1-1 CHAPTER 1. INTRODUCTION
1.1 Purpose.
T his AC provides guidance for establishing the certification basis for changed aeronautical products pursuant to Title 14 of the Code of Federal Regulations (14 CFR)
21.101, Designation of the applicable regulations. The guidance is intended to help applicants and delegated organizations determine if it will be necessary to apply for a new type certificate (TC) under § 21.19, Changes requiring a new type certificate. The guidance describes the process for establishing the certification basis for an amended TC, supplemental type certificate (STC), and amended STC, detailing the requirements (evaluations, classifications, and decisions) throughout the process.
1.2 Applicability.
1.2.1 This AC is for applicants and holders of delegated organizations applying for amended TCs, STCs, or amended STCs.
1.2.2 This AC applies to major type design changes under § 21.101 for aeronautical products certificated under 14 CFR parts 21, 23, 25, 27, 29, 31, 33, and 35. References to “design change” include the design change and areas affected by the design change pursuant to § 21.101.
1.2.3 Minor type design changes are automatically considered not significant under the “does not contribute materially to the level of safety” provision of § 21.101(b).
1.2.4 This AC also applies to aircraft certificated under §§ 21.17(b), 21.19, 21.24, 21.25, and
21.27.
1.2.5 The term aeronautical product, or product, means a type certificated aircraft, aircraft engine, or propeller.
1.2.6 This AC is not intended to be used to determine the applicable aircraft noise, fuel venting, and exhaust emission requirements for changed products.
1.2.7 This AC is not mandatory and is not a regulation. This AC describes an acceptable means, but not the only means, to comply with § 21.101. However, if you use the means described in this AC, you must follow it entirely.
1.3 Cancellation.
This AC cancels AC 21.101-1A, dated September 3, 2010.
1.4 AC Content.
This AC contains 5 chapters and 10 appendices.
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1.4.1 This chapter clarifies the purpose of this AC, describes its content, specifies the intended audience affected by this AC, clarifies which changes are within the scope of this AC, and references the definitions and terminology used in this AC.
1.4.2 Chapter 2 provides a general overview of §§ 21.101 and 21.19, clarifies the main principles and safety objectives, and directs applicants to the applicable guidance contained in subsequent chapters of this AC.
1.4.3 Chapter 3 contains guidance for implementation of § 21.101(b) to establish the type certification basis for changed aeronautical products. It describes in detail the various steps for developing the certification basis, a process that applies to all major design changes to aeronautical products. Chapter 3 also addresses § 21.19 considerations for identifying conditions under which an applicant for a type design change is required to submit an application for a new TC and provides guidance at which stage of the process this assessment is performed.
1.4.4 Chapter 4 provides guidance about products excepted from the requirement of § 21.101.
1.4.5 Chapter 5 contains considerations for—
• Design-related operating requirements,
• Determining which policy to apply to a design change,
• Defining a baseline product,
• Predecessor regulations,
• Using special conditions under § 21.101(d),
• The effective period of application for a change to a TC under § 21.101(e),
• Other category aircraft under § 21.101(f),
• Clarification of § 21.101(g) regarding 14 CFR part 26 requirements,
• Documenting revisions to the TC basis,
• Incorporating STCs into the type design,
• Removing design changes,
• Determining a certification basis after removing an approved design change, and
• Sequential design changes.
1.4.6 Appendix A contains examples of typical type design changes for small airplanes, transport airplanes, rotorcraft, engines, and propellers. The Federal Aviation Administration (FAA) has categorized these examples into individual tables according to the classifications of design change—“substantial,” “significant,” and “not significant.”
1.4.7 Appendix B contains application charts for applying the § 21.101 process, including the excepted process.
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1.4.8 Appendix C contains one method for determining the changed and affected areas of a product.
1.4.9 Appendix D contains additional guidance on affected areas not discussed in other parts of this AC.
1.4.10 Appendix E provides detailed guidance with examples for evaluating the “impracticality” exception in the rule.
1.4.11 Appendix F provides guidance with examples on the use of relevant service experience in the certification process as one way to show that a later amendment may not contribute materially to the level of safety, allowing the use of earlier requirements.
1.4.12 Appendix G provides an example CPR decision record.
1.4.13 Appendix H provides examples of documenting a proposed certification basis list.
1.4.14 Appendix I lists the FAA regulations and orders related to this AC.
1.4.15 Appendix J lists the definitions and terminology applicable for application of the rule.
1.5 Terms Used in this AC.
1.5.1 The following terms are used interchangeably and have the same meaning:
requirements, regulations, standards, and airworthiness standards.
1.5.2 The terms certification basis, type certification basis, and amendment are used interchangeably to refer to the groups of requirements defined above.
2-1 CHAPTER 2. OVERVIEW OF §§ 21.19 AND 21.101
2.1 Section 21.19.
2.1.1 Section 21.19 requires an applicant to apply for a new TC for a changed product if the FAA finds that the change in design, power, thrust, or weight is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
2.1.2 Changes that require a substantial re-evaluation of the product’s compliance findings are referred to as “substantial changes.” For guidance, see paragraph 3.3 in chapter 3 of this AC. Appendix A of this AC provides examples of type design changes that will require a new TC.
2.1.3 If the FAA determines through § 21.19 that your proposed design change does not require a new TC, see § 21.101 for the applicable requirements to develop the certification basis for your proposed design change. For guidance, see chapter 3 and the examples in appendix A of this AC.
2.2 Section 21.101.
2.2.1 Section 21.101(a).
Section 21.101(a) requires a change to a TC and the area affected by the change to comply with the latest requirements, unless the change meets the criteria for the exceptions identified in § 21.101(b) or (c). The intent of § 21.101 is to enhance safety by incorporating the latest requirements into the type certification basis for the changed product to the greatest extent practicable.
2.2.2 Section 21.101(b).
2.2.2.1 Section 21.101(b) pertains to when an applicant may show that a changed product complies with an earlier amendment of a regulation, provided that the earlier amendment is considered adequate and meets the criteria in § 21.101(b)(1), (2), or (3). When design changes involve features or characteristics that are novel and unusual as compared to the airworthiness standard at the proposed amendment, more recent airworthiness standards and/or special conditions will be applied for these features.
2.2.2.2 You can comply with the earlier requirements consistent with § 21.101(b), when—
2.2.2.2.1 A change is not significant (see § 21.101(b)(1));
2.2.2.2.2 An area, system, component, equipment, or appliance is not affected by the change (see § 21.101(b)(2));
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2.2.2.2.3 Compliance with a later amendment for a significant change does not contribute materially to the level of safety (see § 21.101(b)(3)); or
2.2.2.2.4 Compliance with the latest amendment would be impractical (see § 21.101(b)(3)).
2.2.2.3 Earlier amendments may not precede the regulatory amendment level of the identified baseline product’s type certification basis and any requirement found in 14 CFR 23.2, 25.2, 27.2, and 29.2 or the applicable provision of part 26 related to the change.
2.2.2.4 Section 21.101(b)(1)(i) and (ii) pertain to design changes that meet the automatic criteria where the change is significant.
2.2.3 Section 21.101(c).
Section 21.101(c) provides an exception from the requirements of § 21.101(a) for a change to certain aircraft with less than the specified maximum weight. If you apply for a type design change to an aircraft (other than rotorcraft) of 6,000 pounds or less maximum weight, or to a non-turbine powered rotorcraft of 3,000 pounds or less maximum weight, you can show that the changed product complies with the regulations incorporated by reference in the type certificate. You can also elect to comply or may be required to comply with the later regulations. See paragraph 4.1 of this AC for specific guidance on this provision.
2.2.4 Section 21.101(d).
Section 21.101(d) provides for the use of special conditions, under § 21.16, when the proposed certification basis and any later regulations do not provide adequate standards to the proposed change because of a novel or unusual design feature.
2.2.5 Section 21.101(e).
Section 21.101(e) prescribes the effective period that an application will remain valid for a change.
2.2.6 Section 21.101(f).
Section 21.101(f) pertains to aircraft certificated in certain categories and special classes
(e.g., gliders, airships, other nonconventional aircraft, and balloons certificated under 14 CFR part 31), including the engines and propellers installed on them, under the requirements of §§ 21.17(b), 21.24, 21.25, and 21.27 airworthiness requirements.
2.2.7 Section 21.101(g).
Section 21.101(g) pertains to regulatory compliance of transport category airplanes with the applicable provisions of part 26 and/or corresponding later amendments to part 25.
See paragraph 5.8 of this AC for additional details.
3-1 CHAPTER 3. PROCESS FOR ESTABLISHING THE CERTIFICATION BASIS FOR
CHANGED PRODUCTS
3.1 Overview.
3.1.1 The applicant and the FAA each have a responsibility under § 21.101(a) and (b). As an applicant for the certification of a type design change, you must show that the change and areas affected by the change comply with the latest applicable airworthiness requirements unless you propose exception(s) under § 21.101(b). If you are proposing exception(s), you should make a preliminary classification whether the change is “significant” or “not significant,” and propose an appropriate certification basis. The FAA is responsible for determining whether your classification of the change, and proposal for the certification basis, are consistent with the applicable rules and their interpretation. The FAA determination does not depend on whether the TC holder or applicant for an STC is originating the change. The certification basis can vary depending on the magnitude and scope of the change. The steps below present a streamlined approach for making this determination.
3.1.2 The tables in appendix A of this AC are examples of classifications of typical type design changes. See paragraph 3.6.3 of this chapter for instructions on how to use those tables.
3.1.3 If your proposed change is not in the examples provided in appendix A, you may use the following steps in conjunction with the flowchart in figure 3-1 of this AC to develop the appropriate certification basis for the type design change. For clarification, the design change discussed in the flowchart also includes areas affected by the design change pursuant to § 21.101. See paragraph 3.9.1 of this AC for guidance about affected areas.
Figure 3-1. Developing a Proposed Certification Basis for a Changed Product Pursuant to § 21.101 Step 1: Identify the Proposed Type Design Changes to an Aeronautical Product.
Step 2: Verify the Proposed Type Design Change is Not Substantial. See Note 1.
Step 3:
Will you Use the YES Latest Standards?
§ 21.101(a) NO Step 4: Arrange Changes into Related and Unrelated Groups.
Step 5:
Not Significant NO Is Each Related or Unrelated Group a Significant Change?
§ 21.101(b)(1) YES Step 6: Prepare your Proposed Certification Basis List. See Note 2.
Not Affected Areas Affected Areas § 21.101(b)(2) Step 7:
Do the Latest Requirements Contribute Materially to YES Existing Requirements the Level of Safety and are they Practical?
§ 21.101(b)(3) See Note 2/ NO Earlier Requirements Latest Requirements Step 8: Ensure Proposed Certification Basis is Adequate.
Submit Proposed Certification Basis to the FAA Notes:
1. Changed products that are substantially changed do not follow this flowchart. Refer to § 21.19.
2. Process and propose each applicable requirement individually. If requirements are linked together, then they should be assessed together.
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3.2 Step 1. Identify the Proposed Type Design Changes to an Aeronautical Product.
• Identify the type design you are changing (the baseline product).
• Identify the proposed change.
• Use high level descriptors.
3.2.1 Identify the Type Design You are Changing (the Baseline Product).
Prior to describing the proposed change(s), it is important to clearly identify the specific type design configuration you are changing.
Note: For additional guidance on the baseline product, see paragraph 5.3 of this AC.
3.2.2 Identify the Proposed Change.
3.2.2.1 The purpose of this process step is to identify and describe the change to the aeronautical product. Changes to a product can include physical design changes and functional changes (e.g., operating envelope or performance changes). You must identify all changes and areas affected by the change, including those where you plan to use previously approved data. The FAA considers all of these changes and areas affected by the change part of the entire proposed type design and are considered as a whole in the classification of whether the proposed design change is substantial, significant, or not significant. The change can be a single change or a collection of changes. In addition to the proposed changes, consider the cumulative effect of previous relevant design changes incorporated since the last time the certification basis was upgraded. An applicant for a type design change must consider all previous relevant design changes and the amendment level of the certification basis used for these changes.
3.2.2.2 When you identify the proposed changes, consider previous relevant design changes that create a cumulative effect, as these may influence the decisions regarding the type of design change later in the process. By “previous relevant design changes,” the FAA means changes where effects accumulate, such as successive thrust increases, incremental weight increases, or sectional increases in fuselage length. You must account for any previous relevant design changes in the area affected by the proposed change that did not involve an upgrade of the certification basis in the proposed design change.
3.2.2.3 Example:
An applicant proposes a 5 percent weight increase, but a previous 4 percent and another 3 percent weight increase was incorporated into this aircraft without upgrading the existing certification basis. In the current proposal for a 5 percent weight increase, the cumulative effects of the two previous weight increases that did not involve an upgrade of the certification basis will now be accounted for as an approximate 12 percent increase in weight. Note that the cumulative effects the applicant accounts
3-4 for are only those incremental increases since the last time the airworthiness requirements in the type certification basis applicable to the area affected by the proposed change were upgraded.
3.2.3 Use High Level Descriptors.
To identify and describe the proposed changes to any aeronautical product, use a high level description of the design change that characterizes the intent of, or the reason for, the change. No complex technical details are necessary at this stage. For example, a proposal to increase maximum passenger-carrying capacity may require an addition of a fuselage plug, and as such, a “fuselage plug” becomes one possible high level description of this design change. Similarly, a thrust increase, a new or complete interior, an avionics system upgrade, or a passenger-to-cargo conversion are all high level descriptions that characterize typical changes to the aircraft, each driven by a specific goal, objective, or purpose.
3.2.4 Evolutionary changes that occur during the course of a certification program may require re-evaluation of the certification basis, and those changes that have influence at the product level may result in re-classification of the change.
3.3 Step 2. Verify the Proposed Type Design Change is Not Substantial.
3.3.1 Section 21.19 requires that you apply for a new TC for a changed product if the change in design, power, thrust, or weight is so extensive that a substantially complete investigation of compliance with the applicable regulations is required. A new TC could be required for either a single extensive change to a previously type certificated product or for a changed design derived through the cumulative effect of a series of design changes from a previously type certificated product.
3.3.2 A “substantially complete investigation” of compliance is required when most of the existing substantiation is not applicable to the changed product. In other words, you may consider the design change substantial if it is so extensive (making the product sufficiently different from its predecessor) that the design models, methodologies, and approaches used to demonstrate a previous compliance finding could not be used in a similarity argument. The FAA considers a change substantial when these approaches, models, or methodologies of how compliance was shown are not valid for the changed product.
3.3.3 If it is not initially clear that a new TC is required, appendix A of this AC provides some examples of substantial changes to aid in this classification. A substantial change requires application for a new TC. See §§ 21.17 and 21.19. If the change is not substantial, proceed to Step 3.
3.4 Step 3. Will you Use the Latest Standards?
You can use the latest requirements for your proposed type design change and the area affected by the change. If you use the latest requirements, you will have met the intent
3-5 of § 21.101 and no further classification (significant or not significant) and justification is needed. Even though an applicant elects to use the latest certification requirements, the applicant will still be able to apply § 21.101 for future similar changes, and use the exceptions under § 21.101(b). However, the decision to comply with the latest requirements sets a new regulatory basis for all future related changes in the same affected area for that amended TC.
• If you are using the latest requirements, proceed to Step 6 (in paragraph 3.9 of this AC).
• If you are not using the latest requirements, proceed to Step 4 below.
3.5 Step 4. Arrange Changes into Related and Unrelated Groups.
3.5.1 You should now determine if any of the changes identified in Step 1 are related to each other. Related changes are those that cannot exist without another, are co-dependent, or a pre-requisite of another. For example, a need to carry more passengers could require the addition of a fuselage plug, which will result in a weight increase, and may necessitate a thrust increase. Thus, the fuselage plug, weight increase, and thrust increase are all related, high level changes needed to achieve the goal of carrying more passengers. A decision to upgrade the flightdeck to more modern avionics at the same time as these other design changes may be considered unrelated, as the avionics upgrade is not necessarily needed to carry more passengers (it has a separate purpose, likely just modernization). The proposed avionics upgrade would then be considered an unrelated (or a stand-alone) change. However, the simultaneous introduction of a new cabin interior is considered related since occupant safety considerations are impacted by a cabin length change. Even if a new cabin interior is not included in the product level change, the functional effect of the fuselage plug has implications on occupant safety
(e.g., the dynamic environment in an emergency landing, emergency evacuation, etc.), and thus the cabin interior becomes an affected area. Figure 3-2 below illustrates the grouping of related and unrelated changes using the example of increasing the maximum number of passengers.
Note: If you plan changes in sequence over time, refer to the discussion on “sequential design changes” in paragraph 5.13 of this AC.
3-6 Figure 3-2. Related and Unrelated Changes for Example of Increasing the Maximum Number of Passengers The Aeronautical Product Affected Area Affected Area Grouping of Related Changes (significant change) Thrust Increase (physical and performance changes) MTOW Increase (physical and performance changes) Fuselage Stretch (physical change) Changed Area Comprehensive Flightdeck Upgrade (typically, a stand-alone significant physical change) Not Affected Area
3.5.2 Once you organize the change(s) into groupings of those that are related and those that are unrelated (or stand-alone), proceed to Step 5 below.
3.6 Step 5. Is Each Related or Unrelated Group a Significant Change?
3.6.1 The applicant is responsible for proposing the classification of groups of related design changes or unrelated design changes as significant or not significant. Significant changes are product level changes that could result from an accumulation of changes, or occur through a single significant change that makes the changed product distinct from its baseline product. The grouping of related and unrelated changes is particularly relevant to the FAA’s significant Yes/No decision (§ 21.101(b)(1)) described in Step 5 of figure 3-1. The FAA evaluates each group of related changes and each unrelated (stand-alone) change on its own merit for significance. Thus, there may be as many evaluations for significance as there are groupings of related and unrelated changes.
Step 1 of figure 3-1 explains the accumulation of changes that you must consider.
3-7 Additionally, § 21.101(b)(1) defines a design change as significant when at least one of three automatic criteria applies:
3.6.1.1 Changes where the General Configuration is Not Retained (Significant Change to General Configuration).
A change to the general configuration at the product level is one that distinguishes the resulting product from other product models, for example, performance or interchangeability of major components.
Typically, for these changes, an applicant will designate a new product model, although this is not required. For examples, see appendix A of this AC.
3.6.1.2 Changes where the Principles of Construction are Not Retained (Significant Change to Principles of Construction).
A change at the product level to the materials and/or construction methods that affects the overall product’s operating characteristics or inherent strength and would require extensive reinvestigation to show compliance.
For examples, see appendix A of this AC.
3.6.1.3 Product Level Changes that Invalidate the Assumptions used for Certification of the Baseline Product.
Examples include—
• Change of an aircraft from an unpressurized to pressurized fuselage,
• Change of operation of a fixed wing aircraft from land-based to water-based, and
• Operating envelope expansions that are outside the approved design parameters and capabilities.
For additional examples, see appendix A of this AC.
3.6.2 The above criteria are used to determine if each change grouping and each stand-alone change is significant. These three criteria are assessed at the product level. In applying the automatic criteria and the examples in appendix A of this AC, you should focus on the design change and how it impacts the existing product (including performance, operating envelope, etc.). A design change cannot be classified or re-classified as a significant change on the basis of the importance of a later amendment level.
3.6.3 Appendix A of this AC includes tables of typical changes (examples) for small airplanes, transport airplanes, rotorcraft, engines, and propellers that meet the criteria for a significant design change. The appendix also includes tables of typical design changes that the FAA classifies as not significant. The tables can be used in one of two ways—
3.6.3.1 To identify the classification of a proposed design change listed in the table, or