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
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3.6.3.2 In conjunction with the three automatic criteria, to help classify a proposed design change not listed in the table by comparison to determinations made for changes with similar type and magnitude.
3.6.4 In many cases, a significant change may involve more than one of these criteria and will be obvious and distinct from other product improvements or production changes. There could be cases where a change to a single area, system, component, or appliance may not result in a product level change. There could also be other cases where the change to a single system or component might result in a significant change due to its effect on the product overall. Examples may include the addition of winglets or leading edge slats, or a change in primary flight controls to a fly-by-wire system.
3.6.5 If an unrelated (stand-alone) change or a grouping of related changes is classified as—
3.6.5.1 Significant (§ 21.101(a)):
You must comply with the latest airworthiness standards for certification of the design change and areas affected by change, unless you justify use of one of the exceptions provided in § 21.101(b)(2) or (3) to show compliance with earlier amendment(s). The final certification basis may consist of a combination of the requirements recorded in the certification basis ranging from the original aircraft certification basis to the most current regulatory amendments.
3.6.5.2 Not Significant (§ 21.101(b)(1)):
You may comply with the existing certification basis unless the standards in the proposed certification basis are deemed inadequate. In cases where the existing certification basis is inadequate or no regulatory standards exist, later requirements and/or special conditions will be required. See paragraph 3.11 of this AC for a detailed discussion.
3.6.6 A new model designation to a changed product is not necessarily indicative that the design change is significant under § 21.101. Conversely, retaining the existing model designation does not mean that the design change is not significant. Significance is determined by the magnitude of the type design change.
3.6.7 The FAA determines the final classification of whether a design change is significant or not significant. To assist you in your assessment, the FAA has predetermined the classification of several typical design changes that you can use for reference, and these examples are listed in appendix A of this AC.
3.6.8 At this point, the determination of significant or not significant for each of the groupings of related changes and each stand-alone change is completed. For significant changes, if you propose to comply with an earlier requirement, use the procedure outlined in paragraph 3.7 below. For changes identified as not significant, see paragraph 3.8 below.
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3.7 Proposing an Amendment Level for a Significant Change.
3.7.1 If the classification of the group of related changes is significant, all areas, systems, components, parts, or appliances affected by the change must comply with the airworthiness standards at the amendment level in effect on the date of application for the change. You can justify use of one of the exceptions in § 21.101(b)(2) and (3) to comply with an earlier amendment but no earlier than the existing certification basis.
You must comply with any retroactive requirement found in §§ 23.2, 25.2, 27.2, 29.2 applicable on the date of the application for the change. See paragraphs 3.9 and 3.10 of this AC.
3.7.2 For transport category airplanes only, § 21.101(g) requires that you comply with any applicable provision of part 26 (related to the change), which is applicable on the date of the application for the change, unless you elected or were required to comply with later corresponding part 25 requirements.
3.7.3 The final certification basis may combine latest, earlier (intermediate), and existing regulations, but cannot contain regulations preceding the existing certification basis.
3.8 Proposing an Amendment Level for a Not Significant Change.
3.8.1 When the FAA classifies the type design change as not significant, the rule allows compliance with earlier amendments but not prior to the existing certification basis.
Within this limit, the applicant may propose an amendment level for each certification standard for the affected area. However, you should be aware that the FAA will review your proposal for the type certification basis to ensure that the certification basis is adequate for the proposed change under Step 8. (See paragraph 3.11 of this AC.) You must also comply with the retroactive requirements found in §§ 23.2, 25.2, 27.2, 29.2, applicable on the date of the application for the change.
3.8.2 For transport category airplanes only, § 21.101(g) also requires that you comply with any applicable provision of part 26 (related to the change), which is applicable on the date of the application for the change, unless you elected or were required to comply with later corresponding part 25 requirements. You may comply with a specific airworthiness requirement or a subset of airworthiness requirements at later amendments. In such a case, any other airworthiness requirements that are directly related should be included in the certification basis for the change.
3.9 Step 6. Prepare your Proposed Certification Basis List.
As part of preparing your proposed certification basis list, you must identify any areas, systems, components, equipment, or appliances of the product that are affected by the design change and the corresponding regulatory standards associated with these areas.
For each group, you must assess the physical and/or functional effects of the change on any areas, systems, components, equipment, or appliances of the product. The characteristics affected by the change are not only physical changes, but also functional
3-10 changes brought about by the physical changes. Examples of physical aspects are structures, systems, components, equipment, appliances, and software in combination with the affected hardware. Examples of functional characteristics are performance, handling qualities, aeroelastic characteristics, and emergency egress. The intent is to encompass all aspects where there is a need for re-evaluation, that is, where the substantiation presented for the product you are changing should be updated or rewritten. Appendix H of this AC contains two examples of how to document a proposed certification basis list.
3.9.1 An area affected by the change is any system, component, part, or appliance of the aeronautical product that you physically and/or functionally change. Figure 3-3 of this AC illustrates concepts of physical and functional changes of an affected area.
Appendix C of this AC contains a method used to define the change and areas affected by the change. This appendix is meant to assist you when you propose a large, complex design change. For a type design change, it is important that you properly assess the effects of such change on any areas, systems, components, equipment, or appliances of the product because areas that have not been physically changed may still be considered part of the affected area. If a new compliance finding is required, regardless of its amendment level, it is an affected area.
Figure 3-3. Affected Areas versus Not Affected Areas Physical Change Functional Change Not Affected Area Significant Change and Area Affected by the Significant Change The Aeronautical Product