum takeoff gross weight from greater than 75,000 pounds to 75,000 pounds or less.
AAC Airplane Company has provided a statement of applicability in Section II of this compliance plan.
AAC Airplane Company is not a holder or applicant for any STCs or ATCs for which this rule is applicable.
Compliance Plan Document No. AAC1-26.21-CP-01
26.21(b) Limit of validity. Each person identified in paragraph (c) of this section must comply with the following requirements:
AAC Airplane company will follow the MOC provided in AC 120-104.
Refer to Section V of this document. See following for 26.21(b).
Documents AAC1-P2-WFD, AAC1-C-WFD
Appendix 8 A8-17
26.21(b)(1) Establish a limit of validity of the engineering data that supports the structural maintenance program (hereafter referred to as LOV) that corresponds to the period of time, stated as a number of total accumulated flight cycles or flight hours or both, during which it is demonstrated that widespread fatigue damage will not occur in the airplane.
This demonstration must include an evaluation of airplane structural configurations and be supported by test evidence and analysis at a minimum and, if available, service experience, or service experience and teardown inspection results, of high-time airplanes of similar structural design, accounting for differences in operating conditions and procedures. The airplane structural configurations to be evaluated include— AAC Airplane company will follow the MOC provided in AC 120-104.
Refer to Section V of this document.
Documents AAC1-P2-WFD, AAC1-C-WFD, AAC1-26-LOV, AAC1-26-TPR
26.21(b)(1)(i) All model variations and derivatives approved under the type certificate; and AAC Airplane company will follow the MOC provided in AC 120-104.
Refer to Section IV of this document.
Documents AAC1-P-WFD, AAC1-C-WFD
26.21(b)(1)(ii) All structural modifications and replacements to the airplane structural configurations specified in paragraph (b)(1)(i), mandated by airworthiness directives as of January 14, 2011.
AAC Airplane company will follow the MOC provided in AC 120-104.
Refer to Section IV of this document.
Documents AAC1-P-WFD, AAC1-C-WFD
Appendix 8 A8-18 IX. Deviations to Guidance Material.
Describe any proposed deviations from any applicable guidance material. The description should include the proposed alternative MOC and rationale.
Example: AAC does not plan on deviating from the guidance provided in AC 120-104 (as revised). However, if AAC determines that it may be necessary or appropriate to deviate from this guidance, AAC will notify the responsible Aircraft Certification Service office of the deviation, and work with that office to determine the appropriate course of action.
X. Compliance Documents and Supporting Data.
Identify and summarize the compliance documents and any supporting data. The items that require FAA approval include—
(1) The compliance plan.
(2) An ALS with the LOV incorporated (and supporting data).
(3) The list of any required maintenance actions not mandated by ADs.
(4) A binding schedule for publishing any required service information not yet published.
Example: AAC will provide the following data/documents to the responsible Aircraft Certification Service office for review and approval.
Appendix 8 A8-19 Table 3
Compliance Document Summary Document Number Document Title Document Overview Submittal Date to [responsible Aircraft Certification Service office] AAC1-26.21- CP-01 AAC Models AAC1-P2 and -C: 14 CFR
26.21(d) Certification Compliance Plan Document contains details of how AAC intends to show compliance with the applicable section 26.21 requirements.
90 days after effective date of the final rule Document No.
AAC1-26-LOV WFD Evaluation and LOV Methodology Document describes the method for determining WFD average behavior, demonstrating that WFD will not occur before the LOV, establishing maintenance actions (if applicable), and establishing the LOV.
120 days after effective date of the final rule Document No.
AAC1-2P- Loads, AAC1-C-Loads Passenger Model and Cargo Model Loads Document Documents contain operating loads, loads spectra, and assumptions about operational loading.
Documents provide the loads used in analyses and tests.
18 months after the effective date of the final rule Draft document – 60 days before the 18-month compliance date Document No.
AAC1-26-TPR Fatigue Test Procedures and Reports, and Service Information Document contains fatigue test procedures and reports of the test results, including any analysis of the test data. The fatigue tests will be used either to show freedom from WFD for specific structure or to validate analysis methods. The document also contains data from service experience, including analysis of that data.
18 months after the effective date of the final rule Draft document – 60 days before the 18-month compliance date
Appendix 8 A8-20 Document Number Document Title Document Overview Submittal Date to [responsible Aircraft Certification Service office] Document No.
AAC1-P2-WFD, AAC1-C-WFD AAC Models AAC1-P2, -C:
LOV – WFD Document Documents contain:
o LOV.
o Airplane structural configurations.
o List of all structural modifications and replacements mandated by AD.
o List of all inspections mandated by AD to address WFD.
o Identification of structure susceptible to WFD.
o WFD evaluation of WFD-susceptible structure, including:
• Identification of engineering data used in the WFD evaluation.
• WFD average behavior for each WFD-susceptible area or demonstration that WFD will not occur before the proposed LOV.
• Identification of SMPs and ISPs, if applicable.
o Identification and summary of any maintenance actions necessary to support the proposed LOV.
o Proposed binding schedule for completion of service information, if necessary.
18 months after the effective date of the final rule Draft document – 60 days before the 18-month compliance date Document No.
AAC1-P2-ALS, AAC1-C-ALS AAC Models AAC1-P2, -C: ALS of the ICA Documents contain the LOV. For areas certified to Amendment 25-54 or later, the ALS also contains other ICA of the airplane.
AAC will update the document to reference service information (AAC service bulletins) that describe the WFD maintenance actions that support the LOV.
These actions have been mandated by AD.
18 months after the effective date of the final rule