AC 21.101-1A

U.S. Department of Transportation Federal Aviation Administration Advisory Circular

Subject: Establishing the Certification Basis of Changed Aeronautical Products Date: 09/03/2010 Initiated by: AIR-110 AC No: 21.101-1A

Foreword

This advisory circular (AC) provides guidance for the application of the Changed Product Rule, Title 14 of the Code of Federal Regulations (14 CFR) §§ 21.101 and 21.19, for changes made to type certificated aeronautical products.

David W. Hempe Manager, Aircraft Engineering Division AIR-100

ii Contents Paragraph Page

Chapter 1. Introduction1

1. Purpose and Content of this Advisory Circular1

2. Audience2

3. Applicability2

4. Definitions2

Chapter 2. Overview of 14 CFR §§ 21.19 and 21.1013

1. 14 CFR § 21.193

2. 14 CFR § 21.1013

Chapter 3. The Process for Establishing the Certification Basis for Changed

Products 14 CFR § 21.101(a) and (b)5

1. Overview5

2. Step 1 of Figure 1. Identify The Proposed Type Design Change To An Aeronautical

Product7

3. Step 2 of Figure 1. Is the Change Substantial? (14 CFR § 21.19)9

4. Step 3 of Figure 1. Will the Latest Re quirements be Used? (14 CFR § 21.101(a))10

5. Step 4 of Figure 1. Relation of Changes10

6. Step 5 of Figure 1. Is the Pr oposed Change/Grouping Significant?

(14 CFR § 21.101(b)(1))11

7. Proposing an Amendment Level for a Significant Change13

8. Proposing an Amendment Level for a Not Significant Change15

9. Step 6 of Figure 1. Is the Area Affected By the Proposed Change?

(14 CFR § 21.101(b)(2))16

10. Step 7 of Figure 1. Are the New Require ments Practical and Do They Contribute

Materially to the Level of Safety? (14 CFR § 21.101(b)(3))18

11. Step 8 of Figure 1. Is the Proposed Type Certification Adequate?20

Chapter 4. Other Considerations22

1. Design Related Operating Requirements22

2. Excepted Products under 14 CFR § 21.101(c)22

3. Special Conditions, 14 CFR § 21.101(d)22

4. Effective Period for an Application to Ch ange a Type Certificate. (14 CFR § 21.101(e))

.23

5. Other Category Aircraft (14 CFR § 21.101(f))23

6. Clarification of 14 CFR 21.101 (g) (Part 26 Requirements)25

7. Documentation25

Appendix A. Classification of ChangesA-1

Appendix B. Procedure for Evaluating Impracticality of Applying Latest

Requirements to a Changed ProductB-1

1. IntroductionB-1

2. Procedure for Evaluating Impracticality of Applying Latest Requirements to a Changed

ProductB-2

iii

3. Examples of How to Certify Changed AircraftB-6

Appendix C. The Use of Service Experience in the Certification ProcessC-1

1. IntroductionC-1

2. GuidelinesC-1

3. Example: 14 CFR § 25.1141(f) Powerplant Controls for Transport AirplanesC-3

Appendix D. Definitions and TerminologyD-1

Appendix E. Related Code of Federal Regulations SectionsE-1

1. Related Code of Federal Re gulations ParagraphsE-1

2. How to Get PublicationsE-1

Chapter 1. Introduction

1. Purpose and Content of this Advisory Circular.

a. The Federal Aviation Administration (FAA) wrote this advisory circular (AC) to provide guidance for establishing the certification basis for changed aeronautical products in accordance with Title 14 of the Code of Federal Regulations (14 CFR) § 21.101 and to help identify if it will be necessary to apply for a new type certificate (TC) under 14 CFR § 21.19.

The guidance describes the process for establishing the certification basis for amended TCs, supplemental type certificates (STC) and amended STCs, detailing evaluations, classifications, and decisions made throughout the process.

b. The content of this AC is divided into 4 chapters and 5 appendices:

(1) Chapter 1 explains the purpose of this AC, describes its content, specifies the intended audience, and clarifies which changes are within the scope of applicability of this AC.

(2) Chapter 2 provides a general overview of 14 CFR §§ 21.101 and 21.19, clarifies the principals and safety objectives and directs applicants to the applicable guidance contained in subsequent chapters of this AC.

(3) Chapter 3 contains guidance for implementation of 14 CFR § 21.101(b) to establish the type-certification basis for changed aeronautical products. Chapter 3 describes in detail the various steps of the “top-down” certification basis development approach. Chapter 3 also addresses 14 CFR § 21.19 considerations to identify conditions under which an applicant for a type design change is required to submit application for a new TC and provides guidance at which stage of the process this assessment is to be performed.

(4) Chapter 4 contains considerations for design related operating requirements, approach for changes on certain small airplanes and rotorcraft under specified maximum weight (“excepted products”), use of special conditions under 14 CFR § 21A.101 (d), the effective period of an application, 14 CFR part 26 requirements, documentation of revisions to the typecertification basis and approach to ‘other category aircraft’ under 14 CFR § 21.101 (f).

(5) Appendix A contains examples of typical type design changes for small airplanes, transport category airplanes, rotorcraft, engines, and propellers which are categorized by the FAA into individual tables according to the classifications to the level of design change - substantial, significant, and not significant.

(6) Appendix B provides detailed guidance with examples for evaluating when compliance to the rule would be impractical under the “impracticality” exception in the rule.

(7) Appendix C provides guidance with examples on use of relevant service experience in the certification process as one way to show that a later amendment may not

2 contribute materially to the level of safety, allowing the use of earlier requirements.

(8) Appendix D lists the applicable definitions, and terminology for application of the rule.

(9) Appendix E contains cross references to the requirements of 14 CFR §§ 21.19 and

21.101.

c. This AC is not mandatory and is not a regulation. This AC describes an acceptable means, but not the only means, to comply with 14 CFR § 21.101. However, if you use the means described in this AC, you must follow it entirely.

2. Audience. This AC is for applicants applying for STCs, amended type certificates (ATCs), or amended STCs.

3. Applicability.

a. This document supersedes AC 21.101-1 Change 1, dated April 28, 2003. This document was revised to clarify current policy for complying with 14 CFR § 21.101.

b. This AC applies to major type design changes under 14 CFR § 21.101 for aeronautical products certificated under 14 CFR §§ 21, 23, 25, 27, 29, 31, 33, and 35.

c. Minor type design changes are automatically considered not significant under 14 CFR § 21.101(b) and the existing type certification basis is considered adequate for their approval under 14 CFR § 21.95.

d. This AC also applies to aircraft certificated under 14 CFR §§ 21.17(b), 21.19, 21.24,

21.25, and 21.27.

e. The term aeronautical products, or products, means type certificated aircraft, aircraft engines, and propellers.

f. This AC is not intended to be used to determine the applicable aircraft noise, fuel venting, and exhaust emission requirements for changed products.

4. Definitions. See appendix D in this AC for a list of definitions.

Chapter 2. Overview of 14 CFR §§ 21.19 and 21.101

1. 14 CFR § 21.19.

a. Title 14 CFR § 21.19 requires that as an applicant, you apply for a new TC for a changed product if the change in design, power, thrust, or weight is found by the FAA to be so extensive that a substantially complete investigation of compliance with the applicable regulations is required.

b. Changes that require a substantial re-evaluation of the product’s compliance findings are referred to as “substantial changes”. For guidance see paragraph 3 of chapter 3. Appendix A in this AC provides examples of type design changes that will require application for a new TC.

c. If the FAA has determined through 14 CFR § 21.19 that your proposed design change does not require a new TC, see 14 CFR § 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 in this AC.

2. 14 CFR § 21.101.

a. Title 14 CFR § 21.101(a) requires a change to a TC to comply with the latest requirements, unless the change meets the criteria for the exceptions identified in 14 CFR §§ 21.101(b) and (c). The intent of 14 CFR § 21.101 is to enhance safety through the incorporation of the latest regulatory standards in the type certification basis for changed products to the greatest extent practicable.

b. You can comply with the earlier requirements consistent with the requirements of 14 CFR § 21.101(b), when:

 A change is not significant (see 14 CFR § 21.101 (b) (1)), or

 An area, system, component, equipment or appliance are not affected by the change (see 14 CFR § 21.101 (b) (2)), or

 Compliance with a later amendment for a significant change does not contribute materially to the level of safety (see 14 CFR § 21.101 (b) (3)) , or

 Compliance with a latest amendment would be impractical (see 14 CFR § 21.101(b)(3)).

c. Note that earlier amendments may not precede either the corresponding amendment of the regulation incorporated by reference in the type certification basis and any requirement found in 14 CFR §§ 23.2, 25.2, 27.2, and 29.2. For transport category airplanes only, the provisions of

4 part 26 that is related to the change is also required.

d. Title 14 CFR § 21.101(b) allows a changed product to comply with an earlier amendment of a regulation, provided the earlier amendment is considered adequate and meets the criteria in 14 CFR §§ 21.101(b)(1), (2) or (3). However, when a proposed design change involves features or characteristics considered novel and unusual and the proposed airworthiness standards do not contain adequate or appropriate safety standards for this feature, later amendments and/or special conditions will be applied.

e. Title 14 CFR §§ 21.101(b)(1)(i) and (ii) describe the automatic criteria establishing that a change is significant.

f. Title 14 CFR § 21.101(c) provides an exception from the requirements of 14 CFR § 21.101(a) for a change to certain aircraft with less than a specified maximum weight.

If you apply for a type design change to an aircraft (other than rotorcraft) with a maximum weight of 6,000 pounds or less maximum weight, or to a non-turbine powered rotorcraft with a maximum of 3,000 pounds or less maximum weight, you can show that the changed product complies with the regulations incorporated by reference in the TC. You can also elect to comply, or may be required to comply, with the later regulations. See chapter 4, section 2 in this AC for specific guidance on this provision.

g. Title 14 CFR § 21.101(d) provides for the use of special conditions, under 14 CFR § 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.

h. Title 14 CFR § 21.101(e) prescribes the effective period an application will remain valid for a change. This section is consistent with the requirements of 14 CFR § 21.17 for a new TC.

i. Title 14 CFR § 21.101(f) pertains to aircraft certificated in certain categories and special classes (e.g. gliders, airships, and other nonconventional aircraft), including the engines and propellers installed on them, under the requirements of 14 CFR §§ 21.17(b), 21.24, 21.25, and 21.27 airworthiness requirements.

j. Title 14 CFR § 21.101(g) pertains to regulatory compliance for transport category airplanes with applicable provisions of 14 CFR part 26 and/or corresponding later amendments to 14 CFR part 25. For transport category airplanes, you must comply with each applicable provision of 14 CFR part 26 for the change, unless you have elected or are required to comply with a corresponding amendment to 14 CFR part 25 that was issued on or after the date of the applicable 14 CFR part 26 provisions.

Chapter 3. The Process for Establishi ng the Certification Basis for Changed Products 14 CFR § 21.101(a) and (b)

1. Overview.

a. The applicant and the FAA each have a responsibility under 14 CFR § 21.101(a) and

(b). As an applicant for the certification of a type design change, you must show that the change complies with the latest applicable airworthiness requirements unless you propose an exception per 14 CFR § 21.101(b). If you are proposing exception, you should make a preliminary classification whether the change is significant or not significant, and propose an appropriate certification basis. The FAA determines whether your classification of the change and proposal for the certification basis are consistent with the applicable rules and their interpretation, but should not be dependent on whether the TC holder or applicant for a 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. In addition to assisting in the determination of significance and establishing the certification basis, this guidance will help to establish the appropriate amount of coordination required between the applicant and the FAA.

b. Classifications of typical type design changes are in appendix A, Classification of Changes. See paragraph 6 (c), of this chapter for instructions on how to use appendix A.

c. In cases where the examples in appendix A are not applicable for the proposed change, use the following steps in conjunction with figure 1, on the next page, to develop the appropriate certification basis for the type design change.

6 Figure 1. Establishing the Certification Basis for Changed Product

Step 2.

Is the change substantial?

(§ 21.19) Step 1.

Propose major type design change

- Identify type design to be changed

- Identify proposed change

- Use high level descriptors Step 4.

Arrange changes into related & unrelated groups Step 3.

§ 21.101(a) Will the latest requirements be used?

NEW TYPE

CERTIFICATE § 21.19 Step 5.

Is the proposed change/grouping significant?

§ 21.101(b)(1) Will the latest requirements be used?

Step 6.

For every area, is the area affected by the proposed change?

Step 7.

Are the latest requirements practical or do they contribute materially to the level of safety?

§ 21.101(b)(3) Latest airworthiness requirements Earlier airworthiness requirements but not earlier than the existing certification basis Unaffected areas Impractical or not contributing materially to the level of safety Not significant Yes Yes No No Yes Yes No No Yes No Yes No

PROPOSED CERTIFICATION BASIS FOR THE CHANGE

CONTINUED

COMPLIANCE

WITH THE

EXISTING TC BASIS STOPA

7 A

PROPOSED

CERTIFICATION

BASIS FOR THE CHANGE Step 8.

Is the proposed TC basis adequate?

Proposed certification basis requires later airworthiness requirement(s) and/or special conditions Proposed certification basis completed YesNo

2. Step 1 of Figure 1. Identify The Proposed Type Design Change To An Aeronautical Product.

a. Prior to describing the proposed change(s), it is important to clearly identify the type design configuration to be changed. A series of derivative aircraft, engines, or propellers (for example, x -100, x-200, x-300) may evolve based on predecessor type designs, each with its own design change that make it distinct from the other series. You should identify which model or series within that model the specific configuration that will be modified.

Note: An STC is not a product; it is a change to a product.

When changing or amending an STC the starting point is the existing modified product (TC with existing STC installed).

For example, if you were amending an STC for an external cargo locker and you proposed changing the configuration of the locker, then your starting point would be the existing TC with the existing cargo locker installed by STC. You would then compare that configuration (TC with existing STC installed) to the changed product (TC with proposed amended STC installed).

b. Changes to a product can include physical design changes, changes to an operating envelope, and/or performance changes. The change can be a single change or a collection of changes. The purpose of this process step is to identify and describe the change to the aeronautical product. As an applicant for a type design change you must consider all previous related design changes and the amendment level of the certification basis used for these changes.

Note 1: By definition all previously incorporated changes will have been approved. The purpose of step 1 is to consider the net cumulative effect of the changes since the last time the certification basis for the changed/affected area was upgraded from that of the original type design.

Note 2: For the purpose of classifying the proposed design change, previously approved design data are still considered part of the proposed design and must be considered part of the proposed design change classification.

c. When identifying the changes being proposed as part of a modification, consider previous relevant changes that create a cumulative effect, as these may influence the decisions regarding substantial and significant changes later in the process. By previous relevant changes we mean design changes whose effects accumulate, such as successive thrust increases, incremental weight increases, or sectional increases in fuselage length. Any previous relevant design changes in the area affected by the current change that did not involve an upgrade of the existing certification basis must be taken into account in the next design change proposal.

(1) Example 1: A 5% weight increase is currently being proposed, but a previous 10% and another 15% weight increase has been incorporated into this aircraft without upgrading the existing certification basis. In the current proposal for a 5% weight increase, the cumulative effects of the two previous weight increases that did not involve upgrade of the certification basis will now be accounted for as an approximately 30% increase in weight, for the purpose of making the substantial and/or significant decisions. Note that the cumulative effects to be considered are those incremental increases since the last time the airworthiness requirements, in the type certification basis applicable to the area affected by the current change, were upgraded.

(2) Example 2: The TC for airplane model X lists three series, namely X-300, X-200, and X-100. The X-300 is a derivative of the X-200 which is a derivative of the original X-100 series. An applicant proposes a design change to the X-300 series airplane. During the review of the X-300 certification basis and the regulations affected by the proposed change, it was identified that one regulation, 14 CFR § 25.571 (damage tolerance requirements), remained at the same amendment level as the X-100 original certification basis (exception was granted).

Since the amendment level for this particular regulation was not changed for the two subsequent airplane series (X-200 and X-300), the cumulative effects of these two previous design changes that are related to the proposed change and the damage tolerance requirements must now be addressed.

d. 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.

e. Evolutionary Changes. Evolutionary changes that occur during the course of a certification program may require re-evaluation of the certification basis and may result in reclassification of the change. That is, any evolution in the proposed design change after the certification basis has been agreed to (or established) will necessitate a revisit of the certification basis to ensure that “evolved” aspects of the design change are still covered by the agreed upon certification basis.

3. Step 2 of Figure 1. Is the Change Substantial? (14 CFR § 21.19)

a. Title 14 CFR § 21.19 requires that you apply for a new TC for a changed product if the proposed 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.

b. A “substantially complete investigation” of compliance is required when most of the existing substantiation is not applicable to the changed product. A substantial change proposal will require the need to comply with all requirements applicable to a particular category of product. The number of requirements to which compliance must be re-established for the changed product may not necessarily be the sole determination as to whether the change is substantial, but rather it is the extent of effort to establish compliance, or the depth of investigation required to be done. In other words, the proposed design change may be considered 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.

c. To address if a change is substantial at the beginning of the process, you must evaluate the total or combined effect of all the proposed changes identified in step 1, including the cumulative effects of previous relevant design changes since the last update of the certification basis (as explained in step 1).